TITLE:   GCN CIRCULAR
NUMBER:  41613
SUBJECT: GRB 250830B: Swift-XRT observations
DATE:    25/08/31 04:57:05 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri
(INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea
(PSU), D.N. Burrows (PSU), S. Lanava (PSU) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 250830B, collecting  2.4 ks of Photon Counting (PC) mode data
between T0+11.0 ks and T0+50.8 ks. This event also triggered Einstein
Probe around 25 s after MAXI, and was separately designated EP250830a.

One uncatalogued X-ray source has been detected within the estimated
3-sigma EP error region (296 arcsec), also consistent with the MAXI
error region; it is below the RASS limit and shows no definitive signs
of fading. Therefore, at the present time we cannot confirm this as the
afterglow. Details of this source are given below:

Source 1:
  RA (J2000.0):  105.7399  =  07h 02m 57.59s
  Dec (J2000.0): -64.8525  =  -64d 51' 09.1"
  Error: 3.7 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: 0.0323 +/- 0.0046 ct s^-1   
  Distance: 134 arcsec from EP position.
  Flux: (1.74 +/- 0.25)e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV)

A further uncatalogued X-ray source was also detected, however this was
too far from the EP position to be the afterglow.

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/00021858.

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