TITLE: GCN CIRCULAR NUMBER: 9204 SUBJECT: GRB 090423: Swift-BAT refined analysis DATE: 09/04/23 12:45:50 GMT FROM: Scott Barthelmy at NASA/GSFC D. M. Palmer (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (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 090423 (trigger #350184) (Krimm, et al., GCN Circ. 9198). The BAT ground-calculated position is RA, Dec = 148.891, 18.165 deg, which is RA(J2000) = 09h 55m 33.8s Dec(J2000) = +18d 09' 55.7" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 92%. The mask-weighted light curve shows a couple overlapping peaks starting at ~T-2 sec, peaking at T+4 sec, and ending at ~T+15 sec. T90 (15-350 keV) is 10.3 +- 1.1 sec (estimated error including systematics). The time-averaged spectrum from T-0.7 to T+11.7 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.80 +- 0.50, and Epeak of 48.6 +- 6.2 keV (chi squared 41.4 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 5.9 +- 0.4 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T+3.50 sec in the 15-150 keV band is 1.7 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.90 +- 0.10 (chi squared 59.9 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/350184/BA/