GCN Circular 23418

B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P. Beardmore (U.
Leicester), J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A.
Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Tohuvavohu (PSU) and
P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 7.4 ks of XRT data for GRB 181110A (Evans et al. GCN
Circ. 23413
Not found
 
 
), from 67 s to 24.8 ks after the  BAT trigger. The data
comprise 260 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 23417
Not found
 
 
).

The late-time light curve (from T0+5.2 ks) can be modelled with a
power-law decay with a decay index of alpha=2.10 (+/-0.14).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.88 (+/-0.04). The
best-fitting absorption column is  8.6 (+1.0, -0.9) x 10^20 cm^-2,
consistent with the Galactic value of 7.7 x 10^20 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 1.74 (+0.07,
-0.06) and a best-fitting absorption column consistent with the
Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 3.8 x 10^-11 (4.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.7 (+1.5, -0.0) x 10^20 cm^-2
Galactic foreground: 7.7 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.74 (+0.07, -0.06)

If the light curve continues to decay with a power-law decay index of
2.10, the count rate at T+24 hours will be 2.2 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.3 x
10^-14 (9.3 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00871316.

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