GRB 051221
GCN Circular 4384
Subject
GRB 051221: Redshift from Gemini
Date
2005-12-22T09:33:06Z (20 years ago)
From
Edo Berger at Carnegie Obs <eberger@ociw.edu>
E. Berger (Carnegie Observatories) and A. M. Soderberg (Caltech) report:
"We obtained 2x1200 sec spectra of the afterglow + host galaxy of the
short GRB 051221 (GCN 4383) with Gemini/GMOS. We detect several strong
emission lines at the position of the afterglow+host which we identify as
[OIII]4959,5006, H-beta, and [OII]3727 at a redshift of z=0.5465. Weak
absorption at the CaII H&K and G-band wavelengths at the same redshift may
also be present, but at a low significance.
The detection of strong emission lines indicates that the host galaxy is
under-going active star formation, and is possibly similar to that of GRB
050709 (Fox et al. 2005).
At the redshift of 0.5465, the isotropic-equivalent gamma-ray energy
release of the burst is 9e50 erg, the highest measured to date."
GCN Circular 4383
Subject
GRB 051221: Continued fading of optical afterglow
Date
2005-12-22T06:53:39Z (20 years ago)
From
Edo Berger at Carnegie Obs <eberger@ociw.edu>
E. Berger (Carnegie Observatories), A. M. Soderberg (Caltech), B. P.
Schmidt (ANU), and P. A. Price (IfA) report:
"We obtained a second epoch of r-band imaging with GMOS on Gemini-north
starting on 2005 Dec. 22.195 UT (26.8 hr after the burst and 24 hr after
the previous set of observations). A total of 960 sec were obtained in
excellent seeing conditions. We find that the optical afterglow candidate
(GCN 4375; see also GCNs 4367 & 4369) has faded by about 1.1 mag between
the two epochs, confirming our earlier claim."
GCN Circular 4375
Subject
GRB 051221: Discovery of fading optical afterglow
Date
2005-12-21T19:04:50Z (20 years ago)
From
Alicia Soderberg at Caltech <ams@astro.caltech.edu>
A. M. Soderberg (Caltech) and E. Berger (Carnegie Observatories) report:
"Digital image subtraction performed on the individual 240-s r-band frames
obtained with Gemini/GMOS (GCN 4369) reveal a fading source coincident
with the position of the bright NIR (GCN 4367) and optical (GCN 4369)
object located within the XRT error circle (GCN 4366). The fading source
is offset from the center of the bright object, which we identify as the
host galaxy, by about 0.2" to the west. Given the offset and fading
behavior we conclude that this object is the afterglow of GRB 051221.
Detailed photometry is in progress."
GCN Circular 4374
Subject
GRB 051221: Swift XRT refined analysis
Date
2005-12-21T18:46:53Z (20 years ago)
From
Milvia Capalbi at ISAC/ASDC <capalbi@asdc.asi.it>
M. Capalbi, M. Perri (ASDC), D.N. Burrows, D. Grupe (PSU), P. Boyd
(GSFC-UMBC), W. Voges (MPE) report on behalf of the Swift XRT team:
We have analyzed the first six orbits of the Swift XRT data of GRB
051221 (Parsons et al., GCN 4363).
Data in Windowed Timing (WT) mode started at 01:52:48 UT, 92 seconds
after the BAT trigger, then the XRT switched to Photon Counting mode.
The light curve shows an initial fading behavior up to 2.5 ks with a
decay index of -1.3 � 0.7. At later times, an indication of a
re-brightening is present.
A preliminary spectral fit (simple absorbed power-law) to the WT data in
the 0.5-10. 0 keV band yields a photon index of 2.0+/-0.4 and a column
density value consistent with the Galactic one (6.7E20 cm-2; Dickey &
Lockman 1990).
Extrapolating the initial decay, the unabsorbed 0.5-10.0 keV flux at 24
hours after the burst is estimated to be ~5E-14 erg cm^-2 s^-1.
GCN Circular 4373
Subject
GRB 051221: Swift/UVOT upper limits
Date
2005-12-21T16:53:16Z (20 years ago)
From
Alice Breeveld at MSSL-UCL <aad@mssl.ucl.ac.uk>
A. A. Breeveld (UCL-MSSL), F. Marshall (GSFC), A. Parsons (GSFC), P.
Mezsaros (PSU), M. Chester (PSU) on behalf of the Swift/UVOT team
The Swift/UVOT began the settling exposure of the field of GRB 051221 at
01:52:29 on 2005-12-21, 73s after the BAT trigger (Parsons et al. GCN
4363). The 86s delay reported in GCN 4363 did not include the settling
exposure. No source was detected at the XRT position (Burrows et al. GCN
4366) nor the candidate IR position (Bloom, GCN 4368) down to the
following 5-sigma upper limits. No correction has been made for the
expected visual extinction of about 0.23 magnitudes.
