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GCN Circular 28081

GRB 200711A: Swift-XRT refined Analysis
2020-07-12T06:34:40Z (4 years ago)
Phil Evans at U of Leicester <>
J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (ASDC),
V. D'Elia (ASDC), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B.
Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester) and F.E. Marshall report on behalf of the Swift-XRT team:

We have analysed 6.9 ks of XRT data for GRB 200711A (Marshall et al.
GCN Circ. 28078), from 150 s to 40.4 ks after the  BAT trigger. The
data comprise 29 s in Windowed Timing (WT) mode (the first 10 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode. Using 1145 s of PC mode data and 2 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 = 285.97020, -0.14708
which is equivalent to:

RA (J2000): 19h 03m 52.85s
Dec(J2000): -00d 08' 49.5"

with an uncertainty of 1.6 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.51 (+0.13, -0.14), followed by a break at T+3349 s to
an alpha of 1.41 (+/-0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.01 (+0.22, -0.21). The
best-fitting absorption column is  1.65 (+0.30, -0.27) x 10^22 cm^-2,
in excess of the Galactic value of 5.7 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 5.6 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.65 (+0.30, -0.27) x 10^22 cm^-2
Galactic foreground: 5.7 x 10^21 cm^-2
Excess significance: 6.5 sigma
Photon index:	     2.01 (+0.22, -0.21)

If the light curve continues to decay with a power-law decay index of
1.41, the count rate at T+24 hours will be 9.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.4 x
10^-13 (1.1 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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