K.L. Page, A.P. Beardmore (U. Leicester) and S.T. Holland
(CRESST/USRA/GSFC) report on behalf of the Swift-XRT and UVOT teams:
A follow-up observation of GRB 080515 was performed about 1.5 days after
the initial trigger (Holland et al., GCN Circ. 7721), when the burst was
no longer Sun-constrained. An X-ray source was identified within the BAT
ground-calculated error circle (Fenimore et al., GCN Circ. 7726). A
further observation, 3.5 days later, confirmed that the source is fading,
with alpha = 1.0 +0.7/-0.5. We therefore believe this is the X-ray
afterglow of the GRB.
The position of this source is RA, Dec = 3.16343, 32.57894, which is
RA(J2000) = 00 12 39.22
Dec(J2000) = +32 34 44.2
with an uncertainty of 3.8 arcsec (radius, 90% containment). This is 54
arcsec from the BAT position given by Fenimore et al. in GCN Circ. 7726.
A spectrum of the source can be fitted with a power-law of Gamma = 1.95
+/- 0.34, absorbed by the Galactic column of 4.65x10^20 cm^-2. This
spectrum, averaged over 1.5-6.6 days after the burst, has an observed
(unabsorbed) flux of 2.28x10^-13 (2.59x10^-13) erg cm^-2 s^-1.
The field was observed by UVOT with the v filter for 6262 s between
~1.5 and 2.4 days after the BAT trigger. The XRT error circle is
located in the scattered light halo of the B = 11.4 star TYC 2264-1051-1,
so it is not possible to constrain the presence of an afterglow in the
This circular is an official product of the Swift-XRT and UVOT teams.