The jet model for Sgr A*: radio and X-ray spectrum

TL;DR

This paper models the radio and X-ray spectrum of Sgr A* using a relativistic jet, successfully fitting observations and constraining electron energies, with implications for variability and applicability to other low-luminosity AGN.

Contribution

The study introduces a relativistic jet model that accurately reproduces Sgr A*'s spectrum and constrains electron energy distribution, advancing understanding of low-luminosity galactic nuclei.

Findings

Jet model fits radio and X-ray spectra well

High-energy cutoff at gamma_e ~< 100 is necessary

Jet appears compact, consistent with VLBI limits

Abstract

The preliminary detection of the Galactic Center black hole Sgr A* in X-rays by the Chandra mission, as well as recent mm-VLBI measurements, impose strict constraints on this source. Using a relativistic jet model for Sgr A*, we calculate the synchrotron and synchrotron self-Compton emission. The predicted spectrum provides an excellent fit to the radio spectrum and the the X-ray observations. Limits on the infrared flux and the low X-ray flux require a high-energy cut-off in the electron spectrum at gamma_e ~< 100. The implied lack of a significant power-law tail of high-energy electrons also suppresses the appearance of the extended, optically thin radio emission usually seen in astrophysical jets. The jet therefore appears rather compact and naturally satisfies current VLBI limits. The initial parameters of the model are tightly constrained by the radio spectrum and the "submm-bump" in particular. While the jet most likely is coupled to some kind of accretion flow, we suggest that the most visible signatures can be produced by this outflow. If SSC emission from the jet contributes to the Sgr A* spectrum, significant variability in X-rays would be expected. The model could be generic for other low-luminosity AGN or even X-ray binaries.