GRB 981220
GCN Circular 287
Subject
GRB981220 VLBA observations
Date
1999-03-30T22:18:31Z (27 years ago)
From
Greg Taylor at NRAO <gtaylor@aoc.nrao.edu>
G. B. Taylor (NRAO), D. A. Frail (NRAO), and S. R. Kulkarni (Caltech)
report:
"On 1999 March 10.01 we carried out VLBA observations of the radio
source, J0342+1709, claimed to be a possible afterglow candidate for
GRB 981220 based on early observations at WSRT (GCN #168) and the VLA
(GCN #170). Within the 0.9" x 0.9" error box set by VLA observations
at 8.4 GHz we detect an extended source with a peak flux density at 5
GHz of 404 +/- 60 microJy. The position of the radio source is
ra=03h42m28.9611s dec=17d09'14.669" (equinox J2000) with an
uncertainty of 0.05 arcsec in each coordinate. The integrated flux
density of this source is 528 +/- 90 microJy. The flux density at 5
GHz measured by the VLA on March 8.96 was 510 +/- 26 microJy. The
VLBA image can be viewed at http://www.nrao.edu/~gtaylor/G981220.html.
The standard models and redshift distribution of GRB afterglows
predict that the radio counterpart to G981220 should be unresolved by
our VLBA observations. The "core-jet" morphology of the VLBA image
therefore makes it unlikely that J0342+1709 is associated with
G981220. A more plausible explanation is that it is a highly variable
background intraday-variable (IDV) source. Such sources are known to
vary on timescales of days to weeks, and consist of a strong core and
one-sided jet. This explanation is supported by the location of
J0342+1709 outside of the refined IPN localization (GCN #270) for
G981220."
This message is citeable.
GCN Circular 270
Subject
GRB981220, IPN localization
Date
1999-03-03T18:53:32Z (27 years ago)
From
Kevin Hurley at UCBerkeley/SSL <khurley@sunspot.ssl.berkeley.edu>
K. Hurley (UC Berkeley Space Sciences Laboratory) on behalf of the Ulysses GRB team, and M. Feroci (IAS -
Rome) on behalf of the BeppoSAX GRB Team, report:
A refined IPN annulus for GRB981220 has been obtained
by triangulation between Ulysses and BeppoSAX. It is
centered at RA(2000)=347.398 degrees, Delta(2000)=+07.340 degrees,
with radius 67.118 degrees, and 3 sigma half-width 0.015
degrees. The radio source reported by Frail et al. (GCN 170)
and by Galama et al. (GCN 168) lies 0.027 degrees from the
center line of the annulus, and is therefore outside it.
Further refinement in the annulus half-width is possible,
but we can state with some certainty that the position of
the radio source is incompatible with that of the gamma-ray
burst.
GCN Circular 269
Subject
GRB 981220, radio observations
Date
1999-03-03T18:44:34Z (27 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>
D. A. Frail (NRAO), S. R. Kulkarni (Caltech) and G. B. Taylor (NRAO)
report:
"We have been monitoring the radio source claimed to be a possible
afterglow candidate for GRB 981220 based on early observations at WSRT
(GCN #168) and the VLA (GCN #170). Observations made over a period of
75 days shows that the source has increased in flux density at 4.9 GHz
by nearly a factor of four. However, at 15 GHz the source has remained
constant, while at 8.5 GHz there are only small (<20%) variations.
The behavior of the radio light curves for this source does not
resemble that of previous radio afterglows. Further observations are
planned with the Very Long Baseline Array to ascertain the nature of
this unusual radio variable."
This message is citeable.
GCN Circular 250
Subject
GRB981220, field photometry
Date
1999-02-04T17:32:35Z (28 years ago)
From
Arne A. Henden at USNO/USRA <aah@nofs.navy.mil>
A single BVRI photometric observation of the field of GRB981220
was acquired with the USNO 1.0-m telescope during a January
run. The resultant positions and magnitudes for stars near
the center of the error box can be found on our anonymous ftp
site under
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb981220.dat
Additional observations of this field are planned for next week,
along with the fields of GRB980703 and GRB990123. These data
are being made available to assist in proper calibration of
photometry.
This report is citable.
