GRB 981226
GCN Circular 169
Subject
GRB981226 Optical Observation
Date
1998-12-27T07:00:13Z (26 years ago)
From
Brad Schaefer at Yale <schaefer@grb2.physics.yale.edu>
Bradley E. Schaefer (Yale) reports:
"I have obtained five 15-minute images in the R band of the BeppoSAX 6'
radius region for GRB981226 (Di Ciolo et al. IAUCirc 7074). These images
were obtained from UT 01:03 to 02:25 on 27 December 1998 (15.2 hours after
the burst) with the Yale 1m telescope on Cerro Tololo. The GRB is close
to the Sun, so the observing time on any night is short even from the
southern hemisphere. The seeing varied with altitude from 1.3" to 1.7"
FWHM.
No variable source was identified in or near the GRB981226 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 1.2 hours of time. For the latter
comparison, the limiting magnitude for detecting change is close to R=21
mag. Further analysis will provide both deeper and more accurate limits."
GCN Circular 172
Subject
GRB 981226 optical observations
Date
1998-12-27T23:29:52Z (26 years ago)
From
Paul Vreeswijk at U of Amsterdam <pmv@astro.uva.nl>
T.J. Galama, P. Vreeswijk (U. of Amsterdam), E. Palazzi, F. Frontera,
N. Masetti (ITESRE, CNR, Bologna) J. van Paradijs (U. of Amsterdam and
U. of Alabama in Huntsville), C. Kouveliotou (USRA/MSFC), and
A.C. Cameron (U. of St Andrews, UK) report:
"We have compared Anglo-Australian Telescope (AAT) R-band images (Dec
27.48 1998 UT) with the Digitized Sky Survey (DSS; 'Second Epoch
Southern' survey, UK Schmidt red filter), at the position of the
BeppoSAX NFI source (BeppoSAX mail 98/26) in the error box of GRB
981226 (Di Ciolo et al. IAUCirc 7074). The AAT image shows a point
source at RA = 23h29m35.0s, Dec = -23d56'31'' which is not visible in
the DSS. The position is accurate to 2 arcsec (1-sigma). We calibrated
the field using the standard field PG0231+051 (Landolt 1992, AJ 104,
340) and obtain R = 21.04 +- 0.10 for the point source. We cannot
establish whether the source is related to GRB 981226 as this is a
comparison between different filters, but it is a possible candidate."
This message is citeable.
GCN Circular 173
Subject
GRB 981226 - Infrared Observations
Date
1998-12-28T03:58:18Z (26 years ago)
From
Alberto Castro-Tirado at LAEFF-INTA <ajct@laeff.esa.es>
GRB 981226
A. J. Castro-Tirado and J. Gorosabel, Laboratorio de Astrofisica Espacial y
Fisica Fundamental, Madrid
N. Drory and B. Konig, Universitaetssternwarte, Munich
V. Motta, Univ. de la Republica, Montevideo
N. Gonzalez, Instituto de Astrofisica de Canarias, Tenerife
J. Aceituno, Calar Alto Observatory, Almeria
J. Greiner, Astrophysikalisches Institut, Potsdam
F. Frontera and E. Palazzi, Istituto di Astrofisica Spaziale, Frascati
(on behalf of the BeppoSAX team)
We have obtained J-band images at the 3.5-m telescope (equipped with Omega)
at the German-Spanish Calar Alto Observatory, on Dec 26.76 (300-s) and Dec
27.76 (1700-s). Within the BeppoSAX position for the X-ray source in the
GRB 981226 error box (di Ciola et al. IAU Circ. 7074), we find a variable
object with J = 19.4 (Dec 26.76) and J = 20.5 (Dec 27.76). These values are
still preliminary. The position is RA(2000) = 23 29 35.0, Dec(2000) =
-23 55 42 (+/- 3"). The object reported by Galama et al. (GCN Circ. 172)
does not exhibit any variability larger than 0.1 mag. Further observations
are encouraged in order to confirm whether the above-mentioned object is
the counterpart to GRB 981226.
