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GCN Circular 19408

GRB 160509A: Swift-XRT afterglow detection
2016-05-09T15:04:24Z (8 years ago)
Jamie A. Kennea at PSU/Swift-XRT <>
J. A. Kennea (PSU), T.G.R. Roegiers (PSU), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), D.N. Burrows (PSU), L.M. McCauley (PSU),
C. Pagani (U. Leicester) and P.A. Evans (U. Leicester) report on behalf
of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 160509A (Longo et al. GCN Circ. 19403) in
a series of observations tiled on the sky. The total exposure time is
1.7 ks, distributed over 7 tiles; the maximum exposure at a single sky
location was 560 s. The data were collected between T0+7.3 ks and
T0+7.5 ks, and are entirely in Photon Counting (PC) mode. 

Using 250 s of XRT Photon Counting mode data and 1 UVOT images, we find
an astrometrically corrected X-ray position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 311.75375, 76.10837 which is equivalent to:

RA (J2000):  20 47 00.90
Dec (J2000): +76 06 30.1

with an uncertainty of 2.3 arcsec (radius, 90% confidence). This
position is 24.8 arcmin from the Fermi/LAT position, and 11 arcseconds
from the preliminary XRT position (GCN 19407).	The light curve is
consistent with a constant source of mean count rate 1.4 ct/sec. We
cannot determine fading at this time.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.7 (+/-0.3). The
best-fitting absorption column is  4.6 (+2.3, -1.8) x 10^21 cm^-2, in
excess of the Galactic value of 2.1 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 4.9 x 10^-11 (6.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.6 (+2.3, -1.8) x 10^21 cm^-2
Galactic foreground: 2.1 x 10^21 cm^-2
Excess significance: 2.2 sigma
Photon index:	     1.7 (+/-0.3)

The results of the XRT-team automatic analysis of the likely afterglow
are at
The results of the full analysis of the tiled XRT observations are
available at

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