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GCN Circular 27936

GRB 200613A: Swift-XRT afterglow detection
2020-06-14T04:46:25Z (4 years ago)
Kim Page at U.of Leicester <>
J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU),
J.P. Osborne (U. Leicester), K.L. Page (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 200613A (Ohno et al. GCN Circ. 27931),
collecting 4.9 ks of Photon Counting (PC) mode data between T0+43.6 ks
and T0+67.6 ks. 

Seven uncatalogued X-ray sources are detected, of which one ("Source
2") is above the RASS limit, and is therefore likely the GRB afterglow.
Using 4079 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 = 153.04199, +45.75408 which is
equivalent to:

RA (J2000): 10h 12m 10.08s
Dec(J2000): +45d 45' 14.7"

with an uncertainty of 1.4 arcsec (radius, 90% confidence). This
position is 5.8 arcmin from the Fermi/LAT position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.6 (+/-0.5).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.89 (+0.14, -0.13). The
best-fitting absorption column is  2.3 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 8.4 x 10^19 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.5 x 10^-11 (4.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.3 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 8.4 x 10^19 cm^-2
Excess significance: 7.5 sigma
Photon index:	     1.89 (+0.14, -0.13)

The results of the XRT-team automatic analysis are available at
The results of the full analysis of the XRT observations are available

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