//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17599 SUBJECT: GRB 150318A: Swift detection of a burst DATE: 15/03/18 07:20:45 GMT FROM: David Palmer at LANL C. Pagani (U Leicester), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC), H. A. Krimm (CRESST/GSFC/USRA), C. J. Mountford (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 07:04:53 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150318A (trigger=635289). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 324.971, -61.477d which is RA(J2000) = 21h 39m 53s Dec(J2000) = -61d 28' 35" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 80 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 07:07:14.5 UT, 141.3 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 325.0056, -61.4559 which is equivalent to: RA(J2000) = +21h 40m 1.34s Dec(J2000) = -61d 27' 21.2" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 96 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 150 seconds with the white filter starting 164 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 expected extinction corresponding to E(B-V) of 0.04. Burst Advocate for this burst is C. Pagani (cp232 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: 17600 SUBJECT: GRB 150318A: Enhanced Swift-XRT position DATE: 15/03/18 11:09:49 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 669 s of XRT Photon Counting mode data and 1 UVOT images for GRB 150318A, 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 = 325.00597, -61.45674 which is equivalent to: RA (J2000): 21h 40m 1.43s Dec (J2000): -61d 27' 24.3" 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: 17602 SUBJECT: GRB 150318A : GROND upper limits DATE: 15/03/18 13:14:38 GMT FROM: Karla Varela at MPE P. Wiseman, K. Varela, M.Salvato and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 150318A (SWIFT-635289; Pagani et al., GCN#17599) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile). Observations started on March 18rd, 2015, at 08:27UT, 83 minutes after the GRB trigger. They were performed at an average seeing of 1.3" and at an average airmass of 2.0. We do not detect a source inside the 1.9 arcsec error circle reported by Evans et al. (GCN #17600). Based on a total exposure of 0.67 hours in g’r'i'z'and 0.73 hours in JHK, we measure the following preliminary upper limits (AB magnitudes system): g' > 24.9 mag, r' > 24.8 mag, i' > 24.2 mag, z' > 23.9 mag, J > 21.4 mag, H > 20.9 mag, and K > 18.9 mag. Given magnitudes are calibrated against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.03 mag in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17603 SUBJECT: GRB 150318A: Swift/UVOT Upper Limits DATE: 15/03/18 13:52:59 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and C. Pagani (U Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150318A 151 s after the BAT trigger (Pagani et al., GCN Circ. 17599). No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 17600) 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 151 300 147 >20.8 u_FC 308 558 246 >19.8 white 151 5695 530 >21.4 v 638 6106 432 >20.0 b 736 6762 252 >20.4 u 308 6721 659 >20.4 w1 687 6516 413 >20.2 m2 4676 6311 393 >20.1 w2 4266 5901 393 >20.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17604 SUBJECT: GRB 150318A: Swift-BAT refined analysis DATE: 15/03/18 15:48:56 GMT FROM: Hans Krimm at NASA-GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), C. Pagani (U. Leicester), 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 150318A (trigger #635289) (Pagani, et al., GCN Circ. 17599). The BAT ground-calculated position is RA, Dec = 324.990, -61.461 deg, which is RA(J2000) = 21h 39m 57.6s Dec(J2000) = -61d 27' 41.3" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 44%. The mask-weighted light curve shows two very broad peaks. The first one runs from about T-10 sec to T+50 sec, and the second, brighter peak starts at T+50 sec, peaks at ~T+65 sec and decays to background by T+120 sec. T90 (15-350 keV) is 83.88 +- 12.57 sec (estimated error including systematics). The time-averaged spectrum from T-6.60 to T+98.58 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.00 +- 0.12. The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+66.62 sec in the 15-150 keV band is 1.1 +- 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/635289/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17605 SUBJECT: GRB 150318A: Skynet PROMPT-CTIO Observations DATE: 15/03/18 18:23:19 GMT FROM: Adam S. Trotter at UNC-Chapel Hill/PROMPT/Skynet A. Trotter, D. Reichart, J. Haislip, A. Aji, R. Beauchemin, T. Berger, A. Dow, A. Foster, N. Frank, M. Hinckle, K. Ivarsen, A. LaCluyze, M. Maples, J. Moore, M. Nysewander, C. Salemi, L. Zbinden, and J. A. Crain report: Skynet observed the Swift BAT/XRT localization of GRB 150318A (Pagani et al., GCN 17599, Swift trigger=635289) with with one 24" telescope (PROMPT 8; I band) and four 16" telescopes (PROMPT 1,3,4,5; V,B,R,I bands) of the PROMPT array at CTIO, Chile. Starting at 2015-03-18 06:06:54 UT and continuing until 09:52 UT (t=2m-2.8h post-trigger), Skynet took a total of 376 exposures ranging from 10-160s. We stacked subsets of these images to maximize the S/N ratio, and detected no optical source in any band at the XRT position. Our 3-sigma limiting magnitudes are: ============================================== tmid scope band exposures lim mag ---------------------------------------------- 104m PROMPT8 I 69 x 80s >20.9 104m PROMPT5 I 43 x 160s >20.9 78m PROMPT4 R 37 x 80s >20.9 104m PROMPT1 V 42 x 160s >21.6 125m PROMPT3 B 18 x 160s >21.1 Limiting magnitudes are in the Vega System, calibrated to 3 APASS stars in the field. Magnitudes have not been corrected for line-of-sight Milky Way dust extinction, with expected E(B-V)=0.03 (Schlafly & Finkbeiner 2011). No further Skynet observations are scheduled. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17608 SUBJECT: GRB 150318A: Swift-XRT refined Analysis DATE: 15/03/18 22:20:04 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), A. Amaral-Rogers (U. Leicester), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester) and C. Pagani report on behalf of the Swift-XRT team: We have analysed 6.3 ks of XRT data for GRB 150318A (Pagani et al. GCN Circ. 17599), from 130 s to 40.1 ks after the BAT trigger. The data comprise 191 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 Evans et al. (GCN Circ. 17600). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=3.25 (+0.23, -0.29). At T+187 s the decay steepens to an alpha of 5.30 (+/-0.18) before breaking again at T+628 s to a final decay with index alpha=0.94 (+0.19, -0.21). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.46 (+/-0.06). The best-fitting absorption column is 3.17 (+0.22, -0.21) x 10^21 cm^-2, in excess of the Galactic value of 3.3 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 2.9 x 10^-11 (5.8 x 10^-11) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 3.17 (+0.22, -0.21) x 10^21 cm^-2 Galactic foreground: 3.3 x 10^20 cm^-2 Excess significance: 21.9 sigma Photon index: 2.46 (+/-0.06) If the light curve continues to decay with a power-law decay index of 0.94, the count rate at T+24 hours will be 1.5 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.4 x 10^-14 (8.7 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/00635289. This circular is an official product of the Swift-XRT team.