//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18050 SUBJECT: GRB 150724A: Swift detection of a burst DATE: 15/07/24 06:02:12 GMT FROM: David Palmer at LANL J. L. Racusin (NASA/GSFC), A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 05:46:35 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150724A (trigger=650141). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 97.540, -19.154 which is RA(J2000) = 06h 30m 09s Dec(J2000) = -19d 09' 12" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed multiple peaks structure with a duration of about 40 sec. The peak count rate was ~1412 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 05:48:18.6 UT, 102.6 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source located at RA, Dec 97.56060, -19.16395 which is equivalent to: RA(J2000) = 06h 30m 14.54s Dec(J2000) = -19d 09' 50.2" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 78 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 consistent with the Galactic value of 2.94 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 1.27e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 108 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. The list of sources is typically complete to about 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.27. Burst Advocate for this burst is J. L. Racusin (judith.racusin 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: 18052 SUBJECT: GRB 150724A: Prompt enhanced Swift-XRT position DATE: 15/07/24 06:23:32 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using promptly downlinked XRT event data for GRB 150724A, we find an enhanced XRT position of the afterglow: RA, Dec: 97.5600, -19.1646 which is equivalent to: RA (J2000) = 06 30 14.41 Dec (J2000) = -19 09 52.5 with an uncertainty of 2.0 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/650141. Position enhancement is is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18054 SUBJECT: GRB 150724A: Enhanced Swift-XRT position DATE: 15/07/24 11:32:50 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 2472 s of XRT Photon Counting mode data and 4 UVOT images for GRB 150724A, 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 = 97.56044, -19.16479 which is equivalent to: RA (J2000): 06h 30m 14.51s Dec (J2000): -19d 09' 53.3" with an uncertainty of 1.9 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: 18055 SUBJECT: GRB 150724A: Swift-BAT refined analysis DATE: 15/07/24 12:10:27 GMT FROM: Scott Barthelmy at NASA/GSFC D. M. Palmer (LANL), 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), J. L. Racusin (NASA/GSFC), 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+902 sec from recent telemetry downlinks, we report further analysis of BAT GRB 150724A (trigger #650141) (Racusin, et al., GCN Circ. 18050). The BAT ground-calculated position is RA, Dec = 97.549, -19.147 deg, which is RA(J2000) = 06h 30m 11.7s Dec(J2000) = -19d 08' 48.1" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%. The mask-weighted light curve has at least 4 peaks starting at ~T-10 sec, with peaks at ~T+1 sec, ~T+24 sec, ~T+160 sec, & ~T+220 sec, and the emission ending at ~T+300 sec. T90 (15-350 keV) is 280 +- 44 sec (estimated error including systematics). The time-averaged spectrum from T-1.07 to T+325.42 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.06 +- 0.15. The fluence in the 15-150 keV band is 2.2 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+24.08 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/650141/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18057 SUBJECT: GRB 150724A: Swift/UVOT Upper Limits DATE: 15/07/24 14:41:21 GMT FROM: Massimiliano de Pasquale at IASF-Palermo M. De Pasquale (UCL-MSSL) and J. L. Racusin (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150724A 108 s after the BAT trigger (Racusin et al., GCN Circ. 18050). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 18054) 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 summed exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u_FC 108 358 246 >19.7 v 415 6930 510 >19.2 b 364 12898 1165 >20.6 u 108 12238 1769 >20.7 w1 464 11324 1387 >20.5 m2 439 7135 502 >19.9 w2 390 6726 529 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.27 in the direction of the burst (Schlegel et al. 1998). -- Dr. Massimiliano De Pasquale Research associate - Swift UVOT scientist Mullard Space Science Laboratory, University College London //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18059 SUBJECT: GRB 150724A: Swift-XRT refined Analysis DATE: 15/07/24 18:02:03 GMT FROM: Phil Evans at U of Leicester T.G.R. Roegiers (PSU), B.P. Gompertz (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), L.M. McCauley (PSU), J.A. Kennea (PSU) and J.L. Racusin report on behalf of the Swift-XRT team: We have analysed 11 ks of XRT data for GRB 150724A (Racusin et al. GCN Circ. 18050), from 91 s to 24.4 ks after the BAT trigger. The data comprise 349 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 Goad et al. (GCN Circ. 18052). The late-time light curve (from T0+4.7 ks) is consistent with a constant source of mean count rate 2.2e+00 ct/sec. A power-law fit gives an index of -0.02 (+0.19, -0.20). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.70 (+/-0.04). The best-fitting absorption column is 3.70 (+0.21, -0.20) x 10^21 cm^-2, in excess of the Galactic value of 2.9 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.13 (+0.18, -0.17) and a best-fitting absorption column of 3.6 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (5.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.6 (+0.8, -0.7) x 10^21 cm^-2 Galactic foreground: 2.9 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.13 (+0.18, -0.17) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00650141. This circular is an official product of the Swift-XRT team.