Confronting the jet model of Sgr A* with the Faraday rotation measure observations

TL;DR

This paper tests the jet model of Sgr A* against observed Faraday rotation measures, finding that the pure jet model underpredicts the RM but can be reconciled with observations when including accretion flow contributions, under specific geometric constraints.

Contribution

It provides the first calculation of RM based on the jet model for Sgr A* and explores how combined jet and accretion flow models can match observations.

Findings

Jet model alone underpredicts RM by two orders of magnitude.

Including accretion flow can reconcile model with observed RM.

Required inclination angle conflicts with existing observational estimates.

Abstract

Sgr A* is probably the supermassive black hole being investigated most extensively due to its proximity. Several theoretical models for its steady state emission have been proposed in the past two decades. Both the radiative-inefficient accretion flow and the jet model have been shown to well explain the observed spectral energy distribution. Faraday rotation measure (RM) has been unambiguously measured at submillimeter wavelength, but has only been tested against the accretion flow model. Here we first calculate the RM based on the jet model and find that the predicted value is two orders of magnitude lower than the measured value. We then include an additional contribution from the accretion flow in front of the jet and show that the measured RM may be reconciled with the model under some tight constraints. The main constraint is that the inclination angle should be greater than $\sim 73^{\circ}$. But this requirement is not consistent with an existing observational estimate of the inclination angle.