//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9851 SUBJECT: GRB 090831B: Swift detection of a possible burst DATE: 09/08/31 18:26:54 GMT FROM: David Palmer at LANL M. De Pasquale (UCL-MSSL), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), P. A. Evans (U Leicester), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), P. Romano (INAF-IASFPA), M. Stamatikos (OSU/NASA/GSFC), R. L. C. Starling (U Leicester) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 18:01:14 UT, the Swift Burst Alert Telescope (BAT) triggered and located possible GRB 090831B (trigger=361477). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 3.619, +27.970 which is RA(J2000) = 00h 14m 29s Dec(J2000) = +27d 58' 12" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows nothing significant as is typical for an image trigger. The XRT began observing the field at 18:03:44.9 UT, 149.9 seconds after the BAT trigger. No source was detected in the promptly available XRT data. We are waiting for the full dataset to detect and localise the XRT counterpart. UVOT took a finding chart exposure of 150 seconds with the White filter starting 153 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 25% of the BAT 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 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 0.03. Due to the lack of detection by XRT, we cannot confirm that this is a true astrophysical source. Further analysis of the downlinked data (available in ~3 hours) will be required. Burst Advocate for this burst is M. De Pasquale (mdp AT mssl.ucl.ac.uk). 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: 9853 SUBJECT: GRB 090831B, RIMOTS optical upper limits DATE: 09/08/31 20:02:34 GMT FROM: Kenta Kono at Miyazaki U K.Kono, A.Daikyuji, E.Sonoda, N.Ohmori, H.hayasi, K.Noda, Y.Nisioka, M.Yamauchi (University of Miyazaki) We have observed the field covering the error circle of GRB 090831B (Swift trigger 361477, GCN 9851, M. De Pasquale et al.) with the unfiltered CCD camera on the 30-cm telescope at University of Miyazaki. The observation was started 18:03:42 UT, about 2.5 min after the Swift trigger time. We have compared our data of 30 sec exposures with the USNO-A2.0 catalog, There is no new source at the reported position. (GCN 9851, M. De Pasquale et al.) the upper limits are as follows: -------------------------------------------------------------- Start(UT) End(UT) Num. of frames Limit (mag.) -------------------------------------------------------------- 18:03:42 18:04:12 1 15.4 18:03:42 18:40:05 27 17.2 --------------------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9858 SUBJECT: GRB 090831B: MITSuME optical upper limits DATE: 09/09/01 09:35:30 GMT FROM: Michitoshi Yoshida at Okayama Astrophysical Obs M. Yoshida, D. Kuroda, K. Yanagisawa, Y. Shimizu, S. Nagayama, H. Toda (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 090831B (De Pasquale et al. GCN 9851) with the optical three color (g', Rc and Ic) CCD camera attached to the MITSuME 50cm telescope of Okayama Astrophysical Observatory. The observation started on 2009-08-31 18:03:21 UT (2m 7s after the burst). We did not find any new point source in the BAT error circle reported by De Pasquale et al. (GCN 9851) in all the three bands. Three sigma upper limits of the OT are listed below. We used GSC2.3 catalog for flux calibration. #PDAY MID-UT T-EXP g' Rc Ic -------------------------------------------------- 0.00505 18:09:49 540.0 >19.0 >18.8 >18.1 0.03482 18:52:41 4200.0 >19.9 >19.7 >19.0 -------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9860 SUBJECT: Swift Trigger 361477, called GRB090831B, is probably not real. DATE: 09/09/01 12:45:04 GMT FROM: Massimiliano de Pasquale at MSSL-UCL J.R. Cummings (NASA/UMBC), P.A. Evans (U. Leicester), J.A. Kennea (PSU), C. Pagani (PSU), and M. De Pasquale (MSSL/UCL) on behalf of the Swift team report: The ground analysis of BAT data from trigger 361477 (De Pasquale et al., GCN Circ. 9851) shows a very weak excess in the low energy bands only. The response is consistent with a somewhat unusually large noise fluctuation in the image domain caused by the presence of a bright source in the BAT partially coded field of view (Cyg-X1). The XRT observed the field for 3.23 ks between T0+150 s and T0+10 ks. The data are entirely in Photon Counting mode. We do not find any source in the field of view. A 3-sigma upper limit on covering the BAT onboard error circle is 2.7 x 10^-3 ct/sec. No new source is found in the UVOT white filter finding chart (153-303s after the trigger) inside the BAT error circle down to a 3 sigma upper limit of 20.9. We conclude that the trigger is unlikely to be due to a GRB or any other astrophysical source.