[AAVSO-HEN] GRB 090618, Swift-BAT refined spectral analysis

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
For an archive and more information on circulars visit:
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TITLE:   GCN CIRCULAR
NUMBER:  9534
SUBJECT: GRB 090618, Swift-BAT refined spectral analysis
DATE:    09/06/19 18:13:00 GMT
FROM:    Tilan Ukwatta at GSFC/GWU  <tilan.ukwatta at gmail.com>

T. Sakamoto (GSFC/UMBC), T. N. Ukwatta (GWU/GSFC),
S. D. Barthelmy (GSFC), (i.e. the Swift-BAT team):

Using the data set from T-373 to T+962 sec from the
recent telemetry downlink, we report further spectral
analysis of BAT GRB 090618 (trigger #355083)
(Schady, et al., GCN Circ. 9512).

The time-averaged spectrum from T-4.4 to T+213.6 sec
is best fit by a power law with an exponential cutoff.
This fit gives a photon index 1.42 +/- 0.08,
and Epeak of 134 +/- 19 keV (chi squared 14.6
for 56 d.o.f.).  For this model the total fluence in
the 15-150 keV band is 1.05 +/- 0.01 x 10^-04 erg/cm2
and the 1-sec peak flux measured from T+65.38 sec in
the 15-150 keV band is 38.8 +/- 0.8 ph/cm2/sec.
A fit to a simple power law gives a photon index
of 1.72 +/- 0.02 (chi squared 55.8 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/355083/BA/