//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16842 SUBJECT: GRB 140927A: Swift detection of a burst DATE: 14/09/27 05:35:42 GMT FROM: David Palmer at LANL R. L. C. Starling (U Leicester), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (NASA/GSFC), C. J. Mountford (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and T. N. Ukwatta (LANL) report on behalf of the Swift Team: At 05:15:11 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140927A (trigger=613775). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 291.845, -65.388 which is RA(J2000) = 19h 27m 23s Dec(J2000) = -65d 23' 14" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a spiky structure with a duration of about 30 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~6 sec after the trigger. The XRT began observing the field at 05:17:13.7 UT, 122.3 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 291.79216, -65.39285 which is equivalent to: RA(J2000) = 19h 27m 10.12s Dec(J2000) = -65d 23' 34.3" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 81 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 (7.56 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 4 (+3.21/-2.72) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 250 seconds with the U filter starting 123 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 0.08. Burst Advocate for this burst is R. L. C. Starling (rlcs1 AT star.le.ac.uk). 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: 16843 SUBJECT: GRB 140927A: Enhanced Swift-XRT position DATE: 14/09/27 15:09:54 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 2980 s of XRT Photon Counting mode data and 5 UVOT images for GRB 140927A, 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 = 291.79158, -65.39357 which is equivalent to: RA (J2000): 19h 27m 9.98s Dec (J2000): -65d 23' 36.9" 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: 16844 SUBJECT: GRB 140927A: Swift-XRT refined Analysis DATE: 14/09/27 17:35:04 GMT FROM: Phil Evans at U of Leicester J.A. Kennea (PSU), V. Mangano (PSU), M.C. Stroh (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), M. de Pasquale (INAF-IASFPA) and R.L.C. Starling report on behalf of the Swift-XRT team: We have analysed 7.1 ks of XRT data for GRB 140927A (Starling et al. GCN Circ. 16842), from 108 s to 29.7 ks after the BAT trigger. The data comprise 7 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 Evans et al. (GCN Circ. 16843). The light curve can be modelled with a power-law decay with a decay index of alpha=0.76 (+/-0.05). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.79 (+0.25, -0.23). The best-fitting absorption column is 1.6 (+1.0, -0.8) x 10^21 cm^-2, in excess of the Galactic value of 7.6 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 3.9 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.6 (+1.0, -0.8) x 10^21 cm^-2 Galactic foreground: 7.6 x 10^20 cm^-2 Excess significance: 1.7 sigma Photon index: 1.79 (+0.25, -0.23) If the light curve continues to decay with a power-law decay index of 0.76, the count rate at T+24 hours will be 4.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x 10^-13 (2.3 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/00613775. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16845 SUBJECT: GRB 140927A: Swift-BAT refined analysis DATE: 14/09/27 21:49:44 GMT FROM: Amy Lien at GSFC S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), 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), M. Stamatikos (OSU), R. L. C. Starling (U Leicester) J. Tueller (GSFC), 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 140927A (trigger #613775) (Starling, et al., GCN Circ. 16842). The BAT ground-calculated position is RA, Dec = 291.802, -65.400 deg which is RA(J2000) = 19h 27m 12.5s Dec(J2000) = -65d 23' 58.4" with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 54%. The mask-weighted light curve shows a multi-peaked structure starts at ~ T0 and ends at ~ T+9 s. The structure has roughly two main peaks, at ~ T+3.8 s and ~ T+7.7 s, respectively. T90 (15-350 keV) is 6.26 +- 1.43 sec (estimated error including systematics). The time-averaged spectrum from T+0.43 to T+8.70 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.82 +- 0.30. The fluence in the 15-150 keV band is 2.7 +- 0.5 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+7.70 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/613775/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 16846 SUBJECT: GRB 140927A: Swift-UVOT analysis DATE: 14/09/27 22:34:48 GMT FROM: Craig Swenson at PSU/Swift C. Swenson (PSU) and R. L. C. Starling (U Leicester) report on behalf of the Swift UVOT team: Analysis of the field of GRB 140927A shows a bright DSS source located at RA, DEC= 291.79237,-65.39323, which is 1.7" from the enhanced XRT position (Evans et al., GCN Circ. 16843). No elongation or fading of the known source is observed in the first 10e4 seconds of UVOT observations, meaning that any potential afterglow contribution is being overpowered by the known source.