GCN Circular 22394

K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Tohuvavohu
(PSU), S. J. LaPorte (PSU), J.A. Kennea (PSU) and P.A. Evans report on
behalf of the Swift-XRT team:

We have analysed 5.0 ks of XRT data for GRB 180205A (Evans et al. GCN
Circ. 22381
Not found
 
 
), from 180 s to 33.8 ks after the  BAT trigger. The data
comprise 85 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. Using 3849 s of PC mode data and 7 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 =
126.81966, +11.54210 which is equivalent to:

RA (J2000): 08h 27m 16.72s
Dec(J2000): +11d 32' 31.6"

with an uncertainty of 1.5 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial power-law decay with an
index of alpha=4.8 (+0.6, -0.5), followed by a break at T+279 s to an
alpha of 1.00 (+/-0.04).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.72 (+0.18, -0.17). The
best-fitting absorption column is  8.7 (+2.8, -2.5) x 10^21 cm^-2, at a
redshift of 1.409, in addition to the Galactic value of 3.4 x 10^20
cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index
of 1.89 (+0.15, -0.14) and a best-fitting absorption column of 3.1
(+3.0, -2.6) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10
keV flux conversion factor deduced from this spectrum  is 3.5 x 10^-11
(4.0 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 3.4 x 10^20 cm^-2
Intrinsic column:    3.1 (+3.0, -2.6) x 10^21 cm^-2 at z=1.409
Photon index:	     1.89 (+0.15, -0.14)

If the light curve continues to decay with a power-law decay index of
1.00, the count rate at T+24 hours will be 0.013 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x
10^-13 (5.2 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00808625.

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