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GCN Circular 33365

GRB 230217A: Swift-XRT afterglow detection
2023-02-22T08:59:54Z (a year ago)
Phil Evans at U of Leicester <>
M. Capalbi (INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U.
Toronto), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore
(U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR)
and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has conducted further observations of the field of the
Swift-BAT-detected burst GRB 230217A (Barthelmy et al. GCN Circ.
33363). The observations now extend from T0+45.9 ks to T0+342.9 ks. 

Of the sources reported by Capalbi et al. (GCN Circ. 33348), "Source 3"
is fading with >3-sigma significance, and is therefore likely the GRB
afterglow. Using 874 s of PC mode data and 1 UVOT image, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 280.77002, -28.83740
which is equivalent to:

RA (J2000): 18h 43m 04.80s
Dec(J2000): -28d 50' 14.6"

with an uncertainty of 4.7 arcsec (radius, 90% confidence). This
position is 67 arcsec from the Swift-BAT position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.1 (+0.6, -0.4).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.6 (+0.8, -0.4). The
best-fitting absorption column is  consistent with the Galactic value
of 1.6 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 4.4 x 10^-11 (5.1 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+/-4.1) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.6 (+0.8, -0.4)

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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