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GCN Circular 33736

GRB 230506C: Swift-XRT analysis
2023-05-07T00:20:13Z (a year ago)
Jamie Kennea at Penn State U <>
J. A. Kennea (PSU), A. Tohuvavohu (Toronto), P.A. Evans and 
M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team:

We have analysed 1.6 ks of XRT data for GRB 230506C, from 4.6 ks to
11.0 ks after the BAT trigger. The data are entirely in Photon
Counting (PC) mode. Using 1145 s of PC mode data and 2 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 =
134.36766, +45.13302 which is equivalent to:

RA (J2000): 08h 57m 28.24s
Dec(J2000): +45d 07' 58.9"

with an uncertainty of 2.4 arcsec (radius, 90% confidence).
This circular is an official product of the Swift-XRT team.

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.0 (+0.5, -0.4).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.2 (+0.4, -0.3). The
best-fitting absorption column is 1.2 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 2.2 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 3.0 x 10^-11 (4.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column: 1.2 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 2.2 x 10^20 cm^-2
Excess significance: 2.2 sigma
Photon index: 2.2 (+0.4, -0.3)

If the light curve continues to decay with a power-law decay index of
1.0, the count rate at T+24 hours will be 0.012 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 x
10^-13 (5.1 x 10^-13) erg cm^-2 s^-1.

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

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

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