The properties of the Galactic Ridge X-ray Emission (GRXE) observed in the 2-10 keV band place fundamental constraints on various types of X-ray sources in the Milky Way. Although the primarily discrete origin of the emission is now well established, the responsible populations of these sources remain uncertain, especially at relatively low fluxes. To provide insights into this issue, we systematically characterize the Fe emission line properties of the candidate types of the sources in the solar neighborhood and compare them with those measured for the GRXE. Our source sample includes 6 symbiotic stars (SSs), 16 intermediate polars (IPs), 3 polars, 16 quiescent dwarf novae (DNe) and 4 active binaries (ABs). We find that the mean equivalent width ($EW_{6.7}$) of the 6.7-keV line and the mean 7.0/6.7-keV line ratio are $107\pm16.0$ eV and $0.71\pm 0.04$ for intermediate polars and $221\pm 135$ eV and $0.44\pm 0.14$ for polars, respectively, which are all substantially different from those ($490\pm15 $~eV and $0.2\pm 0.08$) for the GRXE. Instead, the GRXE values are better agreed by the $EW_{6.7}$ ($438\pm 84.6$~eV) and the ratio ($0.27\pm 0.06$) observed for the DNe.
We further find that the $EW_{6.7}$ is strongly correlated with the 2-10-keV luminosity of the DNe, which can be characterized by the relation $EW_{6.7}=(438\pm95 {\rm~eV}) (L/10^{31}~{\rm~ergs~s^{-1} })^{(-0.31\pm0.15)}$. Accounting for this correlation, the agreement can be improved further, especially when the contributions from other classes sources to the GRXE are considered, which all have low $EW_{6.7}$ values. We conclude that the GRXE mostly consists of typically faint, but numerous DNe, plus ABs, while magnetic CVs are probably mainly the high-flux representatives of the responsible populations and dominate the GRXE only in harder energy bands.
Hard X-ray luminosity functions of cataclysmic variables: Joint Swift/BAT and Gaia data
Institut für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Universität Tübingen（蒂宾根大学天文与天体物理研究所、开普勒天文与粒子物理中心）；Kazan (Volga region) Federal University（喀山（伏尔加地区）联邦大学）；Space Research Institute, Russian Academy of Sciences（俄罗斯科学院空间研究所）
Enhancement of the 6.4 keV line in the inner Galactic ridge: Proton-induced fluorescence?
对于银河系弥漫X射线辐射的起源，特别是来自中性和高度电离原子的铁谱线的起源，一个普遍的想法是许多激变变星和日冕活动双星的叠加。在这种情况下，流量应该对称地分布在相对于人马座A $^*$的平面上的东西之间，因为由红外观测确定的恒星质量分布是近似对称的。这种对称性被确认为高度电离的铁线以及连续发射。然而，在银河系中心的近东侧，中性铁谱线比近西侧明显过剩，过剩辐射的通量分布与分子柱密度有很好的相关性。过量发射的X射线谱由幂律连续谱加上6.4 keV的线描述，该线具有$\sim1.3$ keV的大等效宽度，这很难用低能电子轰击方案来解释。过量辐射的经度和纬度分布不利于X射线辐射，无论是人马座A $^*$还是附近的X射线双星。那么低能质子轰击是最可能的起源，尽管需要0.1-1000 MeV的高能量密度$\sim 80$ eV cm $^{-3}$，并且附近没有常规的质子源。
Origin of the Galactic Diffuse X-ray Emission: Iron K-shell Line Diagnostics
本文详细报道了银河系中心X射线发射（GCXE）、银河系凸起X射线发射（GBXE）、银河系脊X射线发射（GRXE）、磁激变变星（mCV）、非磁激变变星（non-mCV）和日冕活动双星（AB）的铁（Fe）和镍（Ni）K壳层线轮廓。为了研究GCXE、GBXE和GRXE的起源，对Fe K $α$、Fe He $α$和Fe Ly $α$谱线的等效宽度进行了光谱分析。通过mCV、非mCV和ABs光谱的组合再现GBXE的全局光谱。另一方面，GRXE谱显示在Fe K $α$和Fe He $α$线能量处的显著数据过量。这意味着需要除了mCV、非mCV和AB之外的附加组件，其具有冷气体和非常高温等离子体的共生现象。GCXE光谱在铁和镍的所有K-壳层线处显示出比GRXE光谱中发现的更大的过量。其中最大的是Fe K $α$、Fe He $α$、Fe Ly $α$和Fe Ly $β$线。结合Fe K $α$、Fe He $α$和Fe Ly $α$谱线的标度高度与中心分子带（CMZ）相似的事实，过量组分可能与CMZ极端扩展中的高能活动有关。
Iron Fluorescent Line Emission from the mCvs and Hard X-ray Emitting Symbiotic Stars as a Source of the Iron Fluorescent Line Emission from the Galactic Ridge
Classifying optical (out)bursts in cataclysmic variables: the distinct observational characteristics of dwarf novae, micronovae, stellar flares and magnetic gating
X-ray luminous late-type giants: an overlooked population contributing to the Galactic ridge iron line emission
INAF – Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；Max-Planck-Institut Extraterrestriche Physik（马克斯·普朗克地外物理研究所）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Department of Physics and Astronomy, University of California, Los Angeles（加州大学洛杉矶分校物理与天文学系）；Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学哥伦比亚天体物理学实验室）；Instituto de Astrofisica de Canarias（加那利群岛天体物理研究所）；Departamento de Astrofisica, Universidad de La Laguna（拉帕尔马大学天体物理学系）
Fe Kα equivalent-width mapping with 3D radiative transfer calculation: A general model and application to the RS Canum Venaticorum-type stars with XRISM/Resolve
Kyoto University（京都大学）；Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA)（日本宇宙航空研究开发机构空间科学研究所）；Laboratory for Atmospheric and Space Physics, University of Colorado Boulder（科罗拉多大学博尔德分校大气与空间物理实验室）；The University of Tokyo（东京大学）；RIKEN Cluster for Pioneering Research（理化学研究所前沿研究集群）
