Periodicity from X-ray sources within the inner Galactic disk
Astronomy & Astrophysics(2024)
摘要
For many years, it has been claimed that the Galactic ridge X-ray emission at
the Galactic Center (GC) is truly diffuse in nature. However, with the
advancement of modern X-ray satellites, it has been found that most of the
diffuse emission is actually comprised of thousands of previously unresolved
X-ray point sources. Further, many studies suggest that a vast majority of
these X-ray point sources are magnetic cataclysmic variables (mCVs) and active
binaries. One unambiguous way to identify these mCVs and other sources is by
detecting their X-ray periodicity. Therefore, we systematically searched for
periodic X-ray sources in the inner Galactic disk, including the GC region. We
have used data from our ongoing XMM-Newton Heritage survey of the inner
Galactic disk (350^∘≲ l≲+7^∘ and
-1^∘≲ b≲ +1^∘) plus the XMM-Newton archival
observations of the GC. We computed the Lomb-Scargle periodogram of the light
curves for the periodicity search. We fitted the energy spectra of the sources
using a simple power-law model plus three Gaussians at 6.4, 6.7, and 6.9 keV
for the iron K emission complex. We detected periodicity in 26 sources. For
14 of them, this is the first discovery of periodicity. For the other 12
sources, we found periods similar to those already known, indicating no
significant period evolution. We also searched for the Gaia counterparts of the
periodic sources to estimate their distances using the Gaia parallax. We found
a likely Gaia counterpart for seven sources. We have classified the sources
into four categories based on the periodicity, hardness ratio, and the
equivalent width of Fe K line emission. Of the 14 sources where we detect the
periodicity for the first time, four are likely to be intermediate polars, five
are likely to be polars, two are neutron star X-ray binaries, and three are of
unknown nature.
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