GRB 051221B
GCN Circular 4378
Subject
Possible GRB 051221B: Swift XRT position
Date
2005-12-21T23:01:31Z (19 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L. Page, J. Racusin, A.P. Beardmore, D.N. Burrows and N. Gehrels report
on behalf of the Swift-XRT team:
We have analysed the first orbit of XRT data for BAT trigger 173904 (GCN
4376, Boyd et al.) and find a fading, uncatalogued source located at
RA(J2000) = 20h 49m 35.1s
Dec(J2000) = 53h 02m 12.2s
with an estimated uncertainty of 4.5 arcsec (90% containment). This
includes the latest XRT boresight correction and is 62 arcsec from the
on-board BAT position given in GCN 4376.
From the current data, it is still not possible to determine whether the
source is a GRB or a hard X-ray transient.
GCN Circular 4379
Subject
GRB 051221B: BOOTES optical observations.
Date
2005-12-22T01:36:01Z (19 years ago)
From
Javier Gorosabel at Danish Space Res Inst <jgu@spacecenter.dk>
A. de Ugarte Postigo, M. Jelinek, S. Vitek, A.J. Castro-Tirado,
J. Gorosabel, S.B. Pandey, S. Guziy (IAA-CSIC, Granada), P. Kubanek and
R. Hudec (Astronomical Institute of the Academy of Sciences, Ondrejov),
report:
"BOOTES-1 in South Spain (El Arenosillo, INTA, Huelva), responded under
non-optimal conditions to GRB 051221 (Swift trigger 173904, Boyd et al.
GCNC 4376). A sequence of RVI-band exposures started at 20:07:15 UT
(235s after the GRB onset). Preliminary analysis does not reveal any
transient optical source in the 3' radius SWIFT/BAT error box, and in
particular at the position reported by SWIFT/XRT (Page et al. GCNC
4378). We set the following R-band upper limits:
=============================================
T-To (s) Exp. Time Lim. Mag. R-band
Mid Exposure (s) (3 sigma)
---------------------------------------------
235 5 14.5
307 10 16.0
353 6x10 16.5
665 5x100+12x10 18.5
=============================================
We notice an important Galactic extinction in the GRB line of sight
(E(B-V)=1.39, Schlegel et al. 1998)"
GCN Circular 4381
Subject
Possible GRB 051221B: MDM Optical Detection
Date
2005-12-22T03:35:54Z (19 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. P. Halpern & S. Tyagi (Columbia U.) report:
"We observed the position of possible Swift GRB 051221B
in the R-band with the MDM 1.3m for 30 minutes starting
on Dec. 22 01:31 UT, or 5.5 hours after the BAT trigger
(Boyd et al., GCN 4376).
We find an object of R=21.8 located at
RA(J2000) = 20h 49m 34.8s
Dec(J2000) = +53d 02' 11.8"
which is consistent in position with the fading XRT source
(Page et al., GCN 4378). (We use a USNO B1.0 comparison star
at 20h 49m 36.08s, +53d 01' 29.65".)
We have not established any optical variability at this time."
GCN Circular 4382
Subject
GRB 051221B: Refined analysis of the Swift-BAT burst
Date
2005-12-22T05:46:05Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
E. Fenimore (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), D. Hullinger (GSFC/UMD),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), F. Marshall (GSFC),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), T. Takahashi (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
Using the full data set from the recent telemetry downlink
covering T-300 to T+300 sec, we report further analysis
of Swift-BAT GRB 051221B (trigger #173904) (Boyd, et al., GCN 4376).
The ground-analysis position is RA,Dec 312.359,+53.040
{20h 49m 26.1s,+53d 02' 23.4"} (J2000)
with an uncertainty of 1.6 arcmin (radius, 90%, stat+sys).
The partial coding fraction is 45%. The lightcurve has two,
possibly 3, peaks starting at T+49 sec with a total duration of 70 sec.
T90 is 61 +- 1 sec. Fitting a simple power law over the full interval
from T+49 to T+119 sec, the photon index is 1.48 +/- 0.18 with a fluence
of 1.13 +/- 0.13 X 10^-6 erg/cm^2. The peak flux in a 1-sec wide window
starting at T+59 sec is 0.54 +/- 0.20 ph/cm^2/sec. All values are
in the 15-150 keV band at the 90% confidence level. A final note:
we think it is very likely that this is a GRB, but we can not rule out
the possibility that it is a hard x-ray transient.
