//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22573 SUBJECT: GRB 180331B: Swift detection of a burst DATE: 18/03/31 15:58:51 GMT FROM: Scott Barthelmy at NASA/GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), A. Deich (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU), K. L. Page (U Leicester) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 15:38:39 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180331B (trigger=820513). Swift executed a delayed slewed due to an observing constraint. The BAT on-board calculated location is RA, Dec 196.820, +61.725, which is RA(J2000) = 13h 07m 17s Dec(J2000) = +61d 43' 30" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 8 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 15:49:43.0 UT, 663.7 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 196.7829, 61.7271 which is equivalent to: RA(J2000) = 13h 07m 07.91s Dec(J2000) = +61d 43' 37.5" with an uncertainty of 2.4 arcseconds (radius, 90% containment). This location is 63 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. We cannot determine whether the source is fading at the present time. No spectrum from the promptly downlinked event data is yet available to determine the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 667 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 0.01. Burst Advocate for this burst is A. Y. Lien (amy.y.lien 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: 22575 SUBJECT: GRB 180331B: Enhanced Swift-XRT position DATE: 18/03/31 19:14:44 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 1501 s of XRT Photon Counting mode data and 2 UVOT images for GRB 180331B, 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 = 196.78337, +61.72625 which is equivalent to: RA (J2000): 13h 07m 8.01s Dec (J2000): +61d 43' 34.5" 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: 22576 SUBJECT: GRB 180331B: Swift-BAT refined analysis DATE: 18/03/31 23:43:44 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), T. Sakamoto (AGU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 180331B (trigger #820513) (Lien et al., GCN Circ. 22573). The BAT ground-calculated position is RA, Dec = 196.781, 61.735 deg which is RA(J2000) = 13h 07m 07.6s Dec(J2000) = +61d 44' 05.9" with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 30%. The mask-weighted light curve shows a double-peaked structure that starts at ~T-20 s and ends at ~T+140 s. The two peaks occur at ~T-20 s and ~T+1 s, respectively. T90 (15-350 keV) is 147.0 +- 33.1 sec (estimated error including systematics). The time-averaged spectrum from T-22.03 to T+142.97 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.48 +- 0.22. The fluence in the 15-150 keV band is 1.9 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.97 sec in the 15-150 keV band is 2.8 +- 0.3 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/820513/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22577 SUBJECT: GRB 180331B: AbAO optical observations DATE: 18/04/01 03:30:42 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Volnova (IKI), A. Pozanenko (IKI), E. Mazaeva (IKI), R. Inasaridze (AbAO), V. Ayvazian (AbAO), O. Kvaratskhelia (AbAO), G. Kapanadze (AbAO), I. Molotov (KIAM), report on behalf of larger GRB follow-up collaboration: We observed the field of GRB 180331B (Lien et al., GCN 22573) with AS-32 (0.7m) telescope of Abastumani Observatory starting on Mar. 31 (UT) 17:49:41. We do not detect any object within enhanced XRT position (Goad et al., GCN 22575). Preliminary photometry of the field is following. Date UT start t-T0 Filter Exp. OT Err. UL (mid, days) (s) 2018-03-31 17:49:41 0.11370 CR 38*60 n/d n/d 22.3 The photometry is based on nearby USNO-B1.0 stars (R2 magnitude). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22578 SUBJECT: GRB 180331B: Swift-XRT refined Analysis DATE: 18/04/01 04:53:44 GMT FROM: Phil Evans at U of Leicester P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA) and report on behalf of the Swift-XRT team: report on behalf of the Swift-XRT team: We have analysed 6.6 ks of XRT data for GRB 180331B, from 671 s to 25.2 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=0.30 (+/-0.04). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+0.13, -0.12). The best-fitting absorption column is 8.7 (+3.5, -3.2) 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 3.7 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.7 (+3.5, -3.2) x 10^20 cm^-2 Galactic foreground: 1.6 x 10^20 cm^-2 Excess significance: 3.7 sigma Photon index: 1.80 (+0.13, -0.12) If the light curve continues to decay with a power-law decay index of 0.30, the count rate at T+24 hours will be 0.082 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x 10^-12 (3.5 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00820513. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22579 SUBJECT: GRB 180331B: Swift/UVOT Upper Limits DATE: 18/04/01 09:38:55 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180331B 668 s after the BAT trigger (Lien et al., GCN Circ. 22573). No optical afterglow consistent with the XRT position Goad er al., (GCN Circ. 22575) is detected in the initial UVOT exposures, consistent with the report of Volnova et al. (GCN Circ. 22577). 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 668 818 147 >21.2 white 668 2066 412 >21.8 v 1056 2115 136 >19.2 b 1156 2041 117 >20.3 u 1130 2016 117 >20.3 w1 849 1992 78 >20.2 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).