//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12279 SUBJECT: GRB 110818A: Swift detection of a burst DATE: 11/08/18 21:00:09 GMT FROM: Scott Barthelmy at NASA/GSFC C. B. Markwardt (NASA/GSFC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL), O. M. Littlejohns (U Leicester), F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), T. A. Pritchard (PSU), A. Rowlinson (U Leicester), T. Sakamoto (NASA/UMBC), C. J. Saxton (UCL-MSSL), M. H. Siegel (PSU) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: At 20:37:49 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 110818A (trigger=500914). Because of an Earth-limb observing constraint, the slew to the burst was delayed by ~4 min. The BAT on-board calculated location is RA, Dec 317.384, -63.970 which is RA(J2000) = 21h 09m 32s Dec(J2000) = -63d 58' 10" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows several peaks with a total duration of about 60 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~7 sec after the trigger. The XRT began observing the field at 20:44:09.7 UT, 380.4 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 317.3382, -63.9814 which is equivalent to: RA(J2000) = 21h 09m 21.17s Dec(J2000) = -63d 58' 53.1" with an uncertainty of 2.1 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 (2.62 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2 (+1.14/-1.05) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the U filter starting 856 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 19.2 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.04. Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt 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: 12281 SUBJECT: GRB 110818A, Swift-BAT refined analysis DATE: 11/08/19 03:02:20 GMT FROM: Craig Markwardt at NASA/GSFC C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), 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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 110818A (trigger #500914) (Markwardt, et al., GCN Circ. 12279). The BAT ground-calculated position is RA, Dec = 317.373, -63.981 deg which is RA(J2000) = 21h 09m 29.6s Dec(J2000) = -63d 58' 52.7" with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 29%. The mask-weighted light curve consists of a single broad peak, with several sharper peaks superimposed. T90 (15-350 keV) is 103 +- 18 sec (estimated error including systematics). The time-averaged spectrum from T-14.2 to T+117.4 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.58 +- 0.11. The fluence in the 15-150 keV band is 4.0 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+27.3 sec in the 15-150 keV band is 1.6 +- 0.3 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/500914/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12283 SUBJECT: GRB 110818A: Swift-XRT refined Analysis DATE: 11/08/19 07:07:01 GMT FROM: Antonia Rowlinson at U.of Leicester A. Rowlinson (U. Leicester) and C. B. Markwardt (NASA/GSFC) report on behalf of the Swift-XRT team: We have analysed 7.8 ks of XRT data for GRB 110818A (Markwardt et al. GCN Circ. 12279), from 384 s to 18.3 ks after the BAT trigger. The data comprise 61 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 317.3378, -63.9813 which is equivalent to: RA (J2000): 21 09 21.07 Dec(J2000): -63 58 52.7 with an uncertainty of 2.0 arcsec (radius, 90% confidence). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=5.8 (+0.6, -0.7). At T+461 s the decay flattens to an alpha of 1.57 (+0.14, -0.11) before breaking again at T+2167 s to a final decay with index alpha=0.95 (+0.10, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.97 (+0.12, -0.11). The best-fitting absorption column is 7.8 (+2.7, -2.4) x 10^20 cm^-2, in excess of the Galactic value of 2.6 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 3.6 x 10^-11 (4.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.8 (+2.7, -2.4) x 10^20 cm^-2 Galactic foreground: 2.6 x 10^20 cm^-2 Excess significance: 5.3 sigma Photon index: 1.97 (+0.12, -0.11) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00500914. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12284 SUBJECT: GRB 110818A: Optical afterglow and redshift from VLT/X-shooter DATE: 11/08/19 07:49:47 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst P. D'Avanzo (INAF/Brera), M. Sparre, D. Watson, J. P. U. Fynbo, D. Malesani, B. Milvang-Jensen (DARK/NBI), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), V. D'Elia (INAF/Rome), and N. R. Tanvir (U. Leicester), report on behalf of the X-shooter GTO GRB collaboration: We observed the field of GRB 110818A (Markwardt et al. GCN 12279) with the ESO VLT equipped with X-shooter. Observations started on 2011-08-19 at 02:47 UT (6.15 hr after the GRB). The acquisition image shows an optical afterglow candidate inside the XRT error circle (Markwardt et al. GCN 12279) at the following coordinates (J2000): RA = 21:09:21.04 Dec = -63:58:52.3 with an uncertainty of about 0.5". The object has a magnitude R ~ 22.3, calibrated assuming R = 19.2 for the USNO-B1 star 0260-0726657 (RA, Dec = 21:09:23.14, -63:58:33.0). A total spectroscopic exposure of 4x1200 s was obtained, covering the spectral range from 300 to 2500 nm. We report a redshift of z = 3.36 based on detection of absorption features from Si II, C IV, Al II, Ca H, Ca K and Mg I. Emission from the [O III] doublet is also observed. We would like to thank the staff at the VLT, in particular, Alain Smette, Patricia Guajardo and Dimitri Gadotti for carrying out the observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 12285 SUBJECT: GRB 110818A: Enhanced Swift-XRT position DATE: 11/08/19 08:28:06 GMT FROM: Phil Evans at U of Leicester J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 4176 s of XRT Photon Counting mode data and 5 UVOT images for GRB 110818A, 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 = 317.33705, -63.98105 which is equivalent to: RA (J2000): 21h 09m 20.89s Dec (J2000): -63d 58' 51.8" with an uncertainty of 1.4 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: 12286 SUBJECT: GRB 110818A: Swift/UVOT Upper Limits DATE: 11/08/19 19:29:06 GMT FROM: Tyler Pritchard at PSU T. A. Pritchard (PSU) and C. B. Markwardt (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 110818A 379 s after the BAT trigger (Markwardt et al., GCN Circ. 12279). No optical afterglow consistent with the Enhanced Swift-XRT position (GCN Circ. 12285) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag v 379 14423 1513 >20.8 b 477 18642 2455 >22.2 u 452 8009 813 >20.4 w1 428 7804 646 >20.9 m2 7399 7599 197 >20.9 w2 6989 13752 1082 >21.2 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: 12287 SUBJECT: GRB 110818A: Fermi GBM observation DATE: 11/08/19 23:02:20 GMT FROM: Shaolin Xiong at UAH S. Xiong (UAH) reports on behalf of the Fermi GBM Team: "At 20:37:54.221 UT on 18 August 2011, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 110818A (trigger 335392676 / 110818860 ), which was also detected by the Swift (Markwardt et al. 2011, GCN 12279). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 96 degrees. This burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve consists of multiple peaks with a duration (T90) of about 75 s (50-300 keV). The time-averaged spectrum from T0-16.4 s to T0+57.3 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.33 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 256.3 +/- 55.3 keV. The event fluence (10-1000 keV) in this time interval is (8.2 +/- 0.6)E-6 erg/cm^2. The 64 ms peak photon flux measured starting from T0+22.66 s in the 10-1000 keV band is 5.0 +/- 1.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."