GRB 990123

A. Fruchter (STScI) reports for the HST GRB collaboration:

It has come to our attention that the web page reported in our last circular,
GCN 712
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 , did not load properly for outside users.  The GRB 990123 page that
they saw was unchanged from last year.

We have corrected this problem.  Readers wishing to see the light curve of
the OT, or the late-time imageing of the host, can either click on the
animated gif of the decline of GRB 990123 at 

http://www.stsci.edu/~fruchter/GRB

or go directly to

http://www.stsci.edu/~fruchter/GRB/990123 .

We have now also included a color image of the host and the wider field about 
GRB 990123 created using the both the open (50CCD) images (see GCN 712
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 )
and the more recent long pass STIS data (GCN 715
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 ).

Stephen Holland, Johan Fynbo, Bjarne Thomsen (University of Aarhus),
Michael Andersen (University of Oulu),
Gunnlaugur Bjornsson (University of Iceland),
Jens Hjorth (University of Copenhagen),
Andreas Jaunsen (University of Oslo),
Priya Natarajan (Universities of Cambridge, & Yale), and
Nial Tanvir (University of Hertfordshire)

	We have obtained 8224 seconds of STIS images with the F28X50LP
(long pass) aperture of the host galaxy of GRB 990123.  This data was
taken as part of the Survey of the Host Galaxies of Gamma-Ray Bursts
(Holland et al. GCN 698
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 ) approximately 509 days after the burst.
Combined images are now available at
"http://www.ifa.au.dk/~hst/grb_hosts/data/index.html".

	Using the light curve fits of Holland et al. (2000, submitted
to A&A) we predict that the optical afterglow will have R = 31.6 on 15
June 2000, and thus will not be visible in the STIS images.
Therefore, we used aperture photometry to determine the AB magnitudes,
in the long pass filter, of the three knots found by Holland & Hjorth
(1999, A&A, 344, L67).  We find the following colours for the three
extended knots where CL is the AB magnitude in the STIS clear
aperture, LP is the AB magnitude in the STIS long pass aperture, and
beta is the corresponding spectral index, f = k*nu^beta.

Knot   CL     LP         CL-LP       beta
  1   28.3   28.2    +0.1 +/- 0.4    -0.4
  2   28.1   27.5    +0.6 +/- 0.4    -2.6
  3   28.0   27.5    +0.5 +/- 0.4    -2.2

       The GRB occurred on the southeast edge of Knot 1.  This knot is
approximately one sigma bluer than the other two knots, and two sigma
bluer than the overall colour of the galaxy (V-R = 0.43 +/- 0.18;
Castro-Tirado et al., 1999, Science 283, 2069).  This suggests that
Knot 1 might be undergoing stronger star formation than the rest of
the galaxy.

A. Fruchter (STScI), S. Thorsett (UCSB), R. Wijers (SUNY) report for the
larger HST GRB collaboration:

Public HST observations in the red (LP) STIS filter should shortly be
available of the host galaxy of GRB 990123.  We therefore report here
on the results of late-time imaging of the host by our group using the
wide-band open (50CCD) filter.  The images described here can be found
at http://www.stsci.edu/~fruchter/GRB , and will be submitted to a
journal shortly.

The field of GRB 990123 was reobserved by HST with the STIS CCD in open
filter (50CCD) mode during two orbits on 7 February 2000, or 380 days
after the GRB.  The optical transient was no longer visible.   However
we have been able to use this image to further refine our earlier
photometry on the OT (Fruchter et al. 1999a,b).    We now find 
a V magnitude for the OT of 25.4 +/- 0.1 on 8 February 1999 and
V = 27.7 +/- 0.15  on 23 March 1999, implying that the late time
late-time light curve falls as t^{-1.7 +/- 0.1}.  This represents a
break of about 0.65 from the power-law decay a couple of days after
outburst, and thus is roughly consistent with the beaming model of
Meszaros and Rees (1999).  However, this also agrees within the errors
with the power-law of the early time light curve reported by ROTSE, and
this may suggest a connection between the early and late-time
emission.

The GRB is found to reside near the edge of the visible stellar field
of the host, and is not superposed on a strong region of star-formation.

References:

Akerlof, C. et al, 1999, Nature, 398 400.
Fruchter, A. et al., 1999, Ap. J. (Letters), 519, L13.
Fruchter, A. et al., 1999, GCN 354
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 .
Meszaros, P. and Rees, M., 1998, MNRAS, 306L, 39.

TITLE: Late-time HST Observations of GRB 990123
Subject: HST/STIS Observations of GRB 990123

A. Fruchter (STScI), S. Thorsett (Princeton), and E. Pian (ITESRE)
report for the HST GRB collaboration:

The field of GRB 990123 was reobserved by HST with the STIS CCD in open
filter (50CCD) mode during two orbits on 23 March 1999, or 59.5 days
after the GRB.  The total exposure time was 5040s.  The optical
transient was visible, but had declined by 2.1 +/- 0.2 mags from that
observed on 8 February 1999 by HST (Fruchter et al. 1999, Kulkarni et
al 1999), to V = 27.55 +/- 0.2 mags.

Both of the HST observations of the OT of GRB 990123 fall well below
the t^{-1.09} power-law behavior of the OT during the first three days
(Fruchter et al. 1999).  The 8 February observation lies more than 2
mags below the continuation of such a power-law.   Additionally, a
power-law fit of the flux density of the OT finds between the two
HST observations finds t^{-1.52 +/- 0.15}; this slope is nearly 3 sigma 
steeper than that found through day 3, but is also noticeably shallower than
that predicted from a break in the power-law due to either our now
observing the edge of a collimated outflow (Meszaros and Rees 1999) or
the sideways expansion of such an outflow (Kulkarni et al. 1999, Rhoads
1999).

The HST images from both epochs will be made available in gif format 
at http://www.stsci.edu/~fruchter/GRB/990123.  The reduced HST data 
from the first epoch are also available in fits format at this
site.   The reduced data of the second observation will be made
available later, in accordance with the HST GRB Collaboration
policy of making reduced data publicly available upon publication 
in a refereed journal.

References:

Fruchter, A. et al., 1999, Ap. J. (Letters), 519, L13.
Kulkarni, S. et al., 1999, Nature, 398, 389.
Meszaros, P. and Rees, M., 1999, MNRAS (submitted), astro-ph/9902367.
Rhoads, J., 1999, Ap. J. (submitted), astro-ph/990399.

The U. S. Naval Observatory GRB Team (A. Henden (USRA/USNO),
R. Stone, F. Vrba, C. Luginbuhl, B. Canzian, J. Munn, S. Levine,
H. Guetter (USNO)) report:

We have been monitoring the Optical Transient position
for GRB 990123 with the USNOFS 0.2-m FASTT system (Stone et.
al. 1996, AJ 111, 1721).
As this is a converted transit telescope, we were not
able to begin observations until the field started to
transit in darkness.  However, we have single-epoch
data for the following nights (yymmdd UT):
    990225 990302 990303 990304 990305
    990309 990310 990316 990320 990321
    990322 990323 990329 990330 990331
Typical limiting magnitude at R was 18.3.  We saw no
recurrence of the transient during this period.

We also report single-epoch JHK measures (with the USNO
1.55-m telescope and infrared camera) on 990202, and
J measures on 990328 and 990427.  Typical limiting magnitude at
J was 17.5.  No recurrence was seen.

BVRI photometry in the field of GRB 990123 was performed with
the USNO 1.0-m telescope in Flagstaff during the February dark run.
Results of that photometry have been posted at:
  ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990123.dat
with a more complete description of the photometric procedures in:
  ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990123.readme

Objects 1-18 in the photometry file are numbered identically to
Nilakshi, et. al. (GCN 252
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 ).  Other objects are either fainter
stars in the same field, or else brighter stars within the 11x11
arcmin field of the CCD to be used for field identification.
We have omitted the obviously extended objects 7, 9, and 16.
We note some photometric differences between Nilakshi and this
new photometry.

S. C. Odewahn, J. S. Bloom, S. Djorgovski, S. R. Kulkarni,
and F. Harrison (CIT) report on behalf of the Caltech-NRAO-CARA 
GRB Collaboration:

We have processed the HST STIS images of GRB 990123 using a variety
of techniques and have deduced the following magnitudes: 

Estimates of Gunn r magnitudes from the Median stack STIS image:
  r(OT)          = 25.25 -+0.2      systematic+accidental error
  r(OT+GAL)      = 24.16 -+0.1      accidental error only
  r(A2)          = 27.18 -+0.02     accidental error only
  r(OT+GAL+A2)   = 24.09          

Estimates of Gunn r magnitudes from the drizzled STIS image: 
  r(OT)          = 25.28 -+0.2    systematic+accidental error 
  r(OT+GAL)      = 24.12 -+0.1    systematic+accidental error 
  r(A2)          = 27.23 -+0.02   systematic+accidental error         
  r(OT+GAL+A2)   = 24.06         

Details of the reduction, the image properties and a map defining 
the apertures for OT, GAL, and A2 (a discrete source 0.9" from
the OT) may be found at:
http://astro.caltech.edu/~sco/sco1/research/grb/grb990123/stis.html

In this website we detail the procedure for obtaining by anonymous 
ftp our final STIS images, a deep Keck R-band image, and the Palomar 
60-inch OT discovery image discussed in GCN 201
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 .  These data may be 
used without any need to cite the source.

This message may be cited.

Christian Veillet reports:

The optical transient (OT) associated with the gamma ray burst GRB990123
has been observed with the new wide field camera CFH12k at the prime focus
of the 3.6-m CFH Telescope for two additional nights on 1999 Feb. 8.6 and
9.6 by C. Veillet in the course of the French GRB follow-up program
at CFHT (M. Boer, CESR, C. Veillet, CFHT) with the assistance of
J. Anderson (University of Victoria - Canada), as a continuation
of the observations reported in GCN 253
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  from the three previous nights. 


Using only the last three nights (image quality better than 1 arc-second),
photometric measurements in B, V and R using the star #18  published by 
Nilakshi et al. (GCN 252
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 ) give the following results:

R = 23.41 (0.1)  on 1999 Feb. 8.6  - 130 mn total integration time
V = 24.05 (0.1)  on 1999 Feb. 8.6  -  50 mn total integration time
B = 24.46 (0.15) on 1999 Feb. 9.6  -  30 mn total integration time

The V magnitude is in good agreement with the HST estimate
of the OT+galaxy magnitude (V~24 GCN 255
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 ).


As suspected from the first published image based on the first three nights
(GCN 253
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 ) with the first two of poor image quality, the surrounding galaxy 
is now clearly resolved.  A composite image in R and contour maps
of the GRB area and of a nearby comparison star are available at the Web site
http://www.cfht.hawaii.edu/~veillet/grb990123.html 
 

This message may be cited.

J. P. Halpern, Y. Yadigaroglu, K. M. Leighly, & J. Kemp (Columbia U.)
report on behalf of the MDM Observatory GRB follow-up team:

"We imaged the field of GRB 990123 in the R band on Feb. 14.50 UT using
the MDM Observatory 2.4m telescope.  A total of 100 minutes exposure was
obtained in seeing of 0.9 arcsec.  An object is detected at a position
consistent with that of the GRB host galaxy as measured in the HST STIS
image (Bloom et al. astro-ph/9902182).  Its magnitude is R = 23.77 +/- 0.10 
(referenced to the comparison star of GCN #207
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 ), equivalent to Gunn r = 24.10.
Since this is consistent with the estimate of r = 24.0-24.2 for the host
galaxy alone by Bloom et al., we conclude that the optical transient is no
longer making a detectable contribution to the total light in ground-based
images.

We also report a revised magnitude on Feb. 3.54 of R = 23.55 +/- 0.24,
after more detailed analysis of those data.

Further HST observations are therefore needed to follow the unusual afterglow 
decay of this most energetic GRB.

The latest MDM image will be posted at http://cba.phys.columbia.edu/grb/

This message may be cited.

GRB 990123:  Discovery of the Probable Host Galaxy

S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, G. Neugebauer, C. Koresko
(Caltech), L. Armus (IPAC), S. C. Odewahn, B. R. Oppenheimer, R. R. Gal 
(Caltech), N. Kobayashi (NAOJ), and D. A. Frail (NRAO), report on behalf 
of the Caltech-CARA-NRAO GRB collaboration: 

We confirm the detection of a faint galaxy approximately 0.6 arcsec due north 
from the optical transient (OT) associated with GRB 990123, in the K-band
images obtained with the NIRC instrument at the Keck-I 10-m telescope, on the
nights of 29 January 1999 and 6, 7, and 8 February 1999 UT.  The presence of
this object was already suggested in the Keck K-band images obtained on 27
January 1999 UT by Malkan et al., and its K-band magnitude was estimated to 
be about 22 to 23 (see Djorgovski et al., GCN 243
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 ).  The galaxy is clearly 
resolved from the OT in the images obtained on 29 January by Neugebauer and 
Armus; it has about an equal magnitude as the OT in the images taken on 7 
and 8 February by Kulkarni and Oppenheimer, i.e., K =~ 22 +- 0.7 mag.