Filter T_range(s) Summed exposure times 5sigUL(mag)
V 73 - 12530 1109 19.2
B 453 - 19212 2098 20.8
U 399 - 18305 2098 20.2
W1 345 - 14127 1080 20.3
M2 290 - 13437 1298 20.7
W2 562 - 8341 1119 20.7
white 507 - 934 99.5 19.2
GCN Circular 4372
Subject
GRB 051221: Possible nearby cluster
Date
2005-12-21T09:26:41Z (20 years ago)
From
Edo Berger at Carnegie Obs <eberger@ociw.edu>
E. Berger (Carnegie Observatories) reports:
"Further examination of the Gemini data reveals a clustering of faint
galaxies extending about 1.5' eastward from the position of the X-ray
afterglow (GCN 4366) and the optical/near-IR source possibly associated
with the burst (GCNs 4367-9):
http://www.ociw.edu/~eberger/grb051221-gemini.tif
Additional multi-band photometry and an analysis of spatial clustering are
required in order to verify whether this is a true galaxy cluster and
whether the optical/near-IR source is related to this possible structure.
This analysis is in progress."
GCN Circular 4371
Subject
GRB 051221: No variability in Gemini data
Date
2005-12-21T08:18:37Z (20 years ago)
From
Edo Berger at Carnegie Obs <eberger@ociw.edu>
E. Berger (Carnegie Observatories) reports:
"Further analysis of the Gemini GMOS data reveals that the object located
within the XRT error circle (GCNs 4367-9) has not changed in brightness
between 227 and 271 min after the burst to a limit of about 0.05 mag in
comparison to several nearby stars. We note that a typical decay rate of
t^-1 would result in a change of about 0.2 mag. The lack of variability
suggests that this is either the host galaxy or an unrelated object, or
that the decay rate is unusually shallow, |alpha|<0.25."
GCN Circular 4370
Subject
GRB 051221: Correction to GCN #4368
Date
2005-12-21T07:38:51Z (20 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
J. S. Bloom reports:
Correction. GCN 4368 incorrectly stated that our discovery of the
long-wavelength counterpart to 051221 was the first IR counterpart
for a short-hard GRB: the Magellan/PANIC detection of 050724 (Berger
et al. Nature, 438, 988-990, 2005) was the first. I apologize for
this referencing oversight and thank E. Berger for pointing out this
error.
GCN Circular 4369
Subject
GRB 051221: Gemini observations
Date
2005-12-21T07:21:11Z (20 years ago)
From
Edo Berger at Carnegie Obs <eberger@ociw.edu>
E. Berger (Carnegie Observatories) reports:
"We observed the BAT error circle of the short GRB 051221 (GCN 4365) with
GMOS on the Gemnini-north telescope starting on 2005 Dec. 21.194 UT (2.8
hours after the burst). A total of 40 min were obtained in the r-band
under excellent seeing conditions (0.45"). Within the XRT error circle
(GCN 4366) we detect a single source at a position coincident with the
source reported in GCN 4367:
RA = 21:54:48.64
DEC= +16:53:27.44
Further analysis is in progress."
GCN Circular 4368
Subject
GRB 051221: Improved astrometry of the IR counterpart
Date
2005-12-21T07:20:22Z (20 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
J. S. Bloom (UC Berkeley) reports:
We have reduced the second epoch of our PAIRITEL imaging (beginning
2005-12-21 03:02:32 UTC; total integration = 690 sec) and detect the
source mentioned in GCN 4367 in a stacked mosaic. The source appears
to be best detected in the full stack J-band image at a revised
position of J2000:
21:54:48.662 +16:53:26.97
The uncertainty relative to the USNOB1.0 is 180 mas in each
coordinate (the previous two circulars were based upon an astrometric
match using far fewer 2MASS sources in the field). This position is
1.41 arcsec from the Burrows et al. XRT position (GCN 4366). Because
the source is observed near the detection level, we cannot confirm
fading behavior at this time. Still, given the proximity to the XRT
location, we advance that this source is the IR counterpart to GRB
051221 (GCN 4363). If so, this would be the first infrared
counterpart detected for a short-hard GRB.
This message may be cited.
GCN Circular 4367
Subject
GRB051221: K-band source
Date
2005-12-21T05:28:42Z (20 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
J. S. Bloom (UC Berkeley) reports:
Following the discovery of the XRT position of GRB 051221 (Burrows
GCN 4366), we inspected our PAIRITEL mosaics (GCN 4365) and found a
faint, red source to the south of the XRT position by 3.2 arcsec with
the coordinates:
21:54:48.65, +16:53:25.1
Photometry and improved astrometry are still in progress.
