TITLE: GCN CIRCULAR NUMBER: 6158 SUBJECT: GRB 070227, Swift-BAT refined analysis DATE: 07/02/28 21:20:42 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift 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), C. Pagani (PSU), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-2.0 to T+8.1 sec, we report further analysis of BAT GRB 070227 (trigger #262347) (Pagani, et al., GCN Circ. 6156). The BAT ground-calculated position is RA, Dec = 120.566, -46.305 (J2000) RA: +08h 02m 16s Dec: -46d 18' 17" with an uncertainty of 2.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 3%. Because this was a failed trigger on-board, this is all the detailed BAT data we are going to get on this burst. The burst had two weak overlapping peaks with spectral evolution. The larger peak was at T+1 and the smaller at T+6 sec. There is no additional strong emission at times later than T+8, but we cannot rule out weak emission. T90 (15-350 keV) is 7 +- 2 sec (estimated error including systematics). The time-averaged spectrum from T+0.0 to T+8.0 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.54 +- 0.27. The fluence in the 15-150 keV band is 1.6 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+0.00 sec in the 15-150 keV band is 2.7 +- 0.4 ph/cm2/sec. The quoted errors are at the 90% confidence level considering the statistical and usual systematic effects. However, because of the extreme partial coding of this burst, and particularly the reduced sensitivity to low energy photons at the edge of the FOV, we expect an extra systematic uncertainty contribution of about 10%.