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GCN Circular 22380

Subject
GRB 180204A: Swift-BAT refined analysis
Date
2018-02-04T22:02:03Z (6 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
J. R. Cummings (CPI), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), J. P. Norris (BSU),
K. L. Page (U Leicester), 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-186 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180204A (trigger #808483)
(Page et al., GCN Circ. 22375).  The BAT ground-calculated position is
RA, Dec = 330.123, 30.852 deg which is
  RA(J2000)  =  22h 00m 29.5s
  Dec(J2000) = +30d 51' 07.5"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 70%.

The mask-weighted light curve shows two distict pulses. The first
pulse starts and peaks at ~T0, and ends at ~T+0.2. The second pulse
starts at ~T+0.6 s, peaks at ~T+1 s, and ends at ~T+1.3 s.
T90 (15-350 keV) is 1.16 +- 0.12 sec (estimated error including systematics).

For the first pulse, the lag analysis finds a lag of -0.2 +- 1 ms for the
100-350 keV to 25-100 keV, and 0.2 +- 1.5 ms for the 50-100 keV to 15-25 keV
band. The second pulse has a lag of 5.6 +- 3.9 ms for the 100-350 keV to
25-100 keV, and 3.2 +- 6.6 ms for the 50-100 keV to 15-25 keV band.
These values are consistent with those of a short GRB.

The time-averaged spectrum from T-0.05 to T+1.29 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.09 +- 0.10.  The fluence in the 15-150 keV band is 4.8 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.05 sec in the 15-150 keV band
is 3.6 +- 0.3 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/808483/BA/
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