A finding chart can be retrieved via anonymous ftp to laeff.esa.es
(under /pub/users/ajct/grb981226).
This report is quotable in any publication.
GCN Circular 174
Subject
GRB981226, BeppoSAX Christmas GRB
Date
1998-12-28T05:03:57Z (26 years ago)
From
Luigi Piro at IAS/CNR Frascati <piro@alpha1.ias.rm.cnr.it>
L. Piro and the BeppoSAX team report:
A GRB (GB981226) was detected by the GRBM and WFC of BeppoSAX on Dec.26,
around 9:47 U.T.
Preliminary coordinates from WFC are:
R.A.(2000)=352.433
DEC(2000)=-23.942
The error radius is about 8', including a systematic error due a
less-than-optimal attitude configuration.
A follow-on with NFI is being planned.
[GCN OP NOTE: This Circular was received 26 Dec 1998 15:00 UT. However,
it was not sent to the automated system, and I was away on holiday without any
computer access to catch it sitting in my inbox. I am distributing it
for the record even though most of the community knows of this burst, and
several have made follow-up observations: GCN Circulars 169, 172, and 173.
I will attempt to correct such shortcomings plus the GCN Notice format problem
for future events.]
GCN Circular 177
Subject
Optical Observations of GRB981226
Date
1998-12-29T05:19:21Z (26 years ago)
From
Przemyslaw R. Wozniak at Princeton U. Obs. <wozniak@astro.princeton.edu>
Przemyslaw R. Wozniak reports for OGLE team:
An attempt to observe optical transient of GRB981226 was made
in BeppoSAX 6' radius region reported by Di Ciolo et al. (IAUCirc 7074).
On three nights following the announcement, Dec 27-29, approximately
between 1:15 and 2:30 UT I collected 10 and 15-minute frames in I band,
with the 1.3 m Warsaw University Observatory Telescope on Las Campanas.
This amounted to 70,70,80 minutes of integration each night
at 1.4, 1.3 and 1.2" seeing respectively.
On the first night a faint object at R.A. = 23h29m27s.3, Decl. = -23d56'54"
with approximate magnitude I = 20.3 showed some evidence for decline of the
flux. Two following nights did not confirm variability. It is most likely
a faint galaxy close to detection limit on single exposures.
I also looked at object reported by Castro-Tirado et al. (GCN#173)
at R.A. = 23 29 35.0, Dec = -23 55 42 (J2000). On averages of frames from
each night I can barely discern the object at estimated I = 21.4, close
to detection limit, however I don't see evidence for variability in my data.
GCN Circular 178
Subject
GRB981226, BeppoSAX-NFI follow-up
Date
1998-12-29T14:40:10Z (26 years ago)
From
Luigi Piro at IAS/CNR Frascati <piro@alpha1.ias.rm.cnr.it>
L. Piro on behalf of the BeppoSAX team report:
A follow-up with the NFI of GB981226 started yesterday Dec.26
around 20:34 U.T.
Preliminary analysis of the LECS and MECS detectors for the first 6 orbits
shows a previously unknown source (a few x 10**-13 erg/cm2/s) within the
WFC error box.
Preliminary position is:
R.A.(2000)= 352.40
DEC(2000)= -23.93
i.e. 1.2' from the center of the WFC error box
The error radius is 1.5'.
At this stage of the observation we cannot yet establish whether the
source is fading. The observation will finish tomorrow evening.