GCN Circular 196
Subject
Optical Observations of GRB 981220
Date
1999-01-20T19:15:53Z (28 years ago)
From
Josh Bloom at CIT <jsb@astro.caltech.edu>
Optical Observations of GRB 981220
J. S. Bloom, S. G. Djorgovski, S. R. Kulkarni (CIT), J. Brauher (IPAC),
D. A. Frail (NRAO), R. Goodrich, F. Chaffee (CARA) report on behalf of
the Caltech-NRAO-CARA GRB Collaboration:
"On 14 January 1999 UT we imaged the region of the radio transient
(GCN #168; GCN #170) of GRB 981220 (GCN #159; GCN #160) with the Keck
II 10-m telescope. Total integration time in R-band was 1300-s in
~0.6 arcsec seeing (FWHM). An astrometric plate solution was obtained
on the stacked image using the USNO-A2.0 catalogue. The r.m.s. errors
of the 26 tie stars surrounding the radio position was 0.24 arcsec (in
ra) and 0.18 arcsec (in dec). A Landolt standard field (PG0231+051)
was also observed for photometric calibration.
Our Keck images can be found at the web location,
http://astro.caltech.edu/~jsb/GRB/grb981220.html. There are two
sources in the vicinity of the radio transient, 'J' and 'K'. Source
'J' coincides with the radio position as reported earlier (GCN #176).
On Jan 14.30, the magnitudes of source 'J' and 'K' are respectively
26.4 (+/- 0.3 statistical; +/- 0.4 zero-point error) and R = 25.6 (+/-
0.2 statistical; +/- 0.4 zero-point error); the zero-point error
includes uncertainties in the local sky level determination, aperture
correction, and the photometric zero-point of the standard stars.
We note that on Dec 23.4 1998 (GCN #176) both 'J' and 'K' have
comparable brightness whereas 'J' is clearly fainter than 'K' in the
Jan 14.30 image. We conclude that the optical source coincident with
the radio transient position has faded by ~0.8 mag between the two
epochs. Since the inferred decay is shallower than that found in other
GRB afterglow, we suggest that the first epoch flux measure of the
optical transient (GCN #176) was partly contaminated by the host
galaxy.
Masetti et al. (GCN #179) had claimed that the source at the radio
position had a 4-arcsec extension. As can be seen from our images, the
extension is likely an artifact resulting from poorer seeing in the
B-band image of Masetti et al.
We conclude that source 'J' is the host galaxy of GRB 981220 and it is
not unusually large but has typical angular size of other host
galaxies.
This message can be cited."
GCN Circular 194
Subject
GRB981220
Date
1999-01-14T20:30:01Z (28 years ago)
From
Fredrick J. Vrba at USNO <fjv@nofs.navy.mil>
F. J. Vrba reports, on behalf of the U.S. Naval Observatory GRB
team, that an error was made in the calibration of GRB 981220 photometry
reported in GCN 171. An incorrect exposure time was used with the
result that all photometry reported in GCN 171 should be
brightened by 1.945 magnitudes. For convenience, we provide a corrected
version below and apologize for any confusion that may have resulted.
We report the results of photometric reductions of the I-band observations of
of GRB 981220 taken at the U. S. Naval Observatory 1.55-m telescope.
(See preliminary reports and details of observations in GCN 164 and 166.)
One hour integrations on two consecutive nights were centered in time
at UT 1998 December 23.280 and 24.266 and reached limiting magnitudes on
each night of I = 22.6 for photometric errors of < 0.20 mag. Standardization
was accomplished by observation of two nearby Landolt fields comprising
nine standard stars and assuming a mean extinction coefficient for the site,
adding about 0.008 mag error to the total error budget (details can be obtained
by contacting the authors at fjv@nofs.navy.mil). Photometry was obtained for
all objects in an area centered on the intersection of the 5.0-arcmin wide
(90% confidence) RXTE localization (GCN 159) and the 2.4-arcmin wide (99% confidence)
IPN annulus (GCN 160), but with dimensions 3.4-arcmin by 10.5-arcmin in order
to be confident of covering the actual GRB location. Photometry for a total
of 267 objects brighter than I = 22.6 was obtained, of which approximately
100 objects lie within the formal RXTE/IPN localization intersection.
No object was found to vary by more than 2-sigma of its standard error of
unit weight (approximately 0.01 mag for I < 19.1; 0.05 mag for I = 21.1,
0.15 mag for I = 22.1). Specifically, the object suggested as a possible
counterpart and marked "1" on the ARC 3.5-m image taken by Dierks and Deutsch
(http://www.astro.washington.edu/deutsch/grb/grb981220/) had I-band magnitudes
of 19.729 +/- 0.020 and 19.722 +/- 0.020 on UT December 23 and 24, respectively.
We find no counterpart to the detection limit of our frames estimated to be
I = 23.1 for the radio source reported in GCN 168 and suggested to be the radio
afterglow in GCN 170.
This GCN note can be cited.
