//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22468 SUBJECT: GRB 180311A: Swift detection of a burst DATE: 18/03/11 18:18:00 GMT FROM: David Palmer at LANL K. L. Page (U Leicester), A. Deich (PSU), S. W. K Emery (UCL-MSSL), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 18:03:49 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180311A (trigger=813721). Swift slewed to the burst after a brief delay to clear the Earth limb observing contraint. The BAT on-board calculated location is RA, Dec 3.433, -54.479 which is RA(J2000) = 00h 13m 44s Dec(J2000) = -54d 28' 43" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex peak structure with a duration of about 30 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 18:08:24.5 UT, 275.3 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 3.39027, -54.49162 which is equivalent to: RA(J2000) = 00h 13m 33.66s Dec(J2000) = -54d 29' 29.8" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 100 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 (1.59 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.9 (+3.32/-2.86) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 279 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 26% 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 expected extinction corresponding to E(B-V) of 0.01. Burst Advocate for this burst is K. L. Page (klp5 AT leicester.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: 22469 SUBJECT: GRB 180311A: Prompt enhanced Swift-XRT position DATE: 18/03/11 19:03:38 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 180311A, we find an enhanced XRT position of the afterglow: RA, Dec: 3.3872, -54.4914 which is equivalent to: RA (J2000) = 00 13 32.93 Dec (J2000) = -54 29 29.0 with an uncertainty of 2.1 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/813721. 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: 22470 SUBJECT: GRB 180311A: Enhanced Swift-XRT position DATE: 18/03/11 22:50:21 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 3908 s of XRT Photon Counting mode data and 5 UVOT images for GRB 180311A, 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 = 3.38761, -54.49145 which is equivalent to: RA (J2000): 00h 13m 33.03s Dec (J2000): -54d 29' 29.2" 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: 22473 SUBJECT: GRB 180311A: Swift-XRT refined Analysis DATE: 18/03/12 03:53:59 GMT FROM: Phil Evans at U of Leicester A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB) and K.L. Page report on behalf of the Swift-XRT team: We have analysed 8.3 ks of XRT data for GRB 180311A (Page et al. GCN Circ. 22468), from 284 s to 20.1 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 22469). The light curve can be modelled with an initial power-law decay with an index of alpha=3.1 (+0.9, -0.6), followed by a break at T+636 s to an alpha of 0.57 (+0.10, -0.09). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.07 (+0.20, -0.19). The best-fitting absorption column is 5.5 (+4.3, -3.7) x 10^20 cm^-2, in excess of the Galactic value of 1.6 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 3.1 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.5 (+4.3, -3.7) x 10^20 cm^-2 Galactic foreground: 1.6 x 10^20 cm^-2 Excess significance: 1.7 sigma Photon index: 2.07 (+0.20, -0.19) If the light curve continues to decay with a power-law decay index of 0.57, the count rate at T+24 hours will be 0.012 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.6 x 10^-13 (4.2 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/00813721. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22474 SUBJECT: GRB 180311A, Swift-BAT refined analysis DATE: 18/03/12 13:00:00 GMT FROM: Amy Lien at GSFC M. Stamatikos (OSU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), K. L. Page (U Leicester), T. Sakamoto (AGU), 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 180311A (trigger #813721) (Page et al., GCN Circ. 22468). The BAT ground-calculated position is RA, Dec = 3.379, -54.491 deg which is RA(J2000) = 00h 13m 31.0s Dec(J2000) = -54d 29' 26.6" with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 94%. The mask-weighted light curve shows a single-peaked structure that starts at ~ T0, peaks at ~T+3 s, and ends at ~T+26 s. T90 (15-350 keV) is 23.0 +- 8.7 sec (estimated error including systematics). The time-averaged spectrum from T-0.2 to T+26.6 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.78 +- 0.29. The fluence in the 15-150 keV band is 3.3 +- 0.7 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+2.88 sec in the 15-150 keV band is 0.6 +- 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/813721/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22475 SUBJECT: GRB 180311A: Swift/UVOT Upper Limits DATE: 18/03/12 16:42:41 GMT FROM: Frank Marshall at Swift/UVOT F. E. Marshall (NASA/GSFC) and K. L. Page (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180311A 280 s after the BAT trigger (Page et al., GCN Circ. 22468). No optical afterglow consistent with the enhanced XRT position (Goad et al. GCN Circ. 22470) 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 280 430 147 >20.3 white 280 6742 589 >21.2 v 437 7155 333 >19.4 b 536 8600 488 >20.9 u 511 7770 561 >20.5 w1 486 7565 330 >20.2 m2 7160 7360 197 >20.3 w2 1187 6950 255 >20.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.01 in the direction of the burst (Schlegel et al. 1998).