TITLE: GCN CIRCULAR NUMBER: 7727 SUBJECT: Swift-BAT refined analysis for Trigger 311603: Galactic source DATE: 08/05/15 14:08:55 GMT FROM: Scott Barthelmy at NASA/GSFC W. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+489 sec from recent telemetry downlinks, we report further analysis of BAT trigger #311603 (Krimm, et al., GCN Circ. 7713). The BAT ground-calculated position is RA, Dec = 263.868, -35.675 deg, which is RA(J2000) = 17h 35m 28.4s Dec(J2000) = -35d 40' 29.0" with an uncertainty of 3.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 45%. The mask-weighted light curve shows the event starting at ~T-90 sec, slowly rising to a peak at ~T+25 sec, and returning to background around T+60 sec. The apparent peak at T+90 sec is due to the slewing and is not thought to be real. The lightcurve rises again starting at ~T+120 sec, but this is though to be due entering the SAA. All of this activity is solely in the 15-25 keV band. T90 (15-350 keV) is 120 +- 40 sec (estimated error including systematics). The time-averaged spectrum from T-100 to T+90 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 5.8 - 0.6,+1.3. The fluence in the 15-150 keV band is 6.3 +- 1.2 x 10^-7 erg/cm2. All the quoted errors are at the 90% confidence level. Given the very soft spectrum and galactic coordinates of 353.18,-1.70 (l,b), it very likely that this is a galactic transient. There will be an ATEL issued on this event.