GCN Circular 193
Subject
GRB981220, Correction to GCN 179
Date
1999-01-13T09:07:17Z (28 years ago)
From
Elena Pian at ITESRE-CNR,Bologna <pian@tesre.bo.cnr.it>
N. Masetti, E. Palazzi, E. Pian (ITESRE-CNR, Bologna), by apologizing with
the GCN readers, would like to notify them about a change in GCN N. 179
(optical ESO-NTT observations of GRB981220): the observation time of the B
and I observations is incorrect, and should be modified from 'Dec
23.04-23.07 UT' to 'Dec 24.04-24.07 UT'.
Therefore, the upper limit of B > 25.4 given in GCN 191 implies a
variation of more than 1 magnitude in ~3.5 hours, namely a much steeper
lower limit for the power-law decay index than that suggested in GCN 191.
GCN Circular 192
Subject
GRB981220, Optical Observations
Date
1999-01-11T10:10:55Z (28 years ago)
From
Holger Pedersen at Copenhagen U Obs <holger@astro.ku.dk>
H. Pedersen, B. Lindgren, J. Hjorth (University of Copenhagen),
M. I. Andersen (Nordic Optical Telescope),
A. O. Jaunsen (University of Oslo),
J. Sollerman (Stockholm Observatory), and
J. Smoker, C. Mooney (Queens University, Belfast) report:
"Images of GRB 981220 (GCN 159, 160), including the position
of the proposed radio counterpart (Galama et al., GCN 168;
Frail and Kulkarni, GCN 170) were obtained with the 2.5-m
Nordic Optical Telescope, La Palma, on 1998 Dec 22.927 UT
(900 sec, R, FWHM = 1.4"), and with the 1.5-m Danish telescope,
La Silla, on 1998 December 23.110 UT (300 sec, R, FWHM = 1.3").
No optical source was detected at the position of the radio source.
The upper limits for 3-sigma detections are m(R) > 23.8 on
December 22.927, and m(R) > 23.0 on December 23.110.
This message can be cited in publications."
GCN Circular 191
Subject
GRB 981220 Optical observations
Date
1999-01-09T00:35:46Z (28 years ago)
From
Mark R. Metzger at CIT <mrm@astro.caltech.edu>
GRB 981220 Optical Observations, BVRI
M. R. Metzger, C. Martin, and B. Kern (Caltech) report:
Images of the GRB 981220 joint localization errorbox (GCN 159,160)
were obtained on UT Dec 23.15 (VRI, GCN 163) , UT Dec 24.2 (BVRI), and
UT Dec 27.2 (VRI) at the Palomar 5m telescope using COSMIC. The
seeing varied between 1.4 and 2.0 arcsec (FWHM). Photometric
calibration was perfomed on UT Dec 24 using Landolt standards, and
astrometry was computed using a solution of 70 nearby stars from USNO
A2.0. For reference, on this system we find the following magnitudes
for calibrating objects near the Galama et al (GCN 168) radio source:
mag(+-)
Pos (J2000) B V R Ic
03 42 28.69 +17 09 26.1 23.81(14) 22.98(13) 22.34(09) 22.00(15)
03 42 28.90 +17 09 33.0 21.61(03) 20.75(04) 20.12(03) 19.56(04)
03 42 30.51 +17 09 20.9 22.12(06) 20.58(06) 19.65(04) 18.61(05)
03 42 28.33 +17 09 42.8 19.46(02) 18.47(04) 17.97(02) 17.36(02)
At the radio position of Frail and Kulkarni (GCN 170), no source was
detected on Dec 23.15 to the limits (2-sigma) I > 23.0, R > 23.8, V >
24.2. The object marked "1" on the APO image referred to by Vrba et
al on GCN 171 has I = 19.6 +- 0.1 on Dec 23.15 and Dec 24.2 at rough
position 03h42m31.7 +17:10:04; it is fairly red, with (V-I) ~= 2.
This disagrees with the photometry reported on GCN 171, and could be
due to a difference in photometric zero point or different object.
We can also place B-band upper limits at the radio position. On Dec
24.2, there is no significant detection (though possibly a very faint
peak), which puts a limit of B >= 25.4 (1-sigma). Any host is less
blue and fainter than implied on GCN 179 given the Echelberger et
al. (GCN 176) magnitude. The detection of flux by Masetti et al. (GCN
179) with B ~= 24 on Dec 23 would imply variability, and thus may be
the optical afterglow of GRB 981220. The V limit on Dec 23 is
consistent with a blue spectrum, and the power law time decay in B
would be steeper than alpha = -1.7 (though uncertainties are large).
No significant variability of objects (other than asteroids) is
detected over the Dec 23 to Dec 27 interval in V, R, or I, consistent
with other reports. A B-band image from Dec 24 may be found at
http://astro.caltech.edu/~mrm/grb981220.html.
