GRB 980613
GCN Circular 99
Subject
GRB980613, BeppoSAX WFC positions
Date
1998-06-13T15:35:21Z (27 years ago)
From
SAX Science Operations at IAS/CNR Frascati <saxsci@ias.rm.cnr.it>
Luigi Piro and Enrico Costa on behalf of BeppoSAX team report:
The GRBM of BeppoSAX was triggered by a GRB (GB980613) on June 13 at
04:51:06 UT. The burst was detected by WFC (n.2).
The preliminary WFC position was
RA(2000)=154.55
Dec(2000)=71.486
with an error radius of 5'.
The refined WFC position is now
RA(2000)=154.44
Dec(2000)=71.499
with an error radius of 4'.
A BeppoSAX follow up with the NFI is being planned.
GCN Circular 101
Subject
GRB980613 Near Infra-Red Observations
Date
1998-06-14T05:15:09Z (27 years ago)
From
Richard McMahon at Inst.Astonomy, U Cambridge <rgm@ast.cam.ac.uk>
R. G. McMahon, M.G. Beckett, M. Hoenig, G. Gilmore and R. Wyse
report, on behalf of the CIRSI GRB team.
On June 13th, between UT 21:16 and 22:19, we observed the BeppoSax error
box of the Gamma Ray Burst GRB980613 (GCNC#99) in the near-IR, H band with
the Isaac Newton Telescope, on LaPalma, using the Cambridge Infra-Red
Survey Instrument.
Our H band image covers a field of view of 7.8arcmin x 7.8arcmin with
spatial resolution of around 1 arcsec. The image is not photometrically
calibrated yet.
Comparison with the DSS optical image reveals no obvious candidate
for a near-IR counterpart to GRB980613. We plan to reobserve the field
again on subsequent nights.
This image is available, for comparison with future observations, at
http://www.ast.cam.ac.uk/~optics/cirsi/grb/. Calibration information
will be added in due course.
-------------------------------------------------------------------
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-------------------------------------------------------------------
GCN Circular 102
Subject
GRB 980613 optical/IR obs.
Date
1998-06-14T11:56:29Z (27 years ago)
From
Alberto Castro-Tirado at LAEFF-INTA <ajct@laeff.esa.es>
Alberto J. Castro-Tirado (Laboratorio de Astrofisica Espacial y Fisica
Fundamental, LAEFF-INTA, Madrid)
Javier Gorosabel (LAEFF-INTA)
Jochen Greiner (Astrophysikalisches Institut, Potsdam)
Dimitra Rigopoulou (Max Planck Institut fur Extraterrestrische Physik, Garching)
Dave Clements (IAS, Univ. Paris XI)
Marco Barden (MPE Garching)
Georg Lamer (University of Southampton)
and E. Costa and F. Frontera (on behalf of the BeppoSAX team)
Report:
We have obtained K'-band images of a 10' x 10' region centred at the
BSAX/WFC error box for GRB 980613, with the 3.5-m telescope (+ OMEGA) at the
German-Spanish Calar Alto Observatory, on June 13.87-13.92 . R-band
and I-band images were also obtained at the 1.23-m telescope on June
13.88-14.00. No variable object, by more than 0.5 mag, is seen when
comparing the co-added R-band image with the POSS chart, down to R = 20.5.
We notice however, the presence of a point-like object on several IR images,
with K' = 17.5 +/- 0.5 (very preliminary). The object is not seen on the
R-band image (limiting magnitude R = 22), implying R-K' > 4. Its position
is AR(2000) = 10 18 23.15, Dec(2000) = +71 32 18.5 (+/- 1"). Further IR
and radio observations are encouraged in order to discern whether this is
the true IR counterpart to GRB 980613, resembling that of GRB 980329.