A finding chart will be posted to
http://astro.berkeley.edu/~jbloom/grb051221-xrt.ps
GCN Circular 4366
Subject
GRB 051221: XRT position
Date
2005-12-21T05:09:26Z (20 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
D. N. Burrows (PSU), M. Capalbi (ASDC), and D. Grupe (PSU) report on behalf
of the Swift XRT team:
The Swift XRT began observing GRB 051221 (Parsons et al., GCN 4363) at
01:52:44 UT (88 s after the burst). We find a bright, rapidly fading
source located at:
RA(J2000) = 21:54:48.71
Dec(J2000) = +16:53:28.2
The estimated uncertainty is 3.5 arcseconds (90% containment radius),
including corrections for the XRT boresight.
GCN Circular 4365
Subject
GRB 051221: Refined analysis of the Swift-BAT short hard burst
Date
2005-12-21T05:07:18Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
J. Cummings (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cannizzo (GSFC-UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (GSFC/UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), M. Tashiro (Saitama U.), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
Using the data from the recent telemetry downlink, we report
further analysis of Swift-BAT GRB 051221 (trigger #173780)
(Parsons, et al., GCN 4363). We have received data covering T-60
to T+120 seconds. The ground-analysis position is
RA,Dec 328.711,+16.892 {21h 54m 50.7s,16d 53' 31.9"} (J2000)
with an uncertainty of 0.8 arcmin (radius, 90%, stat+sys).
T90 is 1.4 +- 0.2 sec. The partial coding fraction is 63%.
The lightcurve has an initial hard spike at T+0.3 sec (FWHM of ~0.25 sec)
followed by 3 softer peaks at T+0.4, T+0.8, and T+1.2 sec.
Fitting a simple power law over the time-averaged interval (T+0.2 to T+2.4 sec),
gives a hard spectrum with a photon index of 1.39 +/- 0.06 and a fluence
of 1.16 +/- 0.04 X 10^-6 erg/cm^2. The peak flux in a 1-sec wide window
starting at T+0.2 sec is 12.1 +/- 0.4 ph/cm^2/sec. All values are
in the 15-150 keV band at the 90% confidence level.
GCN Circular 4364
Subject
GRB 051221: IR Observations at GRB+1hr
Date
2005-12-21T04:45:45Z (20 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
J. S. Bloom (UC Berkeley), on behalf of a larger collaboration, reports:
"We began observations of the bright short burst GRB 051221 (Parsons
GCN #4363) with the PAIRITEL 1.3m at 2005-12-21 02:54:02 UTC, about
30 minute after the GCN circular and 1hr3min after the GRB. In a
stack of the first 313sec, we detect no new sources to at least the
2MASS limit in JHKs bands. A visual comparison with the DSS-2 (F-
plate) shows that most of the sources fainter than 2MASS in the
PAIRITEL mosaics have optical counterparts. Some of the faintest IR
sources do not have detected counterparts but this is likely due to
the redness/faintness of the sources. In particular, we point out
objects at J2000:
A: 21:54:57.84 +16:53:07.5 (inside the error circle)
B: 21:55:00.89 +16:56:50.2 (red, outside the error circle)
C: 21:55:01.58 +16:57:07.1 (red, outside the error circle,
extended)
Further analysis is ongoing but we suggest that these sources be
monitored for variability, especially object A."
A RGB (=KsHJ) finding chart may be found at:
http://astro.berkeley.edu/~jbloom/grb051221.ps
This message may be cited.
GCN Circular 4363
Subject
GRB 051221: Swift detection of a bright short burst
Date
2005-12-21T02:24:36Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
A. Parsons (GSFC), S. Barthelmy (GSFC), D. Burrows (PSU), M. Capalbi (ASDC),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), C. Gronwall (PSU),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), F. Marshall (GSFC),
K. Page (U Leicester), D. Palmer (LANL),
on behalf of the Swift team:
At 01:51:16 UT, Swift-BAT triggered and located GRB 051221 (trigger=173780).
The spacecraft slewed immediately. The BAT on-board calculated location
is RA,Dec 328.711d,+16.896d {21h 54m 51s,+16d 53' 45"} with an uncertainty
of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve shows
a single bright short peak at T0 with a duration less than 128 msec
followed by a 2nd smaller and much softer peak at T+1 sec with an exponential
decay lasting ~3 sec. The peak count rate was ~70,000 counts/sec (15-350 keV),
at ~0 seconds after the trigger.
The XRT began observing the target at 01:52:44 UT, 88 sec after the burst.
There was no source bright enough for an on-board centroid determination,
but the TDRSS spectrum and lightcurve suggest the presence of an X-ray source
in the field of view. Further analysis will require the full data dump
through the Malindi ground station.
UVOT took a finding chart exposure of 199.9 seconds with the V filter
starting 86.1 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers
25% of the BAT error circle. The typical 3-sigma upper limit is about 18.7 mag.
The 8'x8' region for the list of sources generated on-board covers 100%
of the BAT error circle. The list of sources is typically complete
to about 18.0 mag. No correction has been made for the expected
visual extinction of about 0.23 magnitudes.