TITLE: GCN CIRCULAR NUMBER: 9337 SUBJECT: GRB 090510: Swift-BAT refined analysis DATE: 09/05/10 06:08:40 GMT FROM: Scott Barthelmy at NASA/GSFC T. N. Ukwatta (GWU) S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), E. A. Hoversten (PSU), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) (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 090510 (trigger #351588) (Hoversten, et al., GCN Circ. 9331). The BAT ground-calculated position is RA, Dec = 333.552, -26.598 deg, which is RA(J2000) = 22h 14m 12.6s Dec(J2000) = -26d 35' 51.1" with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 16%. The mask-weighted light curve shows a small precursor peak at ~T-0.54 sec (width ~ 30 msec). Then the main peak starts at ~T-0.05 sec, peaks at T+0.04 sec with a width of ~50 msec. Then come two smaller peaks at T+0.24 and T+0.32 sec, each about 40 msec in width. At the 3-sigma level, there is the possibility of low-level emission between T+110 sec to ~T+170 sec. T90 (15-350 keV) is 0.3 +- 0.1 sec (estimated error including systematics). The time-averaged spectrum from T+0.0 to T+0.4 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 0.98 +- 0.20. The fluence in the 15-150 keV band is 3.4 +- 0.4 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.30 sec in the 15-150 keV band is 9.7 +- 1.1 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/351588/BA/