General relativistic magnetohydrodynamical $\kappa$-jet models for Sgr A*

TL;DR

This paper models jets from supermassive black holes using GRMHD simulations with a modified electron distribution to explain observed spectra of Sgr A*, highlighting the impact of accelerated electrons on emission properties.

Contribution

It introduces a novel $ ho$-distribution model for electrons in GRMHD jet simulations, improving the understanding of electron acceleration effects on observed spectra.

Findings

$ angle$-jet models show increased radio flux and spectral index with decreasing $ angle$.

A specific model with $ angle=3.5$, $ m ext{acc}=5-10 ext{ extperthousand}$ fits Sgr A*'s flaring state.

Different $ angle$ values can explain quiescent and flaring states of Sgr A*.

Abstract

The observed spectral energy distribution of an accreting supermassive black hole typically forms a power-law spectrum in the Near Infrared (NIR) and optical wavelengths, that may be interpreted as a signature of accelerated electrons along the jet. However, the details of acceleration remain uncertain. In this paper, we study the radiative properties of jets produced in axisymmetric GRMHD simulations of hot accretion flows onto underluminous supermassive black holes both numerically and semi-analytically, with the aim of investigating the differences between models with and without accelerated electrons inside the jet. We assume that electrons are accelerated in the jet regions of our GRMHD simulation. To model them, we modify the electrons' distribution function in the jet regions from a purely relativistic thermal distribution to a combination of a relativistic thermal distribution and the $\kappa$-distribution function. Inside the disk, we assume a thermal distribution for the electrons. We calculate jet spectra and synchrotron maps by using the ray tracing code {\tt RAPTOR}, and compare the synthetic observations to observations of Sgr~A*. Finally, we compare numerical models of jets to semi-analytical ones. We find that in the $\kappa$-jet models, the radio-emitting region size, radio flux, and spectral index in NIR/optical bands increase for decreasing values of the $\kappa$ parameter, which corresponds to a larger amount of accelerated electrons. The model with $\kappa = 3.5$, $\eta_{\rm acc}=5-10\%$ (the percentage of electrons that are accelerated), and observing angle $i = 30^{\rm o}$ fits the observed Sgr~A* emission in the flaring state from the radio to the NIR/optical regimes, while $\kappa = 3.5$, $\eta_{\rm acc}< 1\%$, and observing angle $i = 30^{\rm o}$ fit the upper limits in quiescence.