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GCN Circular 23604

GRB 190103B: Swift-XRT refined Analysis
2019-01-04T04:24:42Z (6 years ago)
Phil Evans at U of Leicester <>
B. Sbarufatti (INAF-OAB/PSU), J.P. Osborne (U. Leicester), K.L. Page
(U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB),
V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU), A.
Tohuvavohu (PSU) and A.Y. Lien report on behalf of the Swift-XRT team:

We have analysed 7.8 ks of XRT data for GRB 190103B (Lien et al. GCN
Circ. 23602), from 99 s to 18.1 ks after the  BAT trigger. The data
comprise 437 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 23603).

The late-time light curve (from T0+4.2 ks) can be modelled with a
power-law decay with a decay index of alpha=1.03 (+/-0.10).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.38 (+/-0.06). The
best-fitting absorption column is  4.27 (+0.28, -0.27) x 10^21 cm^-2,
in excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.89 (+/-0.11) and a
best-fitting absorption column of 3.9 (+0.6, -0.5) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.1 x 10^-11 (6.0 x 10^-11) erg cm^-2

A summary of the PC-mode spectrum is thus:
Total column:	     3.9 (+0.6, -0.5) x 10^21 cm^-2
Galactic foreground: 1.4 x 10^20 cm^-2
Excess significance: 11.8 sigma
Photon index:	     1.89 (+/-0.11)

If the light curve continues to decay with a power-law decay index of
1.03, the count rate at T+24 hours will be 0.027 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-12 (1.6 x 10^-12) 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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