TITLE:   GCN CIRCULAR
NUMBER:  43678
SUBJECT: GRB 260204A: Swift-XRT afterglow detection
DATE:    26/02/10 08:34:30 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi 
(INAF-IASFPA) , M. Capalbi (INAF-OAR), D.N. Burrows (PSU), S. Lanava
(PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed a second epoch of follow-up observations of GRB
260204A (Pillas et al., GCN Circ. 43613), collecting a further 2.6 ks
between T0+363 ks and T0+458 ks. "Source 1" (Evans et al., GCN Circ.
43622), which corresponds to the fading optical counterpart (Li et al.,
GCN Circs 43620, 43623), is no longer detected and has faded with
>3-sigma significance. The upper limit is 6.97e-3 ct/sec, compared to
the previous detection level of (2.36 +/- 0.46)e-2 ct/sec, giving a
power-law decay index of alpha >0.4.

Using 1659 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 = 205.10623, +1.93075 which is
equivalent to:

RA (J2000): 13h 40m 25.49s
Dec(J2000): +01d 55' 50.7"

with an uncertainty of 4.4 arcsec (radius, 90% confidence). 

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/03000405.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/SVOM/SVOM_FIELD00057.

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