GCN Circular 4386
Subject
GRB 051221B: TAROT optical limits
Date
2005-12-22T12:11:37Z (19 years ago)
From
Alain Klotz at CESR-CNRS <Alain.Klotz@free.fr>
Klotz, A. (CESR-OMP), Boer M. (OHP), and Atteia, J.L. (LAT-OMP) report:
We imaged the entire field of GRB 051221B (173904) detected by SWIFT
(Boyd et al. GCNC 4376) with the TAROT robotic telescope (D=25cm) located at
the Calern observatory, France. Observations started 9 seconds after the GCN
notice (and 216 sec. after the GRB). The field had an elevation of 35
degrees above horizon at the beginning of the observations and then
decreased. The humidity was rather high (90%), and haze appeared after few
minutes of observation.
We compared the � 1.6 arcmin field centred on the XRT position (Fenimore et al.
GCNC 4382) with stars of the USNO-B1 catalogue and with the DSS2-R atlas. We
did not find any new source. Following is the observation log and the upper
limits we derived:
Since-trig Mag.
start end
+216s to +276s R>14
+282s to +312s R>18.2
+319s to +349s R>18.2
This message may be cited.
GCN Circular 4387
Subject
GRB 051221B: ROTSE-III Optical Limits
Date
2005-12-22T14:52:55Z (19 years ago)
From
Brad Schaefer at LSU <schaefer@grb.phys.lsu.edu>
B. E. Schaefer (Louisiana State Univ.) report on behalf of the ROTSE
collaboration:
ROTSE-IIId, located at the Turkish National Observatory at Bakirlitepe,
Turkey, responded to GRB 051221B (Swift trigger 173904), producing images
beginning 10 s after the GCN notice time. An automated response took the
first image at 20:06:57.2 UT, 217.1 s after the burst, under excellent
conditions. We took 10 5-sec, 138 20-sec eposures. These unfiltered images
are calibrated relative to USNO A2.0 (R).
Comparison to the DSS (second epoch) reveals no new sources within the
3-sigma error circle, for both single images and coadding into sets of 10.
In particular, we find nothing unusual inside the Swift XRT positional
circle (Fenimore et al. GCN4382). Individual images have limiting
magnitudes ranging from 15.1-17.1; we set the following specific limits.
start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd?
--------------------------------------------------------------------
20:06:57.2 20:07:02.2 5 16.6 217.1 N
20:06:57.2 20:09:02.9 125 17.4 217.1 Y
GCN Circular 4417
Subject
GRB051221B: Radio observations
Date
2005-12-29T22:59:29Z (19 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>
Dale A. Frail (NRAO) reports on behalf of a larger collaboration:
"We used the Very Large Array to observe the Swift burst GRB051221B
(GCN 4376; GCN 4382) at a frequency of 8.46 GHz on 2005 Dec. 27.92 UT
(i.e. 6.9 days after the burst). No radio emission is detected within
the XRT error circle (GCN 4378). The rms noise was 31 uJy.
No further observations are planned.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 4420
Subject
GRB 051221B: Optical Observations with Kuiper 1.54m
Date
2005-12-30T21:41:55Z (19 years ago)
From
Peter A. Milne at Super-LOTIS <pmilne@as.arizona.edu>
P.A.Milne (Steward Obs),
on behalf of the Super-LOTIS GRB team reports:
We observed the field of GRB 051221B (SWIFT-BAT trigger 173904)
on Dec. 21, 2005,
starting at UT=02:35:53 (06:32:33 after the burst)
with the 61" Kuiper telescope at Mt. Bigelow, AZ.
We obtained 11 x 300-sec R-band images.
Observing conditions were considered good. The field was
subsequently observed the next night starting at UT=01:33:50.
We obtained 7 x 300 second images in the R-band on the second night.
Inspection of a subtraction image produced from co-added images
reveals no fading source at the location of the candidate
optical counterpart reported by Halpern & Tyagi (GCN 4381).
