Radiative Acceleration and Collimation of Jets from TCAF Discs

Abstract

Matter spiraling onto black holes are known to suffer centrifugal pressure supported shocks [1]. In the post-shock region entropy goes up, density goes up, and the hot and dense post-shock matter puffs up in the form of a torus, and is abbreviated as CENBOL (CENtrifugal pressure supported BOundary Layer). Hot and puffed up CENBOL intercepts ‘soft photons’ from cooler Keplerian disc, and inverse-Comptonize to produce power-law tail of ’hard photons’ [2]. However, if the Keplerian accretion rate increases, excess soft photons will cool down the hot CENBOL electrons. In the process the puffed up CENBOL slumps, cannot intercept significant soft photons. On the top of that the electrons in CENBOL being cold, cannot produce the high energy photons, thus generating the so-called soft state. Such a disc model is called Two Component Accretion Flow (hereafter TCAF) model. Excess thermal gradient force in CENBOL can also drive matter along the axis of symmetry to produce jets [3]. However only thermal gradient force may not be sufficient to produce relativistic terminal speeds observed in some black hole candidates [4]. Chattopadhyay and Chakrabarti [5] showed, that normal plasma cannot be accelerated by disc radiation to over 90% velocity of light (c), though pair dominated jets may achieve relativistic terminal speed v∞ [6]. The question which can be raised in this context is, what should be the spectral state of the disc in which such relativistic outflows are collimated? We aim to do so in this paper. In the next section, we discuss model assumptions, equations of motion and the result. In the last section we draw conclusion.