GRB 051221A
GCN Circular 4416
Subject
GRB 051221A: VLA Radio Observations
Date
2005-12-29T22:53:24Z (20 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>
Dale A. Frail (NRAO) reports on behalf of a larger collaboration:
"We observed the position of the GRB 051221A afterglow at 8.5 GHz with
the Very Large Array on 2005 December 21.99 UT, December 23.02 UT,
December 24.83 UT, and December 27.96 UT (GCN 4366; GCN 4367; GCN
4369). On the first epoch (2005 December 21.99 UT) we detect weak
radio emission coincident with the X-ray and optical afterglow, with a
peak flux density of 88 +/- 26 uJy. The source is not detected on any
subsequent epochs with rms noise levels of 24 to 32 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 4394
Subject
Konus-Wind observation of GRB 051221A
Date
2005-12-24T15:51:40Z (20 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team report:
The GRB 051221A (Swift-BAT trigger #173780;
Parsons et al., GCN 4363; Cummings et al., GCN 4365;
Norris et al., GCN 4388)
triggered Konus-Wind at T0=6672.976 s UT (01:51:12.976).
The Konus-Wind light curve consists of a soft weak precursor
and the main episode with five ~15-ms peaks.
The first peak at T0-16 ms to T0+10 is
substantially softer than the others
(there is no emission in the 380-1160 keV energy range).
After T0+0.250 sec a weak soft emission is marginally seen only
in the G1 (18-70 keV) range up to ~1 sec .
As observed by Konus-Wind the burst had
a fluence of 3.2(-1.7, +0.1)x10^-6 erg/cm2 and
peak flux on 4-ms time scale 4.6(-2.5, +0.2)x10^-5 erg/cm2/sec
(both in the 20 keV - 2 MeV energy range).
The time-integrated spectrum of the GRB (from T0 to T0+0.256 sec)
is well fitted (in the 20 keV - 2 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ E^(-alpha) * exp(-E/E0)
with alpha = 1.08(-0.14, +0.13)
and E0 = 436(-116, +165) keV (chi2 = 65/69dof).
The peak energy Ep = 402(-72, +93) keV.
The fitting by a single power law gives an unacceptable
result: chi2 = 152/70dof (null hypothesis probability = 5.423E-08).
All the quoted errors are at the 90% confidence level.
Assuming z = 0.5465 (Berger and Soderberg, GCN 4384)
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.3, Omega_\Lambda = 0.7,
the isotropic energy release is E_iso ~2.5x10^51 erg,
the maximum luminosity is (L_iso)_max ~5.5x10^52 erg/sec.
The Konus-Wind light curve of this GRB can be seen
at http://www.ioffe.rssi.ru/LEA/GRBs/GRB051221_T06672/
GCN Circular 4393
Subject
GRB051221A: Suzaku WAM observation of the prompt emission
Date
2005-12-24T05:10:53Z (20 years ago)
From
Kazutaka Yamaoka at Aoyama Gakuin U <yamaoka@phys.aoyama.ac.jp>
Y.Endo, M.Tashiro, K.Abe, S. Hong, K.Onda (Saitama U.),
K.Yamaoka, S.Sugita (Aoyama Gakuin U.), M.Ohno,
T.Takahashi, Y.Fukazawa (Hiroshima U.), Y.Terada (RIKEN),
K.Nakazawa, G.Sato, T.Takahashi (ISAS/JAXA), R.Miyawaki,
M.Kokubun, K.Makishima (Univ. of Tokyo) and the HXD-II team
The bright and short burst, GRB 051221A (Parsons et al., GCN4363),
triggered by Swift/BAT was also detected with the Suzaku Wideband
All-sky Monitor (WAM) which covers an energy band of 50 keV - 5 MeV
at 01:51:16 (UT).
The observed light curve exhibits two intense short spikes
with a total duration (T90) of 0.22 sec.
The fluence in 100 - 2000 keV was (2.4 +/- 0.4)X10^-6 erg/cm2.
