GCN Circular 5064

G. Sato (ISAS), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/ORAU), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), M. Koss (UMD),
C. Markwardt (GSFC/UMD), J. Norris (GSFC), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), M. Stamatikos (GSFC/ORAU),
E. Troja (INAF-IASFPA), J. Tueller (GSFC)
on behalf of 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 060502B (trigger #208275)
(Troja, et al., GCN 5055
Not found
 
 
).  The BAT ground-calculated position is RA,Dec =
278.949, 52.642 deg {18h 35m 47.7s, 52d 38' 32.5"} (J2000) +- 1.8 arcmin,
(radius, sys+stat, 90% containment).  The partial coding was 92%.
 
The lightcurve consists of two spikes.  The main peak starts at ~T-0.060
and has a FWHM of ~40 msec.  Its rise is faster than the decay.
There is also a possible second peak (a precurrsor) starting at
T-0.3 sec with a FWHM of ~100 msec and a significance of only ~4 sigma.
T90 (15-350 keV) is 90 +- 20 msec (estimated error including systematics).

The lag analysis shows this burst to be cleanly in the short hard burst class
(Norris and Bonnell, 2006, ApJ, accepted; see, Figure 3).
Specifically, the measured lags for the main peak are:
   -4.0 ms +- 3.0 ms  (15-25 keV vs.  50-100 keV)
   -0.2 ms +- 2.8 ms  (25-50 keV vs. 100-350 keV)
 
The time-averaged spectrum from T-0.05 to T+0.04 is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.92 +- 0.23.  The fluence in the 15-150 keV band is
4 +- 0.5 x 10^-8 erg/cm2.  The 1-sec peak photon flux measured
from T-0.43 sec in the 15-150 keV band is 4.4 +- 0.6 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.