//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23383 SUBJECT: GRB 181027A: Swift detection of a burst DATE: 18/10/27 01:57:37 GMT FROM: David Palmer at LANL A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester), D. M. Palmer (LANL) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:48:59 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 181027A (trigger=868984). Swift could not slew to the burst due to an observing constraint. The BAT on-board calculated location is RA, Dec 225.383, +30.891 which is RA(J2000) = 15h 01m 32s Dec(J2000) = +30d 53' 28" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 80 sec. The peak count rate was ~1200 counts/sec (15-350 keV), at ~49 sec after the trigger. Due to a Sun observing constraint, Swift cannot slew to the BAT position until 03:50 UT on 2018 November 06. There will thus be no XRT or UVOT data for this trigger before this time. 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: 23384 SUBJECT: GRB 181027A: Swift-BAT refined analysis DATE: 18/10/27 13:06:40 GMT FROM: Takanori Sakamoto at AGU 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), M. Stamatikos (OSU), 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 181027A (trigger #868984) (Lien, et al., GCN Circ. 23383). The BAT ground-calculated position is RA, Dec = 225.361, 30.937 deg which is RA(J2000) = 15h 01m 26.7s Dec(J2000) = +30d 56' 12.6" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%. The mask-weighted light curve shows a weak emission followed by a bright peak. The emission starts at T-18.4 sec, peaks at T+47.5 sec and ends at T+85.4 sec. T90 (15-350 keV) is 81.16 +- 10.55 sec (estimated error including systematics). The time-averaged spectrum from T-18.45 to T+85.44 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.42 +- 0.09. The fluence in the 15-150 keV band is 2.8 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+47.81 sec in the 15-150 keV band is 1.2 +- 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/868984/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23385 SUBJECT: GRB 181027A: Fermi GBM detection DATE: 18/10/27 19:12:34 GMT FROM: Peter Veres at UAH P. Veres (UAH) and E. Bissaldi (Politecnico & INFN Bari) report on behalf of the Fermi GBM Team: "At 01:49:47.31 UT on 27 October 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 181027A (trigger 56229779 / 181027076), which was also detected by the Swift/BAT (Lien et al. 2018, GCN 23383). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 61 degrees. The GBM light curve consists of two pulses with a duration (T90) of about 90 s (50-300 keV). The time-averaged spectrum from T0-84.5 s to T0+44.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.10 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 183 +/- 27 keV. The event fluence (10-1000 keV) in this time interval is (7.76 +/- 0.57)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.64 s in the 10-1000 keV band is 2.48 +/- 0.22 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."