Milky Way X-Ray Sources

ChaMPlane, Bulge Windows and Bulge Latitude Surveys

A major survey using Chandra archival data as well as optical imaging and spectroscopy for source identifications has been underway since 2001. The Chandra Multi-wavelength Plane (ChaMPlane) Survey uses archival ACIS-I and -S images from Chandra pointings within |b| < 11 deg and exposure times T > 10 ksec, in order to make an unbiased survey for the low-luminosity point source population of X-ray sources in the Galaxy. Only images without bright point sources, clusters or diffuse emission for their original targets, are selected. The primary objective is to measure or constrain the various populations of accretion-powered sources: accreting white dwarfs (cataclysmic variables), neutron stars and black holes (quiescent low-mass X-ray binaries) and the most numerous high-mass X-ray binaries containing Be stars as mass donors. The principal secondary objective is to study the populations of stellar coronal sources in the Galaxy. With the remarkable Chandra sensitivity and spatial resolution, ChaMPlane is able to discover and locate sources with Lx ~1031 erg/s at distances ~3-10 kpc (depending on exposure) so that source populations on Galactic scales can be studied for the first time.

ChaMPlane has now accumulated some 125 distinct fields (observed in more than 200 pointings) that are observed with deep optical (V, R, I and Halpha) images from a parallel Long Term Survey program supported by NOAO (2001-2006). Deep near-infrared images (J, H and K) and follow-up spectroscopy supported by a second NOAO Long Term Survey (ChaMPlane-II) will be obtained beginning in 2007.

Three low-extinction Windows in the Galactic Bulge have been targeted by the ChaMPlane Team to do deeper exposures together with HST/ACS imaging (of the central 6.7 x 6.7 arcmin2 of the ACIS field). Baade's Window was observed in 2003, "Stanek's Window" in 2004, and a "Limiting Window" (the moderate extinction window closest to the Galactic Center) in 2005.

Finally, the ChaMPlane Team is conducting a "Bulge Latitude Survey" (BLS) to measure the latitude distribution of faint point sources in the region |b| = ±1.5 deg, l = ±0.4deg centered at l = 0deg to complement the previous survey of Wang et al. for the longitude distribution of sources in the central Bulge.