TITLE: GCN CIRCULAR NUMBER: 32892 SUBJECT: GRB 221027B: Swift-BAT refined analysis DATE: 22/10/30 16:03:48 GMT FROM: Amy Lien at GSFC amy.y.lien@nasa.gov
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC), T. Sakamoto (AGU), M. Stamatikos (OSU) (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 221027B (trigger #1131397) (Lien et al., GCN Circ. 32867). The BAT ground-calculated position is RA, Dec = 225.601, 47.451 deg which is RA(J2000) = 15h 02m 24.2s Dec(J2000) = +47d 27' 04.4" with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 45%.
The mask-weighted light curve shows a structure with two pulses that start at ~T-6 s and end at ~T+4 s. The first weaker peak occurs at ~T-5 s, followed by the main peak that occurs at ~T0. T90 (15-350 keV) is 8.66 +- 1.10 sec (estimated error including systematics).
The time-averaged spectrum from T-5.98 to T+4.20 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.39 +- 0.19. The fluence in the 15-150 keV band is 5.8 +- 0.6 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.08 sec in the 15-150 keV band is 3.4 +- 0.4 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/1131397/BA/