The origin of the 6.4 keV line emission and H${}_2$ ionization in the diffuse molecular gas of the Galactic center region

Abstract

We investigate the origin of the diffuse 6.4 keV line emission recently detected by Suzaku and the source of H_2ionization in the diffuse molecular gas of the Galactic Center (GC) region. We show that Fe atoms and H_2 molecules in the diffuse interstellar medium of the GC are not ionized by the same particles. The Fe atoms are most likely ionized by X-ray photons emitted by Sgr A* during a previous period of flaring activity of the supermassive black hole. The measured longitudinal intensity distribution of the diffuse 6.4 keV line emission is best explained if the past activity of Sgr A$* lasted at least several hundred years and released a mean 2-100 keV luminosity > 10^38} erg s^{-1}. The H_2 molecules of the diffuse gas can not be ionized by photons from Sgr A*, because soft photons are strongly absorbed in the interstellar gas around the central black hole. The molecular hydrogen in the GC region is most likely ionized by low-energy cosmic rays, probably protons rather than electrons, whose contribution into the diffuse 6.4 keV line emission is negligible.

5 pages, 4 figues, accepted for publication in the Astrophysical Journal Letters

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Cited by in corpus (13)

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• Physical laboratory at the center of the Galaxy
• An X-ray survey of the central molecular zone: variability of the Fe Ka emission line
• Spectrum of Relativistic and Subrelativistic Cosmic Rays in the 100 pc Central Region
• Constraining the cosmic ray spectrum in the vicinity of the supernova remnant W28: from sub-GeV to multi-TeV energies
• On the Origin of the 6.4 keV Line in the Galactic Center Region
• Sgr B2 hard X-ray emission with INTEGRAL after 2009: still detectable?
• New Constraints on Cosmic Particle Populations at the Galactic Center using X-ray Observations of the Molecular Cloud Sagittarius B2
• Time-Variability of equivalent width of 6.4 keV line from the Arches Complex: reflected X-rays or charged particles?
• Cosmic rays cannot explain the high ionisation rates in the Galactic centre
• Nuclear de-excitation line emissions from giant molecular clouds
• Origin of X-ray and gamma-ray emission from the Galactic central region
• High Energy Emission from the Galactic Center