Detection capabilities of the Athena X-IFU for the warm-hot intergalactic medium using gamma-ray burst X-ray afterglows

Abstract

At low redshifts, the observed baryonic density falls far short of the total number of baryons predicted. Cosmological simulations suggest that these baryons reside in filamentary gas structures, known as the warm-hot intergalactic medium (WHIM). As a result of the high temperatures of these filaments, the matter is highly ionised such that it absorbs and emits far-UV and soft X-ray photons. Athena, the proposed European Space Agency X-ray observatory, aims to detect the “missing” baryons in the WHIM up to redshifts of z = 1 through absorption in active galactic nuclei and gamma-ray burst (GRB) afterglow spectra, allowing for the study of the evolution of these large-scale structures of the Universe. This work simulates WHIM filaments in the spectra of GRB X-ray afterglows with Athena using the SImulation of X-ray TElescopes framework. We investigate the feasibility of their detection with the X-IFU instrument, through O VII (E = 573 eV) and O VIII (E = 674 eV) absorption features, for a range of equivalent widths imprinted onto GRB afterglow spectra of observed starting fluxes ranging between 10−12 and 10−10 erg cm−2 s−1, in the 0.3−10 keV energy band. The analyses of X-IFU spectra by blind line search show that Athena will be able to detect O VII−O VIII absorption pairs with EWO VII > 0.13 eV and EWO VIII > 0.09 eV for afterglows with F > 2 × 10−11 erg cm−2 s−1. This allows for the detection of ≈ 45−137 O VII−O VIII absorbers during the four-year mission lifetime. The work shows that to obtain an O VII−O VIII detection of high statistical significance, the local hydrogen column density should be limited at NH < 8 × 1020 cm−2.

The warm-hot circumgalactic medium around EAGLE-simulation galaxies and its detection prospects with X-ray and UV line absorption

“…This is for 50 ks exposure times and a quasar background source with a 2-10 keV flux of 10 −11 erg cm −2 s −1 and a photon spectral index Γ = 1.8 (Lumb et al 2017). Blind detections of pairs of O vii and O viii absorption lines should be possible at lower EWs than this, at least against bright gamma-ray burst background sources (Walsh et al 2020). We convert these minimum EWs to minimum column densities using the best-fitting relations shown in Fig.…”

Probing the physical properties of the intergalactic medium using gamma-ray bursts

“…However, tracing individual features of the IGM metals in X-ray with current instruments is very limited. Athena, the proposed European Space Agency X-ray observatory, aims to study the IGM through detailed observations of O VII (E = 573 eV) and O VIII (E = 674 eV) absorption features (Walsh et al 2020).…”

A new benchmark of soft X-ray transition energies of $$\mathrm {Ne}$$, $$\mathrm {CO}_2$$, and $$\mathrm {SF}_6$$: paving a pathway towards ppm accuracy

“…Due to the success of these measurements, future astrophysical X-ray observatories such as XRISM , Athena , Arcus , or Lynx , envision spectral resolving powers as high as 5000, implying the ability to accurately determine centroids to 10 ppm, or absolute Doppler velocity [ 12 – 17 ]. These instruments will open up the field of spatially resolved, high-resolution X-ray spectroscopy, and will allow scientists to access techniques that are currently not available to X-ray astronomy such as X-ray Fine Structure Absorption measurements for solids [ 18 ], the imaging of velocity fields in galaxy clusters [ 19 ], or diagnosing the properties of the Warm and Hot Intergalactic Medium [ 20 ].…”