A Leptonic Model of Steady High-Energy Gamma-Ray Emission from Sgr A${}^{\ast }$

Abstract

Recent observations of Sgr A${}^{\ast }$ by Fermi and HESS have detected steady gamma-ray emission in the GeV and TeV bands. We present a new model to explain the GeV gamma-ray emission by inverse Compton scattering by nonthermal electrons supplied by the NIR/X-ray flares of Sgr A${}^{\ast }$. The escaping electrons from the flare regions accumulate in a region with a size of $\sim 10^{18}$ cm and magnetic fields of $\lesssim 10^{-4}$ G. Those electrons produce gamma-rays by inverse Compton scattering off soft photons emitted by stars and dust around the central black hole. By fitting the GeV spectrum, we find constraints on the magnetic field and the energy density of optical-UV radiation in the central 1 pc region around the supermassive black hole. While the GeV spectrum is well fitted by our model, the TeV $\gamma$-rays, whose spectral index is different from that of the GeV emission, may be from different sources such as pulsar wind nebulae.

11 pages, 5 figures, 2 tables. Accepted for publication in the Astrophysical Journal

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• Angular Momentum Transport and Particle Acceleration during Magnetorotational Instability in a Kinetic Accretion Disk
• VERITAS Observations of the Galactic Center Region at Multi-TeV Gamma-Ray Energies
• Observations of Sagittarius A* during the pericenter passage of the G2 object with MAGIC
• Gamma rays from the Galactic Centre region: a review
• Very-high energy observations of the Galactic center region by VERITAS in 2010-2012
• Hadronic origin of multi-TeV gamma rays and neutrinos from low-luminosity active galactic nuclei: implications of past activities of the Galactic center
• Gamma-rays from millisecond pulsar population within the central stellar cluster in the Galactic Center
• Leptonic origin of the 100 MeV gamma-ray emission from the Galactic Centre
• Hybrid model of GeV-TeV gamma ray emission from Galactic Center
• Fermi LAT observations of Sagittarius A*: Imaging Analysis
• Detection of positron in-flight annihilation from the Galaxy
• Stratified Simulations of Collisionless Accretion Disks
• Constraints on Axion-like Particles from the gamma-ray observation of the Galactic Center
• Origin of X-ray and gamma-ray emission from the Galactic central region