The K-band light curve containing the light from both objects begins to show
a flattening due to the presence of this galaxy.  The deviation from the
power-law light curve in the K-band (Bloom et al., GCN 240
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 ), assumed to 
have the slope alpha = -1.15 (as measured in the r band), implies the galaxy 
magnitude K =~ 22.4 (+0.9, -0.4; 1-sigma), in a good agreement with the 
previous estimates.

We interpret this object as the most likely counterpart of the absorber
at z = 1.600 (IAUC 7096, GCN 219
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 , GCN 249
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 , GCN 251
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 ), and the probable
host galaxy of the GRB.  Its observed K-band magnitude is reasonable for
a normal galaxy at z = 1.6.

Analysis of the HST images of the field shows the same object (GCN 255
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 ),
and further details will be reported shortly.

A Keck image of the field will be posted at:
http://astro.caltech.edu/~george/grb/grb990123.html

This report is citeable.

Andrew Fruchter, Kailash Sahu, Harry Ferugson, Mario Livio 
      and Mark Metzger on behalf of the larger HST GRB 
      collaboration report:

We have reduced the HST STIS CCD clear (50CCD) images of
GRB 990123 announced earlier today by the Director of STScI,
Steven Beckwith, in GCN 254
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 .

We find the optical transient to be superposed on an extended
irregular galaxy.   A quick photometric reduction shows that
the OT has a magnitude of V=25.4 +/- 0.1 and the galaxy has 
V=24.3 +/- 0.15.  The total integrated magnitude of the galaxy 
and OT is therefore V~24, which agrees with Palomar 5-m observations 
taken approximately 12 hours before the HST observations, and
which will be reported in a succeeding GCN.  No correction
to the STIS magnitude has yet been made to take into account
the colors of the objects, which could change the estimated 
magnitudes from the broad STIS clear filter by ~0.1 mag.

The faint magnitude of the OT suggests that it may be declining
more rapidly than the earlier power-law would predict, as 
suggested by the MDM group in GCN 248
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 .

The probable host galaxy is itself composed of several irregular 
pieces, extended over a region more than 1" across.  The major 
fraction of the light in the host is to the north of the OT, thus 
agreeing with the probable extension reported by Djorgovski et
al. in GCN 243
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 .

A gif image as well as the reduced FITS files will be posted
by 16:00 EST today (9 February 1999) on 

http://www.stsci.edu/~fruchter/GRB/990123

We welcome the use of the reduced FITS image by others; 
however, we ask that those who do use this image cite 
this GCN, or a formal publication that may succeed it
(the bibliographic reference of which would be available 
on the above web page).

HST Images of GRB 990123 Now Publicly Available

The Space Telescope Science Institute is pleased to announce that recent 
observations of GRB 990123 are now available in the HST Data Archive. The 
program ID is 8394. The three orbits of STIS CCD imaging were done as a 
Director's Discretionary Program as a service to the astronomical community, 
in response to suggestions by Fruchter, Kulkarni, and others. The data can 
also be found in the archive's anonymous ftp area, 
ftp://archive.stsci.edu/pub/misc/grb/GRB990123/
and gzipped versions of the same fits files are also available in the 
compressed/ subdirectory.

[GCN OP NOTE:  I deleted the HTML-version duplicate of the circular
that was attached in the original submitted/distributed circular.]

Nilakshi,  R.K.S. Yadav, V. Mohan, A.K. Pandey and R.Sagar of U.P. State 
 Observatory, Manora Peak, Nainital, India report:

We have determined the Johnson BV and Cousins RI CCD magnitudes of 18 objects
in the field of GRB 990123 with the 104-cm Sampurnanand telescope of 
the U.P. State Observatory, Manora Peak, Nainital under good photometric 
sky conditions. The photometric standards present in the field of open 
star cluster M67 have been used for calibration. The BVRI standard 
magnitudes of these objects alongwith RA, DEC (J2000) and DAOPHOT 
photometric errors prefixed with S are given below. 
------------------------------------------------------------------------
Object    RA         Dec  
      h   m    s    o  '  ''    V   SV   B-V S(B-V) V-R S(V-R) V-I S(V-I)
-------------------------------------------------------------------------
 1   15  25  27.0  44 46 23.2 14.84 0.00 0.57 0.00  0.32 0.00  0.58 0.00
 2   15  25  36.5  44 44 37.6 15.47 0.00 0.63 0.01  0.36 0.01  0.67 0.01    
 3   15  25  11.8  44 46  2.1 15.96 0.00 0.64 0.00  0.41 0.01  0.78 0.01   
 4   15  25  21.1  44 46 46.9 16.28 0.00 0.67 0.00  0.39 0.00  0.71 0.01    
 5   15  25  38.6  44 43 20.3 16.72 0.00 0.60 0.01  0.32 0.01  0.63 0.01    
 6   15  25  21.7  44 46 52.7 16.80 0.00 1.35 0.01  0.82 0.00  1.54 0.01    
 7   15  25  38.8  44 44 30.1 17.65 0.06 1.29 0.07  0.83 0.08  1.34 0.08    
 8   15  25  17.9  44 46 29.5 18.10 0.01 1.13 0.01  0.66 0.01  1.17 0.01    
 9   15  25  39.1  44 44 46.1 18.48 0.05 1.32 0.07  0.67 0.08  1.25 0.07    
10   15  25  19.6  44 47 53.0 18.66 0.01 1.45 0.02  0.86 0.01  1.64 0.01    
11   15  25  19.3  44 45 58.1 18.72 0.01 0.47 0.01  --------   0.53 0.02   
12   15  25  15.6  44 45  5.6 18.96 0.03 0.87 0.04  0.53 0.04  0.98 0.05    
13   15  25  32.7  44 44 29.9 19.01 0.01 0.53 0.02  0.37 0.01  0.69 0.02    
14   15  25  25.3  44 45 24.7 19.16 0.05 1.36 0.07  0.70 0.07  1.23 0.07    
15   15  25  16.4  44 47 28.4 19.65 0.02 1.39 0.04  0.88 0.02  1.71 0.03    
16   15  25  13.8  44 44 50.1 19.87 0.03 0.43 0.04  0.27 0.03  0.34 0.06    
17   15  25  26.6  44 43 55.3 20.14 0.03 1.06 0.06  0.80 0.03  1.23 0.04    
18   15  25  27.5  44 44 43.6 20.31 0.03 0.48 0.05  0.40 0.03  0.43 0.09    
--------------------------------------------------------------------

 At the Web site http://www.rri.res.in/grb990123/ the manuscript dealing
with the above data are available. The title of the paper is " BVRI CCD
photometric standards in the field of GRB 990123". It has been accepted
for publication in the Bull. Astron. Soc. India.

This message may be cited.

GRB 990123: Updated Keck Spectroscopy Results

S. G. Djorgovski, S. R. Kulkarni (CIT), G. D. Illingworth (UCSC),
D. D. Kelson (DTM), J. S. Bloom, S. C. Odewahn, R. R. Gal (CIT), 
M. Franx (Leiden), P. van Dokkum (Groningen), D. Magee (UCSC), and 
D. A. Frail (NRAO) note on behalf of the Caltech-UC-CARA-NRAO 
collaboration:

Our re-reduction of the Keck spectrum of the optical transient associated
with GRB 990123 (Kelson et al., IAUC 7096) gives the following results:

We detect 12 (13) absorption lines in the spectrum of the OT, as follows:

 W_obs,air  W_rest,vac   z    Line ID

  4843.74   1862.78   1.6010   Al III 
  5267.29   2026.14   1.6004   Zn II 
  5361.77   2062.23   1.6007   Cr II | blend
  5361.77   2062.66   1.6002   Zn II |
  5877.17   2260.78   1.6003   Fe II 
  6096.14   2344.21   1.6012   Fe II 
  6173.87   2373.73   1.6016   Fe II 
  6195.29   2382.76   1.6008   Fe II 
  6725.75   2586.64   1.6009   Fe II 
  6759.94   2600.18   1.6005   Fe II 
  7269.47   2796.35   1.6003   Mg II 
  7289.49   2803.53   1.6008   Mg II 
  7416.97   2852.97   1.6005   Mg I 

The mean redshift is 1.6004 +- 0.0005 (random) +- 0.0005 (systematic).
This agrees to within the quoted error with the new determination of
the absorber redshift by Hjorth et al. (GCN 249
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 ).

We note the remarkably small velocity dispersion implied by these data,
less than about 60 km/s in the restframe, suggesting that the lines arise 
from a single subgalactic-size cloud (which of course may be a part of the 
host galaxy's ISM), rather than from an ansamble of clouds moving within 
the potential well of a normal, massive galaxy.  It is also possible that 
the GRB host is a dwarf galaxy, in which case the object detected near the 
line of sight both in the K band (Djorgovski et al., GCN 243
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 ) and in the 
R band (Yadigaroglu and Halpern, GCN 248
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 ) may be a foreground galaxy.

No other convincing absorption systems, and no emission lines are detected
in these data, in the useful wavelength range of approximately 4700 to 9000
Angstroms.  We do not detect Ca II H+K absorption, nor any other common
absorption lines, e.g., Na D, nor any common emission lines (e.g., [O II] 
3727, H alpha, H beta, etc.) from either of the two absorption systems 
originally proposed by Hjorth et al. (GCN 219
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 ).

We have also measured the redshift of the galaxy approximately 10 arcsec
west of the OT.  From 4 relatively "clean" lines, Ca II H+K, H beta, and
H alpha, we derive for its redshift z = 0.2783 +- 0.0005.  From 4 blended
lines, CH G-band 4300, Mg I 5173+5184, Fe I + Ca I 5267, and Na D 5893,
we derive z = 0.278 +- 0.001, again in an excellent agreement with Hjorth
et al. (GCN 249
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 ).  No absorption or emission lines corresponding to this 
redshift are seen in the spectrum of the OT.  

This report may be cited.

GRB 990123 NOT Spectrum Update

J. Hjorth (Copenhagen), M. I. Andersen (NOT), H. Pedersen (Copenhagen), 
M. R. Zapatero-Osorio (IAC), E. Perez (IAA) and 
A. J. Castro Tirado (LAEFF, IAA) report:

"We have conducted an improved analysis of the NOT spectra reported in 
GCN #219
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 . We detect several absorption lines in addition to the ones found 
in the preliminary analysis, including Al III (185.5 and 186.3 nm). The 
suggested assignment of two significant absorption lines with Zn II (202.6 
and 206.3 nm) is uncertain. The resulting updated redshift is 1.598 +- 0.001. 
The detection of an emission line associated with a system at z = 0.286 is not 
confirmed. This considerably reduces the significance of the proposed line 
system at z = 0.286. The significance of the line system at z = 0.21 is 
unchanged and its reality remains uncertain. These findings are consistent 
with the Keck results (IAUC #7096; GCN #223
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 ; GCN #235
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 ). The orientation of the 
slit during the observations was along the parallactic angle (roughly E-W) and 
covered the galaxy ~10" to the W of GRB 990123. The redshift of this galaxy is 
0.278 +- 0.001 based on Ca II K and H (393.3 nm and 396.9 nm), G band 
(400.3 nm) and Mgb (517.4 nm)."

I. A. Yadigaroglu & J. P. Halpern (Columbia U.)
report on behalf of the MDM Observatory GRB follow-up team:

"We imaged the field of GRB 990123 in the R band on Feb. 3.54 UT using
the MDM Observatory 2.4m telescope.  A total of 60 minutes exposure was
obtained in seeing of 1.2 arcsec.  An object is detected at magnitude 
R = 23.9 +/- 0.25 (referenced to the comparison star of GCN #207
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 ).
However, its position is approximately 0.6 arcsec north of the previous 
position.  The new position is (J2000) RA 15:25:30.343, Dec +44:45:59.86, 
whereas the position on Jan. 30.52 was (J2000) RA 15:25:30.330,
Dec +44:45:59.27.  These positions are measured with respect to the 
same set of comparison stars, and they each have a statistical uncertainty
of 0.3 arcseconds in radius, but negligible systematic difference.
A possible extension in a Jan. 27 K-band image 0.5 arcsec to the north 
of the OT was described by Djorgovski et al. (GCN #243
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 ).  Our new R-band
image is consistent with that report.

