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 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 (SIXTE) 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 EW${}_{\mathrm{OVII}}>0.13$ eV and EW${}_{\mathrm{OVIII}}>0.09$ eV for afterglows with $F>2\times 10^{-11}$ erg cm${}^{-2}$ s${}^{-1}$. This allows for the detection of $\approx$ 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 $N_{\mathrm{H}}<8\times 10^{20}$ cm${}^{-2}$.

Accepted for publication in Astronomy & Astrophysics

References in corpus (12)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• An online repository of Swift/XRT light curves of GRBs
• Active Galactic Nuclei: what's in a name?
• On the use of C-stat in testing models for X-ray spectra
• On the Putative Detection of z>0 X-ray Absorption Features in the Spectrum of Markarian 421
• HERMES: An ultra-wide band X and gamma-ray transient monitor on board a nano-satellite constellation
• Detection of the Missing Baryons toward the Sightline of H1821+643
• The abundance and physical properties of O VII and O VIII X-ray absorption systems in the EAGLE simulations
• The Physical Origins of the Identified and Still Missing Components of the Warm-Hot Intergalactic Medium: Insights from Deep Surveys in the Field of Blazar 1ES1553+113
• Hot WHIM counterparts of FUV OVI absorbers: Evidence in the line-of-sight towards quasar 3C 273

Cited by in corpus (6)

• Synergies of THESEUS with the large facilities of the 2030s and guest observer opportunities
• Probing the physical properties of the intergalactic medium using gamma-ray bursts
• A new benchmark of soft X-ray transition energies of Ne, CO${}_2$, and SF${}_6$: paving a pathway towards ppm accuracy
• Probing the physical properties of the IGM using SRG/eROSITA spectra from blazars
• The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase
• Future Detections of the Warm-Hot Intergalactic Medium using Bright Power Law Sources with NewAthena