GCN Circular 38256

R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR),
D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Swift-BAT-detected burst GRB 241115A, collecting 11.3 ks of Photon
Counting (PC) mode data between T0+92 s and T0+102.8 ks. 

An uncatalogued X-ray source is detected consistent with being within
296 arcsec of the Swift-BAT position and is above the RASS 3-sigma
upper limit at this position and fading with >3-sigma significance, and
is therefore likely the GRB afterglow. Using 2620 s of PC mode data and
5 UVOT images, we find an enhanced XRT position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 86.77097, -0.67462 which is equivalent to:

RA (J2000): 05h 47m 05.03s
Dec(J2000): -00d 40' 28.6"

with an uncertainty of 2.2 arcsec (radius, 90% confidence). This
position is 50 arcsec from the Swift-BAT position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.13 (+/-0.07).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.0 (+/-0.4). The
best-fitting absorption column is  1.7 (+0.6, -0.5) x 10^22 cm^-2, in
excess of the Galactic value of 3.3 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 5.9 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.7 (+0.6, -0.5) x 10^22 cm^-2
Galactic foreground: 3.3 x 10^21 cm^-2
Excess significance: 4.5 sigma
Photon index:	     2.0 (+/-0.4)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01267921.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/01267921.

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