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
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) 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
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.