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GCN Circular 27179

Subject
GRB 200224A: Swift-XRT refined Analysis
Date
2020-02-24T16:21:20Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J. D. Gropp (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P.
Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB), M.G. Bernardini (INAF-OAB), A. Tohuvavohu (U. Toronto), 
 and  report on behalf of the Swift-XRT team: report on behalf of the
Swift-XRT team:

We have analysed 12 ks of XRT data for the Swift-detected burst GRB
200224A, from 105 s to 34.0 ks after the  Swift trigger. The data are
entirely in Photon Counting (PC) mode. Using 4055 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 = 248.76655, +41.61133 which is equivalent to:

RA (J2000): 16h 35m 03.97s
Dec(J2000): +41d 36' 40.8"

with an uncertainty of 1.7 arcsec (radius, 90% confidence). This
position is 4.0 arcmin from the Swift position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.86 (+0.10, -0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.09 (+0.39, -0.29). The
best-fitting absorption column is  3.2 (+7.4, -2.3) x 10^20 cm^-2,
consistent with the Galactic value of 8.9 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 3.0 x 10^-11 (3.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.2 (+7.4, -2.3) x 10^20 cm^-2
Galactic foreground: 8.9 x 10^19 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.09 (+0.39, -0.29)

If the light curve continues to decay with a power-law decay index of
0.86, the count rate at T+24 hours will be 9.9 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x
10^-14 (3.3 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00958141.

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

[GCN OPS NOTE(24feb20): This is the eighth Circular in the sequence of 8 circulars
which were all labeled A because of the sequence assigner being offline.  
This circular was correctly labelled A.]
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