XZ: Deriving redshifts from X-ray spectra of obscured AGN

Simmonds, Charlotte; Buchner, Johannes; Salvato, M.; Hsu, Li-Ting; Bauer, F. E.

doi:10.1051/0004-6361/201833412

Cited by 36 publications

(68 citation statements)

References 43 publications

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“…For the latter, we used XSPEC v12.10.1 45 with its Python-oriented interface pyXSPEC. eROSITA source-plus-background spectra were fitted including a model component for the background, which was determined via a principal component analysis from a large sample of eROSITA background spectra 46 (J.B. et al, manuscript in preparation). XMM-Newton EPIC-pn spectra were instead fitted using wstat, namely the XSPEC implementation of the Cash statistic 47 , given the good count statistics in both source and background spectra.…”

Section: Methodsmentioning

confidence: 99%

X-ray quasi-periodic eruptions from two previously quiescent galaxies

Arcodia

Merloni

Nandra

et al. 2021

Nature

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140

171

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Quasi-periodic eruptions (QPEs) are very-high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central supermassive black holes of galactic nuclei1,2. It is currently unknown what triggers these events, how long they last and how they are connected to the physical properties of the inner accretion flows. Previously, only two such sources were known, found either serendipitously or in archival data1,2, with emission lines in their optical spectra classifying their nuclei as hosting an actively accreting supermassive black hole3,4. Here we report observations of QPEs in two further galaxies, obtained with a blind and systematic search of half of the X-ray sky. The optical spectra of these galaxies show no signature of black hole activity, indicating that a pre-existing accretion flow that is typical of active galactic nuclei is not required to trigger these events. Indeed, the periods, amplitudes and profiles of the QPEs reported here are inconsistent with current models that invoke radiation-pressure-driven instabilities in the accretion disk5–9. Instead, QPEs might be driven by an orbiting compact object. Furthermore, their observed properties require the mass of the secondary object to be much smaller than that of the main body10, and future X-ray observations may constrain possible changes in their period owing to orbital evolution. This model could make QPEs a viable candidate for the electromagnetic counterparts of so-called extreme-mass-ratio inspirals11–13, with considerable implications for multi-messenger astrophysics and cosmology14,15.

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Section: Methodsmentioning

confidence: 99%

X-ray quasi-periodic eruptions from two previously quiescent galaxies

Arcodia

Merloni

Nandra

et al. 2021

Nature

Self Cite

140

171

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“…X-ray spectra were analysed using the Bayesian X-ray Analysis software (BXA, Buchner et al 2014), which connects the nested sampling algorithm MultiNest (Feroz & Hobson 2008) with the fitting environment CIAO/Sherpa (Freeman et al 2001) and XSPEC (Arnaud 1996). The spectra were fitted unbinned using the C-statistic (Cash 1976), and the eROSITA and XRT backgrounds were both modelled using the principal component analysis (PCA) technique described in Simmonds et al (2018). For each set of eROSITA and XRT spectra, a joint fit on both the source and background spectra was run.…”

Section: X-ray Spectral Fittingmentioning

confidence: 99%

AT 2019avd: a novel addition to the diverse population of nuclear transients

Malyali

Rau

Merloni

et al. 2021

A&A

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We report on SRG/eROSITA, ZTF, ASAS-SN, Las Cumbres, neoWISE and Swift XRT/UVOT observations of the unique ongoing event AT 2019avd, located in the nucleus of a previously inactive galaxy at z = 0.029. eROSITA first observed AT 2019avd on 2020-04-28 during its first all sky survey, when it was detected as an ultrasoft X-ray source (kT ∼ 85 eV) that was 90 times brighter in the 0.2 − 2 keV band than a previous 3σ upper flux detection limit (with no archival X-ray detection at this position). The ZTF optical lightcurve in the ∼ 450 days preceding the eROSITA detection is double peaked, and the eROSITA detection coincides with the rise of the second peak. Follow-up optical spectroscopy shows the emergence of a Bowen fluorescence feature and high ionisation coronal lines ([Fe x] 6375 Å, [Fe xiv] 5303 Å), along with persistent broad Balmer emission lines (FWHM∼ 1400 km s −1). Whilst the X-ray properties make AT 2019avd a promising tidal disruption event (TDE) candidate, the optical properties are atypical for optically-selected TDEs. We discuss potential alternative origins that could explain the observed properties of AT 2019avd, such as a stellar binary TDE candidate, or a TDE involving a super massive black hole binary.

