The Origin of X-ray Emission from a Galactic Center Molecular Cloud: Low Energy Cosmic Ray Electrons

Abstract

The Galactic center region near l$\approx 0.2^0$ hosts a mixture of nonthermal linear filaments and thermal radio continuum features associated with the radio Arc. Chandra observations of this region reveal an X-ray filament and diffuse emission with an extent of roughly 60${}^{\prime \prime }\times 2^{\prime \prime }$ and 5${}^{\prime }\times 3^{\prime }$, respectively. The X-ray filament lies at the edge of the nonthermal radio filaments and a dense molecular shell G0.13-0.13 that has an unusually high kinetic temperature $\ge$70K. These observations demonstrate that the G0.13--0.13 molecular cloud and the nonthermal radio filaments of the Arc are interacting. The diffuse X-ray emission is correlated with the molecular shell and is fitted either by two-temperature (1 and 10 keV) thermal emission or by power-law and 1 keV thermal gas. Fluorescent 6.4 keV line emission is also detected throughout the molecular shell. This cloud coincides within the error circle of a steady unidentified EGRET source 3EGJ1746--2851. We argue that low-energy cosmic ray electrons (LECRe) produce the power-law continuum by bremsstrahlung and 6.4 keV line emission from the filament and the diffuse cloud with the implication on the origin of the Galactic ridge X-ray emission. The strong 6.4 keV Fe-line emission seen from other Galactic center clouds could be produced in a similar fashion rather than via fluorescent emission induced by a transient hard X-ray source in the Galactic center. In addition, heating by ionization induced by LECRe are also responsible for the high temperature of G0.13-0.13. The gamma-ray source is a result of brehmsstrahlung by the high-energy tail of the electron energy distribution.

14 pages, 5 figures, 1 table, accepted for publications in ApJ Letter

References in corpus (2)

• Chandra Observations of Diffuse X-Rays from the Sagittarius B2 Cloud
• ASCA Discovery of Diffuse 6.4 keV Emission Near the Sgr C Complex: A New X-ray Reflection Nebula

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