//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8653 SUBJECT: GRB 081211: Swift detection of a burst DATE: 08/12/11 12:16:45 GMT FROM: Hans Krimm at NASA-GSFC H. A. Krimm (CRESST/GSFC/USRA), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), P.A. Curran (MSSL-UCL), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), O. Godet (U Leicester), C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC), S. D. Hunsberger (PSU), N. P. M. Kuin (MSSL), V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester), K. L. Page (U Leicester), A. M. Parsons (GSFC), P. Romano (INAF-IASFPA), R. L. C. Starling (U Leicester), T. N. Ukwatta (GSFC/GWU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 11:48:10 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 081211 (trigger=337115). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 328.087, -33.815 which is RA(J2000) = 21h 52m 21s Dec(J2000) = -33d 48' 53" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a weak structure with a duration of about ~20 sec. The peak count rate was ~400 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 11:50:00.6 UT, 109.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 328.1161, -33.8361 which is equivalent to: RA(J2000) = 21h 52m 27.85s Dec(J2000) = -33d 50' 09.8" with an uncertainty of 2.3 arcseconds (radius, 90% containment). This location is 115 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.87e+20 cm^-2, Kalberla et al. 2005), with an excess column of 1.9 (+2.21/-1.92) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 114 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.03. Burst Advocate for this burst is H. A. Krimm (krimm AT milkyway.gsfc.nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8655 SUBJECT: GRB 081211: Enhanced Swift-XRT position DATE: 08/12/11 20:12:10 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 2165 s of XRT Photon Counting mode data and 3 UVOT images for GRB 081211, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 328.1163, -33.8364 which is equivalent to: RA (J2000): 21h 52m 27.91s Dec (J2000): -33d 50' 10.9" with an uncertainty of 1.6 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401 http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an extension of this method. This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8656 SUBJECT: GRB 081211: Swift/UVOT detection of an optical afterglow DATE: 08/12/11 21:33:35 GMT FROM: Stefan Immler at NASA/GSFC S. Immler (CRESST/UMD/GSFC), S. T. Holland (CRESST/USRA/GSFC), and H. A. Krimm (CRESST/GSFC/USRA) report on behalf of the Swift UVOT team: Further analysis of Swift Ultraviolet/Optical Telescope (UVOT) data of GRB 081211 (Krimm et al., GCN Circ. 8653), starting 113 sec after the BAT trigger, gives a detection of an optical source within the enhanced Swift-XRT position (Beardmore et al., GCN Circ. 8655) at RA (J2000) 21:52:27.97 = 328.11654 (deg) Dec (J2000) -33:50:08.3 = -33.83565 (deg) with an uncertainty of 0.7 arcseconds (radius, 90% containment) in the white filters at 4.5-sigma level of confidence. The source is not present in DSS, the USNO-B1.0 catalogue, or the 2MASS point source catalogue. It is not detected in any of the other UVOT filters at the limiting magnitudes reported below. Filter Tstart(s) Tstop(s) Exp(s) Magnitude wh 113 7134 588 21.23+/-0.39 u 326 6724 265 >20.23 (3-sigma UL) b 582 741 293 >20.24 (3-sigma UL) uvw2 632 7318 371 >20.40 (3-sigma UL) v 656 11966 386 >19.38 (3-sigma UL) uvm2 681 6314 136 >19.58 (3-sigma UL) uvw1 706 6519 196 >19.87 (3-sigma UL) The values quoted above are in the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) and are not corrected for the expected Galactic extinction along the line of sight which corresponds to a reddening of E(B-V)=0.077 mag (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8657 SUBJECT: GRB 081211: Swift XRT refined analysis DATE: 08/12/11 22:08:03 GMT FROM: Rhaana Starling at U of Leicester R.L.C. Starling (U. Leicester) and H.A. Krimm (CRESST/GSFC/USRA) report on behalf of the Swift XRT team: We have analysed data from the first 2 orbits of Swift XRT observations of GRB 081211 (trigger=337115, Krimm et al. GCN Circular 8653) from 113 s to 24 ks after the BAT trigger, all collected in Photon Counting (PC) mode. The enhanced Swift XRT position for this GRB is given in Beardmore et al. (GCN Circular 8655). We confirm that the source is fading, however, the light curve is not well constrained at present. A power law fit results in a decay slope of alpha=0.6+/-0.1, but we note that flaring may be present from 350-1000 s. The time-averaged spectrum can be fit with an absorbed power law with photon index Gamma=2.4+/-0.3. There is significant absorption above the Galactic value (nH_Gal=1.9e20 cm^-2, Kalberla et al. 2005) amounting to a column of nH=(1.2+/-0.6)e21 cm^-2 (at z=0). The observed (unabsorbed) 0.3-10 keV flux is 3.1 (5.0) e-12 erg cm^-2 s^-1. The observed (unabsorbed) count rate to flux conversion derived from this spectrum is 1 count s^-1 = 3.3 (5.3) e-11 erg cm^-2. The predicted count rate at T+24h, assuming a decay of alpha=0.6, is 0.01 count s^-1. The results of the XRT automatic analysis are available at http://www.swift.ac.uk/xrt_products/00337115. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8658 SUBJECT: GRB 081211: Swift-BAT refined analysis DATE: 08/12/11 22:42:23 GMT FROM: Hans Krimm at NASA-GSFC Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 081211 (trigger #337115) (Krimm, et al., GCN Circ. 8653). The BAT ground-calculated position is RA, Dec = 328.082, -33.818 deg which is RA(J2000) = 21h 52m 19.7s Dec(J2000) = -33d 49' 05.9" with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 42%. The mask-weighted light curve shows a single weak peak extending in time from T-1 to T+3 seconds. There is a possible precursor at ~T-180 sec. T90 (15-350 keV) is 3.5 +- 0.9 sec (estimated error including systematics). The time-averaged spectrum from T-1.1 to T+2.7 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.34 +- 0.41. The fluence in the 15-150 keV band is 1.3 +- 0.3 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.19 sec in the 15-150 keV band is 0.8 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/337115/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8914 SUBJECT: GRB 081211B: Nearby cluster DATE: 09/02/23 05:25:22 GMT FROM: Daniel Perley at U.C. Berkeley D. A. Perley, J. S. Bloom, and N. R. Butler (UC Berkeley) report: GRB 081211B was discovered in the Swift-BAT slew survey (Copete et al, GCN 8661) and, based on observations by Konus-Wind (Golenetskii et al., GCN 8676), was classified as a possible short burst with an extended emission component. We note that the GRB localization lies within a visual galaxy overdensity in SDSS archival imaging, and near the centers of several reported clusters in the literature, which likely correspond to the same physically extended structure: ZW 3893, Abell 1196, and MaxBCG J168.22310+53.83028. Redshifts from the Sloan Digital Sky Survey of the brightest two apparent cluster members place this cluster at a probable redshift of z=0.216. On the night of 2009-02-19 (UT) we observed the field with Keck I (+ LRIS) for an exposure time of 990 sec (g-band) and 870 sec (R-band) simultaneously through thin cloud cover. No host galaxy underlying the XRT position (Page et al., GCN 8666) is detected to approximately R > 25, g > 26 mag. The nearest catalogued objects are: SDSS J111303.09+534953.8 g=21.26 r=20.26 i=20.03 (7" = 24 kpc) SDSS J111304.73+534959.5 g=20.56 r=19.25 i=18.84 (16" = 56 kpc) An additional very faint extended object is located 3" west of the center of the XRT position, outside the 90% confidence error circle. Images of the field (from our observations and from SDSS) are posted to: http://lyra.berkeley.edu/~dperley/081211b/081211b_keck.png http://lyra.berkeley.edu/~dperley/081211b/081211b_sdss.png If the BAT detection represents extended emission from this event and no fainter host galaxy is found, this would constitute an additional case of a short GRB event with detected extended emission occurring without a coincident host galaxy (after GRB 080503 - arXiv:0811.1044), as well as an additional example of a short burst occurring within a galaxy cluster (see also e.g. GRBs 050509B, 050813, 051210, 061201). The isotropic gamma-ray energy release at the cluster redshift would be 7 x 10^49 erg in the BAT bandpass, comparable to values measured for other short GRBs. We encourage deeper observations of the field.