The 1-sec peak flux was 4.7 +/- 0.8 photons/cm2/s in the
same energy range.
Preliminary result shows that the time-averaged spectrum
is well fitted by a single power law with a photon index
of 1.95 +/- 0.18.
All the quoted errors are at statistical 90% confidence level.
The WAM onboard calibration is still under way, and
systematic errors, such as the flux calibration uncertainties of
about 20%, are not included in the errors.
The WAM light curve of this event is available at
http://www.astro.isas.ac.jp/suzaku/research/HXD-WAM/WAM-GRB/grb/grb_table.html
Further detailed analyses are in progress.
GCN Circular 4392
Subject
GRB 051221A: MDM Optical Observations
Date
2005-12-23T23:04:14Z (20 years ago)
From
Markus Boettcher at Ohio U <mboett@helios.phy.ohiou.edu>
M. Boettcher and M. Joshi (Ohio University) report:
Starting on 21 Dec., UT 04:02, we observed the optical
afterglow of GRB 051221A (Parsons et al. GCN 4363) with
the MDM 1.3 m telescope in three 600 s exposures (beginning
2.1, 2.4, and 2.6 hr after the trigger). We detect a faint
source consistent with the locations of the IR (Bloom,
GCN 4367 and 4368), optical (Berger, GCN 4369, 4371;
Berger and Soderberg, GCN 4375; Berger et al. GCN 4383),
and X-ray (Burrows et al., GCN 4366; Grupe et al. GCN 4389)
afterglows. Photometry, calibrated on the R-band magnitudes
of 6 comparison stars in our field of view as given by
Aladin, from the UCD data base (UCD: PHOT_PHG_R), yields
the following magnitude estimates (t = time after GRB trigger):
t | R
-------------------
2.1 hr | 19.88 +/- 0.40
2.4 hr | 19.93 +/- 0.39
2.6 hr | 19.98 +/- 0.34
Consequently, there is no evidence for variability between
the three frames. Seeing was rather poor (~ 2 arc sec.), so
the optical afterglow is not resolved from the host galaxy
(Soderberg and Berger, GCN 4375). Given the RAPTOR upper
limit on the fading counterpart of R > 20.2 at 1.3 hr
after the trigger (Wren et al., GCN 4380), our measurement
might in fact be dominated by the host galaxy contribution.
This message may be cited.
GCN Circular 4390
Subject
GRB 051221A: Detection at 251nm with Swift UVOT
Date
2005-12-23T19:05:11Z (20 years ago)
From
Pete Roming at PSU <roming@astro.psu.edu>
P. Roming (PSU), A. A. Breeveld (UCL-MSSL), F. Marshall, A. Parsons, R.
Fink (GSFC), & M. Ajello (MPE) on behalf of the Swift/UVOT team:
We have created a summed image from 2.78 ksec of exposure on GRB051221A
(Parsons et al., GCN 4363) through the "UVW1" filter of the Swift UVOT.
From the summed image we detect a source at 4.8-sigma confidence with a
position coincident with the one reported by Bloom (GCN 4367) and Berger
(GCN 4369). The magnitude of the source is 20.2+/-0.2 as determined by the
Swift analysis tool, uvotsource.
Examination of individual frames suggests that the source is not
distinguishable above background in the individual short (50-s and 100-s)
exposures and is only visible at the 3-sigma level in one of the early ~600
second exposures of the sequence.