GCN Circular 103
Subject
GRB 980613 new optical/IR observations
Date
1998-06-15T19:53:08Z (27 years ago)
From
Alberto Castro-Tirado at LAEFF-INTA <ajct@laeff.esa.es>
GRB 980613. NEW OPTICAL/IR OBSERVATIONS
---------------------------------------
Alberto J. Castro-Tirado (Laboratorio de Astrofisica Espacial y Fisica
Fundamental, LAEFF-INTA, Madrid)
Javier Gorosabel (LAEFF-INTA)
Jochen Greiner (Astrophysikalisches Institut, Potsdam)
Dimitra Rigopoulou (Max Planck Institut fur Extraterrestrische Physik,
Garching)
Dave Clements (IAS, Univ. Paris XI)
Marco Barden (MPE Garching)
Georg Lamer (University of Southampton)
Arturo Manchado, Maite Rozas, Victor Sanchez-Bejar, Maria Rosa Zapatero-
Osorio (Instituto de Astrofisica de Canarias)
and E. Costa and F. Frontera (on behalf of the BeppoSAX team)
Report:
New images in the K'-band obtained on June 14.87-14.93 at the 3.5-m CAHA
telescope (+ OMEGA) indicate that the red object reported by us (GCN 102)
is a slow-moving object, probably an asteroid, and therefore unrelated
to GRB 980613. One of the K'-band images can be seen at
http://laeff.esa.es/~jgu/grb980613.html .
I-band images were also taken on June 13.89 and June 14.87 with the IAC-80
telescope at Observatorio del Teide (Canary Islands). No variable object
(by more than 0.2 mag) is seen within the BSAX/WFC error box, down to a
limiting magnitude of I = 21.5 .
GCN Circular 104
Subject
GRB980613 BeppoSAX-NFI follow up
Date
1998-06-15T23:10:17Z (27 years ago)
From
SAX Science Operations at IAS/CNR Frascati <saxsci@ias.rm.cnr.it>
GRB980613: follow-up with NFI:
Luigi Piro on behalf of the BeppoSAX team report:
Two previously unknown X-ray sources have been found in the WFC error
circle by the MECS during the follow up observation started 9 hrs after
the GRB.
Source A is at
R.A.(2000)= 10h17m53s
Dec.(2000)= +71d27'24"
Source B is at
R.A.(2000)= 10h18m04s
Dec.(2000)= +71d33'30"
The error radius is 50".
Source B does not show substantial variability.
Source A shows a rather strong decay during the observation, and is very
likely the X-ray afterglow of GB980613.
GCN Circular 105
Subject
GRB980613 observations from Palomar
Date
1998-06-16T13:01:02Z (27 years ago)
From
Steve Odewahn at Caltech <sco@astro.caltech.edu>
S. Odewahn, C. Thomas, S. Djorgovski and S. Kulkarni report that
the optical counterpart to GRB980613 detected by BeppoSAX was
searched for with the Palomar 60" on Jun15,98 and Jun16,98 (UT).
Images were obtained with CCD13 in Gunn gri at an airmass of 1.6
and integration times of (900,600,600) seconds respectively under
photometric conditions and seeing measured at 1.0" fwhm. Images and
details of observations are given in:
http://astro.caltech.edu/~sco/sco1/research/grb/grb980613.html
The faintest source shown in our map at r=20.96 (object 6 in Fig1) is
detected at better than 5-sigma. No such source (r<21) has been found
to vary in the MECS error box with delta mag greater than 0.5 mags in
the period from Jun15,98 to Jun1698 (UT). In Figure 2 of our web page
we show the Jun15 and Jun16 (UT) 600 second r images from the Palomar 60"
with the latest position and errorbox from the L. Piro (MECS). The 8'
diameter error box is centered on 10:17:45.6 +71:29:56.0 (J2000). The
Jun16 image is shifted into the coordinate system of the Jun15 image. We
also show for comparison the corresponding DSS field. A more thorough
photometric analysis of the our images will be reported following the
completion of our Palomar observing run (Jun18,98).
