The origin of optical emission lines in the soft state of X-ray binary outbursts: The case of MAXI J1820+070
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2023)
Abstract:
<jats:title>Abstract</jats:title> <jats:p>The optical emission line spectra of X-ray binaries (XRBs) are thought to be produced in an irradiated atmosphere, possibly the base of a wind, located above the outer accretion disc. However, the physical nature of – and physical conditions in – the line-forming region remain poorly understood. Here, we test the idea that the optical spectrum is formed in the transition region between the cool, geometrically thin part of the disc near the mid-plane and a hot, vertically extended atmosphere or outflow produced by X-ray irradiation. We first present a VLT X-Shooter spectrum of XRB MAXI J1820+070 in the soft state associated with its 2018 outburst, which displays a rich set of double-peaked hydrogen and helium recombination lines. Aided by ancillary X-ray spectra and reddening estimates, we then model this spectrum with the Monte Carlo radiative transfer code Python, using a simple biconical disc wind model inspired by radiation-hydrodynamic simulations of irradiation-driven outflows from XRB discs. Such a model can qualitatively reproduce the observed features; nearly all of the optical emission arising from the transonic ‘transition region’ near the base of the wind. In this region, characteristic electron densities are on the order of 1012 − 13 cm−3 , in line with the observed flat Balmer decrement (Hα/Hβ ≈ 1.3). We conclude that strong irradiation can naturally give rise to both the optical line-forming layer in XRB discs and an overlying outflow/atmosphere that produces X-ray absorption lines.</jats:p>Correction to: Evidence for a moderate spin from X-ray reflection of the high-mass supermassive black hole in the cluster-hosted quasar H1821+643
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 517:1 (2022) 1006-1006
Connecting radio emission to AGN wind properties with broad absorption line quasars
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 515:4 (2022) 5159-5174
Evidence for a moderate spin from X-ray reflection of the high-mass supermassive black hole in the cluster-hosted quasar H1821+643
Monthly Notices of the Royal Astronomical Society Oxford University Press 514:2 (2022) 2568-2580
Abstract:
We present an analysis of deep Chandra Low-Energy and High-Energy Transmission Grating archival observations of the extraordinarily luminous radio-quiet quasar H1821+643, hosted by a rich and massive cool-core cluster at redshift z = 0.3. These data sets provide high-resolution spectra of the AGN at two epochs, free from contamination by the intracluster medium and from the effects of photon pile-up, providing a sensitive probe of the iron-K band. At both epochs, the spectrum is well described by a power-law continuum plus X-ray reflection from both the inner accretion disc and cold, slowly moving distant matter. Adopting this framework, we proceed to examine the properties of the inner disc and the black hole spin. Using Markov chain Monte Carlo (MCMC) methods, we combine constraints from the two epochs assuming that the black hole spin, inner disc inclination, and inner disc iron abundance are invariant. The black hole spin is found to be modest, with a 90 per cent credible range of a ∗=0.62+0.22-0.37 and, with a mass MBH in the range log (MBH/M·) ∼9.2-10.5, this is the most massive black hole candidate for which a well-defined spin constraint has yet been obtained. The modest spin of this black hole supports previous suggestions that the most massive black holes may grow via incoherent or chaotic accretion and/or SMBH-SMBH mergers.A Decade of Black-Hole X-ray Binary Transients
Proceedings of Science 401 (2022)