GCN Circular 180
Subject
radio observations of GRB 981226
Date
1998-12-29T23:20:35Z (26 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 X-ray source (GCN #178) in the error box of GRB
981226 (GCN #174) with the Very Large Array (VLA) at 4.86 GHz on
Dec. 27.00 UT and at 8.46 GHz on Dec 29.92 UT. No sources are visible
within the region bounded by the NFI error circle above a 4-sigma
level of 148 microJy (4.86 GHz) and 108 microJy (8.46 GHz) on these
two days. In particular, we find no radio counterparts to the two
optical objects noted by Galama et al. (GCN #172) and Castro-Tirado et
al. (GCN #173)."
This message is citeable.
GCN Circular 181
Subject
GRB 981226 optical observations
Date
1998-12-30T05:52:14Z (26 years ago)
From
James Rhoads at KPNO <rhoads@noao.edu>
James Rhoads (KPNO), Jerome A. Orosz (Penn State University),
John Lee (Yale University), and Keivan Stassun (U Wisconsin);
report on behalf of the KPNO GRB followup team:
We have observed the field of GRB 981226 on 1998 December 27.156 (J.
Lee observing), 28.100 (J. Lee observing), and 29.096 (K. Stassun
observing) using the 0.9m telescope and CCD Mosaic Camera at Kitt Peak
National Observatory. Total integration times were 24, 24, and 40
minutes on the three nights. Intermittent cloud on the first night
resulted in a comparatively shallow image, with limiting magnitude R ~
20.5. Limiting magnitudes on the 2nd and 3rd nights were R ~ 21.
(These are very approximate estimates based on the USNO-A catalog
magnitude R=16.9 for the star at 23:29:29.3 -23:57:36 [J2000].) The
full field of view is 1 degree, and so covers the entire BeppoSAX WFC
error region and more.
Sections of the reduced images are available in FITS format
at http://www.noao.edu/noao/grb/981226.html together with further details.
Preliminary analysis yields no new sources clearly above the detection
limits for the POSS plates, and no convincingly variable sources. We
do not detect any object at the position of the J band transient reported
by Castro-Tirado et al. The source reported by Galama et al (GCNC 172) is
apparent in all of our images and does not appear to vary more than 20%;
tighter limits will require deeper images.
In addition, J. Orosz observed the field on the same three nights using the
KPNO 2.1m telescope with R band (Dec 27, 28 UT) and I band (Dec 29 UT) filters.
The data cover part of the original BeppoSAX WFC error box.
These data are also available from the same web site.
Further analysis of both data sets is underway.
This report is citable.
GCN Circular 182
Subject
GRB 981226
Date
1998-12-30T07:02:49Z (26 years ago)
From
Josh Bloom at CIT <jsb@astro.caltech.edu>
GRB 981226: Optical Observations
J. S. Bloom, R. R. Gal, and J. Meltzer (Caltech), on behalf of the
Caltech/NRAO GRB collaboration, report:
"On 27.1 and 28.1 December 1998 UT we obtained optical images of the X-ray
localization (GCN #174; GCN #178) of GRB 981226 at the Palomar 60-inch.
Total integration time was 1800-s and 3450-s with an approximate gunn-i
object detection threshold of 23.5 and 24.3 (on 27.1 Dec, 28.1 Dec,
respectively). An astrometric plate solution was obtained by comparing
field stars to that from USNO-A2 Catalogue; the rms fit in either axes was
found to be 0.18 arcsec. We assumed the standard zero-point for the
instrument; for comparison, this zero-point gives gunn-i = 20.47 for the
star at ra: 23:29:43.5, dec: -23:54:13.8 (J2000).
The J-band source reported by Castro-Tirado et al. (GCN #173) is not
detected at either epoch, implying a J - i of greater than about 3.5 mag
on 27.1 Dec UT. The source reported by Galama et al. (GCN #172) did not
vary significantly (delta m = 0.12 mag, consistent within the photometric
error of r.m.s. = 0.1 mag) and is not likely to be the optical transient
of this GRB. These statements are consistent with those by Rhoads et al.
(GCN #181).
