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GCN Circular 30725

Subject
GRB 210826A: Swift-XRT observations
Date
2021-08-27T10:16:23Z (3 years ago)
From
Paolo D'Avanzo at INAF - OAB <paolo.davanzo@inaf.it>
A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D.
Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato
(INAF-OAB) 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 210826A (Ohno et al. GCN Circ. 30721), for
a total exposure time of 4.9 ks. The data were collected between
T0+36.5 ks and T0+49.7 ks, and are entirely in Photon Counting (PC)
mode.

Eight uncatalogued X-ray sources have been detected, however none of
them is above the RASS limit or shows definitive signs of fading.
Therefore, at the present time we cannot identify which, if any, is the
afterglow. We notice that one of the sources (Source 8) is consistent
with a catalogued galaxy at redshift z = 0.05. Details of these sources
are given below:

Source 1:
  RA (J2000.0):  45.3361  =  03:01:20.66
  Dec (J2000.0): -71.7072  =  -71:42:25.8
  Error: 8.7 arcsec (radius, 90% conf.)
  Count-rate: (1.46 [+0.80, -0.61])e-3 ct s^-1	 
  Distance: 48 arcsec from Fermi/LAT position.

Source 2:
  RA (J2000.0):  45.0955  =  03:00:22.93
  Dec (J2000.0): -71.6531  =  -71:39:11.1
  Error: 5.0 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: (3.06 [+1.16, -0.94])e-3 ct s^-1	 
  Distance: 286 arcsec from Fermi/LAT position.
  Flux: (8.2 [+3.1, -2.5])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 4:
  RA (J2000.0):  45.1820  =  03:00:43.67
  Dec (J2000.0): -71.5711  =  -71:34:15.8
  Error: 9.7 arcsec (radius, 90% conf.)
  Count-rate: (1.36 [+0.80, -0.59])e-3 ct s^-1	 
  Distance: 483 arcsec from Fermi/LAT position.
  Flux: (8.2 [+4.8, -3.6])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)
This source is 10" away from  the AGN candidate WISEA
J030045.23-713422.8 (Assef et al., 2018, ApJS, 234, 23)

Source 5:
  RA (J2000.0):  45.4777  =  03:01:54.65
  Dec (J2000.0): -71.6539  =  -71:39:13.9
  Error: 8.4 arcsec (radius, 90% conf.)
  Count-rate: (3.7 [+1.3, -1.0])e-3 ct s^-1   
  Distance: 260 arcsec from Fermi/LAT position.
  Flux: (5.8 [+2.0, -1.6])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 6:
  RA (J2000.0):  45.1850  =  03:00:44.41
  Dec (J2000.0): -71.7836  =  -71:47:00.9
  Error: 10.0 arcsec (radius, 90% conf.)
  Count-rate: (1.60 [+0.86, -0.65])e-3 ct s^-1	 
  Distance: 327 arcsec from Fermi/LAT position.
  Flux: (4.2 [+2.2, -1.7])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 7:
  RA (J2000.0):  45.3683  =  03:01:28.39
  Dec (J2000.0): -71.6617  =  -71:39:42.1
  Error: 10.3 arcsec (radius, 90% conf.)
  Count-rate: (1.54 [+0.84, -0.63])e-3 ct s^-1	 
  Distance: 158 arcsec from Fermi/LAT position.
This source is 6" away from  the AGN candidate WISEA
J030129.33-713938.6 (Assef et al., 2018, ApJS, 234, 23)

Source 8:
  RA (J2000.0):  44.7903  =  02:59:9.68
  Dec (J2000.0): -71.6112  =  -71:36:40.2
  Error: 9.3 arcsec (radius, 90% conf.)
  Count-rate: (1.11 [+0.78, -0.56])e-3 ct s^-1	 
  Distance: 660 arcsec from Fermi/LAT position.
This source is 9" away from the catalogued galaxy 2MASX
J02591150-7136430 at redshift z = 0.05

Source 9:
  RA (J2000.0):  45.6834  =  03:02:44.02
  Dec (J2000.0): -71.6574  =  -71:39:26.7
  Error: 8.8 arcsec (radius, 90% conf.)
  Count-rate: (2.16 [+1.02, -0.79])e-3 ct s^-1	 
  Distance: 460 arcsec from Fermi/LAT position.
  Flux: (8.1 [+3.8, -3.0])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00101.

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