GCN Circular 20620
Subject
GRB 170206B: Swift-XRT refined Analysis
Date
2017-02-07T09:46:41Z (7 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU),
S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB) and A.Y. Lien report on behalf of the Swift-XRT team:
We have analysed 7.4 ks of XRT data for GRB 170206B (Lien et al. GCN
Circ. 20618), from 88 s to 24.5 ks after the BAT trigger. The data
comprise 7 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. Using 2057 s
of PC mode data and 3 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 = 271.77062, +11.19383 which is equivalent
to:
RA (J2000): 18h 07m 04.95s
Dec(J2000): +11d 11' 37.8"
with an uncertainty of 1.6 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=2.48 (+0.19, -0.20).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.46 (+0.18, -0.17). The
best-fitting absorption column is 4.9 (+0.8, -0.7) x 10^21 cm^-2, in
excess of the Galactic value of 1.1 x 10^21 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 (6.9 x 10^-11) erg
cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
Total column: 4.9 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 8.5 sigma
Photon index: 2.46 (+0.18, -0.17)
If the light curve continues to decay with a power-law decay index of
2.48, the count rate at T+24 hours will be 2.5 x 10^-7 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.8 x
10^-18 (1.8 x 10^-17) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00737125.
This circular is an official product of the Swift-XRT team.