//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21410 SUBJECT: GRB 170804A: Swift detection of a burst with optical counterpart DATE: 17/08/04 12:13:26 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT A. Cholden-Brown (PSU), D. N. Burrows (PSU), P. A. Evans (U Leicester), J. A. Kennea (PSU), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 12:01:37 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 170804A (trigger=766194). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 6.433, -64.748 which is RA(J2000) = 00h 25m 44s Dec(J2000) = -64d 44' 52" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 40 sec. The peak count rate was ~1400 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 12:03:39.9 UT, 122.6 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 6.39106, -64.78341 which is equivalent to: RA(J2000) = 00h 25m 33.85s Dec(J2000) = -64d 47' 00.3" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 142 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 in excess of the Galactic value (1.79 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.4 (+3.30/-2.37) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 5.37e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 131 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 00:25:34.45 = 6.39354 DEC(J2000) = -64:47:03.0 = -64.78416 with a 90%-confidence error radius of about 0.63 arc sec. This position is 6.9 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.01 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02. Burst Advocate for this burst is A. Cholden-Brown (aaronb AT swift.psu.edu). 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: 21413 SUBJECT: GRB 170804A: Enhanced Swift-XRT position DATE: 17/08/04 16:14:01 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 1208 s of XRT Photon Counting mode data and 2 UVOT images for GRB 170804A, 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 = 6.39233, -64.78429 which is equivalent to: RA (J2000): 00h 25m 34.16s Dec (J2000): -64d 47' 03.4" with an uncertainty of 1.8 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: 21414 SUBJECT: GRB 170804A: Swift-XRT refined Analysis DATE: 17/08/04 20:01:28 GMT FROM: Phil Evans at U of Leicester D.N. Burrows (PSU), K.L. Page (U. Leicester), B. Mingo (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), S. J. LaPorte (PSU) and A. Cholden-Brown report on behalf of the Swift-XRT team: We have analysed 6.5 ks of XRT data for GRB 170804A (Cholden-Brown et al. GCN Circ. 21410), from 112 s to 19.6 ks after the BAT trigger. The data comprise 95 s in Windowed Timing (WT) mode (the first 8 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 Evans et al. (GCN Circ. 21413). The light curve can be modelled with an initial power-law decay with an index of alpha=2.90 (+0.34, -0.22), followed by a break at T+519 s to an alpha of 1.13 (+0.20, -0.13). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.37 (+0.16, -0.13). The best-fitting absorption column is consistent with the Galactic value of 1.8 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.97 (+0.16, -0.14) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.2 x 10^-11 (3.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.8 (+2.4, -0.0) x 10^20 cm^-2 Galactic foreground: 1.8 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.97 (+0.16, -0.14) If the light curve continues to decay with a power-law decay index of 1.13, the count rate at T+24 hours will be 8.3 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.7 x 10^-14 (2.8 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/00766194. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21415 SUBJECT: GRB 170804A: Swift/UVOT Detection DATE: 17/08/04 21:03:59 GMT FROM: Samantha Oates at MSSL S. R. Oates (U. Warwick) and A. Cholden-Brown (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170804A 132 s after the BAT trigger (Cholden-Brown et al., GCN Circ. 21410). A fading source consistent with the XRT position (Evans et al., GCN Circ. 21413) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 0:25:34.29 = 6.39288 (deg.) Dec (J2000) = -64:47:03.1 = -64.78419 (deg.) with an estimated uncertainty of 0.5 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 132 281 147 18.9 +/- 0.1 white 871 1020 147 20.0 +/- 0.2 u_FC 289 539 246 18.7 +/- 0.1 v 796 1243 58 >18.7 b 545 565 19 18.9 +/- 0.4 uvw1 671 1292 78 >19.0 uvw2 596 1392 97 >19.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998). --------------------------------------------- Dr Samantha Oates Leverhulme Early Career Fellow Department of Physics University of Warwick Coventry CV4, UK Tel: +44 (024) 765 23383 Email: s.oates@warwick.ac.uk ----------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21416 SUBJECT: GRB 170804A: Swift-BAT refined analysis DATE: 17/08/05 15:45:14 GMT FROM: Amy Lien at GSFC H. A. Krimm (NSF/USRA), S. D. Barthelmy (GSFC), A. Cholden-Brown (PSU), J. R. Cummings (CPI), 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+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 170804A (trigger #766194) (Cholden-Brown et al., GCN Circ. 21410). The BAT ground-calculated position is RA, Dec = 6.404, -64.781 deg which is RA(J2000) = 00h 25m 37.0s Dec(J2000) = -64d 46' 50.9" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 75%. The mask-weighted light curve shows several over-lapping pulses that start at ~T0 and end at ~T+60 s. T90 (15-350 keV) is 43.4 +- 9.8 sec (estimated error including systematics). The time-averaged spectrum from T+1.98 to T+60.90 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.67 +- 0.13. The fluence in the 15-150 keV band is 1.3 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+25.10 sec in the 15-150 keV band is 0.9 +- 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/766194/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21417 SUBJECT: GRB 170804A: LCO Observations DATE: 17/08/05 16:53:45 GMT FROM: Antonino Cucchiara at UVI A. Cucchiara, D. Morris (U. of the Virgin Islands), and N. Orange (OrangeWave), report on behalf of a larger collaboration: "On August 4.79 UT (T_0 +7.0h) we began observing the center of the field of GRB 170804A (Cholden-Brown et al. GCN 21410, Emery et al. GCN 21411) using the Las Cumbres Observatory 1m telescope located in Siding Spring Observatory. Under poor sky conditions (seeing ~2.6 arcseconds) we performed a series of 5x240s observations in SDSS r' and i’ bands for a total of 20 minutes on sky in each filter at average airmass of 1.3. In the full median stacked images we identified no optical counterpart within the center of the Swift-XRT refined position or at the UVOT optical counterpart location (Evans et al. GCN 21413, Emery et al. GCN 21411) at the following 3-sigma limits: r' > 21.4 mag i' > 21.1 mag These magnitudes are calibrated against nearby USNO-B1 sources, converted in SDSS bands, and not corrected for Galactic extinction."