//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15141 SUBJECT: GRB 130831B: Swift detection of a burst DATE: 13/08/31 14:13:29 GMT FROM: David Palmer at LANL D. Malesani (DARK/NBI), J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC), D. Grupe (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), V. Mangano (PSU), F. E. Marshall (NASA/GSFC), C. J. Mountford (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU), T. N. Ukwatta (MSU) and B.-B. Zhang (UAH) report on behalf of the Swift Team: At 13:48:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 130831B (trigger=568855). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 192.446, -29.177 which is RA(J2000) = 12h 49m 47s Dec(J2000) = -29d 10' 35" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 30 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 13:50:26.7 UT, 127.0 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 192.42070, -29.18380 which is equivalent to: RA(J2000) = 12h 49m 40.97s Dec(J2000) = -29d 11' 01.7" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 83 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 (6.20 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.6 (+1.89/-1.67) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 129 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 0.08. Burst Advocate for this burst is D. Malesani (malesani AT dark-cosmology.dk). 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: 15149 SUBJECT: GRB 130831B: Enhanced Swift-XRT position DATE: 13/08/31 21:35:40 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 2499 s of XRT Photon Counting mode data and 5 UVOT images for GRB 130831B, 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 = 192.42038, -29.18331 which is equivalent to: RA (J2000): 12h 49m 40.89s Dec (J2000): -29d 10' 59.9" 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) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15154 SUBJECT: GRB 130831B: Swift-XRT refined Analysis DATE: 13/09/01 04:13:03 GMT FROM: Phil Evans at U of Leicester M.C. Stroh (PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Maselli (INAF-IASFPA) and D. Malesani report on behalf of the Swift-XRT team: We have analysed 6.8 ks of XRT data for GRB 130831B (Malesani et al. GCN Circ. 15141), from 112 s to 35.4 ks after the BAT trigger. The data comprise 8 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN. Circ 15149). The late-time light curve (from T0+5.1 ks) can be modelled with a power-law decay with a decay index of alpha=1.24 (+0.12, -0.11). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.07 (+0.16, -0.15). The best-fitting absorption column is 1.6 (+/-0.4) x 10^21 cm^-2, in excess of the Galactic value of 6.2 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.6 (+/-0.4) x 10^21 cm^-2 Galactic foreground: 6.2 x 10^20 cm^-2 Excess significance: 4.2 sigma Photon index: 2.07 (+0.16, -0.15) If the light curve continues to decay with a power-law decay index of 1.24, the count rate at T+24 hours will be 9.4 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.5 x 10^-13 (5.0 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00568855. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15158 SUBJECT: GRB 130831B: GROND upper limits DATE: 13/09/01 15:08:32 GMT FROM: Vladimir Sudilovsky at MPE V. Sudilovsky, M. Tanga, and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 130831B (Swift trigger 568855; Malesani et al. 2013, GCN #15141) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla Observatory (Chile). Observations started at 23:22 UT on 31 Aug. 2013, 10 hours after the GRB trigger. They were performed at an average seeing of 2.2" and at an average airmass of 2.2. Based on five co-added images with individual exposures of 6 min in g'r'i'z' and 4 min exposure in JHK, we do not detect a source within the 3.6 arcsec Swift-XRT error circle reported by Malesani et al. (2013; GCN #15141) down to (all in the AB system) g' > 23.4, r' > 23.2, i' > 22.6, z' > 22.3, J > 20.8, H > 20.2, and K > 19.6 The given limits are derived based on calibrating the images against GROND zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.08 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15160 SUBJECT: GRB 130831B: Swift/UVOT Upper Limits DATE: 13/09/01 17:28:26 GMT FROM: Frank Marshall at GSFC F.E. Marshall (NASA/GSFC) and D. Malesani (DARK/NBI) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 130831B 130 s after the BAT trigger (Malesani et al., GCN Circ. 15141). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 15149) 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) exposures and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 130 279 147 >20.3 u_FC 288 537 246 >19.6 white 130 6384 439 >20.9 v 618 5490 274 >19.7 b 543 6312 274 >20.5 u 288 6106 501 >20.3 w1 667 5901 274 >20.2 m2 642 5695 255 >20.9 w2 593 5285 274 >20.7 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.08 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 15163 SUBJECT: GRB 130831B, Swift-BAT refined analysis DATE: 13/09/01 21:51:29 GMT FROM: Tilan Ukwatta at MSU W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU), D. Malesani (DARK/NBI), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+902 sec from the recent telemetry downlink, we report further analysis of BAT GRB 130831B (trigger #568855) (Malesani, et al., GCN Circ. 15141). The BAT ground-calculated position is RA, Dec = 192.454, -29.187 deg which is RA(J2000) = 12h 49m 48.9s Dec(J2000) = -29d 11' 13.5" with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 14%. BAT mask-weighted light curve shows a multi peak episode starting from ~T-12 sec highest peak around T+1 sec and ending at ~T+30 sec. T90 (15-350 keV) is 37.8 +- 10.4 sec (estimated error including systematics). The time-averaged spectrum from T-13.9 to T+30.6 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.88 +- 0.21. The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T-0.05 sec in the 15-150 keV band is 2.4 +- 0.5 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/568855/BA/