[vsnet-grb-info 2332] GRB051022: Swift XRT measurement of jet break

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4169
SUBJECT: GRB051022: Swift XRT measurement of jet break
DATE:    05/10/27 17:10:41 GMT
FROM:    Judith Racusin at PSU  <racusin at astro.psu.edu>

J. Racusin, J. Kennea, D. Fox, D. Burrows, N. Cucchiara (PSU), P. Schady 
(MSSL), A. Wells (U. Leicester), N. Gehrels, T. Sakamoto (GSFC), C. 
Kouveliotou (MSFC), S. Patel (MSFC) on behalf of the Swift XRT team:

We have analyzed the observations of the X-ray afterglow (Racusin et al., 
GCN 4141, Butler et al, GCN4165) of GRB 051022 (Olive et al., GCN 4131) 
beginning approximately 3.5 hours after its discovery by HETE on October 
22 and continuing for 4.8 days.  We find the early decay slope of 1.33 +/- 
0.07 (Butler et al, GCN 4165) extends to 2.9 +/- 0.2 days after the burst, 
after which it steepens to a late time decay slope of 3.6 +/- 0.4. 
Further observations are planned.

Given the redshift of 0.8 (Gal-Yam et al., GCN 4156) and the different 
measured fluences and Epeak by Konus-Wind (Golenetskii et al., GCN 4150) 
and HETE (Doty et al, GCN 4145), assuming n=0.1 cm^-3 and our jet break 
time, we calculate the following Eiso, Egamma, and jet opening angles:

HETE:
alpha=-1.2, beta=-10.0, Epeak=306 keV, 2-400 keV fluence=1.6e-4 erg cm-2
Eiso = 3.8e53 erg
Jet opening angle = 4.3 degrees
Egamma = 1.1e51 erg

Konus-Wind:
alpha=-1.2, beta=-10.0, Epeak=510 keV, 20 keV-2 MeV fluence=2.6e-4 erg cm-2
Eiso = 3.1e53 erg
Jet opening angle = 4.4 degrees
Egamma = 9.1e50 erg