TITLE:   GCN CIRCULAR
NUMBER:  27676
SUBJECT: GRB 200424A: Swift-XRT afterglow detection
DATE:    20/05/02 08:48:04 GMT
FROM:    Paolo D'Avanzo at INAF - OAB  <paolo.davanzo@inaf.it>

M. Perri (ASDC), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), D.N. Burrows
(PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester) 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
INTEGRAL-detected burst GRB 200424A (Mereghetti et al. GCN Circ.
27634). The observations now extend from T0+17.1 ks to T0+633.1 ks. 

Of the sources reported by Perri et al. (GCN Circ. 27640), "Source 1"
is fading with 3-sigma significance, and is therefore likely the GRB
afterglow. Using 1970 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 = 307.50547, -39.70013
which is equivalent to:

RA (J2000): 20h 30m 01.31s
Dec(J2000): -39d 42' 00.5"

with an uncertainty of 3.0 arcsec (radius, 90% confidence). This
position is 22 arcsec from the INTEGRAL position.  The source is fading
with alpha >0.3.

The results of the XRT-team automatic analysis of the likely afterglow
are at https://www.swift.ac.uk/ToO_GRBs/00020989/Source1.php.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00020989.

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