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GCN Circular 27157

Subject
GRB 200219C: Swift-XRT afterglow detection
Date
2020-02-20T20:10:40Z (4 years ago)
From
Valerio D'Elia at ASDC <valerio.delia@ssdc.asi.it>
D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), 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 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 200219C (Dirirsa et al. GCN Circ. 27151)
in a series of observations tiled on the sky. The total exposure time
is 2.4 ks, distributed over 4 tiles; the maximum exposure at a single
sky location was 2.4 ks. The data were collected between T0+43.0 ks and
T0+56.0 ks, and are entirely in Photon Counting (PC) mode. 

Two uncatalogued X-ray sources are detected, of which one ("Source 2")
is above the RASS limit, and is therefore likely the GRB afterglow.
Using 2417 s of PC mode data and 5 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 = 262.50899, +10.53933 which is
equivalent to:

RA (J2000): 17h 30m 02.16s
Dec(J2000): +10d 32' 21.6"

with an uncertainty of 2.1 arcsec (radius, 90% confidence). This
position is 12.9 arcmin from the Fermi/LAT position.  The light curve
is consistent with a constant source of mean count rate 1.1e-01 ct/sec.
A power-law fit gives an index of 0.9 (+1.4, -1.5).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+/-0.4). The
best-fitting absorption column is  3.2 (+1.6, -1.4) x 10^21 cm^-2, in
excess of the Galactic value of 1.2 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.1 x 10^-11 (4.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.2 (+1.6, -1.4) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^21 cm^-2
Excess significance: 2.4 sigma
Photon index:	     2.1 (+/-0.4)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020973.
The results of the full analysis of the tiled XRT observations are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00088.

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