TITLE: GCN CIRCULAR NUMBER: 31968 SUBJECT: GRB 220427A: Swift-BAT refined analysis DATE: 22/04/29 13:45:22 GMT FROM: Amy Lien at GSFC M. Stamatikos (OSU) S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC), T. Sakamoto (AGU) (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 220427A (trigger #1104343) (D'Ai et al., GCN Circ. 31960). The BAT ground-calculated position is RA, Dec = 275.922, -56.257 deg which is RA(J2000) = 18h 23m 41.2s Dec(J2000) = -56d 15' 23.7" with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 62%. The mask-weighted light curve shows a single-peaked structure that starts at ~T+3 s and peaks at ~T+8 s, and followed by a long tail emission that ends at ~T+70 s. T90 (15-350 keV) is 57.2 +- 12.2 sec (estimated error including systematics). The time-averaged spectrum from T+3.09 to T+68.06 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.23 +- 0.13. The fluence in the 15-150 keV band is 2.1 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+7.83 sec in the 15-150 keV band is 3.0 +- 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/1104343/BA/