//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6475 SUBJECT: GRB 070531: Swift detection of a burst DATE: 07/05/31 02:30:45 GMT FROM: Scott Barthelmy at NASA/GSFC C. B. Markwardt (GSFC/UMD), L. M. Barbier (NASA/GSFC), S. D. Barthelmy (GSFC), M. M. Chester (PSU), N. Gehrels (NASA/GSFC), S. D. Hunsberger (PSU), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift Team: At 02:10:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070531 (trigger=280958). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 6.678, +74.304 which is RA(J2000) = 00h 26m 43s Dec(J2000) = +74d 18' 14" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single FRED-like peak with a duration of about 20 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began taking data at 02:12:25 UT, 128 seconds after the BAT trigger. The XRT on-board centroid algorithm did not find a source in the image and no prompt position is available. We are waiting for down-linked data to detect and determine a position for the source. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 131 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 18.5 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 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.38. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6476 SUBJECT: GRB 070531: Liverpool Telescope Optical Observations DATE: 07/05/31 03:55:08 GMT FROM: Andreja Gomboc at LT,ARI,Liverpool JMU A. Gomboc (Univ. of Ljubljana), R.J. Smith, C.G. Mundell, A. Melandri, I.A. Steele, D. Carter, A. Monfardini, C.J. Mottram, S. Kobayashi, D. Bersier, M. Burgdorf (Liverpool JMU) and C. Guidorzi (Uni-Bicocca/INAF-OAB) report: The 2-m Liverpool Telescope robotically followed up GRB 070531 (Swift trigger 280958, GCN 6475 Markwardt et al.) and started observing the field at 3.7 min after the trigger time with the RINGO polarimeter. Photometric observations started at 11.9 min after the trigger time. In first images we do not detect any new object down to: Filter t_mid (min from GRB) Tot_Exp (s) Lim ------------------------------------------------------------------- r' 13.2 60 18.2 i' 19.0 120 17.9 ------------------------------------------------------------------ Magnitudes were calibrated vs R2 and I mag from the USNOB1 catalogue. Further analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6477 SUBJECT: GRB 070531: Swift-XRT position DATE: 07/05/31 06:04:29 GMT FROM: Kim Page at U.of Leicester K.L. Page (U. Leicester) & C.B. Markwardt (GSFC/UMD) report on behalf of the Swift-XRT team: We have analysed the first orbit of data (930 seconds in Photon Counting mode) for GRB 070531 (trigger number 280958) and find an uncatalogued, fading X-ray source at a position of RA, Dec 6.73989, 74.3131, which is RA(J2000) = 00 26 57.57 Dec(J2000) = +74 18 47.0 with an uncertainty of 3.7 arcsec (radius, 90% containment). This is 69 arcsec from the on-board BAT position (GCN Circ. 6475, Markwardt et al.), within the BAT error circle. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6479 SUBJECT: GRB 070531: Swift-BAT refined analysis DATE: 07/05/31 15:05:12 GMT FROM: Scott Barthelmy at NASA/GSFC G. Sato (GSFC/ISAS), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+963 sec from recent telemetry downlinks, we report further analysis of BAT GRB 070531 (trigger #280958) (Markwardt, et al., GCN Circ. 6475). The BAT ground-calculated position is RA, Dec = 6.722, 74.316 deg which is RA(J2000) = 00h 26m 53.3s Dec(J2000) = 74d 18' 58" with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 44%. The mask-weighted light curve shows a singe FRED peak starting at T_0 with a long weak tail out to at least T+150 sec. There is a 20-sec gap in the data -- the weak emission is back to background by T+170 sec. T90 (15-350 keV) is 44 +- 2 sec (estimated error including systematics). The time-averaged spectrum from T-2.4 to T+44.6 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.41 +- 0.20. The fluence in the 15-150 keV band is 1.1 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+1.08 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6480 SUBJECT: GRB 070531: NOT nIR observations DATE: 07/05/31 15:09:03 GMT FROM: Antonio Deugarte at IAA-CSIC A. de Ugarte Postigo, A.J. Castro-Tirado (IAA-CSIC, Granada), C. Gonzalez (IAC Tenerife), A. Cabrera (GTC Project Office) on behalf of a larger collaboration, report: "We have observed the field of GRB 070531 (Markwardt et al., GCNC 6475) in J, H and K-bands using the 2.5mNOT (+NOTCAM) Roque de los Muchachos Observatory (Spain) starting at 04:17 UT (2.11 hours after the burst). We do not detect any source in the XRT error box (Page et al. GCNC 6477) down to J~19.5 (3-sigma)." This message can be quoted //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6481 SUBJECT: Swift/UVOT refined analysis of GRB070531 DATE: 07/05/31 20:28:55 GMT FROM: Massimiliano de Pasquale at MSSL-UCL M. De Pasquale (MSSL/UCL) and C. B. Markwardt (GSFC/UMD) report, on the behalf of Swift UVOT team: The Swift Ultraviolet/Optical telescope (UVOT) began its White filter finding chart exposure of GRB070531 (Markwardt et al., GCN circ. 6475) 135 seconds after the trigger. No optical afterglow is detected inside the refined XRT error circle (Page et al., GCN circ. 6477), in the initial V and White filter exposures and the summed exposures in all filters. In the following table, we report the 3 sigma upper limits for any optical afterglow . Filter Time (s) Exp(s) 3sigma UL Mag White 132-231 98 19.5 White 132-966 207 19.9 V 238-637 393 19.2 V 238-1111 524 19.3 B 716-726 10 18.2 U 692-4845 76 18.9 UW1 668-4803 236 19.2 UM2 643-4598 236 19.5 UW2 745-764 20 17.8 No correction has been made for the Galactic reddening toward the burst, E(B-V)=0.38