//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21405 SUBJECT: GRB 170803A: Swift detection of a burst with an optical counterpart DATE: 17/08/03 17:42:50 GMT FROM: David Palmer at LANL S. J. LaPorte (PSU), A. Cholden-Brown (PSU), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 17:30:27 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 170803A (trigger=766081). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 174.950, -16.311 which is RA(J2000) = 11h 39m 48s Dec(J2000) = -16d 18' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multiple-peaked structure with a duration of about 5 sec. The peak count rate was ~15000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 17:32:27.0 UT, 120.1 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 174.93532, -16.31155 which is equivalent to: RA(J2000) = 11h 39m 44.48s Dec(J2000) = -16d 18' 41.6" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 50 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 (3.54 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3 (+2.47/-2.15) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 88 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 11:39:44.11 = 174.93381 DEC(J2000) = -16:18:37.9 = -16.31052 with a 90%-confidence error radius of about 0.75 arc sec. This position is 6.1 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.12 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.04. Burst Advocate for this burst is S. J. LaPorte (extragsam AT gmail.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: 21406 SUBJECT: GRB 170803A: Fermi GBM observation DATE: 17/08/03 23:03:54 GMT FROM: Peter Veres at UAH P Veres and C Meegan (both UAH) report on behalf of the Fermi GBM Team: "At 17:30:27.112 UT on 3 August 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170803A (trigger 523474232 / 170803729) which was also detected by the Swift/BAT (LaPorte et al., GCN 21405). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 40 degrees. The GBM light curve consists of a single pulse with a duration (T90) of about 3.6 s (50-300 keV). The time-averaged spectrum from T0-0.1 s to T0+2.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.71 +/- 0.12 and the cutoff energy, parameterized as Epeak, is 154 +/- 13 keV. The event fluence (10-1000 keV) in this time interval is (1.65 +/- 0.076)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.1 s in the 10-1000 keV band is 9.1 +/- 0.3 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: 21407 SUBJECT: GRB 170803A: Enhanced Swift-XRT position DATE: 17/08/04 01:08:11 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 2272 s of XRT Photon Counting mode data and 1 UVOT images for GRB 170803A, 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 = 174.93434, -16.31002 which is equivalent to: RA (J2000): 11h 39m 44.24s Dec (J2000): -16d 18' 36.1" 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: 21408 SUBJECT: GRB 170803A: Swift-XRT refined Analysis DATE: 17/08/04 03:59:45 GMT FROM: Phil Evans at U of Leicester B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), B. Mingo (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Cholden-Brown (PSU) and S.J. LaPorte report on behalf of the Swift-XRT team: We have analysed 6.1 ks of XRT data for GRB 170803A (LaPorte et al. GCN Circ. 21405), from 68 s to 30.1 ks after the BAT trigger. The data comprise 312 s in Windowed Timing (WT) mode (the first 9 s were 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. 21407). The late-time light curve (from T0+5.6 ks) can be modelled with a power-law decay with a decay index of alpha=1.00 (+/-0.28). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.86 (+0.13, -0.12). The best-fitting absorption column is 1.3 (+/-0.4) x 10^21 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 (4.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.3 (+/-0.4) x 10^21 cm^-2 Galactic foreground: 3.5 x 10^20 cm^-2 Excess significance: 4.5 sigma Photon index: 1.86 (+0.13, -0.12) If the light curve continues to decay with a power-law decay index of 1.00, the count rate at T+24 hours will be 6.3 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x 10^-13 (2.8 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/00766081. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21411 SUBJECT: GRB 170803A: Swift/UVOT Detection DATE: 17/08/04 13:04:24 GMT FROM: Sam Emery at MSSL-UCL S.W.K. Emery (UCL-MSSL) and S. J. LaPorte (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170803A 88 s after the BAT trigger (LaPorte et al., GCN Circ. 21405). GRB 170803A was also triggered by Fermi GBM (Veres and Meegan GCN Circ. 21406) A fading source consistent with the XRT position (Beardmore et al., GCN Circ. 21407) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 11:39:44.11 = 174.93380 (deg.) Dec (J2000) = -16:18:38.0 = -16.31055 (deg.) with an estimated uncertainty of 0.44 arc sec. (radius, 90% confidence). 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 88 238 147 18.10 +/- 0.06 white 580 2241 322 19.69 +/- 0.12 u_FC 300 550 246 18.58 +/- 0.16 u 775 2366 175 >19.34 b 556 2386 191 20.02 +/- 0.35 uvw1 6216 23821 982 >20.74 uvm2 17025 17715 679 >20.57 uvw2 5602 30135 990 >21.05 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: 21412 SUBJECT: GRB 170803A: Swift-BAT refined analysis DATE: 17/08/04 14:01:17 GMT FROM: Amy Lien at GSFC J. R. Cummings (CPI), S. D. Barthelmy (GSFC), H. A. Krimm (NSF/USRA), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), 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-240 to T+200 sec from the recent telemetry downlink, we report further analysis of BAT GRB 170803A (trigger #766081) (LaPorte et al., GCN Circ. 21405). The BAT ground-calculated position is RA, Dec = 174.947, -16.312 deg which is RA(J2000) = 11h 39m 47.2s Dec(J2000) = -16d 18' 41.9" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 94%. The mask-weighted light curve shows a multi-peaked structure that starts at ~T-0.7 s and ends at ~T+4 s. The main peak occurs at ~T+0.1 s T90 (15-350 keV) is 3.82 +- 0.23 sec (estimated error including systematics). The time-averaged spectrum from T-0.69 to T+4.14 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.65 +- 0.28, and Epeak of 100.2 +- 20.5 keV (chi squared 47.53 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 9.8 +- 0.4 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T-0.12 sec in the 15-150 keV band is 6.5 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.39 +- 0.06 (chi squared 71.10 for 57 d.o.f.). 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/766081/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21418 SUBJECT: GRB 170803A: Swift/BAT spectral lag results DATE: 17/08/05 20:05:59 GMT FROM: Amy Lien at GSFC J. P. Norris (BSU), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), A. Y. Lien (GSFC/UMBC) report on behalf of the Swift-BAT team: We report the spectral lag analysis for GRB 170803A (LaPorte et al., GCN Circ. 21405) based on the BAT data. The lag analysis finds a lag of 43 (+12, -12) ms for the 100-350 keV to 25-50 keV band, and 76 (+40, -26) ms for the 50-100 keV to 15-25 keV band. These values are consistent with those of long GRBs.