//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18373 SUBJECT: GRB 151001A: Swift detection of a burst with an optical counterpart DATE: 15/10/01 16:38:56 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT M. Stamatikos (OSU/NASA/GSFC), S. D. Barthelmy (GSFC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), S. L. Gibson (U Leicester), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), C. Pagani (U Leicester), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 15:04:22 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 151001A (trigger=657286). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.731, +10.971 which is RA(J2000) = 15h 34m 55s Dec(J2000) = +10d 58' 16" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a couple overlapping peaks with a duration of about 100 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~10 sec after the trigger. The XRT began observing the field at 15:05:26.9 UT, 64.0 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 233.7289, 10.9669 which is equivalent to: RA(J2000) = 15h 34m 54.94s Dec(J2000) = +10d 58' 00.8" with an uncertainty of 2.0 arcseconds (radius, 90% containment). This location is 16 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 (3.53 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 1.3 (+1.39/-1.27) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 67 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 15:34:54.90 = 233.72874 DEC(J2000) = +10:58:02.1 = 10.96724 with a 90%-confidence error radius of about 0.62 arc sec. This position is 3.8 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.94 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.04. Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT nasa.gov). 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: 18375 SUBJECT: GRB 151001A: Fermi GBM detection DATE: 15/10/02 01:01:32 GMT FROM: Bagrat Mailyan at UAH B. Mailyan (UAH), P. Veres (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 15:04:22.41 UT on 01 October 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 151001A (trigger 465404666 / 151001628) which was also detected by the Swift/BAT and XRT (M. Stamatikos et al. 2015, GCN 18373) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 22 degrees. The GBM light curve has a duration (T90) of about 15.1 s (50-300 keV). The time-averaged spectrum from T0-6.1 s to T0+4.1 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -0.54 +/- 0.21 and the cutoff energy, parameterized as Epeak, is 213.80 +/- 36.90 keV. The event fluence (10-1000 keV) in this time interval is (1.798 +/- 0.195)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.75 s in the 10-1000 keV band is 2.2 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18376 SUBJECT: GRB 151001A: Enhanced Swift-XRT position DATE: 15/10/02 02:33:32 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 2627 s of XRT Photon Counting mode data and 5 UVOT images for GRB 151001A, 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 = 233.72875, +10.96720 which is equivalent to: RA (J2000): 15h 34m 54.90s Dec (J2000): +10d 58' 01.9" with an uncertainty of 1.5 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: 18378 SUBJECT: GRB 151001A: Swift-XRT refined Analysis DATE: 15/10/02 06:19:04 GMT FROM: Phil Evans at U of Leicester A. Melandri (INAF-OAB), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), K.L. Page (U. Leicester), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and M. Stamatikos report on behalf of the Swift-XRT team: We have analysed 8.2 ks of XRT data for GRB 151001A (Stamatikos et al. GCN Circ. 18373), from 49 s to 36.0 ks after the BAT trigger. The data comprise 9 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 Beardmore et al. (GCN Circ. 18376). The late-time light curve (from T0+4.8 ks) can be modelled with a power-law decay with a decay index of alpha=1.18 (+0.23, -0.20). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.78 (+/-0.14). The best-fitting absorption column is 8.0 (+4.0, -3.6) x 10^20 cm^-2, in excess of the Galactic value of 3.5 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 3.7 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.0 (+4.0, -3.6) x 10^20 cm^-2 Galactic foreground: 3.5 x 10^20 cm^-2 Excess significance: 2.1 sigma Photon index: 1.78 (+/-0.14) If the light curve continues to decay with a power-law decay index of 1.18, the count rate at T+24 hours will be 2.8 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x 10^-13 (1.2 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/00657286. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18379 SUBJECT: GRB 151001A: NOT imaging DATE: 15/10/02 09:07:50 GMT FROM: Thomas Kruehler at MPE Garching T. Kruehler (MPE), J. P. U. Fynbo, D. Malesani (DARK/NBI), and P. Jakobsson (U. Iceland) report on behalf of a larger collaboration: We observed the field of GRB 151001A (Swift trigger 657286, Stamatikos et al., GCN Circ. 18373) with the 2.5-m Nordic Optical Telescope (NOT) equipped with ALFOSC on the evening of 01-Oct-2015 between 19:55-20:24 UT (5 hr after the burst). In SDSS filters r and g we clearly detect the optical afterglow of GRB 151001A at the position given by UVOT (Stamatikos et al., GCN Circ. 18373). We derive AB magnitudes of g = 22.18 +/- 0.05 r = 21.51 +/- 0.08 calibrated against SDSS field stars. The g-r color of the afterglow is relatively red compared to typical afterglows. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18381 SUBJECT: GRB 151001A: Swift/UVOT Detection DATE: 15/10/02 12:44:45 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 151001A 46 s after the BAT trigger (Stamatikos et al., GCN Circ. 18373). A fading source consistent with the enhanced XRT position (Beardmore et al. GCN Circ. 18376) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 15:34:54.90 = 233.72875 (deg.) Dec (J2000) = +10:58:02.2 = 10.96728 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence). 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 67 217 147 17.82 ± 0.06 white 559 578 20 19.5 ± 0.3 v 46 1403 110 18.78 ± 0.29 b 534 1502 97 19.60 ± 0.29 u 279 529 246 19.13 ± 0.15 w1 657 1453 97 >19.3 m2 806 1428 39 >18.0 w2 1358 1552 39 >18.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18387 SUBJECT: GRB 151001A: Swift-BAT refined analysis DATE: 15/10/03 00:12:58 GMT FROM: Amy Lien at GSFC M. Stamatikos (OSU), 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), 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 151001A (trigger #657286) (Stamatikos, et al., GCN Circ. 18373). The BAT ground-calculated position is RA, Dec = 233.722, 10.984 deg which is RA(J2000) = 15h 34m 53.2s Dec(J2000) = +10d 59' 01.1" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted light curve shows a single-peaked structure that starts at ~T-6 s, peaks at ~T0, end ends at~T+5 s. T90 (15-350 keV) is 8.94 +- 1.07 sec (estimated error including systematics). The time-averaged spectrum from T-6.28 to T+4.53 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.17 +- 0.11. The fluence in the 15-150 keV band is 6.7 +- 0.5 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.04 sec in the 15-150 keV band is 1.3 +- 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/657286/BA/