The optical transient has faded at an accelerated rate since our last
reported observation on Jan. 30.52 (GCN #242
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 ).  A continuation of the 
alpha_r = -1.13 decay (Bloom et al. GCN #240
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 ) would have predicted an
R magnitude of 23.47 on Feb. 3.54.  Since the position of the optical
centroid has shifted, we conclude that our measured R = 23.9 represents
an upper limit to the magnitude of both the OT and any coincident galaxy,
and that we are beginning to detect either an intervening galaxy or
the host galaxy of the burst.  We note that the accelerated decay of
the OT could be an indication that the cooling frequency has passed below
the optical band, or that a jet which initially was highly collimated 
toward us has begun to spread.  An alternative interpretation in which
the initial OT has disappeared, and at the same time been replaced by
a fainter lensed component, seems less likely.

The new MDM image will be posted in the near future at
http://cba.phys.columbia.edu/grb/

This message may be cited.

Xiangdong Shi and Geza Gyuk (UC, San Diego):

In GCN#211
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 ,239
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  S. R. Kulkarni and D. A. Frail reported radio observations
of GRB990123, which show a "radio flare" on Jan. 24. GRB990123 appears
otherwise to be radio-quiet as of yet (GCN#200
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 ,212
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 ,239
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 ).  We suggest the
possibility that this "flare" resulted from the GRB external shock running
into a cloud off line-of-sight. This section of the shock was decelerated
efficiently and its sychrotron frequency quickly fell into the range of
radio waves. This inhomogeneity of the medium may explain the abruptness
and shortness of the radio emission.  The "flares" in other wavelengths
were brief and might also have been buried in the main afterglow.

We speculate that the cloud may have been composed of prior ejecta from
the gamma-ray burst progenitor. If there are still other nearby clouds, it
will be interesting to see whether the "flares" recur.

One implication of this hypothesis, if it is true, is that the GRB990123
is not likely to be strongly beamed (>10).  Its intrinsic energy output
would in turn be indeed huge.

This message is citable.

Andrew Fruchter, on behalf of the HST GRB Collaboration, reports:

As the Director of STScI, Steven Beckwith, has announced in GCN 245
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 ,
service observations of GRB 990123 by HST using the STIS CCD will be 
released to the community immediately upon their having been 
processed through the standard HST data pipeline and fully ingested 
by the HST Archive.   However, the standard data pipeline will 
not combine the 6 separate dither pointings, nor do a complete removal 
of the hot pixels and cosmic rays.  

Therefore, because of the great community interest in these
observations, the HST GRB Collaboration (whose time begins again
with Cycle 8) plans to fully reduce the data, and make the resulting 
FITS images publicly available to the community via the web within 
a day of the release of the data by the HST Archive (the wait may 
be significantly less, depending upon the timing of the release
of the data from the archive).   A GCN containing information on how 
to retrieve the fully reduced images will be sent as soon as they are 
available.

Steven Beckwith on behalf of STScI reports:

Owing to world-wide interest in GRB 990123, the Space Telescope 
Science Institute will carry out imaging observations with the
HST STIS \ CCD 50CCD (clear filter), dithered, using 3 orbits of Director's 
Discretionary Time as a service to the community.  The observations are 
scheduled to start Monday, 8 February at 23:06:54 UT, and finish Tuesday, 
9 February, 03:21:43 UT.  In the spirit of a cooperative multiwavelength
attempt to better identify and understand the nature of gamma-ray bursts, 
the HST data will be publicly available with no proprietary period 
immediately upon placement into the HST Data Archive, within a day or two 
of the observations.  When we know the exact time of placement in the 
Archive, we will post it.

Guy Pooley, MRAO, University of Cambridge, reports the following:

Five observations of the field of GRB990123 have been made
with the Ryle Telescope, Cambridge UK at 15 GHz.  No significant detection
was made.  This is a summary: 

 date       UT           S     sigma
                       -- microJy --
990125  0120-1116      160      180 
990126  0116-1140      -12      180
990129  0104-0727     -197      200
990130  0738-1122      106      420
990131  0734-1119       48      300

GRB 990123:  New Constraints on Possible Foreground Galaxies

S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, C. Koresko, R. R. Gal, 
S. C. Odewahn (Caltech), M. A. Malkan, I. S. McLean (UCLA), H. I. Teplitz
(GSFC), D. Koerner (U. Penn.), D. Kirkpatrick (IPAC), and D. A. Frail (NRAO), 
report on behalf of the Caltech-UC-NRAO-CARA GRB collaboration:

We performed a new differential astrometry between the Palomar discovery 
images of the optical transient (OT) associated with GRB 990123 (GCN 201
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 , 
GCN 205
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 ) and the DPOSS F (red) plate containing the field.  The results 
indicate that the apparent foreground galaxy near the OT position (GCN 201
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 , 
GCN 206
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 , GCN 207
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 ) is offset by 2.4 arcsec to the N and 1.0 arcsec to the E 
of the OT, with the estimated errors of 0.13 arcsec (systematic) + 0.3 arcsec 
(random) in each coordinate.  As we noted before, at R ~ 21.5 mag this 
object corresponds to approximately 2-sigma detection on the plate scan.

We detect no objects down to a limiting magnitude K ~ 23 in this location
in the stack of deep K-band images obtained at the Keck-I telescope on 24 
and 27 January 1999 UT (GCN 240
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 ).  The implied limiting color is so blue 
that we can exclude even the most actively star-forming galaxies.  We thus
conclude that the sky survey detection was spurious.  This is in a complete
agreement with the findings by Yadigaroglu et al. (GCN 242
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 ) in the R band.

This leaves open the question of the identification of galaxies responsible
for the absorption systems at z = 0.286 and z = 0.210 reported by Hjorth
et al. (GCN 219
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 ), as well as the z = 1.60 absorption system itself (Kelson
et al., IAUC 7096; and GCN 219
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 ).

Using the best-fit R-band light curve power-law slope alpha = -1.13 +/- 0.03
(GCN 208
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 , GCN 240
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 ) normalized to the K-band detection from 24 January 1999,
we estimate the maximum allowed contribution to the observed K-band light
in our measurements from 27 and 28 January 1999 UT from any underlying galaxy
(either the host and/or the foreground absorbers).  We obtain K > 22 mag for
any such objects.

However, in our best-seeing (FWHM ~ 0.5 arcsec) images, from 27 January 1999 
UT, we detect a faint, galaxy-like extension to the N of the OT, with an 
apparent center about 0.5 arcsec from the OT itself.  Its rough estimated 
magnitude is in the range of K ~ 22 to 23 mag, in agreement with the limits
derived from the light curve analysis.

Pending an independent confirmation of this detection, this object may be
either a foreground dwarf galaxy responsible for one of the absorption
systems reported by Hjorth et al., or a highly luminous host of the GRB
itself (possibly responsible for the absorption system at z=1.6).

While there is no clear observational evidence for a strong gravitational 
lensing of this burst, the possibility remains open, and the presence of 
foreground galaxies along the line of sight suggests that some lensing 
magnification must be taking place (regardless of the extraordinary apparent 
energetics of this burst).  Forthcoming observations from the Keck and the 
HST should clarify the situation.

This report is citeable.

I. A. Yadigaroglu, J. P. Halpern, R. Uglesich, & J. Kemp (Columbia U.)
 report on behalf of the MDM Observatory GRB follow-up team:

"We imaged the field of GRB 990123 in the R band on Jan. 30.52 using the
 MDM Observatory 2.4m telescope.  A total of 40 minutes exposure was
 obtained in seeing of 0.9-1.0 arcsec.  The optical transient is clearly
 detected at magnitude R = 23.01 +/- 0.24 (referenced to the comparison 
 star of GCN #207
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 , assuming r - R = 0.4).  An independent calibration
 using a Landolt standard also gives a consistent magnitude.  The OT 
 position, measured with respect to the USNO-A2.0 reference system,
 is (J2000) RA 15:25:30.34, Dec +44:45:59.2 with an uncertainty of
 0.3 arcseconds in radius.  This position is consistent with that of the
 original detection of the OT (GCN #206
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 ).  The temporal power-law decay 
 slope connecting our observation to the first Palomar detection is 
 alpha_r = -1.15 +/- 0.07, consistent with all previous observations,
 which gave alpha_r = -1.13 +/- 0.03 (GCN #240
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 ).

 Thus, the OT appears to be unresolved, at a fixed position, and following
 a power-law decay in time.

 However, we see no object corresponding to a suggested intervening
 galaxy that was estimated to lie 1.8 arcsec north of the OT (GCN #206
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 ).
 In fact, there is no other object on our image within 5 arcsec of the
 OT, to a limiting magnitude of approximately R = 24.  Since this galaxy
 was only reported to be seen marginally on one POSS II red plate with
 R = 21.5 +/- 0.5 (GCN #213
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 ), we conclude that it probably does not
 exist.  If true, this eliminates one of the arguments for hypothesizing
 that the burst is lensed."

 The MDM image will be posted in the near future at
 http://cba.phys.columbia.edu/grb/

 This message may be cited.

Bradley E. Schaefer (Yale):

In the last few days, the GCN has had several discussions about the
possibility that GRB990123 might be lensed with a high amplification.
This note is to provide balance and point out several problems with this
possibility.  In particular, the arguments suggest that there will be no
repeat lens events on short (or long) time scales.

(1) The idea of GRB990123 lensing has weak motivation.
	The motivation that GRB990123 is lensed is (A) to reduce the
deduced isotropic-equivalent energy (2.3x10^54 erg) to a level that can be
readily explained by models, (B) to account for the lack of previous
optical flash detection by LOTIS and ROTSE [GCN #216], (C) to account for
GRB970627 as a lensed image [GCN #234], and (D) to explain the large radio
variability [GCN #239].
	(A) To claim that GRB990123 is too energetic requires a knowledge
of the burst energy budget, whereas no such answer is known.
Nevertheless, within current reasonable models (e.g., collapsars, merging
compact objects) the typical gamma ray energies range up to ~10^52 ergs.
[This forces the lens amplification, A, to be >200 or so.]  Any such
argument would already require that GRB971214 [3x10^53 erg; Kulkarni et
al. 1998, Nature, 393, 35] and GRB980703 [2x10^53 erg; GCN #139
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 , GCN #143
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 ]
must also be lensed with large amplitude.  The likelihood of three high
amplitude lenses among the 17 SAX bursts is close to zero.
	(B) The optical flash luminosity is indeed large [it would appear
brighter than our Sun at a distance of 1 kpc], but we have no idea of what
is expected, so with A=200 the source still has M~-30.7 and this is still
astounding.  More to the point, no previous search would have detected an
optical flash with the E_gamma/E_opt ratio for GRB990123 (i.e., V~9 [GCN
#205] for a gamma ray fluence of 5.1x10^-4 erg cm^-2 [GCN #224]).  For
example, the highest fluence event seen by GROCSE is 1.9x10^-5 erg cm^-2
with an optical limit of 8.1 mag [H. S. Park et al. 1997, ApJ, 490, 99].
For LOTIS, the strictest limit comes from GRB970223 with a fluence of
4.8x10^-5 erg cm^-2 and an optical limit of 11.0 mag [H. S. Park et al.
1997, ApJLett, 490, L21].  So there are no missing-optical-flashes to
motivate a lens suggestion.
	(C) For GRB970627 to be a lensed image, it must have the same
light curve, spectrum, and position as GRB990123.  [Microlensing could
conceivably make mild changes in the light curve or spectrum by imaging
different portions of the fireball, but then the time delay between images
cannot be 1.5 years without simultaneously invoking high amplitude
microlensing on top of high amplitude macrolensing.]  The two bursts have
peak-to-peak times of 12s and 17s, have greatly different peak intensity
ratios, have greatly different peak shapes, and GRB970627 lacks the late
time flux prominent in GRB990123.  The two bursts have greatly different
hardness ratio in BATSE channels 1, 2, and 3, with H21 equal 1.37 versus
0.56 and H32 equal 5.83 versus 1.14
[http://www.batse.msfc.nasa.gov/data/grb/catalog/flux.html].  The
GRB990123 OT position is 4.23 degrees away from the IPN annulus for
GRB970627 which has a 3-sigma width of 0.065 degrees [GCN #235].  Thus,
GRB970627 is certainly not a lensed image of GRB990123.
	(D) The radio observations of GRB990123 to date show >10X
variations in flux [GCN #239], but this is not qualitatively different
from the 4X variations already known from GRB scintillation [e.g., Frail
et al. 1997, Nature, 389, 261].  Nevertheless, GCN #239
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  suggests that
normal variation of a GRB cannot account for this variation, and instead
propose that the radio detection is of an earlier lensed image of the same
GRB.  However, this alternative suggestion has exactly the same problem as
what it was trying to replace, since then the earlier lensed image is
required to vary by >10X.  That is, lensing does not solve the posed
problem.  So logically, there is no motivation to invoke lensing.

