TITLE: GCN CIRCULAR NUMBER: 22998 SUBJECT: GRB 180720B: Swift-BAT refined analysis DATE: 18/07/21 17:11:45 GMT FROM: Amy Lien at GSFC S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. H. Siegel (PSU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (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 180720B (trigger #848890) (Siegel et al., GCN Circ. 22973). The BAT ground-calculated position is RA, Dec = 0.528, -2.925 deg which is RA(J2000) = 00h 02m 06.8s Dec(J2000) = -02d 55' 31.3" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 8%. The mask-weighted light curve shows a multi-peaked structure, with the main peak occurs around ~T+11 s. The burst emission starts around ~T-20 s, although there might be additional emission before the GRB came into the BAT FOV at ~T-57 s. The burst lasts beyond the available event data range (until T+962 s). Analysis using the BAT survey data shows that the burst emission extends at least till ~ T+2000 s, when Swift went into SAA and no more data were collected. The burst came back into the BAT FOV at ~ T0+5626 s, and the burst was no longer detected (signal-to-noise ratio < 3 sigma). The time-averaged spectrum from T-20.0 to T+961.1 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.36 +- 0.03. The fluence in the 15-150 keV band is 8.6 +- 0.1 x 10^-05 erg/cm2. The 1-sec peak photon flux measured from T+10.94 sec in the 15-150 keV band is 67.9 +- 2.6 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/848890/BA/