GCN Circular 19320

A. D'Ai (INAF-IASFPA), A. Maselli  (INAF-IASFPA), A. Melandri
(INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N.
Burrows (PSU), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester) and P. D'Avanzo report on behalf of the
Swift-XRT team:

We have analysed 8.0 ks of XRT data for GRB 160417A (D'Avanzo et al.
GCN Circ. 19316
Not found
 
 
), from 117 s to 23.2 ks after the  BAT trigger. The
data comprise 41 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
Osborne et al. (GCN Circ. 19318
Not found
 
 
).

The light curve can be modelled with an initial power-law decay with an
index of alpha=4.4 (+0.4, -0.3), followed by a break at T+305 s to an
alpha of 0.59 (+/-0.06).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.05 (+0.15, -0.08). The
best-fitting absorption column is  consistent with the Galactic value
of 2.9 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 3.1 x 10^-11 (3.4 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.9 (+/-1.9) x 10^20 cm^-2
Galactic foreground: 2.9 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.05 (+0.15, -0.08)

If the light curve continues to decay with a power-law decay index of
0.59, the count rate at T+24 hours will be 0.013 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.9 x
10^-13 (4.3 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00683076.

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