Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
Introducing Einstein Probe, Astro Flavored Markdown, and Notices Schema v4.0.0. See news and announcements

GCN Circular 33285

GRB 230204B: Swift-XRT afterglow detection
2023-02-06T15:16:26Z (a year ago)
Phil Evans at U of Leicester <>
V. D'Elia (SSDC & INAF-OAR), A.P. Beardmore (U. Leicester), P. D'Avanzo
(INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) ,
D.N. Burrows (PSU), J. D. Gropp (PSU), S. Dichiara (PSU), 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 MAXI-detected
burst GRB 230204B (Serino et al. GCN Circ. 33265). A possible optical
counterpart was reported by GIT (Swain et al. GCN Circ. 33269).
Swift-XRT observations consist of 4.2 ks of Photon Counting (PC) mode
data between T0+80.5 ks and T0+97.9 ks.

One uncatalogued X-ray source has been detected consistent with the GIT
position. The source is below the RASS limit but does not show
definitive signs of fading. This is most likely the afterglow, given
also the reported redshift of z=2.14 (Saccardi et al. GCN Circ. 33281)
but further observations are required to assess for fading. Details of
this source are given below:

Source 3:
  RA (J2000.0):  197.6441  =  13:10:34.58
  Dec (J2000.0): -21.7164  =  -21:42:58.9
  Error: 7.4 arcsec (radius, 90% conf.)
  Count-rate: (5.6 +/- 1.5)e-3 ct s^-1	 
  Distance: 8 arcsec from MAXI position.
  Flux: (3.8 +/- 1.0)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

This circular is an official product of the Swift-XRT team.
Looking for U.S. government information and services? Visit