TITLE:   GCN CIRCULAR
NUMBER:  31874
SUBJECT: GRB 220408A: Swift-BAT refined analysis
DATE:    22/04/11 12:34:25 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto@phys.aoyama.ac.jp>

D. M. Palmer (LANL), S. D. Barthelmy (GSFC), R. Caputo (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), T. Parsotan (GSFC/UMBC),
T. Sakamoto (AGU), M. Stamatikos (OSU)
(i.e. the Swift-BAT team):
  
Using the data set from T-119 to T+183 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 220408A (trigger #1101675)
(Caputo, et al., GCN Circ. 31848).  The BAT ground-calculated position is
RA, Dec = 202.399, 47.065 deg which is
    RA(J2000)  =  13h 29m 35.7s
    Dec(J2000) = +47d 03' 55.4"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 34%.
  
The mask-weighted light curve shows a multi-peaked structure that
starts at T-2 s and peaks at T+3 s.  There is a weak emission which
peaks at T+17 s.  T90 (15-350 keV) is 17.25 +- 1.10 sec
(estimated error including systematics).
  
The time-averaged spectrum from T-0.55 to T+18.26 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.19 +- 0.57,
and Epeak of 35.3 +- 8.8 keV (chi squared 62.40 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+2.48 sec in the 15-150 keV band is
4.9 +- 0.4 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.14 +- 0.13 (chi squared 72.77 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/1101675/BA/