TITLE:   GCN CIRCULAR
NUMBER:  20337
SUBJECT: GRB 161224A: Swift-BAT refined analysis
DATE:    16/12/25 18:23:24 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), 
A. Cholden-Brown (PSU), J. R. Cummings (CPI),
N. Gehrels (GSFC), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 161224A (trigger #728268)
(Cholden-Brown et al., GCN Circ. 20335).  The BAT ground-calculated position is
RA, Dec = 204.820, -18.028 deg which is 
   RA(J2000)  =  13h 39m 16.9s 
   Dec(J2000) = -18d 01' 41.7" 
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 48%.
 
The mask-weighted light curve shows a single pulse structure that starts at 
~ T+12 s, peaks at ~T+33 s, and ends at ~T+65 s. T90 (15-350 keV) is 
47.04 +- 12.12 sec (estimated error including systematics).
 
The time-averaged spectrum from T+12.46 to T+65.18 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index -0.21 +- 1.56, 
and Epeak of 34.5 +- 5.6 keV (chi squared 44.84 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is (8.2 +- 1.3) x 10^-7 erg/cm2
and the 1-sec peak flux measured from T+32.88 sec in the 15-150 keV band is
0.8 +- 0.3 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.21 +- 0.21 (chi squared 57.66 for 57 d.o.f.).  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/728268/BA/