GCN Circular 28850

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

We have analysed 4.9 ks of XRT data for GRB 201104B (Sbarufatti et al.
GCN Circ. 28825
Not found
 
 
), from 105 s to 131.7 ks after the  BAT trigger. The
data comprise 347 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. Using 546 s of PC mode data and 3 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 =
5.21441, +7.84185 which is equivalent to:

RA (J2000): 00h 20m 51.46s
Dec(J2000): +07d 50' 30.7"

with an uncertainty of 2.3 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.11 (+0.11, -0.12), followed by a break at T+338 s to
an alpha of 1.21 (+0.05, -0.04).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.80 (+/-0.07). The
best-fitting absorption column is  1.12 (+0.30, -0.28) x 10^22 cm^-2,
at a redshift of 1.954, in addition to the Galactic value of 5.7 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 3.7 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Galactic foreground: 5.7 x 10^20 cm^-2
Intrinsic column:    1.12 (+0.30, -0.28) x 10^22 cm^-2 at z=1.954
Photon index:	     1.80 (+/-0.07)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01004168.

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