Maureen van den Berg, Kyle Penner, JaeSub Hong, Jonathan E. Grindlay, Ping Zhao, Silas Laycock, Mathieu Servillat
The Chandra Multiwavelength Plane (ChaMPlane) Survey aims to constrain the
Galactic population of mainly accretion-powered, but also coronal,
low-luminosity X-ray sources (Lx <~ 1e33 erg/s). To investigate the X-ray
source content in the plane at fluxes Fx >~ 3e-14 erg/s/cm^2, we study 21 of
the brightest ChaMPlane sources, viz. those with >250 net counts (0.3-8 keV).
By excluding the heavily obscured central part of the plane, our
optical/near-infrared follow-up puts useful constraints on their nature. We
have discovered two likely accreting white-dwarf binaries. CXOPS
J154305.5-522709 (CBS 7) is a cataclysmic variable showing periodic X-ray flux
modulations on 1.2 hr and 2.4 hr; given its hard spectrum the system is likely
magnetic. We identify CXOPS J175900.8-334548 (CBS 17) with a late-type giant;
if the X-rays are indeed accretion-powered, it belongs to the small but growing
class of symbiotic binaries lacking strong optical nebular emission lines.
CXOPS J171340.5-395213 (CBS 14) is an X-ray transient that brightened >~100
times. We tentatively classify it as a very late-type (>M7) dwarf, of which few
have been detected in X-rays. The remaining sources are (candidate) active
galaxies, normal stars and active binaries, and a plausible young T Tauri star.
The derived cumulative number density versus flux (log N - log S) relation for
the Galactic sources appears flatter than expected for an isotropic
distribution, indicating that we are seeing a non-local sample of mostly
coronal sources. Our findings define source templates that we can use, in part,
to classify the >1e4 fainter sources in ChaMPlane.
View original:
http://arxiv.org/abs/1201.5038
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