TITLE: GCN CIRCULAR NUMBER: 10511 SUBJECT: GRB 100316D: Swift-BAT refined analysis DATE: 10/03/16 23:16:32 GMT FROM: Scott Barthelmy at NASA/GSFC T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), 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 telemetry downlinks, we report further analysis of BAT GRB 100316D (trigger #416135) (Stamatikos, et al., GCN Circ. 10496). The BAT ground-calculated position is RA, Dec = 107.599, -56.275 deg, which is RA(J2000) = 07h 10m 23.8s Dec(J2000) = -56d 16' 28.9" with an uncertainty of 3.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 85%. The mask-weighted light curve is relatively flat. The emission started before T-80 sec when the location came into the BAT FoV during a Swift planned-target slew. Using the event-by-event data, the lightcurve conitinue through the 64-sec integration of the image trigger and out to at least T+240 sec. Using the on-board mask-weighted lightcurve, the lightcurve continues out to at least T+740 sec where the data ends. The time-averaged spectrum using just the T+0.0 to T+64.0 sec image-trigger interval is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.29 +- 0.41. The fluence in the 15-150 keV band is 3.0 +- 0.8 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.00 sec in the 15-150 keV band is 0.1 +- 0.0 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/416135/BA/ We note that this lightcurve is very non-typical for a GRB and that the spectrum is soft. This is similar both in the temporal and spectral properties to the GRB060218-SN2006aj burst (Camapana, et al.; Nature, v224, p1008, Figure 1). In the 060218 burst, the BAT lightcurve was flat from T-50 to T+300 sec. The X-ray temporal decay (Starling, GCN Circ 10505) is shallow as it was in SN2006aj (Campana, Fig 1). We further note that the 5 arcsec XRT error circle (GCN 10496) covers the edge of an extended object (a pair of unresolved stars or a galaxy) in DSS.