A new emulated Monte Carlo radiative transfer disc-wind model: X-Ray Accretion Disc-wind Emulator – xrade

Abstract

We present a new X-Ray Accretion Disk-wind Emulator (xrade) based on the 2.5D Monte Carlo radiative transfer code which provides a physically-motivated, self-consistent treatment of both absorption and emission from a disk-wind by computing the local ionization state and velocity field within the flow. xrade is then implemented through a process that combines X-ray tracing with supervised machine learning. We develop a novel emulation method consisting in training, validating, and testing the simulated disk-wind spectra into a purposely built artificial neural network. The trained emulator can generate a single synthetic spectrum for a particular parameter set in a fraction of a second, in contrast to the few hours required by a standard Monte Carlo radiative transfer pipeline. The emulator does not suffer from interpolation issues with multi-dimensional spaces that are typically faced by traditional X-ray fitting packages such as xspec. xrade will be suitable to a wide number of sources across the black-hole mass, ionizing luminosity, and accretion rate scales. As an example, we demonstrate the applicability of xrade to the physical interpretation of the X-ray spectra of the bright quasar PDS 456, which hosts the best-established accretion-disk wind observed to date. We anticipate that our emulation method will be an indispensable tool for the development of high-resolution theoretical models, with the necessary flexibility to be optimized for the next generation micro-calorimeters on board future missions, like XRISM/Resolve and Athena/X-IFU. This tool can also be implemented across a wide variety of X-ray spectral models and beyond.

The outburst of the changing-look AGN IRAS 23226-3843 in 2019

“…In this version of the disk wind model the f v and µ = cos(i) parameters do not interpolate well between grid points, so we fix these parameters to the closest grid point after the intial fit, and do not calculate errors. This issue is fixed in the new version of the model(Matzeu et al 2022). 2 The normalizations of the xillver and relxill models are defined based on the flux of the incident spectrum, seeDauser et al (2016).…”

Supermassive Black Hole Winds in X-rays: SUBWAYS

“…As we have learned from previous work, in ultra-fast wind systems the ionised emission due to scattered photons from the outflowing material can be as important as the absorption (e.g. Sim et al 2008;Nardini et al 2015;Luminari et al 2018;Matzeu et al 2022). In several SUBWAYS spectra, the shape of the emission and/or absorption profiles is indeed complex/broad, which suggests a superposition/blending of multiple ionised lines.…”

“…After a careful check we confirm that the line detections are genuine as no such issues were found. A thorough characterisation of the physical properties of the winds responsible for the detected Fe K lines will be carried out by using physically motivated models such as xstar, xabs, wine (Luminari et al 2021), and xrade (Matzeu et al 2022), and will be presented in a forthcoming SUBWAYS paper.…”

Constraints on the ultrafast outflows in the narrow-line Seyfert 1 galaxy Mrk 1044 from high-resolution time- and flux-resolved spectroscopy

“…Therefore, given these two benefits, it is promising to deepen our understanding of AGN outflows and identify the UFO launching mechanism with future missions. Moreover, an emulation method recently developed by Matzeu et al (2022b) can be applied to efficiently model the spectral data from future missions, which have the capability to collect photons orders of magnitude larger than that of current facilities.…”