GCN Circular 42943

B. Sbarufatti (INAF-OAB), S. Lanava (PSU), S. Dichiara (PSU), J.A.
Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
A.P. Beardmore (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro
(INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of GRB 251202A. We
searched for X-ray sources in  759 s of Photon Counting (PC) mode data.
The total exposure at the position of the afterglow (see below) is 759
s, obtained between T0+2.4 ks and T0+24.0 ks.

An uncatalogued X-ray source are clearly detected within the Einstein
Probe/WXT error region. Using 411 s of PC mode data and 1 UVOT image,
we find an enhanced XRT position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
122.11512, +40.61228 which is equivalent to:

RA (J2000): 08h 08m 27.63s
Dec(J2000): +40d 36' 44.2"

with an uncertainty of 2.4 arcsec (radius, 90% confidence). This
position is 10.3 arcsec from the EP/FXT position (Zhang et al., GCN
Circ. 42937
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 ) and 2.2 arcsec from the optical counterpart reported by Li
et al. (GCN 42934
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.08 (+0.33, -0.24).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.93 (+0.45, -0.22). The
best-fitting absorption column is  consistent with the Galactic value
of 6.5 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 3.4 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 6.5 x 10^20 cm^-2
Intrinsic column:    6 (+/-166) x 10^20 cm^-2 at z=2.785
Photon index:	     1.93 (+0.45, -0.22)

If the light curve continues to decay with a power-law decay index of
1.08, the count rate at T+24 hours will be 0.018 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x
10^-13 (7.2 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/03000226.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/EP/EP_FIELD00086.

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