TITLE:   GCN CIRCULAR
NUMBER:  39336
SUBJECT: GRB 250215A: Swift-XRT refined Analysis
DATE:    25/02/15 11:39:14 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Perri (SSDC
& INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), S.
Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans
(U. Leicester) reports on behalf of the Swift-XRT team:

We have analysed 1.7 ks of XRT data for the Einstein Probe/WXT-detected
burst GRB 250215A, from 9.5 ks to 16.1 ks after the  Einstein Probe/WXT
trigger, also detected by Fermi/GBM (GCN Circ. 39327) and INTEGRAL (GCN
Circ. 39331). The data are entirely in Photon Counting (PC) mode. 

We detect a bright, previously uncatalogued X-ray source at the
following coordinates: RA/Dec(J2000) = 156.33119, -27.69834, which is
equivalent to 

RA (J2000): 10 25 19.48
Dec(J2000): -27 41 54.0

with an uncertainty of 3.6 arcsec (radius, 90% confidence). This source
is 6 arcsec from the FXT position (GCN Circ. 39329) and 0.35 arcsec
from the NOT optical counterpart (GCN Circ. 39330).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.1 (+/-0.4).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.95 (+0.23, -0.22). The
best-fitting absorption column is  1.2 (+0.7, -0.5) x 10^21 cm^-2,
consistent with the Galactic value of 6.8 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 3.5 x 10^-11 (4.4 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.2 (+0.7, -0.5) x 10^21 cm^-2
Galactic foreground: 6.8 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.95 (+0.23, -0.22)

If the light curve continues to decay with a power-law decay index of
1.1, the count rate at T+24 hours will be 0.038 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.3 x
10^-12 (1.7 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019554.

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