(2) A GRB990123 lensing event is now extremely improbable.
	Within the lensing hypothesis, for simple lenses, the time delay
between images will scale as the mass of the lens, with typical delays of
250 seconds for a 10^9 solar mass lens or 7 hours for a 10^11 solar mass
lens [see E. Turner et al. 1984, ApJ, 284, 1].  So for the simple case,
there can be no lensed event in the future.  For more complex lenses, GCN
#236
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  points out that the time delay between the two brightest and roughly
equal images will be from tens of seconds to a fraction of a day.  In
either case, the lack of a comparable sized lens argues strongly that
there will be no more images arriving in the future and that there has
been no lensing at all.
	The fraction of quasars that are lensed with moderate
amplification is ~10^-3.  The fraction of GRBs with multiple images is
<10^-3 (G. Marani 1998, Thesis, George Mason).  For a GRB distance 
of z=1.6, the expected lensing fraction is ~2x10^-3
(D. Holz et al. 1999, ApJ, 510, 54).  [A correction for amplification bias
is needed for this theoretical estimate, but this will not be large due to
the turn over in the LogN-LogP curve.]  So, for GRBs with A>~2 we expect
the lensing fraction to be ~10^-3.  The lensing probability scales as
A^-2.  For the 17 SAX bursts, we then expect a final probability of
<2x10^-6 that any burst will be amplified as much as required.  This
probability calculation suggests strongly that GRB990123 is not lensed and
thus will not have future lensing events on short or long time scales.

(3) Beaming is a better model.
	Observationally, we know that the burst emission is collimated (to
allow the escape of GeV photons) and that most of burst emission is coming
from very small angular beams (e.g., B. Schaefer & K. C. Walker 1998,
ApJLett, 511, in press; ASTRO-PH/9810271; ASTRO-PH/9802200).
Theoretically, recent models produce small cones of emission, for example
S. Woosley suggests a beaming factor of 0.015 while M. Rees suggests it
can be as low as 10^-4 [Rome GRB Conf.].  So we have every reason to
expect significant beaming factors.  This expectation will immediately
lower the burst energy requirements and eliminate the motivation for a
GRB990123 lens.  Why invoke an extremely improbable solution with no
positive evidence when everyone already knows that beaming solves the
problem and must be present.

GRB 990123:  Detection of the IR Transient, and the Light Curve Fits

J. S. Bloom, C. Koresko, S. R. Kulkarni,  S. G. Djorgovski, R. R. Gal, 
      and S. C.  Odewahn,  Caltech,
H. I. Teplitz, NASA Goddard Space Flight Center,
D. Koerner, Univ. of Pennsylvania,
D. Kirkpatrick, Infrared Processing and Analysis Center,
M. A. Malkan, and I. S. McLean, Univ. of California, LA,
D. A. Frail, National Radio Astronomy Observatory, 
report on behalf of the Caltech-CARA-NRAO GRB collaboration:

"The field of the optical transient of GRB 990123 (GCN 201
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 ) was observed
with the Near Infra-red Camera (NIRC) on the Keck I telescope on
24 January 1999 UT by Koerner and Kirkpatrick.  We report the discovery
of the IR counterpart of the afterglow with K = 18.3 +/- 0.03 mag (epoch 
24.6356 Jan 1999 UT).   The same field was observed by Malkan, Teplitz and
McLean on the nights of January 27.65 and 28.55 UT, and in both instances
the object was readily detected.  Fitting a power law to the three
magnitudes yields a power law exponent of alpha_K= -1.14 +/- 0.08.

Separately, we have carried out a program of recalibrating Gunn r and R 
band magnitudes reported by others via the GCN.  We used those measurements
which reported the magnitude of a reference star (or stars) and have put all 
the measurements on a common photometric system. A fit to these recalibrated 
magnitudes yields a power law slope, alpha_r = -1.13 +/- 0.03.  Within 
errors, the slope of the K band data is fully consistent with that obtained 
from the r/R band data. We adopt a mean alpha of -1.13.

The color difference between the decaying r and K fluxes is (r-K) = 2.75 mag. 
Converting the magnitudes to flux this color difference corresponds to 
beta = -0.82, where f_nu = const * nu^beta.  The ratio alpha/beta = 1.38. 
This suggests that the cooling frequency is higher than the central frequency 
of the r band (about 4x10^14 Hz) even two days after the burst.  We urge 
continued monitoring of the optical transient in the r/R band with the view 
of detecting the passage of the cooling break.

In contrast to the light curves measured in the r and K bands, the light
curve in the B band (calibrated on a uniform photometric system) is not well 
described by a power law.  The origin of this discrepancy is as yet unclear.
Further observations are in progress.

This report is citeable."

S. R. Kulkarni (Caltech) and D. A. Frail (NRAO) report on behalf
of the Caltech-NRAO-CARA gamma-ray burst collaboration the following.

"We have continued monitoring the error box of GRB 990123
(GCN #202
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 ) with the Very Large Array (VLA). All our observations
were  conducted in the 8.46-GHz band. At the position of the
optical transient we obtain the following fluxes:


Here is a summary of all the X-band observations to date.

Jan 23:  <68 microJy  (GCN #200
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 )
Jan 24:  260 microJy  (GCN #211
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 )
Jan 26:  <78 microJy
Jan 27:  <50 microJy
Jan 28:  <50 microJy

Note: The upper limits are indicated by "<" and are 2-sigma.

To summarize, the radio afterglow has been detected only once, on
January 24 1999. The detection was very secure being 8-sigma. The
source was seen in both intermediate frequency (IF) bands and in both
senses of polarization (R and L). In contrast, the average of the flux
for the period January 26-28 is <32 microJy.

This high degree of variability could be due to interstellar scattering
and scintillation (ISS).  However, the factor of 10  variation in the
flux density requires rather extreme ISS.  In addition, we expect the
source to be gradually rising with time. Thus the absence of the source
on three successive days is quite puzzling.

Discarding the ISS hypothesis, we have two choices. First, the radio
emission detected on January 24 is some kind of precursor event to the
main afterglow. Typically, the radio afterglow in the 8.46-GHz band
rises to the peak flux in about 10-20 days. We have little data about
the behavior of radio afterglow within a few days after the burst.
Thus it is difficult to accept or reject this hypothesis.

The alternative hypothesis is that the GRB is lensed (GCN #216
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 ).  At
the present time, there is no firm evidence for lensing. However,  the
lensing idea is economical in energetics. Likewise, the lensing
hypothesis offers a simpler alternative to the curious phenomenon
discussed above.  As discussed by various people (S. Mao GCN#236
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 , R.
Narayan, pers.  comm.) a robust expectation of strong lensing is that
we should first see the faint image "B1" (in the terminology of GCN
#236
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 ). In this framework, we identify the radio source of Jan 24th with
the radio afterglow of the B1 component.  If this interpretation is
correct then the radio afterglow of the brighter components B2 and B3
should become visible in in the next few weeks. We do not possess
sufficient astrometric accuracy to see if the reported (GCN #201
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 )
optical afterglow (which is presumably due to B1+B2) and the radio
afterglow are offset on the sky.  Indeed, the excellent agreement (0.5
arcsec) between the positions of the optical and the radio afterglow
places a limit of a delay of 30 days between components B1 and B2+B3.
Clearly, radio monitoring will refute or confirm this hypothesis.

This report is citeable."

R. J. Nemiroff (Michigan Tech.), 
G. F. Marani (NRC/NASA), J. T. Bonnell (USRA/NASA),
J. P. Norris (NASA/GSFC), and C. A. Meegan (NASA/MSFC) report:

There is, as yet, no primary indication that GRB 990123 has undergone
any type of strong gravitational lensing.

Weak lensing:  Most sources at z>1.6 will be either gravitationally
amplified or (more likely) de-amplified by >5% by inhomogeneities in
the gravitational field between the observer and the source (see, for
example, Holz et al. astro-ph/9804271).

Strong Lensing:

Galaxy lensing: There is, as yet, no primary indication that GRB 990123
is one of multiple macro-images created by an intervening galaxy lens.
In comparison with QSOs, it is not unusual for single image QSOs to be
found within 3 arcseconds of a low mass galaxy (e.g. Claeskens & Surdej
1998, A&A 335, 69) or for a single image QSO to have absorption lines.

As GRB 990123 was the brightest event ever detected with a measured
cosmological redshift, its macrolensing probability is high relative to
other GRBs and afterglows, but still, quite possibly, low in absolute
terms.  The foreground galaxy near GRB 990123 is intriguing but not yet
defining.  The "probability" now all hinges on the unknown masses and
mass distributions internal to foreground galaxies.

No other BATSE triggered GRB has been found that is consistent with a
lensing interpretation.  Twenty-three BATSE GRBS have occurred in the
past three years within a 3-sigma error contour of GRB 990123.  The
closest two in light curve shape were judged to be BATSE triggers 6279
and 6698.  A preliminary visual inspection reveals none of them is a
close light-curve match to GRB 990123.

Millilensing: There is, as yet, no primary indication that GRB 990123
has undergone significant amplification by a compact mass on the
globular-cluster scale.  The two main peaks in the GRB light curve do
not appear to be co-added replicas of a single light curve seperated by
major peak are significantly different (> 5 sigma,  preliminary
analysis) in BATSE channels 1 and 4.  Similarly, the ratios in peak
flux between the first major peak and the last peak are also
significantly different (> 5 sigma, preliminary analysis).

Microlensing: There is, as yet, no primary indication that GRB 990123
has undergone significant light curve distortion due to microlensing by
compact masses on the stellar mass scale.  Microlensing at low optical
depths would create images separated in time by only microseconds
(Nemiroff 1994, ApJ 432, 478; Nemiroff 1998, ApJ 494, L173) to
milliseconds (Williams & Wijers 1997, MNRAS 286, L11), generally below
minimum time scale of BATSE GRB resolution (64-ms).

We encourage, however, continued attempts to recover secondary images
from any GRB or afterglow, including GRB 990123.

The name of C. A. Young, duty scientist at the time of CGRO-COMPTEL's
initial rapid (~10 minute) localization of GRB 990123, was inadvertently
left off the author list.

The correct attribution should be as follows:

"A. Connors, R. M. Kippen and C. A. Young, for the CGRO-COMPTEL Rapid
Burst Response collaboration; and S. Barthelmy and P. Butterworth, for
BACODINE/GCN, report the following:"

This note can be cited.

Shude Mao (Max Planck Inst. for Astrophysics) reports:

   Djorgovski et al. (GCN Circ. 216
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 ) suggested that GRB 990123 might be
highly magnified (A>10) by an intervening galaxy based on a variety of
arguments. A likely scenario is that the bursting source is very close to
a fold caustic. As a result, we have a PAIR of highly magnified images
(we call B2 and B3) plus other additional image(s).

   If this scenario is correct, then from the lensing theory, three points
can be immediately made:

1. There must be a fainter burst that has arrived before GRB 990123. This
   first burst (we call B1) would be offset from GRB 990123 by about ~2".
   This expectation is valid no matter what the lens potential.
   Notice that, in this scenario, all the optical and radio afterglows
   we see now are the sum of the first-arriving burst B1 and GRB 990123.
   High resolution imaging in the radio and in the optical (with HST)
   may reveal the presence of B1.

   The time interval and intensity ratio between B1
   and GRB 990123 does depend on the model. A rough estimate
   of the time delay is a few days to a month, and the intensity
   ratio is around a few to a few tens. These predictions can be made
   more precise when the astrometries and velocity dispersion of the
   foreground galaxy are better known. The gamma-ray burst data archive
   should be searched to see whether there was such a burst. A fourth
   image (B4) much fainter than GRB 990123 may also appear after about a month.
 
2. The gamma-ray burst host galaxy, since it is extended, will be distorted
   into a ring or arcs if the center of the host galaxy does not have
   a significant offset from GRB 990123. Such features can be detected with
   HST imaging (see also Turner, GCN 221
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 ). This expectation is independent
   of the models.

