//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18538 SUBJECT: GRB 151031A: Swift detection of a burst DATE: 15/10/31 06:06:57 GMT FROM: David Palmer at LANL E. Sonbas (Adiyaman Univ.), V. D'Elia (ASDC), L. Izzo (URoma/ICRA), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 05:50:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 151031A (trigger=662330). Swift slewed to the burst after a 6 minute delay due to viewing constraints. The BAT on-board calculated location is RA, Dec 83.199, -39.092 which is RA(J2000) = 05h 32m 48s Dec(J2000) = -39d 05' 28" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 10 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 05:57:43.9 UT, 433.6 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 83.19532, -39.12049 which is equivalent to: RA(J2000) = 05h 32m 46.88s Dec(J2000) = -39d 07' 13.8" with an uncertainty of 4.1 arcseconds (radius, 90% containment). This location is 103 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 2.62 x 10^20 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 439 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 none of the XRT error circle. 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 0.03. Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.com). 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: 18540 SUBJECT: GRB 151031A: VLT/X-shooter optical counterpart and redshift DATE: 15/10/31 07:23:44 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Malesani (DARK/NBI), N. R. Tanvir (Univ. Leicester), T. Kruehler (MPE), A. de Ugarte Postigo (IAA-CSIC and DARK/NBI), H. Flores (GEPI/Paris obs), D. Xu (NAOC/CAS), J.P.U. Fynbo (DARK/NBI), report on behalf of the X-shooter GRB collaboration: We observed the field of GRB 151031A (Sonbas et al., GCN 18538) with the ESO Very Large Telescope UT2 (Kueyen) equipped with the X-shooter spectrograph. Observations were carried out using the automatic "rapid response mode" (RRM), and started immediately following the reception of the XRT position notice. In the acquisition images, we detect a single source consistent with the position of the XRT afterglow, at coordinates (J2000): RA = 05:32:47.11 Dec = -39:07:19.1 We measure for this object R = 20.4 +- 0.1 (calibrated against three nearby USNO stars) in an image taken on Oct 31.2565 UT, that is 18.8 min after the GRB. A sequence of spectra with increasing exposure time (3 to 32 min) was secured covering the wavelength range 3,000 - 25,000 AA. From the analysis of the first 8 min data, several absorption features can be seen on top of the object continuum, which we interpret as due to Ca II, Mg I, Mg II and Fe II in absorption at a common redshift of z = 1.167. In the visible arm, an emission feature is also seen, corresponding to [O ii] at a consistent redshift, which we thus consider to be the redshift of GRB 151031A. Analysis of the full data set is ongoing. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Thomas Rivinius, Marcela Espinoza, and Claudia Cid. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18541 SUBJECT: GRB 151031A: Enhanced Swift-XRT position DATE: 15/10/31 08:21:55 GMT FROM: Phil Evans at U of Leicester P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 436 s of XRT Photon Counting mode data and 1 UVOT images for GRB 151031A, 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 = 83.19596, -39.12134 which is equivalent to: RA (J2000): 05h 32m 47.03s Dec (J2000): -39d 07' 16.8" with an uncertainty of 2.2 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: 18542 SUBJECT: GRB 151031A: Swift-BAT refined analysis DATE: 15/10/31 14:25:39 GMT FROM: Hans Krimm at NASA-GSFC T. N. Ukwatta (LANL),S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), E. Sonbas (Adiyaman Univ.), M. Stamatikos (OSU), (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 151031A (trigger #662330) (Sonbas, et al., GCN Circ. 18538). The BAT ground-calculated position is RA, Dec = 83.189, -39.125 deg which is RA(J2000) = 05h 32m 45.3s Dec(J2000) = -39d 07' 28.3" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 67%. The mask-weighted light curve shows a single FRED-shaped peak, peaking at T+2 sec and returning to background by T+7 sec. T90 (15-350 keV) is 5.00 +- 2.24 sec (estimated error including systematics). The time-averaged spectrum from T+0.30 to T+6.30 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.41 +- 0.18. The fluence in the 15-150 keV band is 3.2 +- 0.3 x 10^-7erg/cm2. The 1-sec peak photon flux measured from T+1.30 sec in the 15-150 keV band is 1.7 +- 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/662330/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18544 SUBJECT: GRB 151031A: Swift-XRT refined Analysis DATE: 15/10/31 18:07:05 GMT FROM: Phil Evans at U of Leicester A. Maselli (INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB) and E. Sonbas report on behalf of the Swift-XRT team: We have analysed 7.5 ks of XRT data for GRB 151031A (Sonbas et al. GCN Circ. 18538), from 443 s to 25.5 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 18541). The light curve can be modelled with a power-law decay with a decay index of alpha=0.56 (+/-0.07). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.13 (+0.22, -0.21). The best-fitting absorption column is 9.4 (+3.8, -3.3) x 10^21 cm^-2, at a redshift of 1.167, in addition to the Galactic value of 2.6 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.2 x 10^-11 (4.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 2.6 x 10^20 cm^-2 Intrinsic column: 9.4 (+3.8, -3.3) x 10^21 cm^-2 at z=1.167 Photon index: 2.13 (+0.22, -0.21) If the light curve continues to decay with a power-law decay index of 0.56, the count rate at T+24 hours will be 0.010 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.3 x 10^-13 (4.7 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/00662330. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18546 SUBJECT: GRB 151031A: Swift/UVOT Detection DATE: 15/10/31 22:42:11 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and E. Sonbas (Adiyaman Univ.) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 151031A 439 s after the BAT trigger (Sonbas et al., GCN Circ. 18538). A source at the VLT position (Malesani et al, GCN Circ. 18540) and consistent with the XRT position (Evans et al. GCN Circ. 18541) is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 439 1020 314 20.63 +/- 0.16 v 595 8257 627 >20.1 b 695 7642 588 >20.2 u 670 7437 430 20.34 +/- 0.28 w1 645 8677 635 >20.0 m2 620 8462 627 >20.0 w2 746 8053 607 >21.0 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18547 SUBJECT: GRB 151031A DATE: 15/11/01 00:29:14 GMT FROM: Daisuke Kuroda at OAO/NAOJ D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ), S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of MITSuME and OISTER collaboration: We observed the field of GRB 151031A (Sonbas et al., GCNC 18538) 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 2015-10-31 15:54:27 UT (10.1 h after the burst). We could not detect the previously reported afterglow (Malesani et al., GCNC 18540; Kuin and Sonbas, GCNC 18546) in all the three bands. Three sigma upper limits of the OT are listed below. We used GSC2.3 catalog for flux calibration. #T0+[day] MID-UT T-EXP[sec] g' Rc Ic ----------------------------------------------------- 0.49617 17:44:59 6000.0 >18.6 >18.9 >18.5 ----------------------------------------------------- T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18550 SUBJECT: GRB 151031A: GROND observation DATE: 15/11/01 22:44:14 GMT FROM: John Graham at MPE/Garching S. Schmidl (TLS Tautenburg), J. Graham, and J. Greiner (both MPE Garching) report on behalf of the GROND team: We observed the field of GRB 151031A (SWIFT trigger 662330; Sonbas et al, GCN 18538) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile). Observations started on November 1, 2015, at 06:42 UT, 1.04 days after the GRB trigger (due to being clouded out the previous night). They were performed at an average seeing of 1.52" and at an average airmass of 1.02. We detect the source reported by Malesani et al. (GCN 18540) and Kuin et al. (GCN 18546). Based on total exposures of 33 minutes in g'r'i'z' and 72 minutes in JHK, we measure the following preliminary magnitudes and upper limits (AB magnitude system): g' = 22.1 +/- 0.1 mag, r' = 21.9 +/- 0.1 mag, i' = 21.7 +/- 0.1 mag, z' = 21.5 +/- 0.1 mag, J = 21.6 +/- 0.3 mag, H = 20.7 +/- 0.3 mag, and K > 19.8 mag. Given magnitudes and upper limits are calibrated against GROND Zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.03 mag in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18551 SUBJECT: GRB 151031A: MITSuME Akeno optical upper limits DATE: 15/11/02 10:02:14 GMT FROM: Taketoshi Yoshii at Tokyo Tech T.Fujiwara, T. Yoshii, Y. Saito, Y. Tachibana, Y. Yano, Y.Ono, S.Harita, Y.Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 151031A (E. Sonbas et al., GCN Circular #18538) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 2015-10-31 16:18:19 UT (10.5 h after the burst). We did not find any new point source within XRT circle in all three bands. We obtained following limits for the magnitudes. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ---------------------------------------------------------- 37669 17:00:37 4440 > 18.8 > 18.9 > 18.3 ---------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration.