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GCN Circular 35456

Subject
GRB 240101A: Swift-XRT refined Analysis
Date
2024-01-02T11:11:51Z (2 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester),
J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAR), T. Sbarrato (INAF-OAB), S. Dichiara (PSU) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 240101A, from 142 s to 57.6
ks after the  BAT trigger. The data are entirely in Photon Counting
(PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.06 (+0.08, -0.07).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+/-0.3). The
best-fitting absorption column is  4.3 (+1.8, -1.5) x 10^21 cm^-2, in
excess of the Galactic value of 5.8 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 3.9 x 10^-11 (6.5 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.3 (+1.8, -1.5) x 10^21 cm^-2
Galactic foreground: 5.8 x 10^20 cm^-2
Excess significance: 4.1 sigma
Photon index:	     2.1 (+/-0.3)

If the light curve continues to decay with a power-law decay index of
1.06, the count rate at T+24 hours will be 1.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.6 x
10^-14 (9.3 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/01205708.

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

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