Dynamical and radiative simulations of γ-ray jets in microquasars

Abstract

The emission of γ-rays in jets emanating from the vicinity of collapsed stellar remnants, in binary systems known as microquasars, is investigated using a three dimensional relativistic hydrocode (PLUTO), in combination with two in-house radiative transfer codes. Even though a great number of stellar systems may be addressed by such models, we restrict ourselves to the concrete example of the SS433 X-ray binary, the only microquasar with a definite hadronic content in its jets, as verified from spectral line observations. A variety of system configurations have been examined, by employing a hadron-based emission mechanism. The dependence of the γ-ray emissions on certain dynamical source properties, such as the hydrodynamic parameters of the mass-flow density, the gas-pressure and the temperature of the ejected matter, is simulated. Radiative properties, especially the assumed high energy proton population inside the jet plasma, and its effect on the calculated emission, are also examined. Two sets of initial conditions of the chosen microquasar are employed, in order to cover different scenarios pertaining to the system under consideration.

Simulations of Gamma-Ray Emission from Magnetized Microquasar Jets

“…Also, the proton acceleration rate cannot affect the γ-ray emission rate, unless β drops below some value. As we will see below, in this work, instead of the proton density ρ, we also use the product ρu 2 [7,13].…”

“…Regarding the particles ejected from a hadronic jet, we consider that they are mostly slow (thermal) protons of density n sp and a small portion of fast (non-thermal) protons of density n f p . The energy distribution of the fast protons (in the jet's frame, see below) is described by [7,13]…”

“…Furthermore, for hydrodynamical jets [12,13] the fast proton current density, J ′ f p (E ′ ), as a function of their energy, is given by…”

“…In conclusion, one can work with laboratory frame quantities only, which are also the jet model quantities (for other symbols the reader is referred to Ref. [12,13,27,28] D.…”

“…In the hydrodynamical (HD) simulations with PLUTO code, as we have done previously [12,13], the magnetic field lines are assumed to follow the matter flow. Their tangling with the jet material makes applicable the fluid approximation within the jet [33].…”