//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18037 SUBJECT: Swift Trigger 649706: a possible GRB or bright Galactic transient DATE: 15/07/20 14:29:11 GMT FROM: Scott Barthelmy at NASA/GSFC E. Sonbas (NASA/GSFC/Adiyaman Univ.), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), S. B. Cenko (GSFC), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC), S. L. Gibson (U Leicester), L. Izzo (URoma/ICRA), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), A. Maselli (INAF-IASFPA), K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 14:02:09 UT, the Swift Burst Alert Telescope (BAT) triggered and located possible GRB 150720A (trigger=649706). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 119.582, -28.301, which is RA(J2000) = 07h 58m 20s Dec(J2000) = -28d 18' 02" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is typical for image trigger (64-sec), there is nothing significant in the real-time TDRSS light curve. The XRT began observing the field at 14:04:23.7 UT, 134.6 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 119.5810, -28.2623 which is equivalent to: RA(J2000) = 07h 58m 19.45s Dec(J2000) = -28d 15' 44.2" with an uncertainty of 2.2 arcseconds (radius, 90% containment). This location is 139 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 5.72 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 0.1 s image was 2.93e-08 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 142 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 19.6 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 mag. No correction has been made for the large, but uncertain extinction expected. The event is near the galactic plane (l=245, b=0.5) and has a rapid decrease in X-ray afterglow. Also, it was a faint image trigger in BAT but very bright in X-rays. We can not rule out that the source is a galactic transient instead of a gamma-ray burst. Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.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: 18038 SUBJECT: GRB 150720A: Swift-BAT refined analysis DATE: 15/07/21 11:56:34 GMT FROM: Scott Barthelmy at NASA/GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), E. Sonbas (NASA/GSFC/Adiyaman Univ.), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-30 to T+273 sec from recent telemetry downlinks, we report further analysis of BAT GRB 150720A (trigger #649706) (Sonbas, et al., GCN Circ. 18037). The BAT ground-calculated position is RA, Dec = 119.577, -28.281 deg, which is RA(J2000) = 07h 58m 18.5s Dec(J2000) = -28d 16' 50" with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted light curve shows 3 peaks starting at T-30 sec and the emission ending at ~T+130 sec. T90 (15-350 keV) is 151 +- 11 sec (estimated error including systematics). The time-averaged spectrum from T-35.1 to T+126.4 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.61 +- 0.33. The fluence in the 15-150 keV band is 5.6 +- 1.0 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+116.68 sec in the 15-150 keV band is 0.3 +- 0.1 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/649706/BA/ We note that this has a soft spectrum (in the bottom ~10-percentile of the BAT hardness range) and that the Galactic lattitude is 0.5deg, so we can not rule out a non-GRB Galactic source origin for this event. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18039 SUBJECT: GRB 150720A: Swift-XRT refined Analysis DATE: 15/07/21 15:27:06 GMT FROM: Valerio D'Elia at ASDC V. D'Elia (ASDC), L. Izzo (URoma/ICRA), K. Page (U Leicester) and E. Sonbas (NASA/GSFC/Adiyaman Univ.) report on behalf of the Swift-XRT team: We have analysed 11 ks of XRT data for the possible GRB 150720A (Sonbas et al. GCN Circ. 18037), from 138 s to 40 ks after the BAT trigger. The data comprise 96 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 119.58144, -28.26249 which is equivalent to: RA (J2000): 07 58 19.55 Dec(J2000): -28 15 45.0 with an uncertainty of 1.8 arcsec (radius, 90% confidence). The late time light curve can be modelled with a power-law decay with a decay index of alpha ~ 1.5. A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 3.16 (+0.10, -0.10). The best-fitting absorption column is 3.1 (+0.6, -0.6) x 10^21 cm^-2, in excess of the Galactic value of 5.72 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 2.7 x 10^-11 (1.6 x 10^-10) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 8.8 (+0.6, -0.6) x 10^21 cm^-2 Galactic foreground: 5.72 x 10^21 cm^-2 Excess significance: 5.1 sigma Photon index: 3.16 (+0.10, -0.10) If the light curve continues to decay with a power-law decay index of 1.5, the count rate at T+24 hours will be 1.8 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.9 x 10^-14 (2.9 x 10^-13) erg cm^-2 s^-1. Given the light curve and spectrum behaviour, we believe that this is a real GRB and not a galactic transient. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18040 SUBJECT: GRB 150720A: Enhanced Swift-XRT position DATE: 15/07/21 15:41:17 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 653 s of XRT Photon Counting mode data and 2 UVOT images for GRB 150720A, 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 = 119.58146, -28.26251 which is equivalent to: RA (J2000): 07h 58m 19.55s Dec (J2000): -28d 15' 45.0" 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: 18045 SUBJECT: GRB 150720A: Swift/UVOT Upper Limits DATE: 15/07/22 16:14:07 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and E. Sonbas (NASA/GSFC/Adiyaman Univ.) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150720A 142 s after the BAT trigger (Sonbas et al., GCN Circ. 18037). No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ. 18040) 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 exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white (fc) 142 292 147 >20.5 u (fc) 301 551 246 >20.4 white 142 1551 392 >21.2 v 631 1601 117 >19.3 b 557 1527 97 >19.6 u 301 1502 324 >20.2 w1 680 1478 97 >19.3 m2 655 1623 114 >19.8 w2 606 1577 117 >19.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.68 in the direction of the burst (Schlegel et al. 1998). [GCN OPS NOTE(22jul15): Added the "A" suffix to the GRB name.]