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“…Fortunately, there is a good prospect that redshifts can be determined solely from X-ray spectra (e.g. Simmonds et al 2018;Peca et al 2021). We simulated mid-IR spectra to evaluate the possibility of measuring the redshift from a SMI-LR-like spectra.…”

Section: Spectroscopic Detectionsmentioning

confidence: 99%

The role of SPICA-like missions and the Origins Space Telescope in the quest for heavily obscured AGN and synergies with Athena

Barchiesi

Pozzi

Vignali

et al. 2021

Publ. Astron. Soc. Aust.

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In the black hole (BH)–galaxy co-evolution framework, most of the star formation (SF) and the BH accretion are expected to take place in highly obscured conditions. The large amount of gas and dust absorbs most of the UV-to-soft-X radiation and re-emits it at longer wavelengths, mostly in the IR. Thus, obscured active galactic nuclei (AGN) are very difficult to identify in optical or X-ray bands but shine bright in the IR. Moreover, X-ray background (XRB) synthesis models predict that a large fraction of the yet-unresolved XRB is due to the most obscured (Compton thick, CT: N $_{\text{H}}\ge 10^{24} \,\mathrm{cm}^{-2}$ ) of these AGN. In this work, we investigate the synergies between putative IR missions [using SPace Infrared telescope for Cosmology and Astrophysics (SPICA), proposed for European Space Agency (ESA)/M5 but withdrawn in 2020 October, and Origins Space Telescope, OST, as ‘templates’] and the X-ray mission Athena (Advanced Telescope for High ENergy Astrophysics), which should fly in early 2030s, in detecting and characterising AGN, with a particular focus on the most obscured ones. Using an XRB synthesis model, we estimated the number of AGN and the number of those which will be detected in the X-rays by Athena. For each AGN, we associated an optical-to-Far InfraRed (FIR) spectral energy distribution (SED) from observed AGN with both X-ray data and SED decomposition and used these SEDs to check if the AGN will be detected by SPICA-like or OST at IR wavelengths. We expect that, with the deepest Athena and SPICA-like (or OST) surveys, we will be able to photometrically detect in the IR more than 90% of all the AGN (down to $L_{2-10\text{keV}} \sim 10^{42}\,\mathrm{erg\ s}^{-1}$ and up to $z \sim 10$ ) predicted by XRB synthesis modeling, and we will detect at least half of them in the X-rays. The spectroscopic capabilities of the OST can provide ${\approx}51\,000$ and ${\approx}3\,400$ AGN spectra with $R= 300$ at 25–588 $\unicode[Times]{x03BC}$ m in the wide and deep surveys, respectively, the last one up to $z\approx 4$ . Athena will be extremely powerful in detecting and discerning moderate- and high-luminosity AGN, allowing us to properly select AGN even when the mid-IR torus emission is ‘hidden’ by the host galaxy contribution. We will constrain the intrinsic luminosity and the amount of obscuration for $\sim\!20\%$ of all the AGN (and $\sim\!50\%$ of those with $L_{2-10\text{keV}} > 3.2 \times 10^{43}\,\mathrm{erg\ s}^{-1}$ ) using the X-ray spectra provided by Athena WFI. We find that the most obscured and elusive CT-AGN will be exquisitely sampled by SPICA-like mission or OST and that Athena will allow a fine characterisation of the most luminous ones. This will provide a significant step forward in the process of placing stronger constraints on the yet-unresolved XRB and investigating the BH accretion rate evolution up to very high redshift ( $z \ge 4$ ).

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XZ: Deriving redshifts from X-ray spectra of obscured AGN

Cited by 36 publications

References 43 publications

X-ray quasi-periodic eruptions from two previously quiescent galaxies

X-ray quasi-periodic eruptions from two previously quiescent galaxies

AT 2019avd: a novel addition to the diverse population of nuclear transients

The role of SPICA-like missions and the Origins Space Telescope in the quest for heavily obscured AGN and synergies with Athena

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