[vsnet-grb-info 3070] GRB 060322: Refined analysis of the Swift-BAT burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4907
SUBJECT: GRB 060322:  Refined analysis of the Swift-BAT burst
DATE:    06/03/23 20:33:57 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

D. Palmer (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), 
A. Parsons (GSFC), M. Perri (ASDC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:

Using the data set from T-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 060322 (trigger #202442)
(Perri, et al., GCN 4903).  The BAT ground-calculated position is
RA,Dec = 274.235,-36.721 deg {18h 16m 56.4s, -36d 43' 14.7"} (J2000)
+- 1.0 arcmin, (radius, sys+stat, 90% containment).  The partial coding was 80%.
 
The mask-weighted lightcurve shows two well separated episodes of emission.
The first episode starts at T-22 sec and ends at T+40 sec with six main peaks
within that interval.  Then the emission drops below the BAT sensitivity
until the second episode.  The second episode starts at T+155 sec and
ends at T+204 sec with six main peaks within that second interval.
There is no further emission out to T+670 sec.  T90 (15-350 keV) is
213 +- 5 sec (estimated error including systematics).
 
The time-averaged spectrum from T-21.7 to T+232.3 is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.04 +- 0.32, 
and Epeak of 94.4 +- 44.7 keV (chi squared 57.29 for 56 d.o.f.).  
For this model the total fluence in the 15-150 keV band is
5.1 +- 0.2 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+182.19 sec
in the 15-150 keV band is 2.1 +- 0.2 ph/cm2/sec.  A fit to a simple
power law gives a photon index of 1.58 +- 0.07 (chi squared 65.5
for 57 d.o.f.).  All the quoted errors are at the 90% confidence level.

Additionally, separate spectral analyses of the two episodes
in the light curve show that the second episode is spectrally softer
than the first.  The best fit to the first episode is a simple power law
with a photon index of 1.36 +- 0.09 (chi squared 30.3 for 56 d.o.f.).
The second episode is best fit by a power law with an exponential
cutoff.  This fit gives a photon index alpha = 0.89 +-0.31 and Epeak 
of 72.8 +- 12.6 keV (chi squared 51.6 for 55 d.o.f.).  Fitting a
simple power law to the second episode yields a power-law index
of 1.69 +- 0.07 (chi squared 70.5 for 56 d.o.f.)  All the quoted errors
are at the 90% confidence level.