Spectral and temporal properties of Compton scattering by mildly relativistic thermal electrons

Abstract

We have obtained new solutions and methods for the process of thermal Comptonization. We modify the solution to the kinetic equation of Sunyaev & Titarchuk to allow its application up to mildly relativistic electron temperatures and optical depths > ∼ 1. The solution can be used for spectral fitting of X-ray spectra from astrophysical sources. We also have developed an accurate Monte Carlo method for calculating spectra and timing properties of thermal-Comptonization sources. The accuracy of our kinetic-equation solution is verified by comparison with the Monte Carlo results. We also compare our results with those of other publicly available methods. Furthermore, based on our Monte Carlo code, we present distributions of the photon emission times and the evolution of the average photon energy for both up and downscattering.

The first simultaneous X-ray broadband view of Mrk 110 with XMM-Newton and NuSTAR

“…Then, we consider the reflkerr where the hard X-ray Comptonisation spectrum is computed with the compps model (Poutanen & Svensson 1996), which appears to be a better description of thermal Comptonisation when compared to Monte Carlo simulations (Zdziarski et al 2020). Moreover, reflkerr has, as physical parameter, either the Compton parameter (y) or the optical depth (τ).…”

AstroSat view of the newly discovered X-ray transient MAXI~J1803--298 in the Hard-intermediate state

“…However, this model setup tbabs*(powerlaw+diskbb) left with significant residuals in the 5 − 9 keV and above ∼ 12 keV bands implying the presence of the iron line and the reflection hump, respectively (see Figure 8). Hence, we have incorporated a gaussian component for the iron line and convolved disk spectrum from the diskbb model with the thcomp model (Zdziarski et al 2020) to account for the Comptonization of the seed photons by the thermal electrons. Since the thcomp model is a convolution model which redistributes a fraction of the seed photons to higher energies, the sampled energy range was extended to 1000 keV.…”

Modelling of Comptonisation in low-mass X-ray binaries in the presence of fast variability

“…When the magnetic loops are Compton-cooled by the soft X-rays from the disc, they can produce a high-energy tail in the spectrum. Finally, simpler geometries such as the "lamp post" (Markoff, Nowak & Wilms 2005;, which assume that the corona is a point source located at a certain height above the compact object, or spherically symmetric extended coronae around the compact object (Zdziarski, Johnson & Magdziarz 1996;Życki, Done & Smith 1999;Zdziarski et al 2020) are used today with success to explain observed spectral and timing features. Throughout this work we have assumed a spherically symmetric corona that can partially or fully cover the soft source, which is either the accretion disc or the NS.…”

“…More accurate formulae for the escape probability can be derived by solving the photon diffusion equation for different seed source spectra and boundary conditions (Sunyaev & Titarchuk 1980). Analytical and numerical frameworks that deal with calculating the SSS of the Kompaneets equation have existed for years (Sunyaev & Titarchuk 1980;Zdziarski, Johnson & Magdziarz 1996;Becker 2003;Zdziarski et al 2020), and models based on those are being extensively used to fit observed energy spectra of XBs in the literature. However, we are interested in explaining the variability imprinted on the SSS and so, in what follows, we assume that one can easily solve for the SSS, n γ,0 , and then build upon that.…”

“…Lightman & Zdziarski (1987) and Zdziarski, Johnson & Magdziarz (1996) treated the same problem numerically, also including relativistic corrections to the Kompaneets equation (Cooper 1971), and their approach was later implemented into the model nthcomp (Życki, Done & Smith 1999) that, to date, is among the primary tools for analyzing observed spectra in the spectral analysis suite Xspec (Arnaud 1996). Other models that treat Comptonisation exist within Xspec, such as comptt (Hua & Titarchuk 1995), compps (Poutanen & Svensson 1996), simpl (Steiner et al 2009), and thcomp (Zdziarski et al 2020).…”