Using radiative energy losses to constrain the magnetisation and magnetic reconnection rate at the base of black hole jets

TL;DR

This paper models radiative energy losses at the base of black hole jets, revealing that jets are highly magnetized and constraining the magnetic reconnection rate based on energy loss limits.

Contribution

It introduces a self-consistent model including radiative losses and in-situ particle acceleration, providing new constraints on jet magnetization and reconnection rates.

Findings

Jets must be highly magnetized at the base, with magnetic energy exceeding leptonic energy by at least 10,000 times.

Radiative losses significantly impact jet spectra, making post-processed spectra overestimate non-thermal emission.

Constraints on reconnection rates are derived based on energy loss limits and jet equipartition distance.

Abstract

We calculate the severe radiative energy losses which occur at the base of black hole jets using a relativistic fluid jet model, including in-situ acceleration of non-thermal leptons by magnetic reconnection. Our results demonstrate that including a self-consistent treatment of radiative energy losses is necessary to perform accurate MHD simulations of powerful jets and that jet spectra calculated via post-processing are liable to vastly overestimate the amount of non-thermal emission. If no more than 95% of the initial total jet power is radiated away by the plasma travels as it travels along the length of the jet, we can place a lower bound on the magnetisation of the jet plasma at the base of the jet. For typical powerful jets, we find that the plasma at the jet base is required to be highly magnetised, with at least 10,000 times more energy contained in magnetic fields than in non-thermal leptons. Using a simple power-law model of magnetic reconnection, motivated by simulations of collisionless reconnection, we determine the allowed range of the large-scale average reconnection rate along the jet, by restricting the total radiative energy losses incurred and the distance at which the jet first comes into equipartition. We calculate analytic expressions for the cumulative radiative energy losses due to synchrotron and inverse-Compton emission along jets, and derive analytic formulae for the constraint on the initial magnetisation.