GCN Circular 29266

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), 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 210104B (trigger #1015919)
(Laha et al., GCN Circ. 29243
Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 53.561, 37.951 deg which is
   RA(J2000)  =  03h 34m 14.7s
   Dec(J2000) = +37d 57' 05.1"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 59%.

The mask-weighted light curve shows a double peaks structure that starts
at ~T0 and ends at ~T+23 s. The two peaks occurs at ~T0 and ~T+11 s,
respectively. T90 (15-350 keV) is 19.94 +- 2.33 sec (estimated error
including systematics).

The time-averaged spectrum from T-0.15 to T+22.76 sec is best fit
by a simple power-law model.  The power law index of the time-averaged
spectrum is 1.83 +- 0.14.  The fluence in the 15-150 keV band is
1.2 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from
T+10.83 sec in the 15-150 keV band is 1.9 +- 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/1015919/BA/