We do find that the object at ra: 23:29:27.33, dec: -23:56:53.7 (+/- 0.18
arcsec), reported as possibly variable by Wozniak (GCN #177), to have
faded by 0.46 (+/- 0.09 rms) mag between the two epochs. Our preliminary
photometry gives i=22.9 +/- 0.2 and i=23.4 +/- 0.2 on the first and second
epochs, respectively. We note that this source is well-outside (~1.5
arcmin) the formal error box of the X-ray NFI position (GCN #178), so its
connection with GRB 981226 remains to be established. If indeed this
source is the transient afterglow of the GRB, then the measured time decay
constant is alpha = -0.5; this is shallower than those found in other
afterglow but can be reconciled if the underlying galaxy host is of
comparable brightness to the transient.
This message may be cited.
GCN Circular 183
Subject
GRB 981226 radio observations
Date
1998-12-30T19:38:44Z (26 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 location of the X-ray source (GCN #178) in the
error box of GRB 981226 (GCN #174) with the Westerbork Radio Synthesis
Telescope (WSRT). We observed for 6.4 hours at 4.88 GHz on Dec 29.70
UT, 1998. We find no sources at the location of the X-ray source down
to 360 microJy (4 sigma). In particular, we find no radio counterparts
to the optical objects noted by Galama et al. (GCN #172), Castro-
Tirado et al. (GCN #173) and Wozniak et al. (GCN #177). These results
are consistent with those by Frail et al. (GCN #180)."
This message is citeable.
GCN Circular 184
Subject
GRB981226 BeppoSAX follow up
Date
1998-12-30T22:44:28Z (26 years ago)
From
Filippo Frontera at ITESRE CNR <filippo@tesre.bo.cnr.it>
F. Frontera, E. Montanari, Universita' Ferrara, Italy, L. A. Antonelli,
Osservatorio Astronomico di Roma, Italy, P. Giommi, Agenzia Spaziale
Italiana, Rome, Italy, M. R. Daniele, D. Ricci, SAX-SDC, Rome, Italy, A.
Coletta, M. Smith, A. Tesseri, SAX-SOC, Rome, Italy, C. De Libero,
SAX-OCC, Rome, Italy, L. Piro, IAS, CNR, Rome, Italy, on behalf of a large
collaboration, report:
"The BeppoSAX Wide Field Camera error box of GRB981226 (IAUC
7074) was observed with the BeppoSAX Narrow Field Instruments (NFI)
starting about 11 hr after the burst in the period Dec. 26.878-29.148 UT.
Preliminary analysis of the MECS2+3 data shows a previously unknown X-ray
source, 1SAXJ2329.6-2356, located at RA = 23h29m36s, Dec = -23o55'58''
(equinox 2000.0), with an error radius of 1'. This position is very
close to the centroid of the WFC error box. During the first 33.3 hours
of observation, the 2-10 keV source flux decreases by a factor 3,
from (4.3 +-1.0)x10E-3 cts/s, corresponding to (3.0 +- 0.7)x10E-13
erg sE-1 cmE-2, down to (1.67+-0.46)x10E-3 cts/s corresponding to (0.98 +-
0.30)x10E-13 erg sE-1 cmE-2. The measurements during the subsequent 18.36
hours show that the flux of 1SAXJ2329.6-2356 does not vary significantly
from the last value.
GCN Circular 185
Subject
GRB981226 Optical Observations
Date
1998-12-31T11:37:38Z (26 years ago)
From
Brad Schaefer at Yale <brad@grb2.physics.yale.edu>
Bradley E. Schaefer (Yale U.), Jonathan Kemp, Irina Feygina, Jules Halpern
(Columbia U.) report:
"We have obtained B, V, and R images with the 0.9-m and 1.0-m telescopes
on Cerro Tololo of the GRB981226 position on the nights of 26/27, 27/28,
and 30/31 December 1998. We find no variable sources, and no significant
changes from the Digitized Sky Survey. This includes the entire BeppoSAX
WFC error circle (Di Ciolo et al. IAUCirc. 7074) as well as the BeppoSAX
NFI error circle (Frontera et al. IAUCirc. 7078).