[GCN Operator's Note: This circular was received at 10:44 UT, but due to
a computer network problem at GSFC its distribution was delayed until now.
GSFC and GCN apologize for the delay.]
GCN Circular 106
Subject
GRB980613 Optical Observations
Date
1998-06-16T23:16:03Z (27 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. Halpern, R. Fesen, E. Costa, & L. Piro report on behalf of the
MDM Observatory GRB followup team and the BeppoSAX team:
We obtained I-band images of the BeppoSAX WFC error circle of GRB 980613
(Smith et al. IAUC 6938) using the MDM Observatory 2.4m telescope beginning on
June 14.17 and June 15.17 UT. No variations at the 0.3 mag level were detected
in the error circle of the fading MECS X-ray source "A" (GCN #104) to a limiting
magnitude of I=22.3. Conditions were photometric and seeing of 0.9 arcsec was
obtained. Total exposure times were 3000 s and 3600 s, respectively, on the
first and second nights. We also obtained 2000 s of R-band exposure beginning
on June 14.19 UT. Photometric calibration of stars in both colors can be made
available if needed.
We also note that this field was observed by the ROSAT PSPC for 7300 s on
1993 May 11, and that an X-ray source was detected at the position (J2000)
10h18m2.4s, +71d33'47.6", consistent with that of MECS source "B" (GCN #104).
Its PSPC count rate is 0.020+/-0.001. No source was detected by ROSAT at
the position of MECS source "A", which supports its identification as the
afterglow of GRB 980613.
GCN Circular 108
Subject
GRB 980613 optical observations
Date
1998-06-18T14:37:20Z (27 years ago)
From
Alan Diercks at U.Washington <diercks@astro.washington.edu>
A. Diercks, E.W. Deutsch, C. Stubbs (U. of Washington);
P.M. Vreeswijk, T.J. Galama (U. of Amsterdam); J. van Paradijs (U. of
Amsterdam; U. of Alabama in Huntsville); C. Robinson, and
C. Kouveliotou (USRA at MSFC-NASA) report:
We observed the BeppoSAX error box of GRB 980613 on June 14.35 UT and
June 15.35 UT in Kron-Cousins I with the APO 3.5m telescope.
Conditions were mostly clear with ~2.0 arcsec seeing.
Photometry on a 30 min series of I-band (Kron-Cousins) images centered
around June 14.35 UT (28 hr after the burst) yields the following
preliminary magnitudes and relative uncertainties for several
reference stars:
ID I mag Rel Err RA (J2000) DEC
-- ----- ------ ------------------------
1 17.28 0.02 10 17 47.48 +71 27 0.6
2 18.74 0.02 10 17 54.83 +71 27 40.2
3 18.70 0.03 10 18 6.55 +71 27 5.1
4 18.58 0.02 10 17 55.29 +71 28 16.5
5 18.25 0.02 10 17 41.45 +71 28 9.3
Absolute calibration is based on a single observation of the PG
2213-006 standard field (Landolt 1992) and a previously determined
airmass correction for this filter and instrument. The uncertainty in
the absolute calibration is 0.1 mag.
The limiting magnitude (SNR~5) for the combined images for each of the
June 14.35 and 15.35 epochs is I~22.0. We find no object at the
position of the slow moving K~17.5 detection reported by
Castro-Tirado(GCN #102,#103).
The error circle was also observed with the 1m JKT telescope in Harris
I on June 13.97 for 1600s and June 14.96 for 420s. Conditions were
clear with ~2.0 arcsec seeing.
Difference imaging between the June 13.97 UT JKT data and the June
14.35 UT APO data reveals no point sources which varied by more than
the flux equivalent of I = 20.6 mags between the two images. Similar
analysis on June 14.35 UT and June 15.35 UT APO data gives an upper
limit of 21.5 mags to any such flux differences.
