TITLE: GCN CIRCULAR NUMBER: 29761 SUBJECT: GRB 210402A: Swift-BAT refined analysis DATE: 21/04/04 20:51:19 GMT FROM: Amy Lien at GSFC S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), K. L. Page (U Leicester), 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-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210402A (trigger #1040123) (Page et al., GCN Circ. 29743). The BAT ground-calculated position is RA, Dec = 198.265, 44.510 deg which is RA(J2000) = 13h 13m 03.7s Dec(J2000) = +44d 30' 36.1" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 69%. The mask-weighted light curve shows a multi-peaked structure that starts at ~T-50 s and ends at ~T+310 s. The main peak occurs at ~T+174 s. T90 (15-350 keV) is 238.7 +- 18.8 sec (estimated error including systematics). The time-averaged spectrum from T-51.60 to T+310.20 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.49 +- 0.27, and Epeak of 63.6 +- 22.9 keV (chi squared 58.82 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 8.6 +- 0.4 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+173.53 sec in the 15-150 keV band is 1.6 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.87 +- 0.06 (chi squared 65.10 for 57 d.o.f.). 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/1040123/BA/ [GCN OPS NOTE(04apr21): The word "DRAFT:" was removed fron the SUBJECT line. The body of the Circular does contain the author's final text.]