[Surveys -- Oral ]
The Galactic Bulge Survey: finding eclipsing X-ray binaries and
understanding the Galactic X-ray binary population
Peter Jonker, SRON \& CfA
C. Bassa (Machester Univ), G. Nelemans (Nijmegen Univ) et al.
The Galactic Bulge Survey is a multi-wavelength project aimed
at understanding the population of faint X-ray sources towards the
Galactic center, though avoiding the Galactic plane itself to avoid the
huge extinction and problems caused by crowding. In order to sample the
populations sufficiently, the total survey area will be 12square degrees. It consists of 2ks-long Chandra observations and optical
Blanco images down to r' = 24. Thus far, the optical data is complete
and the Chandra data covering 8.4 square degrees have revealed ~1350
X-ray sources. For ~1000 sources we have discovered counterparts on our
optical Blanco images. A fraction of ~20 per cent of these are expected
to be interloper stars. The plethora of faint X-ray sources will be
compared to detailed population models in order to constrain binary
evolution models, especially the common envelope phase, by way of number
counts. We are using optical to X-ray flux ratios, optical and X-ray
colours and follow-up optical spectroscopyof the detected optical counterparts to classify all sources. We expect
to find several quiescent and eclipsing neutron star and black hole
LMXBs. These will be used for detailed neutron star and black hole mass
measurements. Mass measuremetns are vital for studies of the neutron
star equation of state and supernova modelling. Lastly, wewill use the distribution of (quiescent) LMXBs to test if LMXB formation
requires a kick imparted on the compact object or not as the apparent
asymmetry in the Galactic distribution of LMXBs suggests. We will
present the first results, and first surprises, of our optical and
Chandra observations and the multi-wavelength follow-up of theseChandra X-ray discovered sources.