Periodicity from X-ray sources within the inner Galactic disk

Abstract

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 ($350^{\circ }\lesssim l\lesssim +7^{\circ }$ and $-1^{\circ }\lesssim b\lesssim +1^{\circ }$) 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.

19 pages, 9 figures, accepted for publication in A&A

References in corpus (21)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Assessing statistical significance of periodogram peaks
• The XMM-Newton serendipitous survey IX. The fourth XMM-Newton serendipitous source catalogue
• Discrete sources as the origin of the Galactic X-ray ridge emission
• Detection of large-scale X-ray bubbles in the Milky Way halo
• A Catalog of X-ray Point Sources from Two Megaseconds of Chandra Observations of the Galactic Center
• The Galactic Centre Chimney
• The Galactic center chimneys: The base of the multiphase outflow of the Milky Way
• New Gamma Cas-like objects: X-ray and optical observations of SAO49725 and HD161103
• CTCV J2056-3014: An X-ray-faint Intermediate Polar Harboring An Extremely Fast-spinning White Dwarf
• CXOGBS J174954.5-294335: A New Deeply-Eclipsing Intermediate Polar
• Study of the excess Fe XXV line emission in the central degrees of the Galactic centre using XMM-Newton data
• Hard X-ray luminosity functions of cataclysmic variables: Joint Swift/BAT and Gaia data
• Discovery of X-ray Pulsations from the HMXB Source AXJ1749.1-2733
• Unveiling the nature of the highly absorbed X-ray source SAXJ1748.2-2808 with XMM-Newton
• Discovery of periodicities in two highly variable intermediate polars towards the Galactic Center
• An intermediate polar candidate toward the Galactic plane
• Spectroscopic classification of X-ray sources in the Galactic Bulge Survey
• Timing analysis of a sample of five cataclysmic variable candidates observed by the XMM-Newton satellite

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• Multiwavelength Evidence for Two New Candidate Transitional Millisecond Pulsars in the Sub-luminous Disk State: 4FGL J0639.1--8009 and 4FGL J1824.2+1231
• XMM-Newton and NuSTAR discovery of a likely IP candidate XMMU J173029.8-330920 in the Galactic Disk
• Unveiling the soft X-ray source population towards the inner Galactic disk with XMM-Newton