An image of the field is posted at:
http://www.astro.washington.edu/deutsch/grb/grb980613/
This note can be cited.
GCN Circular 109
Subject
GRB 980613 Optical Observations
Date
1998-06-18T16:18:04Z (27 years ago)
From
Jens Hjorth at NORDITA <jens@nordita.dk>
GRB 980613 Optical Observations
J. Hjorth, M. I. Andersen, H. Pedersen, A. O. Jaunsen on behalf of the NOT
GRB team and E. Costa & E. Palazzi on behalf of the SAX GRB team report:
On June 13.9 UT and June 17.9 UT we obtained R band images (600 sec each,
seeing FWHM=0.7") of the BeppoSAX error circle of GRB 980613 (Piro & Costa,
GCN #99) with the 2.5-m Nordic Optical Telescope. We have discovered a faint
point source in our June 13.9 image which is not detected in our June 17.9
image (which reaches a similar limiting magnitude). The source is located at
(+- 0.5"):
RA(J2000) = 10 17 57.64
Dec(J2000) = +71 27 26.4
Preliminary photometry (Cousins R) of the source yields:
June 13.8897 UT: R = 22.9+-0.2
June 17.9088 UT: R > 24.0 (formal 10-sigma limit)
These numbers assume R=19.11 for USNO catalogue entry U1575-03105992 located at
RA(J2000)=10 17 54.83, Dec(2000)=+71 27 39.8, consistent with the photometry
of the isolated star 4_r of Odewahn et al. (GCN #105) (assuming r-R=0.35).
The location of the source is consistent with the BeppoSAX WFC error circle
of GRB 980613 (GCN #99) and the BeppoSAX MECS error circle for source A
(Piro, GCN #104; Costa et al., IAUC 6939).
The photometry is consistent with previously reported upper limits for
optically variable objects in the field (R > 20.5 on June 13.9, Castro-Tirado
et al., GCN #102; I>21.5 on June 13.9, Castro-Tirado et al., GCN #103;
r>21.0 on June 16.0, Odewahn et al., GCN #105; I>22.3 on June 14.2, Halpern
et al., GCN #106, I>20.6 on June 14.0 and I>21.5 on June 14.4, Diercks et
al., GCN #108).
Given the consistency with the BeppoSAX error circles of GRB 980613 and
the rapidly fading nature of the source we suggest that the detected object
is the optical afterglow of GRB 980613.
Finding charts and updates of these preliminary results will be posted at
http://www.nordita.dk/~jens/grb980613/
This report may be cited.
GCN Circular 112
Subject
GRB 980613: BATSE Observations
Date
1998-06-19T01:46:59Z (27 years ago)
From
R Marc Kippen at BATSE/UAH/MSFC <marc.kippen@msfc.nasa.gov>
GRB 980613: BATSE Observations
P. Woods, R. M. Kippen (University of Alabama in Huntsville) &
V. Connaughton (NRC & NASA/MSFC) report on behalf of the BATSE GRB
team:
On June 13.20215 UT, BATSE detected a gamma-ray burst coincident with
GRB 980613 (IAUC 6938). The event did not activate the on-board BATSE
trigger because it was not sufficiently intense to override a large
solar flare (trigger number 6821) that occurred ~33 minutes earlier.
The GRB consisted of a single pulse lasting about 20 s with little
resolvable structure on the 1 second time-scale. Its peak flux
(50-300 keV; integrated over 1 s) and fluence (>20 keV) are 0.63 (-/+
0.05) photons cmE-2 sE-1 and 1.71 (-/+ 0.25) x 10E-6 erg cmE-2,
respectively. This ranks it near the middle 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 = 0.93 (-/+ 0.12), which is also average for
events of this duration. The BATSE location is consistent with those
measured by BeppoSAX.
This message is citeable.
