GCN Circular 3222

O. Godet, K. L. Page, M. R. Goad, J. P. Osborne (U. Leicester), M. Capalbi, 
P. Giommi (ASDC), D. Grupe, D. N. Burrows (PSU), S. Campana, G. Chincarini 
(INAF-OAB), V. La Parola, T. Mineo (INAF-IASF/Palermo), S. Barthelmy, L. 
Angelini, N. Gehrels (GSFC), and P. Meszaros (PSU) report on behalf of the 
Swift XRT team:

The Swift XRT instrument observed GRB 050408 as a Target of Opportunity for 
20 ks (exposure time) on 8/9 April 2005, beginning 40 minutes after the 
HETE trigger and lasting for 60 ks of real time .  Analysis of the data 
shows evidence for a possible jet break at about 24 ks post-burst, with the 
following parameters:

initial slope: -0.71 +0.10/-0.12
Break time : 24 +25/-12 ks
later slope -1.43 +0.72/-0.40

Both single power-law and broken power-law fits to the lightcurve are 
statistically acceptable at this point.  Further observations planned for 
April 11 will give more information to help distinguish between the two and 
determine the jet break time.