3. The close pair of images should have roughly equal intensities.
   The time delay between these two images depends strongly
   on the magnification; a simple model shows that it can be between
   tens of seconds to a fraction of a day. This close pair therefore
   should have ALREADY left imprints on the after glow light curves.
   The close pair should have an image splitting of about 0.05" to a
   fraction of arcsecond; HST imaging will either provide a confirmation
   or rule out this scenario.

   If the time delay between the close pair can be as short as tens
   of seconds, this raises an intriguing possibility: is GRB 990123
   itself lensed? That is, GRB 990123 may be superposed by two bursts
   coming from the close pair. These two bursts have a time lag
   of about 15 seconds, producing the first and second peaks in
   the light curve. It will be very interesting to check whether 
   the gamma-ray spectrum and light curve of GRB 990123 are consistent
   with this superposition scenario. If this hypothesis is correct, then
   the close pair should have an imaging splitting of ~0.05" and
   each is magnified by a factor of about 100.

   More information (including figures) can be found at 
	http://www.mpa-garching.mpg.de/~smao/grb.html

   This report may be cited.


[GCN OP NOTE:  This Circular was received at 09:19 UT, but was delayed until
an entry in the distribution list was created.]

K. Hurley, UC Berkeley Space Sciences Laboratory, on behalf of the
Ulysses GRB team, and C. Kouveliotou, Universities Space Research
Association, Marshall Space Flight Center, on behalf of the BATSE team,
report:

GRB 970627 (=BATSE Trigger #6279), suggested as a possible
gravitationally lensed counterpart to GRB 990123 (Rutledge and
Kulkarni, GCN 234
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 ), was detected by the Ulysses GRB instrument and
triangulated to an annulus centered at RA(2000)=153.491,
Decl.(2000)=26.188, with radius 67.841 degrees and 3 sigma width 0.065
degrees.  This annulus intersects the one for GRB 990123 (GCN 222
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 ) at
two locations: around RA(2000)=84.055 degrees, Decl.(2000)=+08.531
degrees, and around RA(2000)=234.866 degrees, Decl.(2000)=+37.878
degrees.  Neither error box, nor the annulus for GRB 970627, includes
the optical transient (GCN 206
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 ).  (We note that the IPN annulus and the
BATSE error circle for GRB 970627 do not intersect, nor does the BATSE
error circle include the optical transient, but this is not unexpected,
given that the error circle is a 1 sigma location.)  We conclude that
GRB 970627 is not the lensed counterpart of GRB 990123.

This message may be cited.

Search for Potential Images of GRB 990123

R. Rutledge and S. R. Kulkarni (CIT) note: 

Djorgovski et al. (GCN #216
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 ) have suggested that GRB 990123 is lensed
by a foreground galaxy identified by Odewahn et al. (GCN #201
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 ) and
presumed to be at redshift 0.21 or 0.28 (Hjorth et al. GCN #219
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 ). The
basis of this argument is two fold: (1) the energetics of the GRB are
reduced, as lensing would provide strong amplification, and (2) the
foreground galaxy, due to its placement and likely mass, must result
in some amount of lensing of a background object at the position of
the optical transient. 

A consequence of this lensing hypothesis is image splitting. The same
burst would arrive at different times,  with the time difference
proportional to the image separation (e.g., Turner et al. GCN #221
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 ).
Motivated by these considerations we have looked into the BATSE
catalog to see if there are GRBs in the general vicinity of the
location of GRB 990123 (Piro et al, GCN #199
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 ) and with close to
identical profile.  The two profiles need not be exactly identical
since microlensing combined with source expansion can lead to changes
in profile.

Within a 4-sigma error radius consistent with the GRB 990123 OT
transient position, we find two double-peaked GRBs.  In one of these
(GRB 970627, BATSE Trigger #6279), the peaks are similar in separation
and peak-width ratio to GRB 990123, although the peak intensity ratio
is different by about 60+/-20%.  In addition, there is excess emission
in GRB 990123 following the two peaks, which is not observed from GRB
970627.  However, based on the characteristics of intensity profiles,
it is possible that GRB 970627 and GRB 990123 are lensed images of the
same GRB event.

We estimate that the chance probability of a similar profile GRB being
consistent in position is about 2%, based on the identification of 8
similar GRB intensity profiles among the approximately 2000 GRBs in
the BATSE catalog. If we include in this statistic GRBs with a  more
dissimilar intensity profile, the chance probability increases.  We
find 24 double-peaked GRBs (of 2000 in the BATSE Catalog) which are
comparable in peak separation (15-25 seconds) but are still dissimilar
to GRB 990123, resulting in a chance probability of 6.4%.  A
comparison between the light curves of these two GRBs is available at
http://www.srl.caltech.edu/personnel/rutledge/0123/bursts.html.

If GRB 970627 is indeed a lensed image of GRB 990123, then to explain
the very long time delay between the two images (1.5 years), the
positional splitting must be several arcseconds in size and would most
certainly require multiple lenses or a cluster.

This message may be cited.

GRB 990123 BVRI Photometry

N. Masetti, E. Palazzi, E. Pian, F. Frontera (ITESRE-CNR, Bologna), C.
Bartolini, A. Guarnieri, A. Piccioni (Astronomy Dept., Univ. Bologna), 
G. Valentini (Teramo Astr. Obs.) and E. Costa (IAS-CNR) report:

"We have imaged the field of GRB990123 with the Bologna Astronomical
Observatory 1.5m telescope equipped with BFOSC, using Johnson B and V, and
Cousins R and I filters in January 24-26. 

Calibrations were done referring to GCN 206
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  for the B image, to GCN 204
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for the R image, and using the standard star BD+252534 (Taylor et al.
1989, AJ 97, 1798) for the V and I images. 

In the appended table the preliminary magnitudes of the optical transient
(GCN 201
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 ) are reported along with the observation dates.

Power-law fits to the R and V band data yield temporal decay indices of
alpha = 1.20 +- 0.08 and alpha = 1.25 +- 0.16, respectively (errors are 1
sigma), with satisfactory chi square values.  No indication is found of a
flattening of the light curve due to an underlying galaxy. 

Suggestion of a slight flux increase is seen on January 25 in both R and V
bands, as opposed to the overall fading trend.  This is however not
significant. 

The BVRI spectral continuum of the optical transient in the first night
(average time of Jan 24.16), dereddened with E(B-V) = 0.016 (GCN 207
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 ), has
a power-law shape (f_nu = k*nu^{-beta}) with best-fit slope 
beta = 1.1 +- 0.2 (1 sigma). 

The BVRI light curves and the radio-to-X-ray spectral energy distribution
of the transient are also shown at the Web site

http://tonno.tesre.bo.cnr.it/~masetti/grb990123.html

Multiwavelength observations, particularly in the near-infrared and
millimetric bands, are needed and urged.



      Date (UT)    mag    error  band
  -----------------------------------
  1998 Jan 24.122  19.36  0.20    I
           24.142  19.79  0.10    R
           24.164  19.97  0.16    V
           24.194  20.64  0.07    B
           24.216  19.92  0.10    R
           25.138  20.91  0.10    R
           25.159  20.77  0.10    R
           25.181  21.01  0.20    V   
           25.203  20.93  0.20    V
           26.154  21.77  0.16    V
           26.154  21.56  0.10    R


This message can be cited."

L.A. Antonelli, A. Di Paola, R.Speziali, Osservatorio Astronomico di 
Roma, Italy, and G. Gandolfi, BeppoSAX Scientific Operation Center, 
Italy, report on behalf of SWIRT Team and BeppoSAX Team:

"We observed the Optical Transient field of GRB 990123 in the J band 
using the 1.1m AZT-24 telescope and the near-infrared 
camera/spectrometer SWIRCAM at the Campo Imperatore Astronomical 
Observatory operated by the Astronomical Observatory of Rome (O.A.R.). 

On 25.22 (UT) January 1999, the OT field was observed for a total
exposure time of 2000 s reaching the limiting magnitude in the
J band of 19.5 +/- 0.3 mag . 
On 26.12 (UT) January 1999 the field was re-observed for a total
exposure time of 3600 s reaching the limiting magnitude in the
J band of 19.3 +/- 0.3 mag. No source has been found in both
observations within the errorbox of the O.T. (IAUC 7094). 

These observations provide an upper limit, in the J band, to the 
infrared counterpart (if any) of GRB 990123 and on its behaviour.

This message may be cited."


[GCN OP NOTE (99/01/27 15:10 UT):  Some of you on the GCN Circulars list
probably received this Circular twice.  Due to a very low probability
occurance of e-mail deliver deamons timing, this notice got deposited
in the "import" queue of the Circulars processing deamon twice.]

S. M. Matz (Northwestern University), G. H. Share, R. Murphy, and J. D.
Kurfess (Naval Research Lab) report on behalf of the OSSE team:

The OSSE instrument on board the Compton Gamma-Ray Observatory detected
strong emission from GRB 990123 in its central detectors and in its
active NaI shields. While the burst was not in the detectors' field of
view, it was still detected to >3 MeV in two 16 s intervals. The rise
and first strong peak (at about trigger+25 s) are roughly (within 1--2
s) aligned at all energies. The low-energy (<100 keV) burst emission
appears to last significantly longer than the higher energy emission.
Detailed spectral analysis is underway; preliminary analysis indicates
that the average spectrum of the main burst can be well described above
0.8 MeV by a photon power law with an index of about -3.

Time histories from the OSSE central detectors in different energy
ranges from 50 keV to >3 MeV are posted on the OSSE burst web page 
( http://www.astro.nwu.edu/astro/osse/bursts/ ) along with a preliminary
spectrum of the burst. Also available are a plot and raw data for the
high time resolution (16 ms) history of the first 60 s of the burst
from the triggered OSSE shield data (>100 keV).
 
This report may be cited.

A. Connors and R. M. Kippen, for the CGRO-COMPTEL Rapid Burst Response
collaboration; and S. Barthelmy and P. Butterworth, for BACODINE/GCN,
report the following:

CGRO-COMPTEL observed GRB 990123 to be extremely bright in its ~MeV energy
range.  The >0.7 MeV emission rose about 18 seconds after the initial BATSE 
trigger at 9h 46m 56.12s U.T. and lasted about 46 seconds, for a 10 sigma
detection, despite its very large zenith angle (59 degrees).  An initial 
detection notice was sent about 10 minutes after burst onset.  Improved
skymaps and light-curves for the full 0.2-30 MeV range have now been posted
at the CGRO-COMPTEL Rapid Burst Response web-site:

     http://wwwgro.unh.edu/bursts 

These are still considered preliminary as our standard energy calibration is
not yet complete.

This message can be cited.

L.A. Antonelli, A. Di Paola, Osservatorio Astronomico di Roma, 
G. Gandolfi (BeppoSAX Scientific Operation Center) report on 
behalf of SWIRT Team and BeppoSAX Team:

"On 25.16 (UT) January 1999, we imaged the Optical Transient field 
in the K band using the 1.1m AZT-24 telescope and the near-infrared 
camera/spectrometer SWIRCAM at the Campo Imperatore Astronomical 
Observatory (http://www.mporzio.astro.it/cimperatore/WWW/) operated 
by the Astronomical Observatory of Rome (O.A.R.). 

The 4'X4' field of view was exposed for 3300 s reaching the limiting
magnitude in the K band of 17.9 +/- 0.2 mag. No source has been found
within the errorbox of the O.T. (IAUC 7094). This observation provides
a more compelling upper limit in K band with respect to the previous
observation in the same band (GCN #214
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 ). The behaviour of the 
source between the two observation, at this wavelenght, is unknown. 

Further near infrared observations are in progress.

This message may be cited."

T. Murakami, M. Ishida and T. Dotani, Institute of Space and
Astronautical Science, and A. Yoshida and N. Kawai, Institute of
Physical and Chemical Research, report:

The X-ray astronomy satellite ASCA has been observing the X-ray afterglow
of GRB990123 since January 25.688 (UT).  The observation started about
55 hours after the burst, but the X-ray afterglow is still bright.  ASCA
will continue observing the source until January 26.806 (UT).  With only
one forth of the dataset down-linked at the tracking station, the flux
is about 1 x 10E-12 erg cmE-2 sE-1 in 2 to 10 keV assuming a power-law
with the photon index of -1.6.