This report may be cited in publications.
GCN Circular 187
Subject
GRB981220, sub-millimeter observations
Date
1999-01-02T22:20:45Z (28 years ago)
From
Ian Smith at Rice U <ian@spacsun.rice.edu>
I. A. Smith (Rice University), R. P. J. Tilanus and F. Baas (Joint
Astronomy Centre) report on behalf of the James Clerk Maxwell Telescope
(JCMT) GRB collaboration:
We used the SCUBA sub-millimeter continuum bolometer array on the JCMT to
observe the variable radio source J034228.94+170914.6 in the error box of
GRB 981220 (Galama et al. GCN #168, Frail et al. GCN #170). The observation,
performed in mediocre weather, started UT 1998 Dec 30.24 and lasted 3.8
hours. No source was detected at this location: the 850 micron flux
density was 0.1 +/- 1.6 mJy.
This report may be cited in publications.
GCN Circular 186
Subject
GRB 981220 and GRB 981226, optical observations
Date
1998-12-31T16:27:27Z (28 years ago)
From
Sylvio Klose at TLS Tautenburg <klose@tls-tautenburg.de>
Sylvio Klose, Thueringer Landessternwarte Tautenburg, Germany, reports:
"The error box of GRB 981220 was observed with the Tautenburg Schmidt
telescope in the night from Dec. 23 to 24. For any OT at the position
of the radio counterpart of GRB 981220 (Galama et al., GCN #168; Frail
et al., GCN #170) the following preliminary data point can be provided:
Dec. 23.717 UT, Gunn z >~ 17 +/- 1 mag (observations from 16:48 to 17:36
UT). A more accurate limit will be published, when photometric standards
are available. Observations have also been performed in the I-band, but
do not reach the limiting magnitude reported by Vrba et al. (GCN #171).
Images are posted on the WWW at http://www.tls-tautenburg.de/research/
grb.html.
The error box of GRB 981226 was observed with the Tautenburg Schmidt
telescope only 6.5 hours after the burst, but under very critical observing
conditions (zenith distance ~75 deg). For the proposed NIR counterpart
of GRB 981226 (Castro-Tirado et al., GCN #173), the object noted by Galama
et al. (GCN #172), as well as for the variable object reported by Wozniak
et al. (GCN #177) and Bloom et al. (GCN #182), the following data point can
be provided: Dec. 26.682 UT, I >~ 16 (observations from 16:07 to 16:40 UT).
This magnitude limit is based on the Hipparcos star 115941 which has I=7.9
(see http://astro.estec.esa.nl/hipparcos_scripts/
HIPcatalogueSearch.pl?hipId=115941) and which is very close to the
GRB error circle."
This message can be cited.
GCN Circular 179
Subject
GRB981220 B, R and I band observations
Date
1998-12-29T15:51:40Z (28 years ago)
From
Elena Pian at ITESRE-CNR,Bologna <pian@tesre.bo.cnr.it>
GRB 981220 B, R and I band observations
N. Masetti, E. Palazzi, E. Pian, F. Frontera (ITESRE-CNR, Bologna), T.
Galama, P. Vreeswijk, J. van Paradijs (Univ. of Amsterdam), O. Hainaut
(ESO), M. Fridlund (ESA/ESTEC), on behalf of a large collaboration, report:
We have imaged the error box of GRB981220 (GCN N. 159 and 160) with the ESO
New Technology Telescope equipped with EMMI plus B and I filters on 1998
Dec 23.04-23.07 UT, and with EMMI plus R filter on 1998 Dec 28.07-28.08 UT,
in seeing conditions of ~1.6 arcsec (FWHM). A preliminary analysis of the
900-seconds B-band exposure shows a marginal (3-sigma) detection of a
slightly extended source (~4 arcsec across) at a position (J2000) RA = 3h
42m 28.8s, Dec = +17o 09' 13.3" (3-sigma error of 1 arcsec), consistent
with the position of the radio source detected by Galama et al. (GCN 168)
and Frail and Kulkarni (GCN 170), identified with the radio afterglow of
the GRB, and with the position of the faint source detected in the R-band
by Eichelberger et al. (GCN 176). The detection of extended emission is
consistent with the suggestion that at least part of the observed optical
signal originates from a host galaxy. The source has a total magnitude of
B ~ 24. Our 1200-seconds R-band exposure and 600-seconds I-band exposure
yield no source detection at the same position, down to 3-sigma limiting
magnitudes of R = 23.5 and I = 23, respectively.
