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GCN Circular 21216

GRB 170607A: Swift-XRT refined Analysis
2017-06-08T07:07:40Z (7 years ago)
Phil Evans at U of Leicester <>
D.N. Burrows (PSU), A. Cholden-Brown (PSU), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), A.
Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), S. J. LaPorte (PSU) and A.
D'Ai report on behalf of the Swift-XRT team:

We have analysed 7.5 ks of XRT data for GRB 170607A (D'Ai et al. GCN
Circ. 21214), from 63 s to 19.1 ks after the  BAT trigger. The data
comprise 395 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Beardmore
et al. (GCN Circ. 21215).

The late-time light curve (from T0+5.1 ks) can be modelled with a
power-law decay with a decay index of alpha=0.54 (+/-0.09).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.003 (+0.038, -0.019). The
best-fitting absorption column is  consistent with the Galactic value
of 4.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.92 (+/-0.08) and a best-fitting absorption column
of 7.1 (+1.9, -1.8) x 10^20 cm^-2. The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 3.4 x
10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.1 (+1.9, -1.8) x 10^20 cm^-2
Galactic foreground: 4.4 x 10^20 cm^-2
Excess significance: 2.5 sigma
Photon index:	     1.92 (+/-0.08)

If the light curve continues to decay with a power-law decay index of
0.54, the count rate at T+24 hours will be 0.13 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x
10^-12 (5.0 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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