This file contains both A and B: 051221A and 051221B //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4363 SUBJECT: GRB 051221: Swift detection of a bright short burst DATE: 05/12/21 02:24:36 GMT FROM: Scott Barthelmy at NASA/GSFC 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4364 SUBJECT: GRB 051221: IR Observations at GRB+1hr DATE: 05/12/21 04:45:45 GMT FROM: Josh Bloom at UC Berkeley 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4365 SUBJECT: GRB 051221: Refined analysis of the Swift-BAT short hard burst DATE: 05/12/21 05:07:18 GMT FROM: Scott Barthelmy at NASA/GSFC 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4366 SUBJECT: GRB 051221: XRT position DATE: 05/12/21 05:09:26 GMT FROM: David Burrows at PSU/Swift 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4367 SUBJECT: GRB051221: K-band source DATE: 05/12/21 05:28:42 GMT FROM: Josh Bloom at UC Berkeley 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 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4368 SUBJECT: GRB 051221: Improved astrometry of the IR counterpart DATE: 05/12/21 07:20:22 GMT FROM: Josh Bloom at UC Berkeley 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4369 SUBJECT: GRB 051221: Gemini observations DATE: 05/12/21 07:21:11 GMT FROM: Edo Berger at Carnegie Obs 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4370 SUBJECT: GRB 051221: Correction to GCN #4368 DATE: 05/12/21 07:38:51 GMT FROM: Josh Bloom at UC Berkeley 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4371 SUBJECT: GRB 051221: No variability in Gemini data DATE: 05/12/21 08:18:37 GMT FROM: Edo Berger at Carnegie Obs 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4372 SUBJECT: GRB 051221: Possible nearby cluster DATE: 05/12/21 09:26:41 GMT FROM: Edo Berger at Carnegie Obs 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4373 SUBJECT: GRB 051221: Swift/UVOT upper limits DATE: 05/12/21 16:53:16 GMT FROM: Alice Breeveld at MSSL-UCL 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 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4374 SUBJECT: GRB 051221: Swift XRT refined analysis DATE: 05/12/21 18:46:53 GMT FROM: Milvia Capalbi at ISAC/ASDC 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4375 SUBJECT: GRB 051221: Discovery of fading optical afterglow DATE: 05/12/21 19:04:50 GMT FROM: Alicia Soderberg at Caltech 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4376 SUBJECT: Swift-BAT detection of a possible burst DATE: 05/12/21 20:51:54 GMT FROM: Scott Barthelmy at NASA/GSFC P. Boyd (GSFC), S. Barthelmy (GSFC), D. Burrows (PSU), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), F. Marshall (GSFC), K. Page (U Leicester), D. Palmer (LANL), A. Parsons (GSFC), J. Racusin (PSU), P. Roming (PSU), T. Sakamoto (GSFC) on behalf of the Swift team: At 20:03:20 UT, Swift-BAT triggered and located a source (trigger=173904). The spacecraft slewed promptly after the end of the image trigger. The BAT on-board calculated location is RA,Dec 312.395d,+53.054d {20h 49m 35s,+53d 03' 14"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). All we have at this time is the TDRSS lightcurve. This plus the fact that this is a 192-sec image trigger means that we can not say if this trigger is due to a real GRB, a hard x-ray transient, or a noise event. We note that the galactic latitude is 6 deg. The XRT began observing the location at 20:07:56 UT, 276 sec after the BAT trigger. The on-board detection algorithm did not centroid on a source due to insufficient counts, so no prompt X-ray position is available. However, both the prompt XRT light-curve and raw spectrum indicate there is a faint X-ray source in the field. More information will be available after the next Malindi pass in a few hours. UVOT took a finding chart exposure of 200 seconds with the V filter starting 275 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 has been about 18th 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 4.6 magnitudes. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4378 SUBJECT: Possible GRB 051221B: Swift XRT position DATE: 05/12/21 23:01:31 GMT FROM: Kim Page at U.of Leicester 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4379 SUBJECT: GRB 051221B: BOOTES optical observations. DATE: 05/12/22 01:36:01 GMT FROM: Javier Gorosabel at Danish Space Res Inst 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)" //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4380 SUBJECT: GRB 051221A: RAPTOR Fading Counterpart Constraint DATE: 05/12/22 02:54:22 GMT FROM: James Wren at LANL 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4381 SUBJECT: Possible GRB 051221B: MDM Optical Detection DATE: 05/12/22 03:35:54 GMT FROM: Jules Halpern at Columbia U. 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4382 SUBJECT: GRB 051221B: Refined analysis of the Swift-BAT burst DATE: 05/12/22 05:46:05 GMT FROM: Scott Barthelmy at NASA/GSFC 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4383 SUBJECT: GRB 051221: Continued fading of optical afterglow DATE: 05/12/22 06:53:39 GMT FROM: Edo Berger at Carnegie Obs 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4384 SUBJECT: GRB 051221: Redshift from Gemini DATE: 05/12/22 09:33:06 GMT FROM: Edo Berger at Carnegie Obs 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4385 SUBJECT: GRB 051221A: WSRT Radio Observations DATE: 05/12/22 10:38:02 GMT FROM: Alexander van der Horst at U of Amsterdam 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4386 SUBJECT: GRB 051221B: TAROT optical limits DATE: 05/12/22 12:11:37 GMT FROM: Alain Klotz at CESR-CNRS 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4387 SUBJECT: GRB 051221B: ROTSE-III Optical Limits DATE: 05/12/22 14:52:55 GMT FROM: Brad Schaefer at LSU 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 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4388 SUBJECT: GRB 051221A: Refined spectral and temporal analysis of the Swift-BAT short hard burst DATE: 05/12/22 17:02:29 GMT FROM: Scott Barthelmy at NASA/GSFC 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4389 SUBJECT: GRB 051221A: Chandra Afterglow Position DATE: 05/12/23 07:14:20 GMT FROM: Dirk Grupe at PSU/Swift-XRT 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) //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4390 SUBJECT: GRB 051221A: Detection at 251nm with Swift UVOT DATE: 05/12/23 19:05:11 GMT FROM: Pete Roming at PSU 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4392 SUBJECT: GRB 051221A: MDM Optical Observations DATE: 05/12/23 23:04:14 GMT FROM: Markus Boettcher at Ohio U 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4393 SUBJECT: GRB051221A: Suzaku WAM observation of the prompt emission DATE: 05/12/24 05:10:53 GMT FROM: Kazutaka Yamaoka at Aoyama Gakuin U 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4394 SUBJECT: Konus-Wind observation of GRB 051221A DATE: 05/12/24 15:51:40 GMT FROM: Valentin Pal'shin at Ioffe Inst 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/ //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4416 SUBJECT: GRB 051221A: VLA Radio Observations DATE: 05/12/29 22:53:24 GMT FROM: Dale A. Frail at NRAO 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4417 SUBJECT: GRB051221B: Radio observations DATE: 05/12/29 22:59:29 GMT FROM: Dale A. Frail at NRAO 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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4420 SUBJECT: GRB 051221B: Optical Observations with Kuiper 1.54m DATE: 05/12/30 21:41:55 GMT FROM: Peter A. Milne at Super-LOTIS 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4614 SUBJECT: Possible GRB 051221B: MDM Correction DATE: 06/01/28 09:39:04 GMT FROM: Jules Halpern at Columbia U. "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." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4796 SUBJECT: GRB 051221B: Swift-XRT Team Refined Analysis DATE: 06/02/20 09:35:13 GMT FROM: Kim Page at U.of Leicester 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.