GRB 051021B
GCN Circular 4126
Subject
GRB 051021B: Swift detection of a burst
Date
2005-10-22T00:21:30Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
A. Retter (PSU), S. Barthelmy (GSFC), D. Burrows (PSU),
M. Chester (PSU), N. Gehrels (GSFC), J. Kennea (PSU),
F. Marshall (GSFC), D. Palmer (LANL), J. Racusin (PSU)
on behalf of the Swift team:
At 23:31:53 UT, Swift-BAT triggered and located GRB 051021B (trigger=160672).
The BAT on-board calculated location is RA,Dec 126.037d,-45.519d
{8h 24m 09s,-45d 31' 09"} (J2000), with an uncertainty of 3 arcmin
(radius, 90% containment, stat+sys). The BAT light curve shows
a single FRED-like peak with structure with a total duration of ~25 sec.
There is some pre-trigger emission starting at T-8 sec. The peak count rate
was ~1800 counts/sec (15-350 keV), at ~2 seconds after the trigger.
The spacecraft slewed immediately and the XRT began observing at 23:33:14 UT
(81 sec after the BAT trigger). The on-board centroiding algorithm was not
able to determine a position, but the prompt lightcurve and spectrum strongly
suggest that a fading source is present in the field of view. Further analysis
will require ground-processed data.
UVOT began observing 23:33:11 UT or 78 sec after the BAT trigger
with a 200 sec V-band image. It is a crowded field with high,
but uncertain extinction. No new sources are seen in either
the small image or the list of sources produced in the on-board processing.
The limiting magnitude in the small image is about 19th mag.
The on-board list of sources covers the entire BAT error region and
is typically complete to about 17th mag.
Further analysis will be delayed due the lack of telemetry downlink passes
for several hours.
GCN Circular 4128
Subject
GRB051021B: Swift XRT Position
Date
2005-10-22T08:03:04Z (20 years ago)
From
Judith Racusin at PSU <racusin@astro.psu.edu>
J. Racusin, D. Morris, C. Pagani, D. Burrows, A. Retter (PSU), N. Gehrels
(GSFC) on behalf of the Swift XRT team:
The Swift XRT began observing GRB 051021B (trigger #160672, Retter et al.,
GCN 4126) at 23:33:14 UT, but was unable to obtain an on-board centroid.
Analysis of the first 2 orbits of the ground data reveal a previously
uncatalogued, fading X-ray source at the following coordinates:
RA(J2000) = 08 24 11.8
Dec(J2000) = -45 32 30.8
We estimate an uncertainty of 4 arcseconds (90% containment), including
corrections for the XRT boresight offset. This position lies 88
arcseconds from the BAT position reported in GCN 4126.
GCN Circular 4135
Subject
GRB 051021B: Refined analysis of the Swift-BAT burst
Date
2005-10-22T15:52:56Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
S. Barthelmy (GSFC), L. Barbier (GSFC), P. Boyd (GSFC-UMBC),
J. Cummings (GSFC/NRC), 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), J. Tueller (GSFC), W. Voges (MPE)
on behalf of the Swift-BAT team:
Using the full data set from the recent telemetry downlink, we report
further analysis of Swift-BAT GRB 051021B (trigger #160672)
(Retter, et al., GCN 4126). The ground-analysis position is
RA,Dec 126.059,-45.537 {8h 24m 14.2s,-45d 32' 13.0"} (J2000)
with an uncertainty of 1.3 arcmin (radius, 90%, stat+sys).
T90 is 47 +- 3 sec. The partial coding fraction is 88 %.
The lightcurve has single FRED peak starting at T-6 sec (FWHM of ~12 sec)
with the decay extending out to greater than T+20 sec. There is
a second, smaller peak at ~T+20. Fitting a simple power law over
the full interval from T-5.5 to T+51.5 sec, the photon index is
1.52 +/- 0.14 with a fluence of 9.1 +/- 0.8 X 10^-7 erg/cm^2.
The peak flux in a 1-sec wide window starting at T-2.5 sec
is 0.63 +/- 0.13 ph/cm^2/sec. All values are in the 15-150 keV band
at the 90% confidence level.
GCN Circular 4146
Subject
GRB051021b: Magellan IR Imaging
Date
2005-10-23T05:45:47Z (20 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
D. L. Kaplan (MIT), H-W. Chen (Chicago), J. S. Bloom (UCB), J. X.
Prochaska (UCO LIck) report on behalf of a large collaboration:
"We obtained deep K-band imaging of the field of GRB 051021b (GCN
4135) with PANIC on the Magellan Baade Telescope starting at 08:42:56
October 22, 2005 UTC. We identify 4 sources within the XRT error
circle (GCN 4128):
08:24:11.803 -45:32:30.79 J2000
08:24:11.598 -45:32:31.93 J2000
08:24:11.622 -45:32:33.70 J2000
08:24:11.724 -45:32:34.20 J2000
The 1 sigma uncertainty relative to 2MASS is 300 mas. As all of
these sources are significantly fainter than the 2MASS detection
limit we cannot identify an obvious afterglow candidate."
This message may be cited.
GCN Circular 4160
Subject
GRB051021B: Swift XRT refined analysis
Date
2005-10-24T23:02:36Z (20 years ago)
From
Judith Racusin at PSU <racusin@astro.psu.edu>
J. Racusin, C. Pagani, D. Morris, A. Retter, D. Burrows (PSU), N. Gehrels
(GSFC) on behalf of the Swift XRT team:
We have analyzed the first 13 orbits of data from GRB051021B (Retter et
al., GCN 4126). XRT observations began in Window Timing mode 87 seconds
after the BAT trigger and continued for 32 seconds before switching to
Photon Counting mode.
The XRT light curve shows an initial decline with a decay slope of
1.9+/-0.1 , followed by a break at ~T+2500s to a shallower decay slope of
0.6+/-0.1.
A preliminary spectral fit using an absorbed power-law to the Photon
Counting mode data yields a photon index of 1.64+/-0.12 in the 0.85-10 keV
band, fixing nH to the Galactic value of 7.7E21 cm-2.
The observed 0.85-10 keV flux for the Photon Counting mode data in the
first orbit is 7.3E-12 ergs cm-2 s-1 corresponding to an unabsorbed flux
of 9.0E-12 ergs cm-2 s-1.
GCN Circular 4167
Subject
GRB051021B: Swift/UVOT Upper limits
Date
2005-10-26T20:33:52Z (20 years ago)
From
Peter Brown at PSU <pbrown@astro.psu.edu>
P. J. Brown (PSU), A. Retter (PSU), F. Marshall (GSFC),
A. Smale (NASA HQ), N. Gehrels (GSFC)
on behalf of the Swift/UVOT team report:
Swift-UVOT observed the field of GRB 051021B
(BAT Trigger=160672; Retter et al. GCN 4126)
starting at 2005-10-21 23:33:11, 78 seconds after the burst.
No source was detected within the XRT error circle
(Racusin et al GCN 4128) during the first 200 second image
(Tmid=178 seconds after the burst) down to a 3 sigma
limiting magnitude of V=19. Using summed images,
we also did not detect a source in any of our 6 filters
down to the following 3-sigma magnitude upper limits:
Filter T_range(sec) Exp(sec) 3sigUL
V 78-19380 1779 19.9
B 444-17793 1634 21.1
U 390-13591 961 19.9
W1 336-12417 1199 19.5
M2 282-12005 1199 19.6
W2 553-18702 1940 20.0
White 498-926 100 19.5
Where T_range is time post-trigger.
We note that this position is near the galactic
plane, so the extinction and background in this line of sight are high.