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GCN Circular 33135

Subject
GRB 221231A: Swift-XRT observations
Date
2023-01-01T16:54:31Z (a year ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M. Perri (SSDC & INAF-OAR), A. Tohuvavohu (U. Toronto), D.N. Burrows
(PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR),
B. Sbarufatti (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
Swift/BAT-GUANO-detected burst GRB 221231A, collecting 5.0 ks of Photon
Counting (PC) mode data between T0+32.4 ks and T0+44.3 ks. 

Five 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. Sources 2 and 5 are inside the error box of Swift/BAT-GUANO,
but source 5 is associated with a known source. Details of these
sources are given below:

Source 1:
  RA (J2000.0):  336.3458  =  22:25:22.98
  Dec (J2000.0): +25.1723  =  +25:10:20.3
  Error: 6.5 arcsec (radius, 90% conf.)
  Count-rate: (9.1 [+7.3, -5.4])e-4 ct s^-1   
  Distance: 303 arcsec from Swift/BAT-GUANO position.

Source 2:
  RA (J2000.0):  336.2560  =  22:25:1.44
  Dec (J2000.0): +25.1298  =  +25:07:47.2
  Error: 3.1 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: 0.0107 [+0.0022, -0.0020] ct s^-1   
  Distance: 34 arcsec from Swift/BAT-GUANO position.
  Flux: (5.44 [+1.13, -1.00])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)


Source 3:
  RA (J2000.0):  336.2019  =  22:24:48.46
  Dec (J2000.0): +25.0298  =  +25:01:47.3
  Error: 5.4 arcsec (radius, 90% conf.)
  Count-rate: (1.87 [+0.97, -0.73])e-3 ct s^-1	 
  Distance: 435 arcsec from Swift/BAT-GUANO position.
  Flux: (7.8 [+4.0, -3.1])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 4:
  RA (J2000.0):  336.2146  =  22:24:51.50
  Dec (J2000.0): +25.2635  =  +25:15:48.7
  Error: 8.9 arcsec (radius, 90% conf.)
  Count-rate: (1.48 [+0.87, -0.64])e-3 ct s^-1	 
  Distance: 474 arcsec from Swift/BAT-GUANO position.
  Flux: (2.7 [+1.6, -1.2])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 5:
  RA (J2000.0):  336.2452  =  22:24:58.84
  Dec (J2000.0): +25.1872  =  +25:11:14.1
  Error: 5.7 arcsec (radius, 90% conf.)
  Count-rate: (5.6 [+1.8, -1.5])e-3 ct s^-1   
  Distance: 182 arcsec from Swift/BAT-GUANO position.
  Flux: (1.12 [+0.37, -0.30])e-13 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/00021534.

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