TITLE: GCN CIRCULAR NUMBER: 17329 SUBJECT: GRB 150120A: Swift-BAT refined analysis DATE: 15/01/20 22:50:07 GMT FROM: Amy Lien at GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), V. D'Elia (ASDC), N. Gehrels (GSFC), J. Norris (BSU), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (LANL) (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 150120A (trigger #627137) (D'Elia, et al., GCN Circ. 17310). The BAT ground-calculated position is RA, Dec = 10.330, 33.980 deg which is RA(J2000) = 00h 41m 19.1s Dec(J2000) = +33d 58' 48.6" with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 71%. The mask-weighted light curve shows a single short spike that starts at ~ T-0.4 s, peaks at ~ T+0.4 s, and ends at ~ T+1.0 s. T90 (15-350 keV) is 1.20 +- 0.16 sec (estimated error including systematics). The time-averaged spectrum from T-0.40 to T+0.95 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.81 +- 0.18. The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.06 sec in the 15-150 keV band is 1.8 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The burst spectrum appears to be at the softer end of short bursts, which have an average spectral index of 1.2 when fitting with a simple power-law model (Sakamoto et al. 2011). However, the fast fading shown in the X-ray light curve (http://www.swift.ac.uk/xrt_curves/00627137/) suggests that this is indeed a short burst. The lag analysis of this burst does not show a constraining result due to the low intensity. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/627137/BA/