Our B measurement and the R magnitude reported in GCN 176 imply that the
detected emission has a very blue spectrum (alpha ~ 5, with f_nu =
k*nu^{alpha}), consistent with no detection in the I-band down to I = 25
(GCN 171). If this emission is dominated by the contribution of an
underlying galaxy, this result can be compared with the finding of Fruchter
et al. (1998, ApJ, in press, astro-ph/9807295) of remarkably blue colors
for the host galaxy of GRB970228.
The B-band image is posted in the site
http://tonno.tesre.bo.cnr.it/~masetti/grb981220.html
This GCN note can be cited.
[GCN OP NOTE: Please see GCN 193 for a correction to this Circular.(13 Jan 99)]
GCN Circular 176
Subject
GRB 981220:Optical Observations
Date
1998-12-29T04:26:33Z (28 years ago)
From
Shri Kulkarni at Caltech <srk@astro.caltech.edu>
GRB 981220: Optical Observations
A. C. Eichelberger, J. S. Bloom, S. R. Kulkarni, R. R. Gal (Caltech),
E. G. Martin (UCB), and D. A. Frail (NRAO) report:
On December 23, 1998 (UT) we obtained four 300-s R-band imaging of the
field of GRB 981220 with LRIS on the Keck II 10-m telescope. Based on
astrometry from the USNO-A2 catalogue, at the position of the transient
radio source (RT; GCN #170) we find a faint source in the stacked
image. Our astrometry is good to 0.3 arcsec (rms) in each coordinate.
Lacking observations of standard stars, we have used the standard
R-band zeropoint of LRIS. Using a 1.2 arcsec aperture we find the
object at the position of the RT to have R= 26.7 +/- 0.7 mag on 23.4
Dec 1998 UT. For reference, this zeropoint implies that the USNO star
at ra: 03:42:28.32, dec: +17:09:42.60 (J2000) has a magnitude of
R=18.35.
Although the object appears somewhat extended in our 0.8 arcsec (FWHM)
seeing, deeper imaging is required to firmly establish that this object
is indeed the host galaxy of the GRB.
This message is citeable.
GCN Circular 175
Subject
GRB 981220 optical R and I observations
Date
1998-12-28T17:11:54Z (28 years ago)
From
Adriano Guarnieri at O.A.di Bologna <adriano@astbo3.bo.astro.it>
GRB 981220 optical observations
C. Bartolini, S. Bernabei, I. Bruni, A. Guarnieri, A. Piccioni,
University of Bologna, and N. Masetti and G. Pizzichini,
ITEsre-CNR, Bologna, communicate: "Four 40 min. R-band and one 40 min.
I-band CCD frames of the error box of GRB 981220 (Hurley et al., GCN #160)
were obtained with the 1.5-m telescope of the University of Bologna from
1998 December 22.86 UT to 23.02 UT.
A preliminary analysis of the R band frames shows no variable object
within 0.3 mag. In the I band frame no new evident objects with respect of
the Palomar Digitized Sky Survey were observed inside the mentioned error
box.
The seeing was 3.8"; the measurable limiting magnitude was R ~ 22 (for the
sum of the four CCD frames) and I ~ 19.7.
This message may be cited.
GCN Circular 171
Subject
GRB 981220
Date
1998-12-27T18:20:07Z (28 years ago)
From
Fredrick J. Vrba at USNO <fjv@nofs.navy.mil>
The U.S. Naval Observatory GRB team (F. J. Vrba, C. B. Luginbuhl,
A. A. Henden, S. E. Levine, J. Munn, B. Canzian, H. H. Guetter),
D. H. Hartmann (Clemson Univ.), and M. C. Jennings (IGPP, UCR visitor)
report the results of photometric reductions of the I-band observations of
of GRB 981220 taken at the U. S. Naval Observatory 1.55-m telescope.
(See preliminary reports and details of observations in GCN 164 and 166.)
One hour integrations on two consecutive nights were centered in time
at UT 1998 December 23.280 and 24.266 and reached limiting magnitudes on
each night of I = 24.5 for photometric errors of < 0.20 mag. Standardization
was accomplished by observation of two nearby Landolt standards and assuming
a mean extinction coefficient for the site, adding about 0.008 mag error
to the total error budget (details can be obtained by contacting
the authors at fjv@nofs.navy.mil). Photometry was obtained for all objects in
an area centered on the intersection of the 5.0-arcmin wide (90% confidence)
RXTE localization (GCN 159) and the 2.4-arcmin wide (99% confidence) IPN
annulus (GCN 160), but with dimensions 3.4-arcmin by 10.5-arcmin in order
to be confident of covering the actual GRB location. Photometry for a total
of 267 objects brighter than I = 24.5 was obtained, of which approximately
100 objects lie within the formal RXTE/IPN localization intersection.
