MoCA: A Monte Carlo code for Comptonisation in Astrophysics

Tamborra, F.; Matt, Giorgio; Bianchi, S.; Dovčiak, Michal

doi:10.1051/0004-6361/201732023

Cited by 46 publications

(51 citation statements)

References 27 publications

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“…(i) An extended corona: we assumed here a lamp-post geometry of the corona for simplicity. However, a more realistic configuration is an extended corona (Wilkins & Fabian 2012;Dovčiak & Done 2016;Tamborra et al 2018;Zhang 2018) that would result in a somewhat different illumination of the disc and thus to different ionisation profile. However, models of irradiation by such an extended corona are not yet available for spectral fitting and are dependent on the physical characteristics and structure of such coronae.…”

Section: Discussionmentioning

confidence: 99%

Steep X-ray reflection emissivity profiles in AGN as the result of radially structured disc ionization

Kammoun

Domček

Svoboda

et al. 2019

Monthly Notices of the Royal Astronomical Society

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X-ray observations suggest high compactness of coronae in active galactic nuclei as well as in X-ray binaries. The compactness of the source implies a strong radial dependence in the illumination of the accretion disc. This will, for any reasonable radial profile of the density, lead to a radial profile of the disc ionisation. Svoboda et al. (2012) showed on a single example that assuming a radially-structured ionisation profile of the disc can cause an artificial increase of the radial-emissivity parameter. We further investigate how the X-ray spectra are modified and quantify this effect for a wide range of parameters. Computations are carried out with the current state-of-the-art models for relativistic reflection. We simulated spectra using the response files of the micro-calorimeter X-IFU, which is planned to be on board of Athena. We assumed typical parameters for X-ray bright Seyfert-1 galaxies and considered two scenarios for the disc ionisation: 1) a radial profile for the disc ionisation, 2) a constant disc ionisation. We found that steep emissivity profiles can be indeed achieved due to the radial profile of the disc ionisation, which becomes more important for the cases where the corona is located at low heights above the black hole and this effect may be even more prominent than the geometrical effects. We also found that the cases with high inner disc ionisation, rapidly decreasing with radius, may result in an inaccurate black hole spin measurements.

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Section: Discussionmentioning

confidence: 99%

Steep X-ray reflection emissivity profiles in AGN as the result of radially structured disc ionization

Kammoun

Domček

Svoboda

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…) as well as polarization has been recently released. Compared to different codes in the literature, such as compTT, compPS, nthcomp (Titarchuk 1994;Poutanen & Svensson 1996;Zdziarski et al 1996;Życki et al 1999), the energy-dependent Klein-Nishina cross section is taken into account (differently from Schnittman & Krolik 2010) and multiple geometries can be tested and investigated (similarly to Beheshtipour et al 2017). Moreover, the Monte Carlo approach implies that no a priori limitations in the parameter space is present.…”

Section: Introductionmentioning

confidence: 99%

A deep X-ray view of the bare AGN Ark 120

Marinucci

Porquet

Tamborra

et al. 2019

A&A

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Context. The spectral shape of the hard X-ray continuum of Active Galactic Nuclei (AGN) can be ascribed to inverse Compton scattering of optical/UV seed photons from the accretion disc by a hot corona of electrons. This physical process produces a polarization signal which is strongly sensitive to the geometry of the scattering medium (i.e. the hot corona) and of the radiation field. Aims. MoCA (Monte Carlo code for Comptonisation in Astrophysics) is a versatile code which allows for different geometries and configurations to be tested for Compton scattering in compact objects. A single photon approach is considered as well as polarisation and Klein–Nishina effects. In this work, we selected four different geometries for the scattering electrons cloud above the accretion disc, namely an extended slab, an extended spheroid and two compact spheroids. Methods. We discuss the first application of the MoCA model to reproduce the hard X-ray primary continuum of the bare Seyfert 1 galaxy Ark 120, using different geometries for the hot corona above the accretion disc. The lack of extra-Galactic absorption along the line of sight makes it an excellent target for studying the accretion disc-corona system. We report on the spectral analysis of the simultaneous 2013 and 2014 XMM-Newton and NuSTAR observations of the source. Results. A general agreement is found between the best fit values of the hot coronal parameters obtained with MoCA and the ones inferred using other Comptonisation codes from the literature. The expected polarization signal from the best fits with MoCA is then presented and discussed, in view of the launch in 2021 of the Imaging X-ray Polarimetry Explorer (IXPE). Conclusions. We find that none of the tested geometries for the hot corona (extended slab and extended/compact spheroids) can be statistically preferred, based on spectroscopy solely. In the future, an IXPE observation less than 1 Ms long will clearly distinguish between an extended slab or a spherical hot corona.

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“…Others depend on accurate simulations of scattering, be it for high-energy processes (e.g. Pozdnyakov et al 1983;Stern et al 1995;Molnar and Birkinshaw 1999;Cullen 2001;Yao et al 2005;Dolence et al 2009;Ghosh et al 2009Ghosh et al , 2010Schnittman and Krolik 2010;Tamborra et al 2018) or from dust-rich structures (e.g. Witt 1977;Yusef-Zadeh et al 1984;Dullemond and Turolla 2000;Bjorkman and Wood 2001;Gordon et al 2001;Misselt et al 2001;Juvela and Padoan 2003;Niccolini et al 2003;Jonsson 2006;Pinte et al 2006;Bianchi 2008;Pinte et al 2009;Jonsson et al 2010;Baes et al 2011;Robitaille 2011;Whitney 2011;Lunttila and Juvela 2012;Camps et al 2013;P.…”

Section: Historical Sketch Of the Monte Carlo Methodsmentioning

confidence: 99%

Monte Carlo radiative transfer

Noebauer

Sim

2019

Living Rev Comput Astrophys

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The theory and numerical modelling of radiation processes and radiative transfer play a key role in astrophysics: they provide the link between the physical properties of an object and the radiation it emits. In the modern era of increasingly high-quality observational data and sophisticated physical theories, development and exploitation of a variety of approaches to the modelling of radiative transfer is needed. In this article, we focus on one remarkably versatile approach: Monte Carlo Radiative Transfer (MCRT). We describe the principles behind this approach, and highlight the relative ease with which they can (and have) been implemented for application to a range of astrophysical problems. All MCRT methods have in common a need to consider the adverse consequences of Monte Carlo (MC) noise in simulation results. We overview a range of methods used to suppress this noise and comment on their relative merits for a variety of applications. We conclude with a brief review of specific applications for which MCRT methods are currently popular and comment on the prospects for future developments.

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MoCA: A Monte Carlo code for Comptonisation in Astrophysics

Cited by 46 publications

References 27 publications

Steep X-ray reflection emissivity profiles in AGN as the result of radially structured disc ionization

Steep X-ray reflection emissivity profiles in AGN as the result of radially structured disc ionization

A deep X-ray view of the bare AGN Ark 120

Monte Carlo radiative transfer

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