TITLE:   GCN CIRCULAR
NUMBER:  22326
SUBJECT: GRB 180103A: Swift-XRT afterglow detection
DATE:    18/01/13 06:08:29 GMT
FROM:    Kim Page at U.of Leicester  <klp5@leicester.ac.uk>

A. Melandri (INAF-OAB), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.A.
Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:

Swift-XRT has conducted further observations of the field of the
Swift/BAT-detected burst GRB 180103A (Beardmore et al. GCN Circ.
22305). The observations now extend from T0+344.2 ks to T0+849.2 ks.
The source previously reported by Melandri et al. (GCN Circ. 22308),
"Source 1", is fading with 3-sigma significance, and is therefore
likely the GRB afterglow. Using 995 s of PC mode data and 1 UVOT image,
we find an enhanced XRT position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
159.60155, -53.55600 which is equivalent to:

RA (J2000): 10h 38m 24.37s
Dec(J2000): -53d 33' 21.6"

with an uncertainty of 3.8 arcsec (radius, 90% confidence). This
position is 35 arcsec from the Swift/BAT position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.53 (+0.05, -1.07).

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/ToO_GRBs/00020786/Source1.php.
The results of the full analysis of the XRT observations are available
at http://www.swift.ac.uk/ToO_GRBs/00020786.

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