Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2010-05-10
2010AJ....140..157B
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
11 pages, 7 figures; to be published in the Astronomical Journal; data available on MAGPIS website at http://third.ucllnl.org/
Scientific paper
Using three epochs of VLA observations of the Galactic Plane in the first quadrant taken ~15 years apart, we have conducted a search for a population of variable Galactic radio emitters in the flux density range 1-100 mJy at 6 cm. We find 39 variable sources in a total survey area of 23.2 sq deg. Correcting for various selection effects and for the extragalactic variable population of active galactic nuclei, we conclude there are ~1.6 Galactic sources per sq deg which vary by more than 50% on a time scale of years (or shorter). We show that these sources are much more highly variable than extragalactic objects; more than 50% show variability by a factor >2 compared to <10% for extragalactic objects in the same flux density range. We also show that the fraction of variable sources increases toward the Galactic center (another indication that this is a Galactic population), and that the spectral indices of many of these sources are flat or inverted. A small number of the variables are coincident with mid-IR sources and two are coincident with X-ray emitters, but most have no known counterparts at other wavelengths. Intriguingly, one lies at the center of a supernova remnant, while another appears to be a very compact planetary nebula; several are likely to represent activity associated with star formation regions. We discuss the possible source classes which could contribute to the variable cohort and followup observations which could clarify the nature of these sources.
Becker Robert H.
Helfand David J.
Proctor Deanne D.
White Richard L.
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