GCN Circular 34676

A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB),
J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester) and P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 7.2 ks of XRT data for GRB 230911C, from 103 s to 74.1
ks after the  BAT trigger. The data comprise 106 s in Windowed Timing
(WT) mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+4.2 ks) can be modelled with a
power-law decay with a decay index of alpha=0.48 (+0.22, -0.18).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.86 (+0.26, -0.21). The
best-fitting absorption column is  1.3 (+0.9, -0.3) x 10^21 cm^-2,
consistent with the Galactic value of 9.4 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 3.6 x 10^-11 (4.4 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.3 (+0.9, -0.3) x 10^21 cm^-2
Galactic foreground: 9.4 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.86 (+0.26, -0.21)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01191188.

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