TITLE: GCN CIRCULAR NUMBER: 32893 SUBJECT: GRB 221028A, Swift-BAT refined analysis DATE: 22/10/30 16:04:53 GMT FROM: Amy Lien at GSFC amy.y.lien@nasa.gov
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), 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 221028A (trigger #1131910) (Lien et al., GCN Circ. 32874). The BAT ground-calculated position is RA, Dec = 314.198, 41.082 deg which is RA(J2000) = 20h 56m 47.5s Dec(J2000) = +41d 04' 56.0" with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 53%.
The mask-weighted light curve shows a short pulse that starts and peaks at ~T0 and ends at ~T+2, followed by several overlapping pulses that lasts till ~T+84 s. The structure resembles those of short GRBs with extended emission. T90 (15-350 keV) is 57.1 +- 15.0 sec (estimated error including systematics).
Due to current detector issues, data below ~50 keV are inaccurate. Thus, only data above 50 keV are used for spectral analysis. The time-averaged spectrum from T-0.1 to T+84.0 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.367 +- 0.325. The fluence in the 15-150 keV band is 1.51 +- 0.14 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.56 sec in the 15-150 keV band is 0.8 +- 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/1131910/BA/