R.Sagar, A.K. Pandey, R.K.S. Yadav, Nilakshi and V. Mohan of U.P. State 
 Observatory, Manora Peak, Nainital, India report:

"We have observed the optical transient (GCN #201
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 ) of GRB
990123 (GCN #199
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 ) with the 104-cm telescope of the U.P. State Observatory,
Manora Peak, Nainital, India in Johnson B and Cousin R photometric 
passband under good photometric sky conditions. We have calibrated the images 
using photometric standards located in the field of open star cluster M67. 
In each filter three images of 20 minutes are obtained and they are stcked to 
improve signal to noise ratio of the optical transient. 
We obtain the following magnitudes: 

      UT date    filter      mag    err

     Jan 24.90      R       21.25   0.1
     Jan 24.99      B       22.05   0.2

 The (B-R) colour of the OT becomes redder by about 0.2 mag compared to our
observations on Jan 23, 1999 (GCN #218
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 ).These results are preliminary
and more accurate results will be published later.

 At the Web site http://www.rri.res.in/grb990123/ all the images taken 
on the nights of Jan 23 and 24 are available. We have also taken
images during the night of 25/26 Jan 99 and will report the results later.
Sky conditions were good for photometric observations on the nights of
24/25 Jan 99 and 25/26 Jan 99 and we have observed the M67 field for 
calibration purposes. Precise determination of the BVRI magnitudes of the stars
as well as of the OT in the field of the GRB990123 are in progress. 

This message may be cited."

GRB 990123 Optical Follow-Up

J. Zhu, J. S. Chen, and H. T. Zhang, on behalf of the Beijing Astronomical
Observatory GRB team report:

"We observed the GRB 990123 OT (GCN #202
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 ) around Jan. 25.9 with
BAO 0.6-m Schmidt telescope under good weather. One 40-min. exposure
was made with BATC band-i filter and the very weak source at RA=15:25:30.35,
Dec=44:45:59.4 (J2000) was detected near the detection limit of the image
which gives a magnitude of 21.3 +/- 0.3 (Jan 25.901) using the No. 1 and
No. 2 stars in GCN #204
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 . Assuming a minimum decay slope of 1.18 (for the
OT) obtained from our previous observations (GCN #217
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 ), we conclude that
the source we detect here is probably the coincident galaxy found on
the digital POSS-II image by Odewahn et al. (GCN #201
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  and IAUC 7094).

This report may be cited."

This GCN is an addendum to GCN 223
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 :
 
Please note that Hjorth et al., GCN 219
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 , do not indicate the position
angle of the slit they used.  Furthermore, to the eye, the OT appears offset
to the south of the apparent host in the finding chart of Odewahn et al.
(GCN 201
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 , see also Gal et al., GCN 213
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 ), while the Keck slit lay in
the E-W direction.  Thus the apparent non-detection by Keck of an object
reported in the NOT spectrum may be due to different position angles having
been used in the observations.

R. M. Kippen (University of Alabama in Huntsville) reports on behalf
of the BATSE GRB team:

GRB 990123 was detected by BATSE on 1998 January 23.407594 as trigger
number 7343.  The event was strong and consisted of a multi-peaked
temporal structure lasting >100 s, with significant spectral
evolution.  The T50 and T90 durations are 29.82 (-/+ 0.10) s and 63.30
(-/+ 0.26) s, respectively.  The burst's peak flux (50-300 keV;
integrated over 1.024 s) and fluence (>20 keV) are 16.42 (-/+ 0.12)
photons cmE-2 sE-1 and 5.09 (-/+ 0.02) x 10E-4 erg cmE-2,
respectively---ranking it in the top 2% (0.3%) of the BATSE burst flux
(fluence) distribution.  The average spectral hardness of the burst,
as estimated by the ratio of 100-300 keV counts to those in the 50-100
keV range, is H32 = 1.51 (-/+ 0.004), which is average among BATSE
bursts.  The BATSE burst location is consistent with those measured by
BeppoSAX (GCN 199
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 ,202
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 ,203
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 ) and with the proposed optical/radio
transient counterpart (GCN 201
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 ; 204-221).  A location sky-map and
lightcurve for this event (and other notable bursts) are available at
the BATSE Rapid Burst Response world-wide-web site:

          http://www.batse.msfc.nasa.gov/~kippen/batserbr/

-eof-

Andy Fruchter reports for Dan Kelson who is in transit:

In addition to the z=1.6 metal absorption lines detected in the Keck spectrum
of the OT associated with GRB 990123 and reported by Kelson et al. in 
IAUC 7096, H and K absorption corresponding to a redshift of z~0.2
were found in a nearby galaxy, thus confirming the redshift reported
by Hjorth et al. in GCN 219
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 .  However, this galaxy is the
one visible in the finding chart of Odewahn et al., GCN 201
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 , which 
lies approximately 10" to the west of the OT.  No evidence of lines
corresponding to a z~0.2 were found in the Keck spectrum any closer on
the sky. 


[GCN OP NOTE (99/01/26 00:07:21 UT):  Please see Addendum revision in GCN 225
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 .]

K. Hurley, on behalf of the IPN3 team, and M. Feroci, on
behalf of the BeppoSAX GRBM team, report: 

We have obtained a preliminary IPN3 annulus for GRB990123
by triangulation using Ulysses and the BeppoSAX GRBM.  The
annulus is centered at RA(2000)=163.7197 degrees, Dec(2000)=
-9.4661 degrees, with a radius of 81.3372 degrees and a
3 sigma width of 2.67 arcminutes.  This annulus reduces slightly
both the 2' radius SAX WFC error circle (BeppoSAX MAIL 99/2)
as well as the 1.5' MECS error circle (BeppoSAX MAIL 99/3),
and contains the optical transient (Bloom et al., GCN 206
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 ).
An image may be found at ssl.berkeley.edu/ipn3/990123/.
Considerable reduction of the annulus width is possible.
This report was delayed due to the fact that Ulysses data
are not processed and distributed over the weekend.

This message may be cited.

GRB 990123 : Multiple and Distorted Images of the Host Galaxy?

E. L. Turner (Princeton Univ. Obsv.):

Djorgovski et al. (GCN Circ. 216
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 ) suggested that GRB 990123 might be
strongly lensed by an intervening galaxy based on the extreme energetics
implied by its high gamma-ray fluence (Feroci et al., IAUC 7095) and
the redshift lower bound of 1.61 (Kelson et al., IAUC 7096) and on the
relatively bright coincident galaxy found on the digital POSS-II images
by Odewahn et al. (GCN Circ. 201
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  and IAUC 7094).  Their prediction that
this galaxy's redshift would be much smaller than 1.6 and probably in
the range 0.2 to 0.3 was quickly confirmed by Hjorth et al. (GCN Circ. 
219
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 ) who in fact found one definite galaxian redshift system at z = 0.286
and a second possible one at z = 0.210, thus providing strong apparent
support for the gravitational lensing hypothesis in GRB 990123.

Hjorth et al. also note that additional images of this GRB may appear on
a time scale of days to months due to differential lensing time delays.

The light from the host galaxy of GRB 990123 will also be affected by any
strong gravitational lensing which has influenced the burst and should
show strongly distorted and probably multiple images if the magnification
factor is large.  Detection and characterization of such lensed host galaxy
images would provide strong additional evidence for the lensing hypothesis
but, more importantly and much more urgently, would also allow detailed
modeling of the lensing mass distribution and geometry and, thus, far more
precise prediction of where and when additional images of the burst are
expected to occur.  

These predictions would make it far more practical (and economical of
observing resources) to detect and intensively study additional images
of the burst as they appear.  Such data would not only be valuable for
probing the early stages of GRB physics but might also allow a sufficiently
precise determination of the time delay(s) to use for a measurement of
the cosmic distance scale.  Thus, deep and high resolution imaging in
search of the possibly distorted and multiple images of the GRB 990123
host galaxy is urgently indicated.

This report may be cited.

A. Maury (Observatoire de la Cote d'Azur), M. Boer, S. Chaty (Centre
d'Etude Spatiale des Rayonnements), report:
We observed GRB 990123 from the Observatoire de la Cote d'Azur 0.9m
Schmidt Telescope. The optical counterpart of the GRB is clearly
detected as well as the host galaxy. Below are the unfiltered
magnitudes, corresponding approximately to R magnitudes, given the
detector response. The mean uncertainty is 0.4 mag. The resulting decay
slope, is 1.35, which is in good agreement with the slope mentionned by
Bloom et al. (GCN Report #208), given the uncertainties.

January
24.037037       19.68
24.052419       19.67
24.057234       20.02
24.061887       19.79
24.066539       19.71
24.071192       19.44
24.075845       20.4
24.080498       19.92
24.08515        20.05
24.094456       20.25
24.099109       20.15
24.113067       19.65
24.117731       19.82
24.122373       20.22
24.127025       20.53
24.131678       20.32
24.136331       20.49
24.140984       20.15
24.145637       19.98
24.150289       20.06
24.154942       20.44
24.159595       20.42
24.164248       20.03
24.1689         20.11
24.178206       20.23
24.182859       20.06
24.201076       20.36

Other images have been taken during the night 24-25/1/99 and will be
reported later.


[GCN OP NOTE (99/01/26 23:47 UT):  An ammended version (extra column
trailing removed and institutional affiliations added) of this circular
was added to the archive at the authors request.  The original distributed
version suffered from extraneious material from the mailer utility used
to create the posting.]

GRB 990123 Spectroscopic Redshifts

J. Hjorth (Copenhagen), M. I. Andersen (NOT), 
L. M. Cairos, N. Caon, M. Zapatero Osorio (IAC), 
H. Pedersen, B. Lindgren (Copenhagen), 
A. J. Castro Tirado (LAEFF, IAA), and E. Perez (IAA) report:

"Three 40 min spectra of GRB 990123 were obtained at NOT on Jan 24.24 UT 1999. 
Based on a preliminary reduction and analysis we detect the following 
ultraviolet absorption lines: Si II (152.6 nm), C IV (154.9 nm), Fe II 
(160.8 nm), Al II (167.1 nm), Zn II (202.6 and 206.3 nm), Fe II (234.4, 237.5, 
and 238.3 nm), and Fe II (258.7 and 260.0 nm) at a redshift of 1.600 +- 0.001. 
This value is in agreement with the redshift found by Kelson et al. (IAU Circ. 
7096).  Several additional absorption lines and two emission lines are detected.
There is one definite system at z = 0.286 +- 0.001 based on [OII] (372.7 nm) 
emission and Ca H and K (393.3 nm and 396.9 nm) absorption and another possible
system at z = 0.210 +- 0.002 based on [OII] emission and Ca K absorption.  One
of these systems are likely to be associated with the galaxy located 
1.8 +- 0.4" from the optical transient (Bloom et al., GCN Circ. 206
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 ).  This 
galaxy has an estimated redshift of z ~ 0.2 - 0.3 (Gal et al., GCN Circ. 213
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 ). 

These observations support the idea that GRB 990123 may be a gravitationally 
lensed gamma-ray burst (Djorgovski et al. GCN Circ. 216
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 ).  The 'source' 
(optical transient) redshift (z >= 1.60) and 'lens' (galaxy) redshift(s) 
(z = 0.29, z = 0.21) as well as the angular separation between the image and 
the lens are typical of those found among multiply imaged QSOs.  The existence
of several galaxies along the line of sight to the GRB enhances the lensing
cross section. If GRB 990123 is multiply lensed, a fainter GRB is expected to 
appear 2-3" north of GRB 990123, within a time scale of months.  In addition, 
two more GRBs may appear within days or weeks from now if GRB 990123 is 
quadruply lensed.  Continued monitoring is urged at all wavelengths in order to 
determine precise time delay(s).

The results reported in this circular are preliminary.  A more detailed
analysis is ongoing." 

This report may be cited.


[GCN OP NOTE:  This archived copy of Circular 219 has been reformatted
by the author, i.e. different than the copy actually distributed.]

GRB 990123: New Optical Observations, Decay Measure

J. S. Bloom, S. R. Kulkarni, S. G. Djorgovski, S. C. Odewahn (CIT), R.
Sagar, A. K. Pandey, Neelakshi, R. K. S. Yadav (U. P. State Observatory,
India) report on behalf of the Caltech-NRAO-CARA GRB collaboration:

"On 24.0 Jan 1999 UT, we imaged the optical transient (GCN #201
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 ) of GRB
990123 (GCN #199
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 ) with the 1.04-m UPSO telescope, India.  In one 50-minute
B-band image the transient is well-detected at B = 20.16 +/- 0.15 (Jan
23.958 UT).  The transient is also well-detected in a 60-minute stacked
R-band exposure at gunn-r = 20.02 +/- 0.11.  The B-band image was
calibrated to the zeropoint of GCN #206
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  with a set of secondary stars in
the OT field.  The R-band photometry was tied the gunn-r system using the
Palomar 60-inch photometry (#207). The error associated with the
calibration between the two somewhat different bandpasses is small
compared to the statistical uncertainties.  These measurements have not
been corrected for Galactic extinction which would amount to A_B = 0.069
and A_r = 0.041 (GCN #207
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 ).  With the Galactic extinction correction, the
transient still blue (ie. has a positive spectral index beta ~= 0.3) at
this second epoch (see GCN #207
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 ).

