//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22007 SUBJECT: GRB 171013A: Swift detection of a possible burst DATE: 17/10/13 00:51:52 GMT FROM: David Palmer at LANL B. Sbarufatti (PSU), J. R. Cummings (NASA/UMBC), J.D. Gropp (PSU), J. A. Kennea (PSU), H. A. Krimm (NSF/USRA), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and A. Tohuvavohu (PSU) report on behalf of the Swift Team: At 00:22:20 UT, the Swift Burst Alert Telescope (BAT) triggered and located a possible GRB 171013A (trigger=778435). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 84.085, +34.449 which is RA(J2000) = 05h 36m 20s Dec(J2000) = +34d 26' 57" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a weak, short (<1 s) peak. The peak count rate was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 00:24:07.6 UT, 107.2 seconds after the BAT trigger. No source was detected in 521 s of promptly downlinked data, which covered 72% of the BAT error circle. 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 110 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 large, but uncertain, extinction expected. Based on the marginal significance of this detection (5.74 sigma in rates, 6.9 sigma in the on-board image, 6.5 in the ground-processed image), the weak structure in the light curve, and the lack of a detection by XRT, we cannot verify that this is a true GRB. In addition, there is considerable background from the source Swift J0243.6+6124 in the field of view, with strong variation at its ~9.86 s period, which makes analysis of the light curve difficult. The determination of the reality of this source will require the full downlinked data. Burst Advocate for this burst is B. Sbarufatti (bxs60 AT psu.edu). 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: 22008 SUBJECT: GRB 171013A: TAROT Calern observatory optical observations DATE: 17/10/13 09:35:10 GMT FROM: Alain Klotz at IRAP-CNRS-OMP Klotz A., Noysena.K., Atteia J.L. (CNRS-OMP-IRAP), Boer, M., Eymar, L. (CNRS-ARTEMIS), Gendre B. (UVI - Etelman Obs.) report: We imaged the field of GRB 171013A detected by SWIFT (trigger 778435) with the TAROT robotic telescope (D=25cm) located at the Calern observatory, France. The observations started 33.3s after the GRB trigger (12.8s after the notice). The elevation of the field increased from 50 degrees above horizon and weather conditions were good. The first image is trailed with a duration of 60.0s (see the description in Klotz et al., 2006, A&A 451, L39). We do not detect any OT with a limiting magnitude of: t0+33.3s to t0+93.3s : Rlim = 16.8 The second image is 30.0s exposure in tracking mode: t0+106.1s to t0+136.1s : Rlim = 17.8 Magnitudes were estimated with the nearby NOMAD1 stars and are not corrected for galactic dust extinction. N.B. Galactic latitude is +1.2 deg and the galactic extinction in R band is higher than 2 magnitudes from D. Schlegel et al. 1998ApJ...500..525S. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22010 SUBJECT: BAT trigger 778435 is not a GRB. DATE: 17/10/13 16:03:27 GMT FROM: Boris Sbarufatti at PSU B. Sbarufatti (PSU), A. Y. Lien (GSFC/UMBC) and S. R. Oates (Uni. of Warwick) report on behalf of the Swift team: We report on further analysis of BAT trigger 778435/possible GRB 171013A (Sbarufatti et al., GCN Circ. 22007). The BAT ground analysis using the data set from T-240 to T+962 s shows nothing significant in the mask-weighted light curve. Also, the BAT image significance in 15-350 keV is only 4.3 sigma. The XRT ground analysis on 6.5 ks of data observed between T+107 s to T+21.6 ks. No X-ray source was detected inside the BAT error circle, down to a 3 sigma upper limit of 5.4e-3 cts s^-1, corresponding to a 0.3-10 keV observed flux of 2.7e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum). The Swift/UVOT began settled observations of the field of GRB 171013A 110 s after the BAT trigger. No optical afterglow consistent with the BAT position is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 110 260 147 >20.2 u_FC 322 572 246 >19.1 white 110 621 167 >20.1 v 652 672 19 >17.0 b 577 597 19 >18.0 u 322 572 246 >19.2 m2 677 696 19 >17.2 w2 628 647 19 >17.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.97 in the direction of the burst (Schlegel et al. 1998). We therefore conclude that BAT trigger 778435 was caused by a noise fluctuation. This circular is an official product of the Swift Team