GCN Circular 114
Subject
GRB 980613: Detection of the probable host galaxy
Date
1998-06-19T07:24:37Z (27 years ago)
From
George Djorgovski at Caltech/Palomar <george@oracle.caltech.edu>
GRB 980613: Detection of the probable host galaxy
S. G. Djorgovski, S. R. Kulkarni, S. C. Odewahn (Caltech), and H. Ebeling
(IfA, Univ. of Hawaii), report on behalf of the Caltech GRB collaboration:
Images of the field of GRB 980613 were obtained bu H. Ebeling at the Keck-II
telescope on UT 1998 June 16.3, in the R band. We detect a galaxy coincident
to within 0.5 arcsec with the optical transient (OT) reported by Hjorth et al.
(GCN circ. 109). The galaxy may include a faint, unresolved source, which
may be the faded OT. The preliminary total magnitude of the object at the
epoch of our observations, assuming the zero-point given by Hjorth et al.
(R = 19.1 for their star 1, which is identical to star 2 of Diercks et al.,
GCN circ. 108), is R ~ 23.3, which is consistent with the conservative
upper limits reported by Hjorth et al. for their June 17 image. We
propose that this is the host galaxy of GRB 980613.
Further analysis of these data is in progress. Images will be posted at:
http://astro.caltech.edu/~george/grb/grb980613.html
This message can be cited.
GCN Circular 117
Subject
GRB 980613: Optical transient and its host galaxy
Date
1998-06-19T23:23:44Z (27 years ago)
From
George Djorgovski at Caltech/Palomar <george@oracle.caltech.edu>
[GCN Operator's Note: This is a redistribution of GCN 117 to correct
a typo in the original distribution. See full explanation below.]
GRB 980613: Optical transient and its host galaxy
S. G. Djorgovski, S. R. Kulkarni, and S. C. Odewahn (Caltech), and H. Ebeling
(IfA, Hawaii) report on behalf of the Caltech GRB collaboration:
Further analysis of the Keck images of the field of GRB 980613 (see GCN 114),
calibrated with the Palomar 60-inch images (see GCN 105) gives the following
results:
We resolve the image of the optical transient (OT) found by Hjorth et al.
(GCN 109) from its host galaxy, which extends up to 1.5 - 2 arcsec from
the point source (the OT) in approximate PA ~ 70 deg.
Magnitudes of stars 1-5 from Diercks et al., GCN 108, in the Gunn r band are:
ARC star 1 r = 18.45 RA = 10 17 47.559 DEC = +71 27 00.75
ARC star 2 r = 19.59 RA = 10 17 54.828 DEC = +71 27 39.81
ARC star 3 r = 20.82
ARC star 4 r = 20.07
ARC star 5 r = 19.51 RA = 10 17 41.456 DEC = +71 28 09.11
The positions given are from the USNO A1.0 catalog where available (J2000).
ARC star 2 is identical to star 1 from Hjorth et al. (GCN 109).
In this system, the integrated magnitude of the optical transient (OT) plus
its apparent host galaxy is: r = 24.15 +- 0.3. The total flux is divided
approximately equally between the two. Assuming the mean zero-point offset
<r-R> = 0.4, this implies the magnitude for the OT at this epoch (June 16.30
UT) of R = 24.5 +- 0.5 (and the same for the host galaxy).
Using the measurement of R = 22.9 +- 0.2 on June 13.9 UT from Hjorth et al.,
the implied power-law decay slope is -1.0, which is perfectly normal for
GRB afterglows.
Images are now posted at:
http://astro.caltech.edu/~george/grb/grb980613.html
This message can be cited.
[GCN Operator's Note: D. Djorgovski, et al., points out that there was a typo
in their original submission to GCN Circular 117. The text above is the
corrected version.
The original quoted the "... its apparent host galaxy is: r = 25.15 +- 0.3",
when it should have said "... its apparent host galaxy is: r = 24.15 +- 0.3."
This second distribution has been given the same serial number. The archive
files on the GCN web site have been corrected.]
