Fr.: arc radio
A large number of narrow filaments in → radio continuum occurring toward the → Galactic Center, about 15 to 20 arc-minutes (some 50 parsecs in projection) north of → Sgr A*. The radio Arc is the prototype of → non-thermal filaments (NTFs) and resolves into a set of more than a dozen vertical filaments with lengths of about 30 pc distributed symmetrically with respect to the → Galactic equator (Yusef-Zadeh et al. 1984, Nature 310, 557). Among more than 100 NTFs found in the Galactic center region, the Arc is the only one known to show inverted spectrum with a → spectral index α = +0.3 (Law et al. 2008, ApJS 177, 515, and references therein). This implies a very hard energy spectrum of particles for a source of → synchrotron radiation.