//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8560 SUBJECT: GRB 081127: Swift detection of a burst DATE: 08/11/27 07:25:04 GMT FROM: David Palmer at LANL J. Mao (INAF-OAB), W. H. Baumgartner (GSFC/UMBC), P. A. Evans (U Leicester), C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), R. Margutti (Univ Bicocca&OAB), C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (NASA/UMBC) and L. Vetere (PSU) report on behalf of the Swift Team: At 07:05:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 081127 (trigger=335715). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 332.093, +6.859 which is RA(J2000) = 22h 08m 22s Dec(J2000) = +06d 51' 33" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peak of 2 seconds on a broader plateau with a total duration of about 30 sec. The peak count rate was ~900 counts/sec (15-350 keV), at ~7 sec after the trigger. The XRT began observing the field at 07:07:10.8 UT, 121.9 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 332.0646, 6.8504 which is equivalent to: RA(J2000) = 22h 08m 15.49s Dec(J2000) = +06d 51' 01.6" with an uncertainty of 2.4 arcseconds (radius, 90% containment). This location is 106 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 consistent with the Galactic value of 6.86e+20 cm^-2 (Kalberla et al. 2005). The initial flux in the 2.5 s image was 9.56e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 130 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 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 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 0.09. The XRT position is 9.8 arcseconds from the B = 13 USNO-B1.0 star 0968-0627697. Burst Advocate for this burst is J. Mao (jirong.mao AT brera.inaf.it). 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: 8563 SUBJECT: GRB 081127: Swift-BAT refined analysis DATE: 08/11/27 15:36:17 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (GSFC/ORAU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), J. Mao (INAF-OAB), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-119 to T+183 sec from recent telemetry downlinks, we report further analysis of BAT GRB 081127 (trigger #335715) (Mao, et al., GCN Circ. 8560). The BAT ground-calculated position is RA, Dec = 332.075, 6.858 deg, which is RA(J2000) = 22h 08m 18.0s Dec(J2000) = +06d 51' 30.2" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 51%. The mask-weighted light curve shows a single peak starting at ~T-30 sec, peaking around T+0 sec, and ending at ~T+55 sec. T90 (15-350 keV) is 37 +- 10 sec (estimated error including systematics). The time-averaged spectrum from T-31.2 to T+8.8 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.10 +- 0.35. The fluence in the 15-150 keV band is 4.9 +- 1.0 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-1.19 sec in the 15-150 keV band is 0.6 +- 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/335715/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8565 SUBJECT: GRB 081127: Enhanced Swift-XRT position DATE: 08/11/27 16:23:08 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 3559 s of XRT Photon Counting mode data and 3 UVOT images for GRB 081127, 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 = 332.0642, +6.8505 which is equivalent to: RA (J2000): 22h 08m 15.40s Dec (J2000): +06d 51' 01.7" with an uncertainty of 1.7 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: 8566 SUBJECT: GRB 081127: Swift-XRT refined analysis DATE: 08/11/27 17:42:56 GMT FROM: Jirong Mao at INAF-OAB J. Mao, C. Guidorzi (INAF-OAB) and R. Margutti (Univ. Bicocca & INAF-OAB) report on behalf of the Swift XRT team: We have analysed the first 4 orbits of Swift-XRT data obtained for GRB 081127 (Mao et al., GCN Circ. 8560), covering from 128 to 219 s in Windowed Timing (WT) and from 220 s to 19.5 ks in Photon Counting (PC) mode data, respectively. The net exposures are 90 s and 9.4 ks for the WT and PC modes data, respectively. The UVOT-enhanced XRT position was given by Beardmore et al. in GCN Circ. 8565. The light curve shows an inital steep decay of index 5.6 until 420 s, then it shows a shallow decay with index of 0.6. After 13.3 ks the lightcurve shows a decay with an index of about 2.0. The WT spectrum can be fit with an absorbed power-law model with a photon index of 4.2 +- 0.2 and an absorbing equivalent hydrogen column density is (2.8 +- 0.3)e21 cm^-2, which is larger than the Galactic one, 6.7e20 cm^-2 (Kalberla et al. 2005). The observed (unabsorbed) 0.3-10 keV flux is 3.7(4.5)e-10 erg cm^-2 s^-1. The PC spectrum can be fit with an absorbed power-law model with a photon index of 2.3 +- 0.3 with an absorbing equivalent hydrogen column density compatible with the Galactic value. If the light curve continues to decay with an index of 2.0, the count rate 24 hours after the burst will be 2.9e-4 c/s, corresponding to an absorbed flux of 9.9e-15 erg cm^-2 s^-1. This is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8567 SUBJECT: GRB 081127: Swift/UVOT Upper Limits DATE: 08/11/27 18:03:49 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/GSFC/USRA) and J. Mao (INAF-OAB) report on the behalf of the Swift UVOT team: The Swift/UVOT observed the field of GRB 081127 starting 113 s after the BAT trigger (Mao, et al. 2008, GCN Circ. 8560). Settled exposures started at T+131 s. We do not find any new source, relative to the DSS or 2MASS, or any variable source inside the UVOT-enhanced XRT error circle (Beardmore, et al. 2008, GCN Circ. 8565). Preliminary 3-sigma upper limits for detecting a source in the white finding chart, and the co-added images, using a 2.5 arcsecond radius circular aperture, are Filter T_start T_stop Exp(s) Mag ------------------------------------------ white 130 380 147 >21.3 v 365 18,799 1473 >21.0 b 466 7263 568 >21.4 u 440 13,713 1246 >21.4 uvw1 415 13,011 1276 >21.6 uvm2 389 19,496 2004 >21.8 uvw2 341 17,885 1473 >21.8 white 490 7468 714 >22.2 ------------------------------------------ The quoted upper limits have not been corrected for the expected Galactic extinction along the line of sight corresponding to a reddening of E_{B-V} = 0.09 mag (Schlegel, et al., 1998, ApJS, 500, 525). All photometry is on the UVOT photometry system described in Poole et al. (2008, MNRAS, 383, 627). The B = 13.15 mag USNO-B1.0 star 0968-0627697 is located approximately 4 arcsec north of the XRT position. UVOT photometry at the location of the X-ray source is contaminated by this star.