GCN Circular 4538
Subject
GRB 060117: Refined analysis of the Swift-BAT burst
Event
Date
2006-01-17T19:16:15Z (20 years ago)
From
Hans Krimm at NASA-GSFC <krimm@milkyway.gsfc.nasa.gov>
J. Cummings (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC)
E. Fenimore (LANL), N. Gehrels (GSFC), K. Gendreau (GSFC),
D. Hullinger (GSFC/UMD), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), P. Meszaros (PSU), J. Norris (GSFC),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
Using the data set from T-60 to T+120 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 060117 (trigger
#177666) (Campana, et al., GCN 4533). The BAT ground-calculated
position is RA,Dec = 327.917, -59.967 {21h 51m 40s, -59d 58' 1"}
(J2000) +- 1.0 arcmin, (radius, sys+stat, 90% containment). This
position includes a small correction for small BAT image distortions.
We note that this error circle formally excludes the position of IRAS
21482-6015 (GCN 4533, GCN4534). We also note that fading afterglow
discovered by the FRAM telescope group (Jelinek et al, GCN 4536) is
0.8 arc min from the center of the BAT 90% error circle. The partial
coding was 25%.
The light curve has multiple peaks, with the main peaks spanning the
time range T-1 to T+17. T90 (15-350 keV) is (16 +- 1) sec (estimated
error including systematics). There does appear to be weak emission
extending out to T+100 seconds.
The best fit to the spectral data for the time averaged period from
T-1.98 to T+26.99 seconds is a power law with an exponential cutoff.
This fit gives a photon index 1.51 +- 0.13, and Epeak of 71 +- 5 keV
(chi squared 40 for 59 d.o.f). For this model the total fluence in the
15-150 keV band is (2.04 +- 0.04) x 10^-05 erg/cm2 and the 1-sec peak
flux measured from T+11.12 sec is 48.9 +- 1.6 ph/cm2/sec. A fit to a
simple power law gives a photon index of 1.93 +- 0.03 (chi square 68
for 59 d.o.f.) All the quoted errors are at the 90% confidence level.
Using the lag-luminosity method of Norris et al. (2000),
and a lag measurement of 25 ms +- 5 ms (1 sigma; 100-350 keV
to 25-50 keV bands), yields a pseudo-redshift of z ~ 1.3 +- 0.3
(includes spectral uncertainties).
The remainder of the expected event data for this burst (from T-300 to T-60
sec and from T+120 to T+300) has not yet been received on the ground. If
we see evidence for emission after T+120 sec in these data, we will
issue another circular.