[vsnet-grb-info 16199] GRB 150219A: Swift-XRT afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17480
SUBJECT: GRB 150219A: Swift-XRT afterglow detection
DATE:    15/02/19 23:34:23 GMT
FROM:    Valerio D'Elia at ASDC  <delia at asdc.asi.it>

K.L. Page (U. Leicester), C. Pagani (U. Leicester), A. Melandri
(INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), J.A. Kennea
(PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P. Beardmore
(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 INTEGRAL-detected
burst GRB 150219A (Mereghetti et al. GCN Circ. 17476), collecting 2.6
ks of Photon Counting (PC) mode data between T0+10.5 ks and T0+23.4 ks.


An uncatalogued X-ray source is detected inside the INTEGRAL error
region and is fading with 3-sigma significance, and is therefore likely
the GRB afterglow.  The position of this source is RA, Dec=271.2507,
-41.5942 which is equivalent to:

RA (J2000): 18:05:0.18
Dec(J2000): -41:35:39.0

with an uncertainty of 3.7 arcsec (radius, 90% confidence).  This
position is 53 arcsec from the INTEGRAL position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.8 (+0.9, -0.7).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.8 (+/-0.4). The
best-fitting absorption column is  1.6 (+0.6, -0.5) x 10^22 cm^-2, in
excess of the Galactic value of 1.4 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 6.3 x 10^-11 (1.1 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+0.6, -0.5) x 10^22 cm^-2
Galactic foreground: 1.4 x 10^21 cm^-2
Excess significance: 4.6 sigma
Photon index:	     1.8 (+/-0.4)

If the light curve continues to decay with a power-law decay index of
2.8, the count rate at T+24 hours will be 5.8 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.6 x
10^-14 (6.2 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/ToO_GRBs/00020483/index_1.php.
The results of the full analysis of the XRT observations are available
at http://www.swift.ac.uk/ToO_GRBs/00020483.

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