The Synchrotron Cut-off Frequency of Relativistic Electrons in the Radio Arc and their Acceleration Area
The Galactic Center region is a nearest central region of spiral galaxy. Unique structures which may relate intrinsic activities in the central region have been found. “gRadio Arc” is a most outstanding one of such features. This consists of two parts with different properties. These are non-thermal “Vertical filament” and thermal “Arched filament” . Although the intensity is abruptly decreased at the both ends of Vertical filament, the positive galactic latitude extension corresponds to the base of a famous off-plane feature, “Galactic Center Ω-shaped lobe”, which was identified by Sofue and Handa (1986) . The lobe also consists of two parts with different properties. The positive longitude part is highly linear polarized up to 50% at 10 GHz, which is non-thermal, and the negative longitude part is non-polarized, which is presumably thermal . It is controversial that the lobe is a real combined structure or an apparent feature by chance superposition in the line of sight. On the other hand, the negative galactic latitude extension is distinctive only in linear polarization map. Two polarized extensions is called “Polarized Lobe” . Radio Arc and Polarized Lobe are presumably a part of large scale poloidal magnetic field through the Galactic center region. It is, however, an open question how much is the strength of the magnetic field. In addition, several vertical continuum features identified in lower frequency map are also a part of such magnetic field . It is also an open question that such magnetic field exists anywhere in the region or is restricted in smaller region. The synchrotron cut-off frequency in the Radio Arc and its distribution presumably provide the informations of the acceleration area of relativistic electrons and the acceleration mechanism.
KeywordsCircular Polarization Relativistic Electron Molecular Cloud Faraday Rotation Spiral Galaxy
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