No object was found to vary by more than 2-sigma of its standard error of
unit weight (approximately 0.01 mag for I < 21.0; 0.05 mag for I = 23.0,
0.15 mag for I = 24.0). Specifically, the object suggested as a possible
counterpart and marked "1" on the ARC 3.5-m image taken by Dierks and Deutsch
(http://www.astro.washington.edu/deutsch/grb/grb981220/) had I-band magnitudes
of 21.674 +/- 0.020 and 21.667 +/- 0.020 on UT December 23 and 24, respectively.
We find no counterpart to the detection limit of our frames estimated to be
I = 25 for the radio source reported in GCN 168 and suggested to be the radio
afterglow in GCN 170.
This GCN note can be cited.
GCN Circular 170
Subject
GRB 981220, radio observations
Date
1998-12-27T17:50:52Z (28 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>
D. A. Frail (NRAO), and S. R. Kulkarni (Caltech) report on behalf of a
larger NRAO/Caltech collaboration:
"We have observed the error box of GRB 981220 (GCN #159, GCN #160)
with the Very Large Array (VLA) for 12 minutes each at 4.86 GHz and
8.46 GHz on Dec 23.14 UT, 1998. On this day we detected a source at RA
= 3h42m28.94s +- 0.01s, Dec = +17d09'14.6'' +- 0.2'' with a 4.86 GHz
flux density of 200 +- 45 microJy and a 8.46 GHz flux density of 370
+- 43 microJy. This is the same radio source reported by Galama et
al. (GCN #168). Noting its unusual rising spectrum we carried out
another set of observations on Dec 27.21. We observed the field for 18
minutes at each frequency and measured a 4.86 GHz flux density of 540
+- 40 microJy and a 8.46 GHz flux density of 460 +- 36 microJy. These
wide swings of flux and spectral index resemble the behavior of radio
afterglows at early times. Other sources in the field have remained
constant during this time. We suggest that J034228.94+170914.6 is the
radio afterglow of GRB 981220. Our position is accurate to 0.2 arcsec
(1-sigma) and should enable deep optical studies. Further radio
observations are in progress."
This message is citeable.
GCN Circular 168
Subject
GRB 981220, radio observations
Date
1998-12-24T18:48:32Z (28 years ago)
From
Titus Galama at U.Amsterdam <titus@astro.uva.nl>
T.J. Galama, P. Vreeswijk (U. of Amsterdam), J. van Paradijs (U. of
Amsterdam and U. of Alabama in Huntsville), C. Kouveliotou
(USRA/MSFC), R. Strom (NFRA and U. of Amsterdam), G. de Bruyn (NFRA
and U. of Groningen) report:
"We have observed the error box of GRB 981220 (Smith et al. 1998, GCN
Circ 159; Hurley et al. 1998, GCN Circ 160) with the Westerbork Radio
Synthesis Telescope (WSRT). We observed for 7 hours switching between
4.88 and 1.38 GHz on Dec 22.98 UT, 1998, and for 12 hours at 4.88 GHz
on Dec 23.88 UT, 1998. We find no sources in the errorbox at 1.38 GHz
down to 200 microJy (4 sigma). At RA = 3h42m28.98s +- 0.07s, Dec =
+17d09'14.7'' +- 1.6'', we detect a source at 4.88 GHz at 260 +- 90
microJy (Dec 22.98), which is not detected at 1.38 GHz. On Dec 23.88
we measure 200 +- 50 microJy (4.88 GHz). The location of the source is
at the edge of the error box of GRB 981220. Whether or not this source
is related to GRB 981220 is unclear. We will continue monitoring the
error box at 4.88 GHz."
This message is citeable.
GCN Circular 167
Subject
GRB 981220: BeppoSAX/GRBM results
Date
1998-12-24T15:40:36Z (28 years ago)
From
Filippo Frontera at ITESRE CNR <filippo@tesre.bo.cnr.it>
F. Frontera and L. Amati (ITESRE/CNR, Bologna),
M. Feroci and E. Costa (IAS/CNR, Rome)
report on behalf of the BeppoSAX/GRBM Team:
"From the high time resolution data the GRBM lightcurve shows a global
three peak structure, with minor (~20-30 ms) structures within
each peak. The time-resolved spectral analysis shows a weak spectral
evolution. The time-averaged spectral power law photon index in the
40-700 keV energy range is (2.1+-0.3).
