高能暂现源 · 每日文献综述

The Fe K<inline-formula><tex-math id="TM0001" notation="LaTeX">$\alpha$</tex-math></inline-formula> fluorescence line at 6.4 keV has long been used to probe the relative geometry between photoionizing X-ray sources and surrounding cold material in a wide range of astrophysical systems. With the advent of the X-ray microcalorimeter XRISM/Resolve, Fe K<inline-formula><tex-math id="TM0002" notation="LaTeX">$\alpha$</tex-math></inline-formula> lines with equivalent widths down to <inline-formula><tex-math id="TM0003" notation="LaTeX">${\sim }5$</tex-math></inline-formula> eV-previously inaccessible-are now detectable, and even non-detections can place upper limits of a few eV, making non-detections themselves valuable for constraining the geometry. Considering that Fe K<inline-formula><tex-math id="TM0004" notation="LaTeX">$\alpha$</tex-math></inline-formula>-based geometric diagnostics are entering a new stage in the microcalorimeter era, we present Fe K<inline-formula><tex-math id="TM0005" notation="LaTeX">$\alpha$</tex-math></inline-formula> equivalent-width maps computed with the three-dimensional Monte Carlo radiative-transfer code SKIRT for a generalized configuration consisting of a spherical reflector of radius <inline-formula><tex-math id="TM0006" notation="LaTeX">$R_{*}$</tex-math></inline-formula> and a point source located at a height h above the surface. The equivalent-width maps exhibit two characteristic features: (1) an increase toward the center of the projected surface of the sphere; and (2) an overall decrease with increasing <inline-formula><tex-math id="TM0007" notation="LaTeX">$h/R_{*}$</tex-math></inline-formula>. The key point is that we confirm these features for equivalent widths of <inline-formula><tex-math id="TM0008" notation="LaTeX">${\lt }40$</tex-math></inline-formula> eV, a regime that has become accessible for the first time thanks to the improved detection threshold from <inline-formula><tex-math id="TM0009" notation="LaTeX">${\sim }50$</tex-math></inline-formula> eV with Chandra/HETG to <inline-formula><tex-math id="TM0010" notation="LaTeX">${\sim }5$</tex-math></inline-formula> eV with XRISM/Resolve. As an illustrative application, we compare the maps with XRISM/Resolve spectra of three RS Canum Venaticorum-type stars (GT Muscae, <inline-formula><tex-math id="TM0011" notation="LaTeX">$\sigma$</tex-math></inline-formula> Geminorum, and HR 1099) and constrain the locations of the flare loop and coronal bright points in these systems. Because the maps are constructed for a highly generalized point-source-spherical-reflector geometry, they are readily applicable to many other objects, including X-ray binaries and cataclysmic variables.