A journal of our observations, the corresponding magnitudes, and limits
are presented in the table below. Our limiting magnitudes are quoted for
a signal-to-noise ratio of 4. For the three variables that have been
proposed previously, we find as follows:
(1) No source is visible at the position of the proposed infrared variable
(Castro-Tirado et al. GCN 173) to the limits stated below. This
implies R-J > 1.7 for this source if it is the afterglow.
(2) There is no significant evidence for variability of the proposed
candidate of Galama et al. (GCN 172).
(3) The source identified by Wozniak et al. (GCN 177) is clearly visible,
but we have no significant evidence of its variability."
-------------------------------------------------------------------
Telescope UT start Band Limit Mag(Galama) Mag(Wozniak)
-------------------------------------------------------------------
CTIO 1.0m Dec 27.044 R 21.6 20.74+-0.13 21.20+-0.20
CTIO 0.9m Dec 27.064 V 21.8 >21.8 >21.8
CTIO 0.9m Dec 27.071 B 21.5 >21.5 >21.5
CTIO 1.0m Dec 28.034 R 21.7 21.06+-0.15 21.15+-0.24
CTIO 0.9m Dec 28.065 V 21.7 >21.7 >21.7
CTIO 0.9m Dec 28.072 R 21.0 20.8 +-0.3 21.03+-0.24
CTIO 0.9m Dec 31.052 R 22.1 21.10+-0.10 21.61+-0.20
------------------------------------------------------------------
GCN Circular 188
Subject
GRB981226, sub-millimeter observations
Date
1999-01-02T22:29:23Z (26 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 source suggested by Castro-Tirado as being the counterpart to
GRB 981226 (GCN #173: 23:29:35.0 -23:55:42 J2000). The observation, performed
in mediocre weather, started UT 1998 Dec 30.15 and lasted 44 minutes. No
source was detected at this location: the 850 micron flux density was
0.6 +/- 3.8 mJy.
This report may be cited in publications.
GCN Circular 190
Subject
GRB 981226 Optical Observations
Date
1999-01-06T12:56:10Z (26 years ago)
From
Jens Hjorth at U.Copenhagen <jens@astro.ku.dk>
GRB 981226 Optical Observations
B. Lindgren, J. Hjorth, H. Pedersen, (University of Copenhagen),
M. I. Andersen (NOT), A. O. Jaunsen (University of Oslo),
J. Sollerman (Stockholm Observatory),
J. Smoker, C. Mooney (Queens University, Belfast) and
E. Palazzi (Istituto TeSRE, Bologna; on behalf of the SAX GRB team)
report:
"R band images of parts of the BeppoSAX WFC error circle of GRB 981226
(Piro, GCN Circ. 174), covering the NFI error circle (Di Ciolo et al.,
IAU Circ. 7074; Frontera et al. IAU Circ. 7078), were obtained on 1998
December 26.82 UT (1440 sec, seeing FWHM = 1.7"), Dec 27.85 UT (2400 sec,
FWHM = 1.6") and Dec 28.83 UT (2400 sec, FWHM = 1.0") with the 2.5-m
Nordic Optical Telescope (NOT) on La Palma and on Dec 27.06 UT (500 sec,
FWHM = 1.5") and Dec 28.09 UT (500 sec, FWHM = 1.5") with the 1.5-m Danish
telescope, La Silla. An I band image was obtained with the NOT on
Dec 28.86 UT (2100 sec, FWHM = 1.2").
Down to a limiting magnitude of R ~ 23 we have found no significant evidence
for a variable source inside the NFI error circle. Finding charts of the
field are posted at http://www.astro.ku.dk/~brian_j/grb981226
The results we obtained for two field reference stars (A,B) and the
three candidate optical counterparts to GRB 981226, reported by Galama
et al. (GCN Circ. 172), Castro-Tirado et al. (GCN Circ. 173) and Wozniak
(GCN Circ. 177), respectively, are presented in the table below.
