Radiatively driven relativistic jets in Schwarzschild space-time

Abstract

We carry out a general relativistic study of radiatively driven, conical fluid jets around non-rotating black holes and investigate the effects and significance of radiative acceleration, as well as radiation drag. We apply relativistic equations of motion in curved space-time around a Schwarzschild black hole for axis-symmetric 1-D jet in steady state, plying through the radiation field of the accretion disc. Radiative moments are computed using information of curved space-time. Slopes of physical variables at the sonic points are found using L$^{\prime}$Hôpital's rule and employed Runge-Kutta's $4^{th}$ order method to solve equations of motion. The analysis is carried out, using the relativistic equation of state of the jet fluid. The terminal speed of the jet depends on how much thermal energy is converted into jet momentum and how much radiation momentum is deposited on to the jet. Many classes of jet solutions with single sonic points, multiple sonic points as well as, those having radiation driven internal shocks are obtained. Variation of all flow variables along the jet-axis has been studied. Highly energetic electron-proton jets can be accelerated by intense radiation to terminal Lorentz factors $γ_{\rm \small T} \sim 3$. Moderate terminal speed $v_{\rm \small T} \sim 0.5$ is obtained for moderately luminous discs. Lepton dominated jets may achieve $γ_{\rm \small T} \sim 10$. Thermal driving of the jet itself and radiation driving by accretion disc photons produce a wide-ranging jet solutions staring from moderately strong jets to the relativistic ones. Interplay of intensity and nature of radiation field and the energetics of the jet result in such a variety in jet solutions. We show that radiation field is able to induce steady shocks in jets, one of the criteria to explain high energy power law emission observed in spectra of some of the astrophysical objects.