TITLE: GCN CIRCULAR NUMBER: 29879 SUBJECT: GRB 210420B: Swift-BAT refined analysis DATE: 21/04/22 02:14:37 GMT FROM: Sibasish Laha at GSFC M. Stamatikos (OSU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), 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+767 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210420B (trigger #1044382) (Moss et al., GCN Circ. 29844). The BAT ground-calculated position is RA, Dec = 254.313, 42.558 deg which is RA(J2000) = 16h 57m 15.1s Dec(J2000) = +42d 33' 28.1" with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 77%. The BAT light curve showed a complex structure with a duration of about ~160 sec. T90 (15-350 keV) is 158.8 +- 29.5 sec (estimated error including systematics). The time-averaged spectrum from T-21.30 to T+160.09 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.49 +- 0.19. The fluence in the 15-150 keV band is 1.5 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+21.02 sec in the 15-150 keV band is 0.5 +- 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/1044382/BA/