The photometric zero point is tied to that of Galama et al. (GCN Circ. 172),
assuming R = 21.04 for their reported object. All photometry is based on PSF
photometry of the NOT R images, and assumes unresolved objects. The data
obtained at the Danish 1.5-m telescope are consistent with these results. The
quoted photometric uncertainties include formal fitting errors only. The
astrometry refers to the USNO-A2.0 system (J2000) and is accurate to +- 0.23"
(mean absolute deviation).
RA (J2000) Dec (J2000) Dec 26.83 Dec 27.85 Dec 28.83
star A 23 29 29.28 -23 57 36.9 16.79+-0.00 16.79+-0.00 16.79+-0.00
star B 23 29 29.57 -23 57 45.6 18.79+-0.01 18.77+-0.01 18.80+-0.00
Galama 23 29 34.94 -23 56 30.5 21.01+-0.05 21.09+-0.07 21.07+-0.04
Castro-Tirado 23 29 34.92 -23 55 41.3 22.47+-0.14 22.36+-0.16 23.05+-0.18
Wozniak 23 29 27.31 -23 56 53.5 (21.31+-0.06)(21.58+-0.11)(21.60+-0.05)
Galama's object is constant within +- 0.05 mag during our observations.
This is consistent with the findings of Castro-Tirado et al. (GCN Circ.
173), Bloom et al. (GCN Circ. 182) and Schaefer et al. (GCN Circ. 185).
Castro-Tirado's object is close to the detection limit in our images,
and we conclude that there is no evidence for variability of this object.
In a combined image of all our R band data the object has R = 22.9 +- 0.1.
If Castro-Tirado's variable (J band) object is the optical afterglow to
GRB 981226, then the object we have detected is the likely host galaxy. It
would be among the brightest host galaxies detected so far.
In our combined R image (FWHM = 1.2") Wozniak's object is clearly extended.
While consistent with that found by Schaefer et al. (GCN Circ. 185), our PSF
photometry is therefore biased and seeing dependent. We conclude that this
object is a galaxy with a constant R = 21.16 +- 0.05 and that any contribution
from a variable source must be small in R.
For our Dec 28.86 I band NOT image we find I = 18.1 (based on an
approximate photometric zeropoint accurate to an estimated +- 0.2 mag)
for the reference star reported to have i = 20.47 (Bloom et al., GCN
Circ. 182). In what follows we adopt our own preliminary zero point and
offset the Bloom et al. values to this system for comparison.
Galama's object has I = 20.35 +- 0.05, i.e., R - I = 0.7. Castro-Tirado's
object is not detected down to I = 22. Wozniak's object is close to the
detection limit; we find I = 21.9 +- 0.5 on Dec 28.86. This value should be
compared to I = 20.3 on Dec 27.1 UT (Wozniak, GCN Circ. 185), and to the
corrected values I = 20.55 on Dec 27.1 UT and I = 21.05 on Dec 28.1 UT (based
on Bloom et al., GCN Circ. 182). Thus, Wozniak's object has continued to fade.
In the simplest scenario, Wozniak's object is a fading red source
(R - I > 2.6) superposed on an extended blue (R - I < -0.7) object. It is
tempting to interpret this as a rapidly fading red optical afterglow
originating in a bright, blue host galaxy. However, given its position more
than one error radius (70") outside the NFI error circle, its relation to
GRB 981226 remains questionable.
The results reported in this circular are preliminary. A more detailed
analysis is ongoing."
This report may be cited.
