M. van den Berg
- The ChaMPlane Bright X-Ray Sources-Galactic Longitudes l = 2°-358°
- Astrophysical Journal
- Pages (from-to)
- Document type
- Faculty of Science (FNWI)
- Anton Pannekoek Institute for Astronomy (API)
The Chandra Multi-wavelength Plane (ChaMPlane) survey aims to constrain the Galactic population of mainly accretion-powered, but also coronal, low-luminosity X-ray sources (L X lsim 1033 erg s-1). To investigate the X-ray source content in the plane at fluxes F X gsim 3 × 10-14 erg s-1 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 gsim100 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 >104 fainter sources in ChaMPlane.
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