  [Abridged] We have discovered 10 periodic X-ray sources from the 1 Ms Chandra
ACIS observation of the Limiting Window (LW), a low extinction region (A_V~3.9)
at 1.4 Deg south of the Galactic center. The observed periods (~1.3 to 3.4
hours) and the X-ray luminosities (10^{31.8-32.9} erg s^-1 at 8 kpc) of the 10
periodic sources, combined with the lack of bright optical counterparts and
thus high X-ray-to-optical flux ratios, suggest that they are likely accreting
binaries, in particular, magnetic cataclysmic variables (MCVs). All of the 10
sources exhibit a relatively hard X-ray spectrum (PLI<2 for a power law model)
and X-ray spectra of at least five show an extinction larger than the field
average expected from the interstellar medium in the region. The discovery of
these periodic X-ray sources in the LW further supports the current view that
MCVs constitute the majority of low luminosity hard X-ray sources (~10^{30-33}
erg s^-1) in the Bulge. The period distribution of these sources resembles
those of polars, whereas the relatively hard spectra suggest that they could be
intermediate polars (IPs). These puzzling properties can be explained by
unusual polars with buried magnetic fields or a rare sub-class of MCVs, nearly
synchronous MCVs. These unusual MCVs may provide important clues in the
evolutionary path of MCVs from IPs to polars. The completeness simulation
indicates >~40% of the hard X-ray sources in the LW are periodic. Therefore,
this discovery provides a first direct evidence of a large MCV population in
the Bulge.
