[vsnet-grb-info 21105] GRB 180904A: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23203
SUBJECT: GRB 180904A: Swift-BAT refined analysis
DATE:    18/09/05 15:28:50 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien at nasa.gov>

D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), A. D'Ai (INAF-IASFPA),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180904A (trigger #859282)
(D'Ai et al., GCN Circ. 23194).  The BAT ground-calculated position is
RA, Dec = 274.260, 46.640 deg which is
  RA(J2000)  =  18h 17m 02.4s
  Dec(J2000) = +46d 38' 23.3"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 56%.

The mask-weighted light curve shows a weak structure that starts at ~T0
and ends at ~T+6 s. T90 (15-350 keV) is 5.40 +- 0.89 sec (estimated error
including systematics).

The time-averaged spectrum from T+0.28 to T+6.18 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.02 +- 0.30.  The fluence in the 15-150 keV band is 2.4 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+5.14 sec in the 15-150 keV band
is 0.5 +- 0.2 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/859282/BA/