Assuming a power-law decay (f_nu[nu] = const*t^alpha) we find

    alpha_B = -0.90 +/- 0.11    (between Jan 23.58 and Jan 23.95)
    alpha_r = -1.04 +/- 0.14    (between Jan 23.56 and Jan 24.00)

This decay is significantly flatter than alpha = -1.5 found at earlier
times (ie. t <= Jan 23.5; GCN #208
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 ). A recalibration of the transient
magnitude reported by Garnavich et al. (GCN #215
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 ) using the reference star
from Gal et al. (GCN #207
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 ), gives r = 21.0 (errors not reported) on Jan
24.547 UT.  This implies a decay of alpha = -1.26, consistent with that
found above.  

An updated light-curve may be obtained at 
http://astro.caltech.edu/~jsb/GRB/grb990123.html

This message may be cited."

GRB 990123 Optical Follow-Up

J. Zhu, J. S. Chen, and H. T. Zhang, on behalf of the Beijing Astronomical
Observatory GRB team report:

"We observed the GRB 990123 OT (GCN #202
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 ) during Jan. 24.730-24.861 with
BAO 0.6-m Schmidt telescope under non-photometric weather. Combination of
two relatively best quality 60-min. images taken with BATC band-i filter
(central wavelength at 6660 A, band width 480 A) gives a detection of 
the object (OT+galaxy) at RA=15:25:30.17, Dec=+44:45:59.7 (J2000) with 
magnitude of 21.0 +/- 0.3 (Jan 24.818) using the No. 1 and No. 2 stars in
GCN #204
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 . No visual seperation between OT and galaxy could be recognized
because of low S/N ratio and bad spatial resolution (1 pixel = 1.7",
seeing = 5.6"). Central 4' X 4' part of the whole 58' X 58' CCD field
will soon be available under 
http://vega.bac.pku.edu.cn/~zj/grb/grb990123.html

Re-reduction of GCN #204
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  observation with only first 2 of the 4 stars
gives same result for the OT+galaxy in magnitude of 19.2 +/- 0.1 (Jan
23.756).

This report may be cited."

GRB 990123: Possible Gravitationally Lensed Burst?

S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, S. C. Odewahn, R. R. Gal 
(CIT), and D. A. Frail (NRAO) note on behalf of the Caltech-CARA-NRAO 
collaboration:

The lower limit to redshift of GRB 990123 (Kelson et al., IAUC, 7096), 
z =< 1.61, implies a luminosity distance D >= 3.73e28 cm, assuming a
standard Friedmann cosmology with H_0 = 65 km/s/Mpc, Omega_0 = 0.2, and
Lambda_0 = 0 (larger if Lambda_0 > 0).

Assuming the gamma-ray fluence reported by Feroci et al. (IAUC 7095), the
implied isotropic gamma-ray energy of this burst would be > 2.3e54 erg,
higher than most (or all) currently viable theoretical models can easily
accomodate.  The absolute magnitude of the optical counterpart at maximum 
light (Akerlof and McKay, GCN Circ. 205
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 ) would be M =< -36.5, i.e.,
> 2e16 L_sun, a remarkable number itself.

The apparent host galaxy of this burst, coincident with the optical
transient (Odewahn et al., GCN Circ. 201
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  and IAUC 7094) detected on DPOSS
(digital POSS-II) images calibrated with new CCD photometry in the field,
has a Gunn r magnitude 21.9 +- 0.4, i.e., R ~ 21.5 +- 0.5 (cf. Gal et al.,
GCN Circ. 213
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 ).  Its probable redshift is likely to be approximately 0.2 to
0.3, and (unless an active nucleus is present, for which there is no
spectroscopic evidence so far) almost certainly not at z = 1.61, the 
absorption line redshift measured by Kelson et al.

We therefore suggest that this may be the first documented case of a 
gravitationally lensed GRB, magnified by at least an order of magnitude by 
a foreground galaxy detected in DPOSS (possibly including some microlensing).  
This hypothesis naturally accounts for all of the data so far: the large 
fluence of the burst, its enormous implied gamma-ray luminosity, its 
remarkably high peak optical brightness and implied luminosity (and makes 
it consistent with previous non-detections of other bursts by the ROTSE and 
LOTIS experiments, with m_lim ~ 14), and the presence of an apparent 
foreground galaxy positionally coincident with the optical transient.

The conclusive test of this hypothesis will be a direct measurement of the 
galaxy's redshift, once the OT fades sufficiently.  If microlensing is
involved, a signature may be seen in the shape of the OT light curve.
Possible image splitting may be detectable, and high-resolution imaging
in radio, near-IR, and optical is urged.

In any case, the early detection by the ROTSE team (GCN Circ. 205
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 ), even if
corrected for a putative large gravitational lensing magnification factor,
suggests that routine early detections of GRBs in the visible light are
within reach, perhaps at ~ 15 mag level.

This message may be cited.

P. Garnavich, S. Jha, K. Stanek and M. Garcia (Center for Astrophysics)
report "an R-band image of the GRB990123 field was obtained with the
Fred L. Whipple Observatory 1.2m telescope and CCD camera on Jan 24.547 UT.
The Optical Tranisent (plus host galaxy) are easily visible and comparison
with star-3 of GCN Circular 204
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  (R=18.5) gives an R magnitude of 20.4
for the OT+galaxy.  This is consistent with the continuing t**(-1.5)
decline shown by Bloom et al. (GCN 208
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 )."


This message is quotable in publications.


[GCN OP NOTE:  This circular was actually received at 17:59:03 UT, but was
delayed in distribution due to the submitter not having prior vetting.]

E. Falco, C. Petry, C. Impey, A. Koekemoer, and J. Rhoads report on behalf
of the KPNO GRB Followup team:

Falco, Petry, and Impey have observed the optical counterpart of GRB 990123
in U band on 1999 January 24.497 UT using the 4 meter Mayall telescope and
CCD Mosaic Camera at Kitt Peak National Observatory.  Conditions were
non-photometric with 1.3 arcsecond seeing.
 
The counterpart (cf. Odewahn et al, GCN 201
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 ) is clearly detected.  Absolute
flux calibration is not yet possible, but the transient is approximately
1.1 magnitude fainter than the reference object at position RA=15:25:32.7,
dec=+44:44:29.7 (J2000).  The statistical uncertainty in the flux
should be of order 3%.  The counterpart is a point source in our data,
suggesting that host galaxy flux contributes only a small fraction of
the current U band brightness.  We suggest that the afterglow may be bluer
than the host galaxy; if so, U band would be a good wavelength to follow
its light curve to late stages.
 
In addition, Koekemoer has observed the counterpart at K band on 1999
January 24.546 UT using the 2.1 meter telescope and ONIS near-infrared
camera at Kitt Peak National Observatory.  Total exposure time was 600
seconds.  The transient is not readily apparent in the coadded image.
The rough limiting magnitude of the K band image can be estimated from
the USNO-A1 catalog, which gives Red and Blue magnitudes 14.4 and 15.5
for a star with signal to noise ratio 10 in the combined K band image.
More careful processing might improve this limit modestly.
Combining these two measurements will yield a limit on the spectral slope
of the afterglow.
 
A section of the U band image is available at
http://www.noao.edu/noao/grb/990123.html .
 
This report is citable.

GRB 990123:  Pre-Burst Detection of an Apparent Host Galaxy

R. R. Gal, S. G. Djorgovski, S. C. Odewahn, J. S. Bloom, and S. R. Kulkarni
(CIT), on behalf of the Caltech DPOSS team and the Caltech-CARA-NRAO GRB
collaboration report:

A faint galaxy coincident with the optical transient discovered at Palomar
(Odewahn et al., GCN Circ. 201
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  and IAUC 7094) was detected on the F (red)
plate of Digital POSS-II (DPOSS), taken on 05 July 1994 UT.  The galaxy was
not detected on J (blue/green) and N (near-IR) plates taken in March 1993.

Using the new CCD calibration of the field, we obtain for the galaxy the
Gunn magnitude r = 21.9 +- 0.4 (corresponding to Johnson R = 21.5 +- 0.5).
Our preliminary calibration gives the upper limits in the other two band,
with g > 22.4 (roughly, B > 22.0), and i > 20.6 (roughly, I > 19.9), with
a net uncertainty of about 0.5 mag.  The limits in g and i are consistent 
with the plate limits and the weak detection in the r band, for typical
galaxies at these magnitude levels.

At this r band magnitude level, the typical redshift for a normal field 
galaxy is about 0.2 to 0.3.  It is extremely unlikely that this galaxy is 
at z > 0.5, unless it contains an active nucleus.  Future spectroscopic 
observations will establish if this is indeed the host galaxy of GRB 990123.

The DPOSS image can be seen at:
http://astro.caltech.edu/~george/grb/grb990123.html

This message may be cited.

T.J. Galama, P. Vreeswijk, E. Rol (U. of Amsterdam), R. Strom (NFRA
and U. of Amsterdam), J. van Paradijs (U. of Amsterdam and U. of
Alabama in Huntsville), C. Kouveliotou (USRA/MSFC), G. de Bruyn (NFRA
and U. of Groningen) report: 

"We observed the error box of GRB 990123 (GCN #199
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 ) at 4.88 GHz with
the Westerbork Synthesis Radio Telescope (WSRT) for 12 hours on
January 24.28 1999 UT. At the position of the optical transient (GCN
#201
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 ) we do not detect a radio source (< 130 microJansky; 3 sigma).
This result, when compared with the January 24.65 UT 8.46 GHz VLA
detection (260 +/- 32 microJansky; GCN #211
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 ) may be due to synchrotron
self-absorption, or otherwise, may indicate that the 4.88 GHz
observation was suppressed by interstellar scintillation.  Further
observations are planned."

This message is citeable.

D. A. Frail (NRAO), and S. R. Kulkarni (Caltech) report on behalf of a
larger NRAO/Caltech collaboration:

"We obtained a second VLA observation of the error box of GRB 990123
(GCN #199
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 ) beginning on January 24.65 UT at 8.46 GHz. At the location
of the optical transient (GCN #201
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 ) there is a new radio source with a
flux density of 260 +/- 32 microJy. A similar image taken on January
23.63 UT (GCN# 200) gives a 2-sigma upper limit at this same location
of 64 microJy. We are likely observing the slow "turn-on" of the
afterglow. Further observations are planned to track its expected rise
to maximum and its subsequent power-law decay."

This message is citeable.

Eran Ofek and Elia M. Leibowitz, Wise Observatory, Tel Aviv University
report:

>From 4 CCD frames of the object taken at the WO between Jan
24.0617-24.1162 we have determined an average R magnitude of
19.87+-0.2, with calibration based on 4 USNO A2.0 stars.  The decay
parameter in the R band over that time interval is -1.9+-0.1.  On Jan
24.0625, the color index of the object was B-R=-0.48+-0.25.


This report may be cited.

GRB990123 Optical Observation at SAO-RAS

V. Sokolov, S. Zharikov (SAO-RAS) and L. Nicastro, M. Feroci, E. Palazzi
on behalf of the BeppoSAX team report:

We obtained an R-band image of the BeppoSAX localization of GRB990123
on 1999 Jan 24.076 UT, 16.04 hours after the GRB event, with the SAO-RAS
6-m telescope.  The weather was cloudy.
In spite of that, in a 15-min exposure image we were able to see an
object at the position of the optical candidate suggested by Odewahn et al.
(GCN #201
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 ).  We estimated a magnitude of 19.6 +/- 0.2 (using star 1 from
GCN #204
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 ) and 19.9 +/- 0.2 (using star 2 from GCN #204
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 ).
These values include the contribution of the proposed underlying host
galaxy.  To have the contribution of the OT alone these value should be
increased by about 0.25 magnitudes.

R = 19.9 +/- 0.2 is compatible with the power-law decay with index
-1.5 found by Bloom et al. (GCN #208
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 ) as we would expect to find
about R = 20.1 using the R = 18.2 on Jan 23.565 UT and R = 21.3 for the
underlying galaxy (GCN #201
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 ).

This report may be cited.