The peak flux and fluence in the same band are (2.4 +/- 0.4)e-6 ergs/cm2/s
and (1.0+/-0.2)e-5 ergs/cm2, respectively. Please note that the latter
value corrects a typo occurred in Feroci et al. (GCN 159)."
This message is citeable.
GCN Circular 166
Subject
GRB981220 I-band Observations
Date
1998-12-24T10:57:03Z (28 years ago)
From
Christian B. Luginbuhl at USNO/Flagstaff <cluginbuhl@nofs.navy.mil>
GRB 981220 I-Band Observations
The U. S. Naval Observatory GRB team (C. B. Luginbuhl, F. J. Vrba, A.
A. Henden, S. E. Levine, J. Munn, B. Canzian, H. H. Guetter), D. H.
Hartmann (Clemson Univ.), and M. C. Jennings (IGPP, UCR visitor) report
follwup I-band observations of the GRB 981220 localization reported in
GCN 164. A second set of 6 dithered 10-min I-band exposures was
obtained with the USNO 1.55-m telescope and Tek 2K CCD on UT 1998
December 24 between UT 05:45:47 and UT 07:00:12. The combined, median
filtered, and high-pixel rejected image can be viewed at the USNO
public website: http://www.nofs.navy.mil/news/grb/grb981220.html
beginning sometime 24 December. The seeing was again rather poor
(1.7-1.9 arcsec, FWHM).
No obvious fading or brightening sources are detected to a preliminary
estimated limiting magnitude of I=22. The source marked "1" on the ARC
3.5m image taken by Dierks and Deutsch
(http://www.astro.washington.edu/deutsch/grb/grb981220/) seems
approximately constant in this preliminary analysis. Complete
photometric reduction of the two nights' USNO observations to determine
the variance vs. magnitude relation and look for outliers is underway,
and will be reported in a followup GCN later today.
This GCN Note can be cited.
GCN Circular 165
Subject
GRB981220 Optical Observations
Date
1998-12-23T20:31:13Z (28 years ago)
From
Brad Schaefer at Yale <schaefer@grb2.physics.yale.edu>
Bradley E. Schaefer (Yale) reports:
"I have obtained 19 images in the V and R bands of the joint RXTE/IPN
region for GRB981220. The total integration time is 2.5 hours in the
V-band and 2.25 hours in the R-band, with the filters alternating in time,
for a total time span of just over 5 hours. These images were obtained
from 23 December 1998 00:52 to 05:55 UT with the Yale 1m telescope on
Cerro Tololo.
No variable source was identified in or near the GRB981220 region.
Comparisons were made with the Digital Sky Survey, for which no 'new'
stars appear. Also, comparisons were made between the first and last
images, separated by roughly 5 hours of time. For the latter comparison,
the limiting magnitude for detecting change is close to V=22.0 mag. As
always, further analysis can push somewhat deeper, yet it is clear that
any associated optical transient must be close to this quoted limit if not
fainter."
GCN Circular 164
Subject
GRB 981220
Date
1998-12-23T20:06:07Z (28 years ago)
From
Fredrick J. Vrba at USNO <fjv@nofs.navy.mil>
GRB 981220 I-Band Observations
The U.S. Naval Observatory GRB team (C. B. Luginbuhl, F. J. Vrba,
A. A. Henden, S. E. Levine, J. Munn, B. Canzian, H. H. Guetter),
D. H. Hartmann (Clemson Univ.), and M. C. Jennings (IGPP, UCR visitor)
report I-band observations of the GRB 981220 localization formed
by the intersection of the RXTE (GCN 159) and IPN (GCN 160) error
boxes. Observations were obtained with the USNO 1.55-m telescope on
UT 1998 December 23 consisting of 6 dithered 10-min exposures
taken between UT 06:05:50 and UT 07:21:06 with a Tek 2K CCD having a
field of view of approximately 6x6 arcmin. The combined, median filtered,
and high-pixel rejected image can be viewed at the USNO public website:
http://www.nofs.navy.mil/news/grb/grb981220.html. Although the seeing
was rather poor (1.5-1.8 arcsec, FWHM), each of the 10-min exposures
is deeper than the Digital Sky Survey POSS-I image and reveals many more
objects than on the DSS. No obvious counterpart is revealed in comparing
to the DSS image. Additionally, the six frames were blinked to
search for variable objects, but none were obvious.
This GCN note can be cited.
GCN Circular 163
Subject
GRB 981220 Optical Observations
Date
1998-12-23T09:41:29Z (28 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. Halpern & E. Gotthelf (Columbia U.), C. Martin & B. Kern (Caltech), report:
"We obtained a 600 s R-band image of the joint RXTE/IPN error region of
GRB 981220 (GCN 159,160) on the Palomar 5m telescope on Dec 23.15.
