GCN Circular 22413

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

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 180210A (Dirirsa et al. GCN Circ. 22408
Not found
 
 
),
collecting 7.5 ks of Photon Counting (PC) mode data between T0+31.0 ks
and T0+117.4 ks. 

Four uncatalogued X-ray sources are detected, of which one ("Source 1",
the brightest) is fading with 3-sigma significance, and is therefore
likely the GRB afterglow. Using 4922 s of PC mode data and 4 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 =
1.84177, +18.55274 which is equivalent to:

RA (J2000): 00h 07m 22.02s
Dec(J2000): +18d 33' 09.9"

with an uncertainty of 1.7 arcsec (radius, 90% confidence). This
position is 12.4 arcmin from the Fermi/LAT position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.57 (+0.36, -0.28).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.3 (+/-0.4). The
best-fitting absorption column is  3.6 (+1.7, -1.4) x 10^21 cm^-2, in
excess of the Galactic value of 3.7 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 2.7 x 10^-11 (5.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.6 (+1.7, -1.4) x 10^21 cm^-2
Galactic foreground: 3.7 x 10^20 cm^-2
Excess significance: 3.7 sigma
Photon index:	     2.3 (+/-0.4)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020787.
The results of the full analysis of the XRT observations are available
at http://www.swift.ac.uk/ToO_GRBs/00020787.

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