arXiv subjects

Ildar I. Khabibullin

Publications and source records attributed to Ildar I. Khabibullin.

4 recordsLinked to original sources

arXiv2026

Iron He-triplet signatures of shocks in the hottest galaxy clusters. Z/W line ratio, line broadening, and electron-ion temperature equilibration

A merger of clusters naturally drives shocks with Mach number $\mathscr{M}\lesssim 3$ in the intra-cluster medium (ICM). This process creates several distinct signatures, including sharp surface brightness "edges", temperature, and gas velocity jumps. The low density of the ICM implies that the ionization balance and electron-ion equilibration times can be long enough to produce a set of additional observable signatures. Here, we focus on two "transient" spectral signatures accessible with the high-energy-resolution telescopes such as XRISM, even for unfavorable geometry, e.g., when we are looking inside the Mach cone of the shock, precluding the appearance of sharp edges in X-ray images. In this work, we focus on (i) the $\mathtt{Z/W}$ line ratio of the Fe~XXV triplet and (ii) the contribution of ions with $T_i>T_{\rm e}$ to the line width, which might be mistakenly interpreted as the gas turbulence. We demonstrate that the $\mathtt{Z/W}$ ratio can serve as a proxy for the non-equilibrium state of the shocked ICM and facilitate interpretation of the line broadening. We conclude that these spectral signatures are within reach with missions like XRISM and can be used to constrain the heating of electrons at the collisionless cluster shocks, as well as the rate of subsequent temperature equilibration between different particle species.

astro-ph.HE↗

arXiv2024

Study of X-ray emission from the S147 nebula by SRG/eROSITA: supernova-in-the-cavity scenario

The Simeis~147 nebula (S147), particularly well known for a spectacular net of ${\rm H}_α$-emitting filaments, is often considered one of the largest and oldest known supernova remnants in the Milky Way. Here, and in a companion paper, we present studies of X-ray emission from the S147 nebula using the data of SRG/eROSITA All-Sky Survey observations. In this paper, we argue that many inferred properties of the X-ray emitting gas are broadly consistent with a scenario of the supernova explosion in a low-density cavity, e.g. a wind-blown-bubble. This scenario assumes that a $\sim 20\,{\rm M_\odot}$ progenitor star has had small velocity with respect to the ambient ISM, so it stayed close to the center of a dense shell created during its Main Sequence evolution till the moment of the core-collapse explosion. The ejecta first propagate through the low-density cavity until they collide with the dense shell, and only then the reverse shock goes deeper into the ejecta and powers the observed X-ray emission of the nebula. The part of the remnant inside the dense shell remains non-radiative till now and, plausibly, in a state with $T_e<T_i$ and Non-Equilibrium Ionization (NEI). On the contrary, the forward shock becomes radiative immediately after entering the dense shell, and, being subject to instabilities, creates a characteristic "foamy" appearance of the nebula in ${\rm H}_α$ and radio emission.

astro-ph.HE↗

arXiv2023

Exploring chemical enrichment of the intracluster medium with the Line Emission Mapper

Synthesized in the cores of stars and supernovae, most metals disperse over cosmic scales and are ultimately deposited well outside the gravitational potential of their host galaxies. Since their presence is well visible through their X-ray emission lines in the hot gas pervading galaxy clusters, measuring metal abundances in the intracluster medium (ICM) offers us a unique view of chemical enrichment of the Universe as a whole. Despite extraordinary progress in the field thanks to four decades of X-ray spectroscopy using CCD (and gratings) instruments, understanding the precise stellar origins of the bulk of metals, and when the latter were mixed on Mpc scales, requires an X-ray mission capable of spatial, non-dispersive high resolution spectroscopy covering at least the soft X-ray band over a large field of view. In this White Paper, we demonstrate how the Line Emission Mapper (LEM) probe mission concept will revolutionize our current picture of the ICM enrichment. Specifically, we show that LEM will be able to (i) spatially map the distribution of ten key chemical elements out to the virial radius of a nearby relaxed cluster and (ii) measure metal abundances in serendipitously discovered high-redshift protoclusters. Altogether, these key observables will allow us to constrain the chemical history of the largest gravitationally bound structures of the Universe. They will also solve key questions such as the universality of the initial mass function (IMF) and the initial metallicity of the stellar populations producing these metals, as well as the relative contribution of asymptotic giant branch (AGB) stars, core-collapse, and Type Ia supernovae to enrich the cosmic web over Mpc scales. Concrete observing strategies are also briefly discussed.

astro-ph.GA↗

arXiv2014

On the area of accretion curtains from fast aperiodic time variability of the intermediate polar EX Hya

We present results of a study of the fast timing variability of the magnetic cataclysmic variable (mCV) EX Hya. It was previously shown that one may expect the rapid flux variability of mCVs to be smeared out at timescales shorter than the cooling time of hot plasma in the post shock region of the accretion curtain near the WD surface. Estimates of the cooling time and the mass accretion rate, thus provide us with a tool to measure the density of the post-shock plasma and the cross-sectional area of the accretion funnel at the WD surface. We have probed the high frequencies in the aperiodic noise of one of the brightest mCV EX Hya with the help of optical telescopes, namely SALT and the SAAO 1.9m telescope. We place upper limits on the plasma cooling timescale $τ<$0.3 sec, on the fractional area of the accretion curtain footprint $f<1.6\times10^{-4}$, and a lower limit on the specific mass accretion rate $\dot{M}/A \gtrsim $3 g/sec/cm$^{-2}$. We show that measurements of accretion column footprints via eclipse mapping highly overestimate their areas. We deduce a value of $Δr/r \lesssim 10^{-3}$ as an upper limit to the penetration depth of the accretion disc plasma at the boundary of the magnetosphere.

astro-ph.HE↗