The limiting magnitude was about 22.7. Preliminary analysis shows
no new object in comparison with the digitized POSS II plate to a limit
of R=20.5. Our image is posted at
http://www.astro.columbia.edu/~evg/grb981220.html"
This message may be cited.
[GCN OP NOTE: 28mar99: The ".edu" was added to the URL.]
GCN Circular 162
Subject
GRB 981220, optical observations
Date
1998-12-23T04:33:28Z (28 years ago)
From
Mark Wagner at Ohio State U. <rmw@as.arizona.edu>
R. Mark Wagner and Sumner Starrfield report:
We visually examined the region bounded by the ASM error box and IPN annulus
for GRB 981220 on 1998 December 23.12 with the intensified acquisition camera
(FOV: 2 arcmin) on the Boller and Chivens CCD spectrograph at the Steward
Observatory 2.3-m telescope. Comparison with the Digitized Sky Survey does
not reveal any new object brighter than about VR = 19.5 in the intersection
of the error regions.
GCN Circular 160
Subject
GRB981220 IPN error box
Date
1998-12-22T18:06:16Z (28 years ago)
From
Kevin Hurley at UCBerkeley/SSL <khurley@sunspot.ssl.berkeley.edu>
K. Hurley (UC Berkeley), on behalf of the Ulysses/GRB team, T. Cline
(NASA-GSFC), E. Mazets, and S. Golenetskii (Ioffe Physico-Technical
Institute), on behalf of the KONUS-Wind team, and D. A. Smith (MIT)
report:
"Ulysses and KONUS detected GRB981220. A preliminary triangulation
annulus for this event is centered at RA(2000)=347.373 degrees,
Decl(2000)=+7.336 degrees, with a radius 67.134 +/- 0.020 degrees
(3 sigma). This annulus intersects the RXTE/ASM error box at
RA(2000) Decl(2000)
3h 42m 28.5s 17o 06.3'
3h 42m 29.0s 17o 11.1'
3h 42m 39.0s 17o 11.6'
3h 42m 38.5s 17o 06.8'
to form a ~2.4' x 4.5' error box with approximately 11 sq. arcmin. area.
The IPN annulus width can be reduced by a factor of 2 to 4. An
image may be found at http://ssl.berkeley.edu/ipn3/newdata.html,
under 981220."
This message is quotable in publications.
GCN Circular 159
Subject
GRB 981220: RXTE/ASM and BeppoSAX/GRBM results
Date
1998-12-22T17:14:20Z (28 years ago)
From
Don Smith at MIT <dasmith@space.mit.edu>
D. A. Smith (MIT) reports on behalf of the RXTE/ASM Team at MIT and
NASA/GSFC:
"The RXTE All-Sky Monitor has detected a hard X-ray flare, beginning
within a few seconds of 1998 December 20, 21:52:21 (UTC) and lasting
for about 20 s. The flare consisted of a single symmetric peak that
reached a maximum flux (1.5-12 keV; 1-s bins) of 1.2+-0.1x10^-7 erg
cm^-2 s^-1. The event was detected in a single camera and was
localized to an error box 5.0' x 60.0' (full width; 90% confidence
including a rough estimate of systematic error due to calibration
drift), centered on the position: R.A. = 03h43m01s, Decl. = +17o09'.0
(J2000.0) at a position angle of 75.54 degrees east of north. This
position is inconsistent with any known X-ray sources. See
http://xte.mit.edu/grb/grb981220/ for a sky map and other relevent
plots."
M. Feroci and B. Preger (IAS/CNR, Rome), L. Amati, F. Frontera and M.
Orlandini (ITESRE/CNR, Bologna) report on behalf of the BeppoSAX/GRBM
Team:
"The BeppoSAX Gamma Ray Burst Monitor was triggered on 1998 December
20, 21:52:25.89365 UTC on a gamma-ray burst of about 15 s duration. The
preliminary estimated fluence in the 40-700 keV energy band is 1.0+-0.2
x 10^-5 erg cmE-2 sE-1, while its peak flux is about 10+-2 photons cmE-2 sE-1.
We therefore confirm that the event reported by the RXTE/ASM Team was
indeed a real GRB."
[GCN OP NOTE, 18:15 UT: This archived copy of the Circular was edited
to fix the typo in the original distribution: "1.0+-0.2 erg cmE-2 sE-1"
was replaced with "1.0+-0.2 x 10^-5 erg cmE-2 sE-1".]
[GCN OP NOTE, This archived copy of the Circular was edited to fix
a mistake in the original distribution: the "degrees west of north"
was changed to "degrees east of north".]