GCN Circular 118
Subject
GRB980613, optical observations
Date
1998-06-22T15:26:21Z (27 years ago)
From
Vladimir Sokolov at SAO RAS <sokolov@sao.ru>
V. Sokolov, S. Zharikov on behalf of the SAO-RAS GRB follow-up team and
L. Piro, E. Costa, L. Nicastro and E. Palazzi on behalf of the SAX GRB team
report:
On Jun. 20.858 we obtained Rc band images with the 6-m BTA telescope of SAO-RAS.
We detected the source reported by Hjorth et al. (GCN #109).
Conditions were not photometric with seeing of 3.0 arcsec.
The total observing time was 3600 s with 600 s per exposure.
For photometric calibration we used star 1 from Hjorth et al. (GCN #109)
and star 4_r from Odewahn et al. (GCN #105) (assuming r-R=0.35).
Preliminary photometry (Cousins R) of the source yields:
June 20.858 UT: Rc = 23.17+/-0.08
This result is not consistent with the upper limit of June 17.9088 UT: R > 24.0
(formal 10-sigma limit) from Hjorth et al. (GCN #109).
Finding charts and updates of these preliminary results will be posted at
http://www.sao.ru/~zhar/home/GRB/980613.html
This message can be cited.
GCN Circular 119
Subject
GRB 980613 Near-IR observations
Date
1998-06-23T20:36:15Z (27 years ago)
From
Jeff Goldader at STScI <goldader@stsci.edu>
J. Goldader (STScI), M. Beasley (U. Colorado), M. Hanson (Steward
Observatory, U. Arizona), and P. Conti (U. Colorado) report:
We imaged part of the initial 8 arcminute diameter error
circle of GRB 980613 (Piro & Costa, GCN 99) at K (2.2 micron) using
ONIS on the KPNO 4m telescope. Our observations covered approximately
(RA=10h 18m 23.90s, DEC=+71d 28' 25") through (RA=10h 17m 29.10s,
DEC=+71d 31' 25"), and also (RA=10h 17m 26.24s, DEC=+71d 28' 25") through
(RA=10h 16m 54.30s, DEC=+71d 31' 25") (J2000.0), and were made between
1998 June 14.22 and 14.26 UT. No objects not present on the DSS
were observed, to a limiting point-source magnitude of K=18.0 +/- 0.2
(3 sigma, estimated by spreading flux evenly over a 4x4 pixel box) in
seeing of ~0.7 arcsec FWHM. The fields observed fall north
of, and do not include, the positions of the fading X-ray
source 1SAX J1017.9+7127 (Costa et al., IAUC 6939; Piro et al.,
GCN 104) and the possibly associated optical transient reported by
Hjorth et al. (GCN 109).
This report may be cited.
GCN Circular 134
Subject
GRB980613 Optical Observations
Date
1998-07-07T18:13:02Z (27 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. P. Halpern (Columbia), and R. Fesen (Dartmouth) report on behalf
of the MDM Observatory GRB follow-up team that the optical afterglow of
GRB 980613 discovered by Hjorth et al. (GCN #109) is also present and
variable on MDM images at a level just below the limit of I = 22.3
previously quoted by us in GCN #106.
Our J2000 position of the OT is (+/- 0.6"):
RA = 10 17 57.82
Dec = +71 27 25.5
Measured magnitudes (at mean epoch) and 1-sigma statistical errors are:
R = 22.96 +/- 0.09 (June 14.24 UT)
I = 22.53 +/- 0.09 (June 14.20 UT)
I = 22.83 +/- 0.15 (June 15.19 UT)
Actual errors are larger, limited by systematic effects of fringing in the
I band. Photometry was calibrated using Landolt standards. Our magnitudes
of the five reference stars measured by Diercks et al. (GCN #108) are given
in the following table, and are in agreement with their values, as well as those
of Djorgovski et al. (GCN #117). Quoted uncertainties are 1-sigma statistical.
