GCN Circular 3395

E. Rol, K. Page (Univ. of Leicester) D. N. Burrows (Penn State), N.
Gehrels (GSFC), M. Goad, C. Hurkett (Univ. of Leicester), J. Kennea (Penn 
State), P
O'Brien (Univ. of Leicester) report on behalf of the Swift XRT team:

We have analyzed the Swift XRT data from the short/hard burst 050509B
(Hurkett et al. 2005, GCN 3381
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 ) using 3 orbits with a total exposure
time of 6648 seconds in Photon Counting (PC) mode, starting 62 seconds
after the trigger. The refined coordinates of the X-ray
afterglow are:

    RA(J2000)  =  12:36:13.9
    Dec        = +28:59:01

with an estimated error of 8 arcseconds (90% containment).  Note that we 
have increased the estimate of the error circle radius to account for 
systematic variations in the centroid position for this source, which has 
very few counts.

The source is detected in the first 400 seconds of PC mode at a count rate 
of 0.03 counts/sec, after which it disappears below background level, and 
is not seen in the data from later orbits, with an estimated decay slope 
steeper than -1.

Assuming a Crab-like spectrum, we estimate an average flux level of 1e-12 
erg/cm^2/s (0.3 - 10 keV), between 62 and 262 seconds after the burst 
trigger. This is the faintest X-ray afterglow yet detected by Swift/XRT at 
such an early time.