GCN Circular 4389
Subject
GRB 051221A: Chandra Afterglow Position
Date
2005-12-23T07:14:20Z (20 years ago)
From
Dirk Grupe at PSU/Swift-XRT <grupe@astro.psu.edu>
GRB 051221A: Chandra Afterglow Position
D. Grupe (PSU), D. N. Burrows (PSU), and S. Patel (NASA/MSFC) report on
behalf of a larger collaboration:
We executed a Chandra ToO observation of GRB 051221A beginning at 2005-12-22
13:55:20 UT (130 ks after the burst) and lasting for 30.2 ks. A fading
X-ray source was found within the XRT error circle (Burrows et al., GCN
4366) at
RA(J2000) = 21:54:48.626
Dec(J2000) = +16:53:27.16
Chandra positions have typical uncertainties of 0.5 arcseconds
(radius). This
position is 0.55 arcseconds from the optical counterpart identified by
Bloom et al. (GCN 4368)
and 0.34 arcseconds from the position reported by Berger (GCN 4369)
GCN Circular 4388
Subject
GRB 051221A: Refined spectral and temporal analysis of the Swift-BAT short hard burst
Date
2005-12-22T17:02:29Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
J. Norris (GSFC), T. Sakamoto (GSFC/NRC), D. Band (GSFC/UMBC), S. Barthelmy (GSFC)
on behalf of the Swift-BAT team:
The time profile of GRB 051221A binned to 1 ms resolution reveals
that the initial pulse structure (GCN 4363 & 4365) comprises 3 separate pulses
of FWHM ~10-15 ms with peak intensities of ~175,000 counts per sec.
We note for comparison that GRB 050525A, the brightest long burst
so far detected by BAT (in one year) had a peak count rate
of 101,000 cts/sec (corrected to match the same partial-coding as 051221A
of 63%). The GRB 051221A time profile is available at:
http://swift.gsfc.nasa.gov/docs/swift/results/releases/images/GRB051221A/
No extended emission is evident in this burst in the interval 30-120 sec
after the initial pulse structure. The 3 sigma upper limit is 1.16 counts/cm2.
The ratio of (extended emission, 15-50 keV) / (initial pulse complex 15-150 keV)
is < 0.1 (3 sigma). The same ratio for GRB 050724 is 1.9.
The spectral lag is negligible, 0.0+-0.4 ms (0.8+-0.5 ms), between the
15-25 and 50-100 keV (25-50 and 100-350 keV) energy bands -- typical
of spectral lags in short bursts (Norris & Bonnell, submitted to ApJ).
We estimate roughly that the peak flux of GRB 051221A lies in the upper 3%
of short bursts detectable by the BAT.
GCN Circular 4385
Subject
GRB 051221A: WSRT Radio Observations
Date
2005-12-22T10:38:02Z (20 years ago)
From
Alexander van der Horst at U of Amsterdam <avdhorst@science.uva.nl>
A.J. van der Horst (University of Amsterdam) reports on behalf of a larger
collaboration:
"We observed the position of the GRB 051221A afterglow at 4.9 GHz with the
Westerbork Synthesis Radio Telescope at December 21 13.90 UT to 18.63 UT,
i.e. 12.05 - 16.78 hours after the burst (GCN 4363).
We do not detect a radio source within the SWIFT/XRT error circle (GCN
4366), in particular at the position of optical (GCN 4369) and infrared
(GCN 4368) counterparts. The formal flux measurement for a point source at
the position of the optical counterpart is 17 +/- 35 microJy."
This message may be cited.
GCN Circular 4380
Subject
GRB 051221A: RAPTOR Fading Counterpart Constraint
Date
2005-12-22T02:54:22Z (20 years ago)
From
James Wren at LANL <jwren@nis.lanl.gov>
J. Wren, W.T. Vestrand, R. White, P. Wozniak, and S. Evans report
on behalf of the RAPTOR team at Los Alamos National Laboratory:
Starting at 02:57:05 UT (1.1 hours after the burst), the RAPTOR-S
telescope began a manually initiated response to the short burst
identified by Swift (Parsons et al. 4363). Within the XRT error circle
(Burrows et al. 4366) at a position consistent with the location of the
candidate J-band infrared (Bloom, GCN 4368) and R-band optical (Berger,
GCN 4369) counterparts, a stack of 20 30-second unfiltered RAPTOR images
yields a marginal detection of a source. Using the USNO-B1 catalog for
calibration and ignoring any extinction along the line of sight, our
derived 5-sigma upper limit on the brightness of an optical counterpart
at that epoch (1.3 hours after the trigger) is R=20.2+/-0.2 magnitude.