TITLE: GCN CIRCULAR NUMBER: 29939 SUBJECT: GRB 210504A: Swift-BAT refined analysis DATE: 21/05/05 02:27:49 GMT FROM: Amy Lien at GSFC S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), J. R. Cummings (CPI), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), 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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210504A (trigger #1046782) (Beardmore et al., GCN Circ. 29929). The BAT ground-calculated position is RA, Dec = 222.379, -30.557 deg which is RA(J2000) = 14h 49m 31.0s Dec(J2000) = -30d 33' 23.5" with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 53%. The mask-weighted light curve shows several overlapping pulses that start at ~T-30 s and end at ~T+150 s. There might be additional burst emission before the GRB came into the BAT FOV at ~T-43 s. T90 (15-350 keV) is 135.06 +- 9.57 sec (estimated error including systematics). The time-averaged spectrum from T-27.55 to T+134.76 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.64 +- 0.13. The fluence in the 15-150 keV band is 2.7 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+87.68 sec in the 15-150 keV band is 0.9 +- 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/1046782/BA/