The limiting magnitude of the co-added image taken on the
first night is roughly 23.0 magnitude.
This message may be cited.
GCN Circular 4614
Subject
Possible GRB 051221B: MDM Correction
Date
2006-01-28T09:39:04Z (19 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
"I revise here the report in GCN 4381 of an optical object at the Swift XRT
position of the possible GRB 051221B (Boyd et al. GCN 4376, Page et al.
GCN 4378, Fenimore et al. GCN 4382), prompted by the non-detections at this
position by Milne (GCN 4420) and Sharapov et al. (GCN 4612). The position
and magnitude given in GCN 4381 were both in error as a result of using an
incorrect entry in the USNO-B1.0 catalog for the quoted comparison star.
The only object that is consistent in position, within 4.5", of the fading
XRT source (Page et al. GCN 4378), is located at
RA(J2000) = 20h 49m 34.86s
Dec(J2000) = +53d 02' 08.3"
It is also faintly visible on the digitized R and I-band POSS-II plates,
and clearly on the image of Sharapov et al.
Since it was not ruled out that this event was a hard X-ray transient,
it is still possible to test that hypothesis by searching for an optical
counterpart. However, there is no evidence in MDM images that the
above object has varied. Observations of it from from 5.5 to 8 hours after
the event using the MDM 1.3m, and again at 30.6 hours using the MDM 2.4m,
are all consistent with its appearance on the POSS, and with measurement
on the CCD images of R = 20.63+/-0.03, referenced to a USNO B1.0 star
at 20h 49m 36.16s, +53d 01' 26.4" having R2 = 17.54. The MDM 2.4m image
further sets a limit of R > 23.8 on any other object in the XRT error circle,
and is shown here:
http://www.astro.columbia.edu/~jules/grb/051221b
Recall that Galactic extinction in this direction, (l,b) = (91.2,+5.8),
is considerable. E(B-V) = 1.37 mag, corresponding to A_R = 3.66 mag
(Schlegel et al. 1998).
This message may be cited."
GCN Circular 4796
Subject
GRB 051221B: Swift-XRT Team Refined Analysis
Date
2006-02-20T09:35:13Z (19 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L. Page (U. Leicester), D.N. Burrows (PSU) and E. Rol (U. Leicester)
report on behalf of the Swift-XRT team:
It has recently been pointed out (Halpern 2006, GCN 4614) that the nature
of GRB 051221B has still not been definitively settled (GRB vs hard X-ray
transient). Prompted by this report, we are providing further analysis
details of the Swift-XRT observation of this source.
The XRT began observing the field of the possible GRB 051221B (GCN 4376,
Boyd et al. 2005) 281 seconds after the trigger. 7 seconds of data in
Windowed Timing (WT) mode were obtained, before switching into Photon
Counting (PC) mode.
The X-ray source was only detected during the first orbit, with 14 counts
in the WT data and 51 counts in 385 seconds of PC data (starting 290
seconds after the trigger). The second orbit, covering 1319 seconds of
exposure time (starting 3.6 ks after the trigger) shows only 1 count at
the position of the source. These later data give a 3-sigma upper limit of
1.5e-3 ct s^-1.
The start of the light-curve falls extremely steeply (alpha ~ 9,
calculated with respect to the trigger time). There is an indication of
flattening at 400 - 500 seconds after the trigger, though this is based on
only 2 bins of data, each containing 5 counts.
Using Cash statistics because of the low number of counts, the spectrum
for the first orbit of PC data (290 - 680 seconds after the trigger) can
be modelled with a power-law of Gamma = 1.27 +/- 0.37, with the estimated
Galactic column fixed at 5.6e21 cm^-2 (Dickey & Lockman 1990). This
spectrum has a mean count rate of 0.15 ct s^-1 and an observed
(unabsorbed) flux of 1.43e-11 (1.77e-11) erg cm^-2 s^-1.
The XRT observations of this source were terminated early in order to
allow followup of the short GRB 051221A. Therefore, no additional data
are available. However, the rapid decline in X-ray flux appears to
support a GRB origin.
This circular is an official product of the Swift-XRT Team.