Coordinates are measured with respect to the USNO A1.0 reference system.
Star RA(2000) Dec(2000) R I
--------------------------------------------------------------------
1 10 17 47.52 +71 26 59.9 17.91 +/- 0.01 17.34 +/- 0.01
2 10 17 54.87 +71 27 39.8 19.20 +/- 0.01 18.76 +/- 0.01
3 10 18 06.61 +71 27 04.7 20.02 +/- 0.05 18.72 +/- 0.01
4 10 17 55.31 +71 28 16.3 19.54 +/- 0.02 18.61 +/- 0.01
5 10 17 41.44 +71 28 08.9 18.70 +/- 0.01 18.31 +/- 0.01
--------------------------------------------------------------------
Our measurement of R = 22.96 for the OT on June 14.24 is similar to that
of Hjorth et al. (R = 22.9 +/- 0.2 on June 13.89), which may be consistent
with a plateau in the first 24 hours after the burst, or perhaps just an
effect of the large error bars. Our R-band measurement combined with the
later detection by Djorgovski et al. (R = 24.5 +/- 0.5 on June 16.30)
implies a power-law decay slope of 1.3.
Our images are posted at http://cba.phys.columbia.edu/grb/980613/
This message may be cited.
GCN Circular 189
Subject
GRB 980613: Spectroscopy of the host galaxy
Date
1999-01-03T22:18:24Z (26 years ago)
From
George Djorgovski at Caltech/Palomar <george@oracle.caltech.edu>
GRB 980613: Spectroscopy of the host galaxy
S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom (Caltech), D. Frail (NRAO),
F. Chaffee and R. Goodrich (CARA/WMKO), on behalf of the Caltech-NRAO-CARA
GRB collaboration, report:
We obtained spectra of the host galaxy of GRB 980613 (see GCN Circ. 114 and
117) at the Keck-I telescope, on 17 Dec 1998 UT. The reduced spectrum shows
a single strong emission line at 7814 Angstroms, which we interpret as the
[O II] 3727 line at z = 1.0964 +- 0.0003, a probable 4000-A break just to
the red of it, and a very blue, featureless continuum blueward of the line.
Other plausible spectroscopic identifications of this line (e.g., Ly alpha,
Balmer lines, [O III], etc.) would predict appearance of other strong
emission lines or continuum breaks, which are clearly not seen in our data.
We thus consider our redshift interpretation to be secure. The spectrum is
typical of star forming galaxies at comparable redshifts.
Both the continuum and the line emission are clearly extended. The images
of the galaxy (which is coincident with the OT discovered by Hjorth et al.,
1998, GCN Circ. 109), show a patchy or asymmetric morphology, suggestive of
an interacting system.
In what follows, we assume the Galactic foreground extinction A(V) = 0.27 mag
from Schlegel et al. (1998, ApJ 500, 525), and a simple Friedman model
cosmology with H_0 = 65 km/s/Mpc, Omega_0 = 0.2, and Lambda_0 = 0. At this
redshift, the luminosity distance is 2.256e28 cm.
The extinction-corrected spectroscopic magnitudes of the host are: B = 24.4,
V = 24.1, and R = 23.85 mag, with the zero-point uncertain by at least 0.2
mag. This is in an excellent agreement with the R-band magnitude in a
comparable aperture, derived from direct images obtained at the Keck-II
telescope on 28 Nov 1998 UT, and consistent with our earlier estimate (GCN
Circ. 117).
From the BATSE fluence of 1.71e-6 erg/cm2 (Woods et al. 1998, GCN Circ. 112)
the implied isotropic gamma-ray energy of the burst was 5.2e51 erg.