[GCN OP NOTE:  This circular was actually received at 12:40:01 UT, but was 
delayed in distribution due to the submitter not having prior vetting.]

GRB 990123: Optical Decay Slope

J. S. Bloom, S. R. Kulkarni, S. G. Djorgovski, S. C. Odewahn, R. R. Gal,
L. M. Lubin (CIT), and D. A. Frail (NRAO) note on behalf of the
Caltech-CARA-NRAO GRB collaboration:

"After an initial rise to about 1 Jy, the early-time optical light-curve
of the transient afterglow of GRB 990123 (as reported by the ROTSE Team;
GCN #205
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 ) displayed a power-law decay.  We note here that the decay
appears to be well-continued by the later time (~3 hours) optical fluxes
of the transient discovered at Palomar (GCN #201
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 ; GCN #206
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 ; GCN #207
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 ).  
The decay constant is approximately alpha = -1.5 (defined as F_nu (t) =
const * t^alpha). This is consistent with the decay constants measured at
late-times in other GRB afterglows.

This suggests a strong phenomenological connection between the emission 
mechanism(s) at very early times (from tens of seconds to few minutes after 
the burst) and at later times (>~ few hours).  The continuity of the power-law
light curve represents a strong constraint for theoretical models of optical 
emission from GRBs and their afterglows.

A lightcurve, which will be actively updated, may be obtained at
http://astro.caltech.edu/~jsb/GRB/grb990123.html

This message may be cited."

GRB 990123 r-band Photometry

R. R. Gal, S. C. Odewahn, J. S. Bloom, S. R. Kulkarni (CIT), D. A. Frail
(NRAO) report on behalf of the Caltech-NRAO-CARA GRB Collaboration:

"We report on a detailed analysis of images obtained at the
Palomar 60-inch telescope, the initial results of which were reported
in GCN 201
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 . Three images of 400-s duration each were obtained of the
field of GRB 990123 localized by BeppoSAX (GCN #200
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 ). These images were
obtained  in the Gunn r-band and not R band as reported in GCN #201
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 .
The seeing was 1.7 arcsec (FWHM) in each image.  Using images obtained
of two Gunn standards (Feige 34 and Feige 67), we obtained a
photometric zero point for the data.  The observation times and
magnitudes for the optical transient reported in Odewahn, Bloom,
Kulkarni (GCN #202
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 ) and the reference star from Bloom et al. (GCN #206
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 )
are:

				 Gunn-r Mag
UT (23 Jan 1999)            OT             Ref. Star
---------------------------------------------------------
13:37:20.3           18.70 +/- 0.04      19.10 +/- 0.04
13:51:03.6           18.78 +/- 0.04      19.11 +/- 0.04
14:02:56.5           18.75 +/- 0.06      19.07 +/- 0.06
--------------------------------------------------------

The uncertainty in the magnitudes include the systematic and
statistical uncertainties, although no color term was applied.  We note
that the second r-band image was taken nearly simultaneous with the
B-band image discussed in Bloom et al. (GCN #206
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 ).

The Galactic extinction in the direction of the optical transient (l,b
= 73.12, 54.64) is E(B-V) = 0.01597 (Schlegel, Finkbeiner, and Davis;
1998 ApJ, 500, 525).  Thus (assuming Rv = 3.1), A_B = 0.069 and A_gunnr
= 0.041. The extinction corrected magnitudes of the transient at epoch
Jan 23.578 1999 UT are thus B = 18.86 and Gunn-r = 18.74.  Assuming the
bandpass zeropoints and effective central wavelength of the Johnson B
and Gunn-r bandpasses from Fukugita, Shimasaku, and Ichikawa (1995
PASP, 107, 945) we get F(B)= 115 microJy F(r) =  94 microJy. Thus the
power law slope beta = 0.5 where beta = log F(nu/log(nu).  the
transient is blue with a spectral index of beta = 0.5 (with beta =dlog
F(nu)/dlog nu).  This spectral behavior has not been seen in previous
GRB afterglows.  In the framework of the afterglow models, this result
can be interpreted to mean that the flux from the afterglow did not
peak in the optical bands by the epoch of our second r-band image.


This message may be cited."

GRB 990123 Optical Follow-Up

J. S. Bloom, R. R. Gal, L. L. Lubin, J. Mulchaey, S. C. Odewahn (CIT), S.
R. Kulkarni
report on behalf of the Caltech-NRAO-CARA GRB Collaboration:

"We obtained a single B-band image (300-s) at the Palomar 200-inch of the
field of GRB 990123 localized by BeppoSAX (GCN #200
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 ).  Using images
obtained of the Landolt standard field 98, we derived a photometric
zeropoint for the GRB data.  The transient first reported in Odewahn,
Bloom, Kulkarni (GCN #202
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 ) is well-detected at B = 18.93 +/- 0.03 mag (Jan
23.578 UT).  The uncertainty includes the systematic and statistical
uncertainties though no color term was applied.  For reference, we find
the following B = 19.59 +/- 0.04 for the object at position ra:
15:25:32.7, dec: +44:44:29.7 (J2000).

Absolute astrometry was obtained by comparison of 34 objects near the
optical transient with the USNO-A2.0 Catalogue.  The r.m.s. uncertainties
of the astrometry are 0.28 arcsec (ra) and 0.26 arcsec (dec).  We find the
position of the optical transient to be, ra: 15:25:30.34, dec: +44:45:59.1
(J2000).  Based on the POSS-II F-Plate of this field, the purported host
galaxy (see GCN #202
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 ) appears offset from the OT by 1.8 arcsec (+/- 0.4
arcsec) to the South.  Further analysis is underway.

This message may be cited."

C. W. Akerlof and T. A. McKay (Univ. of Michigan) report on behalf of the ROTSE
collaboration (Michigan/LANL/LLNL):

We observed the error box of GRB 990123 provided by the BACODINE Burst Position
Notice dated 23-Jan-99 09:46:59 using the ROTSE-I telephoto camera array
located at Los Alamos, New Mexico. The first exposure began at 9:47:18.30,
22.18 seconds after the nominal burst trigger time. A rapidly fading object was
discovered at the coordinates, RA = 231.3754, DEC = 44.7666 (J2000) which is
within 1/3 of a pixel of the optical counterpart reported by Odewahn et al.
(GCN #201
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 ). The light curve for this object is relatively complex: the
luminosity increases by 3 magnitudes between the first and second exposures.
Estimated magnitudes for the first six exposures are given below:

        UTC     exposure     m_v

    9:47:18.3    5 secs.    11.82
    9:47:43.5    5 secs.     8.95
    9:48:08.8    5 secs.    10.08
    9:51:37.5   75 secs.    13.22
    9:54:22.8   75 secs.    14.00
    9:57:08.1   75 secs.    14.53

Note that the ROTSE-I detector system uses an unfiltered broadband CCD so that
magnitude estimates are based on comparisons to catalog values for nearby
stars. Sky patrol images of the same coordinates taken 133 minutes earlier
showed no evidence of the transient to a limit of at least two magnitudes
deeper. A more extensive analysis of this data will be available in the near
future.

The discovery images will be posted on the ROTSE Web page at:
   http://www.umich.edu/~rotse/gifs/grb990123/990123.gif

This message is quotable in publications.


[GCN OP NOTE:  This archived copy has had a typo fixed.  The original version
had the 9:48:08.8 timestamp for the 3rd exposure go out as 9:47:08.8.]

GRB 990123 Optical Observation

J. Zhu, H. T. Zhang, on behave of the Beijing Astronomical Observatory GRB 
team, report:

"R-band image of the BeppoSAX WFC error circle of GRB 990123 (Piro, GCN #199
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 )
were obtained on 1999 Jan 23.756 UT, 8.5 hours after the GRB, with the BAO 
0.6/0.9m Schmidt telescope in Xinglong. The weather was bad, so only one
20-min. exposure image taken under thin cloud was usable (FWHM=6").

Central part of the image is posted at
http://vega.bac.pku.edu.cn/~zj/grb/grb990123.gif.

A faint object could be seen closed to the optical candidate position 
suggested by S. C. Odewahn et al. (GCN, #201). Its position from our 
measurement is RA=15:25:30.28, Dec=+44:45:59.0 (1 sigma = 0.5"), with 
magnitude of 19.2 (+/- 0.5 ?) if using the following 4 stars' magnitude 
information from the USNO-A V1.0 catalogue (David Monet, et. al.):

=========================================================
No. RA_mea (2000.0) Dec_mea  RA_cat (2000.0) Dec_cat mag.
--- -----------------------  ----------------------- ----
1   15:25:27.03 +44:46:23.3  15:25:27.04 +44:46:23.2 14.4
2   15:25:36.47 +44:44:37.6  15:25:36.45 +44:44:37.6 15.3
3   15:25:32.57 +44:44:29.9  15:25:32.66 +44:44:29.9 18.5
4   15:25:27.42 +44:44:42.5  15:25:27.48 +44:44:43.6 19.7
=========================================================

The object in our image seems slightly extended and slightly southwest
comparing with the discovery image of Odewahn et al., but it seems
to be impossible to confirm from only one image in not good quality.
However, it could be concluded that if such an object (in our image)
would not be real, the optical transient in Odewahn et al.'s images must 
be faded largely between the 4.6 hours interval.

This report may be cited."

Luigi Piro on behalf of the BeppoSAX team report:

A BeppoSAX follow-up of GRB990123 initiated around 15:40 UT,
i.e.  6 hr after the burst.  Preliminary analysis of the first 20 minutes
of the data at SOC  shows a previously unknown strong source
(about 10**-11 c.g.s in the 1.6-10 keV) in the center of the WFC error circle.

Preliminary coordinates  are:
R.A.(2000)= 231.374
DEC(2000)= +44.758
The error radius is  1.5'.

Considering its strenght, this X-ray source is very likely the X-ray
afterglow of GB990123.  We will continue to observe it to monitor
its temporal evolution.

Luigi Piro on behalf of the BeppoSSAX team report:

Refined coordinates for GRB990123 from the WFC are:
R.A.(2000)= 231.369
DEC(2000)= +44.758
i.e. 0.3' away from the preliminary position.
The error radius is  2'.

The follow-on with NFI should start around 15:40 UT,
i.e. less than 6 hr after the burst.

GRB 990123: Bright New Source, Possible Optical Transient

S. C. Odewahn, J. S. Bloom, and S. R. Kulkarni (CIT) report on behalf of
the Caltech-NRAO-CARA GRB Collaboration:

"We imaged the BeppoSAX localization (Piro et al. 1999; GCN #199
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 ) of GRB
990123 with a CCD camera on the Palomar 60-inch. In each 400-s R-band
image a source clearly brighter than on DSS was seen at position: RA,DEC =
15:25:30.53, +44:46:00.5 (J2000) (preliminary astrometry).  This
localization is well-within the BeppoSAX error radius.  Though DSS and
R-band are somewhat different bandpasses, given the apparent brightness
of the source relative to the DSS image, we suggest that this source is
the optical transient of GRB 990123.

A faint source at the limit of detectability is seen on the POSS-II
image at this location and we suggest this may is the host galaxy of
the GRB.  If true, we have discovered the brightest host galaxy of any
GRB known thus far --- this would be commensurate with the expectation,
based on the high GRB flux as measured by BeppoSAX, that this burst is
nearer than any localized previously.

Preliminary photometry based on the APM catalogue puts the optical
transient at R = 18.2 (Jan 23.565 UT) and the host galaxy at R ~= 21.3.
More precise photometric and astrometric calibrations are currently under
way.

The discovery image may be obtained at the following web page:
    http://astro.caltech.edu/~jsb/GRB/grb990123.html

Follow-up of this most bright burst is urged at all wavelengths.


This message may be cited."

D. A. Frail (NRAO), and S. R. Kulkarni (Caltech) report on behalf of a
larger NRAO/Caltech collaboration:

"We observed the error box of GRB 990123 (GCN #199
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 ) beginning January
23.63 UT with the Very Large Array (VLA) at 8.46 GHz.  There are no
radio sources brighter than 170 microJy (5-sigma) in the WFC error
circle. Further observations are planned."

This message is citeable.

Luigi Piro on behalf of the BeppoSAX team report:

On Jan.23, 9:47:14 UT BeppoSAX GRBM has been triggered by a burst,
GB990123 (also BATSE trigger n.7343), the strongest detected so far
simultaneously with the  WFC.

Preliminary coordinates from WFC are:
R.A.(2000)= 231.374
DEC(2000)= +44.754
with an error radius of about 5'

A follow-on with NFI is being planned.