Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 19334

GRB 160422A: Swift-XRT afterglow detection
2016-04-23T05:15:14Z (8 years ago)
Alessandro Maselli at INAF/IASF Palermo <>
A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), J.P. Osborne
(U. Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester), P.
D'Avanzo (INAF-OAB) 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 160422A (Yassine et al. GCN Circ. 19329),
collecting 4.9 ks of Photon Counting (PC) mode data between T0+32.6 ks
and T0+45.8 ks. 

Three uncatalogued X-ray sources are detected inside or close to the
Fermi/LAT error region, 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=42.0947, -57.8757 which is equivalent to:

RA (J2000): 02:48:22.74
Dec(J2000): -57:52:32.6

with an uncertainty of 3.6 arcsec (radius, 90% confidence). This
position is 2.0 arcmin from the Fermi/LAT position and 2.6 arcsec from
the Swift-UVOT candidate optical afterglow (Marshall, GCN Circ. 19333).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.3 (+/-1.0).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.3 (+0.4, -0.3). The
best-fitting absorption column is  2.4 (+1.3, -1.0) x 10^21 cm^-2, in
excess of the Galactic value of 2.3 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 3.1 x 10^-11 (5.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.4 (+1.3, -1.0) x 10^21 cm^-2
Galactic foreground: 2.3 x 10^20 cm^-2
Excess significance: 3.5 sigma
Photon index:	     2.3 (+0.4, -0.3)

If the light curve continues to decay with a power-law decay index of
1.3, the count rate at T+24 hours will be 0.017 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.2 x
10^-13 (8.5 x 10^-13) erg cm^-2 s^-1.

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

This circular is an official product of the Swift-XRT team.
Looking for U.S. government information and services? Visit