TITLE: GCN CIRCULAR NUMBER: 6691 SUBJECT: GRB 070731, Swift-BAT refined analysis DATE: 07/07/31 14:00:59 GMT FROM: Scott Barthelmy at NASA/GSFC J. Tueller (GSFC), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), P. Romano (INAF/OAB), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+302 sec from the recent telemetry downlink, we report analysis of BAT GRB 070731 (trigger #286574). The spacecraft did not slew to the location because of a Moon constraint. It will come out of Moon constraint 02 Aug 07 UT. The BAT ground-calculated position is RA, Dec = 328.581, -15.740 deg which is RA(J2000) = 21h 54m 19.5s Dec(J2000) = -15d 44' 23" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 49%. The mask-weighted lightcurve shows a single peak starting at ~T-0.5 sec, peaking at ~T+0.7, and ending at ~T+3 sec. There is no indication of any other emission prior and past the trigger. We note that there is a gap in the currently downloaded data set from T+120 to T+190 sec. T90 (15-350 keV) is 2.9 +- 0.2 sec (estimated error including systematics). The time-averaged spectrum from T-0.1 to T+3.0 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.65 +- 0.23. The fluence in the 15-150 keV band is 1.6 +- 0.3 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.14 sec in the 15-150 keV band is 1.2 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. This burst occurred during a 42-min outage in the TDRSS service and so all the normal real-time messages were not sent to the ground.