TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4993
SUBJECT: GRB 060421: Swift-BAT Refined Analysis
DATE:    06/04/21 15:34:38 GMT
FROM:    Louis M Barbier at NASA/GSFC/Swift  <lmb@cosmicra.gsfc.nasa.gov>

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

Using the data set from T-120 to T+78 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 060421
(trigger #206257)  (Goad, et al., GCN 4985).  The BAT ground-calculated position
is (RA,Dec) = 343.627, 62.730 deg {22h 54m 30.4s, 62d 43' 47.0"} (J2000)
+- 0.8 arcmin, (radius, sys+stat, 90% containment).  The partial coding was 82%.
 
The mask-weighted light curve shows one strong peak followed by 
several smaller peaks extending out to 10 seconds after the trigger.
T90 (15-350 keV) is 11 +- 1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-3.8 to T+10.9 is well fit by 
a simple power-law model. The power law index of the time-averaged 
spectrum is 1.53 +- 0.07. The fluence in the 15-150 keV band is 
1.2 +- 0.1 x 10^-06 erg/cm2.  The 1-sec peak photon flux measured from 
T+2.28 sec in the 15-150 keV band is 3.0 +- 0.2 ph/cm2/sec.  All the quoted 
errors are at the 90% confidence level.

Based on the shape of the light curve and the hard spectrum, we believe that this
is a GRB, however, we can not rule out a hard x-tray transient nature
of this event.