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GCN Circular 6789

GRB 070913: Swift-XRT detection of the possible X-ray afterglow
2007-09-14T15:05:49Z (17 years ago)
Andy Beardmore at U Leicester <>
A.P. Beardmore, K.L. Page (U. Leicester) and C. B. Markwardt 
(CRESST/GSFC/UMD) report on behalf of the Swift-XRT team.

The Swift-XRT began observing the field of the BAT GRB 070913 (trigger
#290843) at 2007-09-13T21:30, 75.2 ks after the BAT trigger (Markwardt
et al., GCN 6782). In 8 orbits of photon counting mode data totalling
7.8 ks we find a faint, uncatalogued source inside the refined
BAT error circle (Sato et al., GCN 6786) at RA, Dec (J2000)
228.75715, -24.29302, which is

RA(J2000)  =  15h 15m 01.7s
Dec(J2000) = -24d 17' 34.9"

with an uncertainty of 6.5 arcsec (radius, 90 percent confidence,
including boresight uncertainties). The source is 5.7 arcsec away
from the TAROT optical afterglow candidate reported by Klotz et al.
(GCN 6787). The source has an observed 0.3-10.0 keV count rate of 
(1.4+/-0.5)e-3 count/s.

We note the presence of a second faint X-ray source with a count rate of 
(1.3+/-0.5)e-3 count/s at RA, Dec (J2000) 228.70481, -24.21053, i.e.

RA(J2000)  =  15h 14m 49.2s
Dec(J2000) = -24d 12' 37.9"

with an uncertainty of 6.6 arcsec (radius, 90 percent confidence,
including boresight uncertainties). This is 4.4 arcmin from the
refined BAT position, and outside its 1.7 arcmin error radius.

It is impossible to say whether either of the sources are fading at
this stage, though the association of the first one with the fading 
optical object makes it the most likely candidate for the GRB X-ray 

This circular is an official product of the Swift-XRT team.
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