3,242 research outputs found
On the origin of two unidentified radio/X-ray sources discovered with XMM-Newton
We aim at clarifying the nature of the emission of two spatially related
unidentified X-ray sources detected with XMM-Newton telescope at
intermediate-low Galactic latitude. Observations reveal a point-like source
aligned with elongated diffuse emission. The X-ray spectra are best-fitted by
absorbed power laws with photon indices ~1.7 for the point-like and ~2.0 for
the extended one. Both sources show nonthermal radio-continuum counterparts
that might indicate a physical association. From the available data, we did not
detect variability on the point-like source in several timescales. Two possible
scenarios are analyzed: first, based on HI line absorption, assuming a Galactic
origin, we infer a distance upper bound of <2 kpc, which poses a constraint on
the height over the Galactic plane of <200 pc and on the linear size of the
system of 10^32 erg/s and
>7.5 x 10^32 erg/s, for the point-like and extended sources, respectively;
second, an extra-Galactic nature is discussed, where the point-like source
might be the core of a radio galaxy and the extended source its lobe. In this
case, we compare derived fluxes, spectral indices, and spatial correlation with
those typical from the radio galaxy population, showing the feasibility of this
alternative astrophysical scenario. From the available observational evidence,
we suggest that the most promising scenario to explain the nature of these
sources is a system consisting of a one-sided radio galaxy, where the
point-like source is an active galactic nucleus and the extended source
corresponds to the emission from its lobe. Other possibilities include a
PSR/PWN origin, where the radio/X-ray emission originates from the synchrotron
cooling of relativistic particles in the PSR magnetic field or a casual
alignment between two unrelated sources, such as an AGN core and a Galactic
X-ray blob.Comment: 6 pages, 2 figures. Accepted for publication in Astronomy and
Astrophysics (A&A
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