ABSTRACT

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ABSTRACT: High-resolution continuum mapping of the Radio Arc has been made at 43 GHz using the Effelsberg 100-m telescope in order to investigate spatial variation of the spectrum. The straight nonthermal filaments, clearly seen at 32 GHz and lower frequencies, are very weak at 43 GHz. The spectral index of the brightest filaments, which is flat at lower frequencies, turns to be as steep as alpha ~ -1 between 32 and 43 GHz, indicating a spectral turnover between these frequencies. Assuming that the magnetic field strength is ~ 1 mG, we estimate the life time of cosmic-ray electrons to be several thousand years, showing that the filaments are short-lived structures. The present result would give a constraint on the location and epoch as well as the initial energy distribution of injected cosmic-ray electrons. On the other hand, ``Sickle" is clearly visible at 43 GHz and has a flat spectrum, which confirms its thermal characteristics. "Pistol" appears to show a peculiarly inverted spectrum, suggesting a two-component spectrum.