GCN Circular 41300

P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi  (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source
GRB 250808A, collecting 1.7 ks of Photon Counting (PC) mode data between T0+3.7 ks
and T0+5.6 ks after the trigger. A candidate counterpart has been found. The details
of this source are:

  Source 1 (SWIFT J041412.2-224923):
  ==================================
    RA (J2000.0):   63.5510  =	04h 14m 12.24s
    Dec (J2000.0):  -22.8231  =  -22d 49' 23.2"
    Error:	    3.9 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    4.9 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    0.140 +/- 0.013 ct s^-1
    Mean flux:	    (4.58 +/- 0.43)e-12 erg cm^-2 s^-1
    Peak rate:	    0.204 +/- 0.046 ct s^-1
    Peak flux:	    (6.7 +/- 1.5)e-12 erg cm^-2 s^-1
    ECF:	    3.27e-11 erg cm^-2 ct^-1
		      assuming NH=1.35e+21 cm^-2, gamma=2.07
		      determined from a spectral fit.
    XMM UL:	    2.2e-12 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is 3.0-sigma above this 3-sigma upper limit.
    The source may be fading, at the 2.1-sigma level.


All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits  from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.

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/SVOM/SVOM_FIELD00027.

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