GCN Circular 195
Subject
GRB 981226: radio variable
Date
1999-01-20T05:07:06Z (26 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>
D. A. Frail reports on behalf of a larger NRAO/Caltech collaboration:
"There is a faint radio source within the NFI error circle (GCN #184)
of GRB 981226 at RA = 23h29m37.21s, DEC = -23d55'53.8" with an error
of +/-0.5". The source was first detected at the VLA on Jan 3.95 UT
with an 8.46 GHz flux density of 169 +/- 28 microJy. It is present but
at a weaker level on at least three other epochs (Dec. 29, Jan 7 and
Jan 11), where its average flux density is 76 +/- 17 microJy. On
January 19.89 UT, the flux density of the source had dropped below
detectablity, with an upper limit of 28 microJy.
This level of short term variability is characteristic of radio
afterglows at early times. In contrast, two other radio sources in the
field have remained constant during this same period. We urge optical
observers to re-examine this location for any indication of a
transient or a faint host galaxy."
This message is citeable.
GCN Circular 749
Subject
GRB981226, HST/STIS observations of the host galaxy
Date
2000-07-07T15:38:22Z (25 years ago)
From
Stephen Holland at IFA, U of Aarhus <holland@ifa.au.dk>
GRB981226, HST/STIS observations of the host galaxy
Stephen Holland, Bjarne Thomsen (University of Aarhus),
Michael Andersen (University of Oulu),
Gunnlaugur Bjornsson (University of Iceland),
Johan Fynbo, Jens Hjorth (University of Copenhagen),
Andreas Jaunsen (University of Oslo),
Priya Natarajan (University of Cambridge, & Yale), and
Nial Tanvir (University of Hertfordshire)
We have obtained 7865 seconds of HST/STIS images with the 50CCD
(clear) aperture and 7909.63 seconds of HST/STIS images with the
F28X50LP (long pass) aperture of the host galaxy of GRB 981226. These
data was taken as part of the Survey of the Host Galaxies of Gamma-Ray
Bursts (Holland et al. GCN 698) approximately 555 (clear) and 558
(long pass) days after the burst. Combined (drizzled) images are now
available at "http://www.ifa.au.dk/~hst/grb_hosts/data/index.html".
The galaxy identified by Frail et al. (1999, ApJL, 525, L81) is
the only object within the error circle of the radio transient (VLT
J232937.2-235553) associated with GRB 981226. This galaxy is located
at (X,Y) = (1033,1056) on the drizzled STIS clear image, has an
ellipticity of approximately 0.65, and its major axis has a position
angle of approximately -75 degrees east of north. We measured the
following AB magnitudes for this galaxy using an aperture with a 1.1
arcsecond radius: CL = 25.04 +/- 0.07 in the STIS clear aperture and
LP = 24.50 +/- 0.10 in the STIS long pass aperture. We used the
photometry of Walker (1994, PASP, 106, 828) to calibrate our data (see
Holland et al. 2000, in preparation, for details) and found V-R = 0.50
+/- 0.14, V = 24.80 +/- 0.08, and R = 24.30 +/- 0.11 in the Johnson
and Kron-Cousins systems. We note that the northeast side of the
galaxy is significantly bluer than the rest of the galaxy (see
"http://www.ifa.au.dk/~hst/grb_hosts/data/grb981226_colour.gif"). We
estimate that the blue structure on the north side of the galaxy has
V-R = 0.1 and the south edge of the galaxy has V-R = 1.5. There is a
compact source at each end of the blue structure. The west source
corresponds to the photometric centre of the galaxy.
Frail et al. (1999) found that the galaxy was located 0.55 +/-
0.53 arcseconds west and 0.41 +/- 0.43 arcseconds south of the radio
afterglow. This error ellipse encompasses the eastern half of the
galaxy and the eastern compact source in the blue structure.
We also note the presence of a faint point source (V ~= 28.4,
V-R ~= 0.3), at (X,Y) = (1015,1064) in the drizzled STIS clear image,
approximately 1.0 arcseconds from the nominal position of the radio
afterglow.