[vsnet-grb-info 16537] GRB 150514A: Swift-XRT afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17818
SUBJECT: GRB 150514A: Swift-XRT afterglow detection
DATE:    15/05/15 09:52:17 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), K.L. Page (U.
Leicester), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), A.
Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB),
D.N. Burrows (PSU) 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 150514A (Kocevski et al. GCN Circ. 17816),
collecting 1.3 ks of Photon Counting (PC) mode data between T0+40.8 ks
and T0+42.2 ks. 

Three uncatalogued X-ray sources are detected, of which one ("Source
1") is above the RASS limit, and is therefore likely the GRB afterglow.
 The position of this source is RA, Dec=74.8750, -60.9691 which is
equivalent to:

RA (J2000): 04:59:30.00
Dec(J2000): -60:58:08.8

with an uncertainty of 3.9 arcsec (radius, 90% confidence).  This
position is 3.6 arcmin from the Fermi/LAT position.  The light curve is
consistent with a constant source of mean count rate 5.4e-02 ct/sec. A
power-law fit gives an index of 3.17 (+0.05, -4.47).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.2 (+0.7, -0.4). The
best-fitting absorption column is  3 (+11, -1) x 10^20 cm^-2,
consistent with the Galactic value of 2.0 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 2.9 x 10^-11 (3.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3 (+11, -1) x 10^20 cm^-2
Galactic foreground: 2.0 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.2 (+0.7, -0.4)

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/ToO_GRBs/00020510/index_1.php.
The results of the full analysis of the XRT observations are available
at http://www.swift.ac.uk/ToO_GRBs/00020510.

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