TITLE:   GCN CIRCULAR
NUMBER:  22241
SUBJECT: GRB 171211A: Swift-BAT refined analysis
DATE:    17/12/11 23:19:15 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

H. A. Krimm (NSF/USRA), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), J. D. Gropp (PSU),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
J. P. Norris (BSU), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU),
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 171211A (trigger #796469)
(Gropp et al., GCN Circ. 22234).  The BAT ground-calculated position is
RA, Dec = 98.154, -58.689 deg which is
  RA(J2000)  =  06h 32m 36.9s
  Dec(J2000) = -58d 41' 19.0"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 57%.

The mask-weighted light curve shows a single-peaked structure that starts and
peaks at ~ T0, and ends at ~T+3 s. T90 (15-350 keV) is 2.32 +- 0.59 sec
(estimated error including systematics).

The time-averaged spectrum from T+0.03 to T+2.70 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.77 +- 0.21.  The fluence in the 15-150 keV band is 2.4 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.03 sec in the 15-150 keV band
is 2.3 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The duration and hardness of this burst show it to be intermediate between the
short and long burst populations.

Using a 64-ms binned light curve, the lag analysis finds a lag of
0.144 (+0.106, -0.066) s for the 50-100 keV to 15-25 keV band.
Despite the large error bars due to the weakness of this burst,
this value is more consistent with those of a long GRB.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/796469/BA/