//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18450 SUBJECT: GRB 151023A: Swift detection of a burst DATE: 15/10/23 14:06:29 GMT FROM: Scott Barthelmy at NASA/GSFC P. D'Avanzo (INAF-OAB), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), C. Pagani (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), T. G. R. Roegiers (PSU), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: At 13:43:04 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 151023A (trigger=661253). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 271.019, -8.323, which is RA(J2000) = 18h 04m 05s Dec(J2000) = -08d 19' 21" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 15 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 13:44:19.5 UT, 74.8 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 270.9847, -8.3165 which is equivalent to: RA(J2000) = 18h 03m 56.33s Dec(J2000) = -08d 18' 59.4" with an uncertainty of 3.3 arcseconds (radius, 90% containment). This location is 124 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 4.10 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 796 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 1.42. Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.inaf.it). 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: 18459 SUBJECT: GRB 151023A: Enhanced Swift-XRT position DATE: 15/10/23 23:09:05 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 1446 s of XRT Photon Counting mode data and 2 UVOT images for GRB 151023A, 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 = 270.98458, -8.31640 which is equivalent to: RA (J2000): 18h 03m 56.30s Dec (J2000): -08d 18' 59.0" with an uncertainty of 2.3 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: 18461 SUBJECT: GRB 151023A DATE: 15/10/24 01:12:00 GMT FROM: Fabian Knust at MPE/GROND F. Knust (MPE Garching), S. Klose (TLS Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 151023A (Swift trigger 661253; D'Avanzo et al., GCN #18450) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 23:52 UT on Oct. 23rd 2015, 10 hrs after the GRB trigger, and are continuing. They were performed at an average seeing of 1.6" and at an average airmass of 1.6 We found a single point source within the 2.3" Swift-XRT error circle reported by Evans et al. (GCN #18459) at RA (J2000.0) = 18:03:56.244 Dec. (J2000.0) = -08:18:57.42 with an uncertainty of 0.2" in each coordinate. Based on the first 4.4 min of total exposures in g'r'i'z' and 4.0 min in JHK, we estimate preliminary magnitudes (all in AB system) of g'> 22.1 mag, r' = 20.2 +/- 0.1 mag, i' = 19.1 +/- 0.1 mag, z' =18.4 +/- 0.1 mag, J = 17.6 +/- 0.2 mag, H = 17.0 +/- 0.1 mag, and K = 17.3 +/- 0.2 mag. Given magnitudes 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)=1.38 mag in the direction of the burst (Schlegel et al. 1998). [GCN OPS NOTE(24oct15): The suffix "A" was added to the Subject-line.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18462 SUBJECT: GRB 151023A: Swift/UVOT Upper Limits DATE: 15/10/24 02:15:35 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU), B. G. Balzer (PSU) and P. D'Avanzo (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 151023A 796 s after the BAT trigger (D'Avanzo et al., GCN Circ. 18450). No optical afterglow consistent with the XRT position (D'Avanzo et al. GCN Circ. 18450) 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 796 946 147 >19.6 white 796 2140 411 >20.0 v 1130 2191 136 >18.5 b 1229 2116 117 >19.3 w1 1354 1374 19 >18.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.42 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18463 SUBJECT: GRB 151023A: Swift-XRT refined Analysis DATE: 15/10/24 03:06:05 GMT FROM: Phil Evans at U of Leicester J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. Melandri (INAF-OAB), V. D'Elia (ASDC), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), C. Pagani (U. Leicester) and P. D'Avanzo report on behalf of the Swift-XRT team: We have analysed 7.4 ks of XRT data for GRB 151023A (D'Avanzo et al. GCN Circ. 18450), from 756 s to 35.7 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. 18459). The light curve can be modelled with a power-law decay with a decay index of alpha=1.32 (+0.27, -0.21). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.7 (+1.1, -0.8). The best-fitting absorption column is 2.7 (+1.8, -1.4) x 10^22 cm^-2, in excess of the Galactic value of 4.1 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.9 x 10^-11 (2.6 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.7 (+1.8, -1.4) x 10^22 cm^-2 Galactic foreground: 4.1 x 10^21 cm^-2 Excess significance: 2.7 sigma Photon index: 2.7 (+1.1, -0.8) If the light curve continues to decay with a power-law decay index of 1.32, the count rate at T+24 hours will be 2.5 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x 10^-14 (6.4 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00661253. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18464 SUBJECT: GRB 151023A: RATIR Observations DATE: 15/10/24 03:59:24 GMT FROM: Nat Butler at UC berkeley Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (GSFC/STScI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report: We observed the field of GRB 151023A (D'Avanzo, et al., GCN 18450) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2015/10 24.09 to 2015/10 24.14 UTC (12.35 to 13.66 hours after the BAT trigger), obtaining a total of 1.07 hours exposure in the r, i, and z bands. We detect the GROND source (Knust, et al., GCN 18461) at a similar brightness level. In comparison with the USNO-B1 catalog, we find: r 20.27 +/- 0.04 i 19.10 +/- 0.02 z 18.29 +/- 0.09 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. We note that this source is present in the DSS at a comparable brightness level and may not, therefore, be the GRB afterglow. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18469 SUBJECT: GRB 151023A: Swift-BAT refined analysis DATE: 15/10/24 19:18:03 GMT FROM: Amy Lien at GSFC C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), P. D'Avanzo (INAF-OAB), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 151023A (trigger #661253) (D'Avanzo, et al., GCN Circ. 18450). The BAT ground-calculated position is RA, Dec = 271.012, -8.289 deg which is RA(J2000) = 18h 04m 02.9s Dec(J2000) = -08d 17' 19.7" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 83%. The mask-weighted light curve shows a single-pulse structure that starts at ~ T-1 s, peaks at ~T0, and ends at ~ T+10 s. T90 (15-350 keV) is 10.66 +- 4.41 sec (estimated error including systematics). The time-averaged spectrum from T-0.65 to T+12.16 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.24 +- 0.24. The fluence in the 15-150 keV band is 2.6 +- 0.4 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.03 sec in the 15-150 keV band is 1.1 +- 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/661253/BA/