TITLE:   GCN CIRCULAR
NUMBER:  30069
SUBJECT: GRB 210520A: Swift-XRT observations
DATE:    21/05/22 10:47:24 GMT
FROM:    Paolo D'Avanzo at INAF - OAB  <paolo.davanzo@inaf.it>

M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai
(INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U.
Toronto), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester)
and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 210520A (Di Lalla et al. GCN Circ. 30062)
in a series of observations tiled on the sky. The total exposure time
is 5.6 ks, distributed over 19 tiles; the maximum exposure at a single
sky location was 649 s. The data were collected between T0+43.1 ks and
T0+62 ks, and are entirely in Photon Counting (PC) mode. 

Two uncatalogued X-ray sources are detected above the RASS 3-sigma
upper limit at this position, matching the afterglow criteria. However,
none of them shows definitive signs of fading, and both of them are
consistent with 2MASS objects within the XRT error circle. Therefore,
none of them is likely the afterglow.

Details of these sources are given below:

Source 2:
  RA (J2000.0):  122.12040 = 08:08:28.90
  Dec (J2000.0): -69.7668 = -69:46:00.5
  Error: 7.7 arcsec (radius, 90% conf.)
  Count-rate: (1.95 [+1.19, -0.85])e-2 ct s^-1	 
  Distance: 28.7' from Fermi/LAT position.

Source 3:
  RA (J2000.0):  124.47176 =  08:17:53.22
  Dec (J2000.0): -69.2963  =  -69:17:46.8
  Error: 8.6 arcsec (radius, 90% conf.)
  Count-rate: (3.0 [+1.6, -1.1])e-2 ct s^-1	 
  Distance: 31.8' from Fermi/LAT position.

The results of the full analysis of the tiled XRT observations are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00099.

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