TITLE:   GCN CIRCULAR
NUMBER:  37249
SUBJECT: GRB 240821A: Swift-XRT observations
DATE:    24/08/23 17:29:30 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

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

Swift-XRT has performed follow-up observations of the
Fermi/GBM,SVOM/ECLAIRs,SVOM/GRM-detected burst GRB 240821A
(GCN circ. 37219, 37220, 37226, 37227, 37239), collecting
5.0 ks of Photon Counting (PC) mode data between T0+91.4 ks
and T0+153.6 ks. 

Four uncatalogued X-ray sources have been detected, however none of
them is above the RASS limit or shows definitive signs of fading.
Source 2 is consistent with the position of galaxy SDSS
J233641.30-100258.0.
The XRT detected sources are detected also in EP-FXT data (GCN Circ.
37230).
The Swift/XRT and EP-FXT fluxes are consistent within the errors.
Therefore, at the present time we cannot identify which, if any, is the
afterglow. 
Details of these sources are given below:

Source 1:
  RA (J2000.0):  354.2899  =  23:37:9.58
  Dec (J2000.0): -10.0537  =  -10:03:13.2
  Error: 7.1 arcsec (radius, 90% conf.)
  Count-rate: (1.90 [+0.98, -0.74])e-3 ct s^-1	 
  Distance: 501 arcsec from SVOM/ECLAIRs position.
  Flux: (6.2 [+3.2, -2.4])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 2:
  RA (J2000.0):  354.1713  =  23:36:41.12
  Dec (J2000.0): -10.0495  =  -10:02:58.0
  Error: 7.4 arcsec (radius, 90% conf.)
  Count-rate: (2.49 [+1.09, -0.86])e-3 ct s^-1	 
  Distance: 513 arcsec from SVOM/ECLAIRs position.
  Flux: (8.2 [+3.6, -2.8])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 3:
  RA (J2000.0):  354.2700  =  23:37:4.80
  Dec (J2000.0): -10.1882  =  -10:11:17.6
  Error: 10.3 arcsec (radius, 90% conf.)
  Count-rate: (1.53 [+0.83, -0.63])e-3 ct s^-1	 
  Distance: 144 arcsec from SVOM/ECLAIRs position.
  Flux: (6.6 [+3.6, -2.7]e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 4:
  RA (J2000.0):  354.1714  =  23:36:41.14
  Dec (J2000.0): -10.1776  =  -10:10:39.4
  Error: 5.8 arcsec (radius, 90% conf.)
  Count-rate: (1.30 [+0.80, -0.59])e-3 ct s^-1	 
  Distance: 207 arcsec from SVOM/ECLAIRs position.
  Flux: (3.0 [+1.8, -1.3])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021704.

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