The extinction-corrected [O II] line flux is 4.4e-17 erg/cm2/s, giving the
line luminosity of 2.8e41 erg/s. The implied unobscured SFR, using the
conversion from Kennicutt (1998, ARAA 36) is 3.9 Msun/yr. The observed,
extinction-corrected monochromatic flux at the rest wavelength of 2800 A is
0.9 microJy, corresponding to the restframe power of 2.76e28 erg/s/Hz. The
implied unobscured SFR, using the estimator from Madau et al. (1998, ApJ 498,
106) is 3.5 Msun/yr, in an excellent agreement with the [O II] line estimate,
although both may be uncertain by as much as 20-50%. This agreement suggests
that the host galaxy as a whole is not heavily obscured. We note that this
SFR is rather moderate, despite the very blue color of the host galaxy.
Further observations and analysis are in progress. This report may be cited.
GCN Circular 777
Subject
HST/STIS observations of the chaotic environment of GRB 980613
Date
2000-08-21T20:31:38Z (25 years ago)
From
Stephen Holland at IFA, U of Aarhus <holland@ifa.au.dk>
HST/STIS observations of the chaotic environment of GRB 980613
Stephen Holland, Bjarne Thomsen (University of Aarhus),
Jens Hjorth, Johan Fynbo (University of Copenhagen),
Michael Andersen (University of Oulu),
Gunnlaugur Bjornsson (University of Iceland),
Andreas Jaunsen (ESO),
Priya Natarajan (University of Cambridge, & Yale), and
Nial Tanvir (University of Hertfordshire)
We have used the Space Telescope Imaging Spectrograph (STIS) on
the Hubble Space Telescope to image the environment where GRB 980613
occurred. We obtained 5851 seconds of STIS/CCD images with the 50CCD
(clear) aperture and 5936 seconds of images with the F28X50LP (long
pass) aperture. This data was taken as part of the Survey of the Host
Galaxies of Gamma-Ray Bursts (Holland et al., GCN 698) approximately
799 days after the burst. Combined images are now available at
"http://www.ifa.au.dk/~hst/grb_hosts/data/index.html".
A comparison with ground-based R-band images of the optical
afterglow associated with GRB 980613, taken with from the Nordic
Optical Telescope (NOT) (Hjorth et al., GCN 109) suggests that the GRB
occurred at X = 1023.95 +/- 1.52, Y = 1068.73 +/- 0.96 on the drizzled
50CCD image. The quoted uncertainties are the uncertainties in the
transformation between the NOT and STIS images. They do not reflect
the uncertainty in the position of the optical afterglow in the NOT
images due to the GRB being superimposed on a fragmented, extended
structure (object A in Djorgovski et al., astro-ph/0008029). This
systematic uncertainty means that the position of the optical
afterglow may be consistent with the position of a blue, compact
source at the southeast end of the A complex. This source has a
full-width at half-maximum of 0.13 arcsec (the resolution of the
drizzled STIS images is 0.089 arcsec), and AB magnitudes of CL = 26.3
+/- 0.1 and LP = 26.2 +/- 0.1 in an aperture of radius 0.25 arcsec.
An image of the complex structure where GRB 980613 occurred is
available at "http://www.ifa.au.dk/~hst/grb_hosts/data/grb980613cd.gif".
There are several extended objects within a few arcseconds of the GRB
(Djorgovski et al., astro-ph/0008029). These objects have a wide
range of colours, significant substructure, and some of them appear to
have extended tails that may be due to tidal interactions. The total
diameter of the chaotic environment around GRB 980613 is approximately
eight arcseconds. If we assume that all of the structure lies at the
same redshift (z = 1.0969, Djorgovski et al., astro-ph/008029), and
adopt a cosmology with H0 = 70, Omega_matter = 0.3, and Omega_lambda =
0.7, then this corresponds to a diameter of approximately 65 proper
kpc. The total light in this region is CL = 23.0 +/- 0.1, LP = 22.9
+/- 0.2. A detailed analysis of this data is in progress (Hjorth et
al., in preparation).