[Paper Review] The Galactic Center radio jet

H. Falcke, K. Mannheim+1 more|arXiv (Cornell University)|Aug 24, 1993

Astrophysical Phenomena and Observations3 citations

TL;DR

This paper proposes a Blandford & Königl-type jet model coupled with an accretion disk to explain the radio and near-infrared emission from Sgr A*, the Galactic Center's compact source. Using observational constraints on flux and size, the model confirms a lower limit on the accretion rate (Ñ.M > 10^-8.5 M⊙/yr) and shows that jet power is comparable to disk luminosity, explaining the submillimeter excess and lack of non-thermal IR emission in a low-accretion-rate system.

ABSTRACT

Recent observations of the radio and NIR source Sgr A* reinforce the interpretation of the Galactic Center as a scaled down version of an AGN. The discovery of an elongated structure at 43 GHz and increasing evidence for the presence of an accretion disk surrounding a Black Hole lead us to assume that both, an accretion disk and a jet, are present in the Galactic Center and are physically linked. We model the radio emission of Sgr A* successfully with a Blandford & K"onigl type jet and analyze the energetics of the coupled jet-disk system in Sgr A* where jet and disk are parametrized in terms of the accretion power. With this method we are able to confirm independently the lower limit of the Sgr A* accretion rate \dot M >> 10^-8.5 M_sun found previously. Moreover, using the limits imposed by observational data, we show that within such a jet-disk model, the total jet power Q_jet is of comparable order as the radiated disk luminosity L_disk. A jet model together with the assumption of an 10^6 M_sun Black Hole also qualitatively explains the submm excess and the lack of non-thermal IR radiation. The small size of the visible part of the jet (< 1 mas) is due to the low accretion rate of Sgr A*. <<>>

Motivation & Objective

• To explain the radio and near-infrared emission from Sgr A* as arising from a jet-disk system linked to a black hole.
• To determine the accretion rate of Sgr A* using jet emission modeling and observational constraints.
• To assess the energetics of the jet-disk system, particularly the relationship between jet power and disk luminosity.
• To explain the observed submillimeter excess and absence of non-thermal infrared radiation in Sgr A*.
• To understand the physical origin of the compact jet size (<1 mas) in the context of low accretion rates.

Proposed method

• Modeling the radio emission of Sgr A* using a Blandford & Königl-type relativistic jet with parameters tied to accretion power.
• Parametrizing both the jet and accretion disk in terms of the accretion luminosity to link their energetics.
• Applying observational constraints on flux density and angular size (less than 1 mas) to limit model parameters.
• Using the 43 GHz VLBI observations of an elongated structure to infer jet properties and orientation.
• Comparing predicted jet luminosity with observed disk luminosity to assess energy budget.
• Assessing the model's ability to reproduce the submillimeter excess and lack of non-thermal IR emission.

Experimental results

Research questions

• RQ1 Can a jet-disk model explain the observed radio and near-infrared emission from Sgr A*?
• RQ2 What is the lower limit on the accretion rate of Sgr A* based on jet emission and observational constraints?
• RQ3 How does the jet power compare to the radiated disk luminosity in the Sgr A* system?
• RQ4 Why is there a submillimeter excess and no detectable non-thermal infrared emission in Sgr A*?
• RQ5 What physical mechanism explains the compact size of the visible jet in Sgr A*?

Key findings

• The model successfully reproduces the observed radio emission of Sgr A* using a Blandford & Königl-type jet.
• The accretion rate is constrained to exceed 10^-8.5 M⊙ per year, confirming previous estimates independently.
• Jet power (Q_jet) is found to be of comparable magnitude to the radiated disk luminosity (L_disk), indicating a balanced energy budget.
• The small angular size of the visible jet (<1 mas) is explained by the low accretion rate, which suppresses jet luminosity and extent.
• The model qualitatively accounts for the submillimeter excess and the absence of non-thermal infrared radiation in Sgr A*.
• The 10^6 M⊙ black hole mass assumption is consistent with the observed jet and disk energetics.