A Radio Polarimetric Study of the Galactic Center Threads

Multi-frequency, polarimetric VLA observations of the non-thermal filaments(NTF's), G0.08+0.15, and G359.96+0.09, also known as the Northern and SouthernThreads are presented at 20, 6, 3.6 and 2 cm, with high enough spatialresolution to be resolved for the first time at 6 and 3.6 cm. The 20 cm imagereveals a wealth of new detail in the radio sources lying within the inner 60pc of the Galaxy. The Southern Thread has a prominent split along its length,similar to splitting at the ends of previously studied NTF's. With resolutionsas fine as 2'', the 3.6 and 6 cm images reveal a high degree of continuity andlittle substructure internal to the filament. The spectral index of theNorthern Thread has been determined over a broad range of frequencies. Its fluxdensity falls with frequency, alpha=-0.5 between 90 and 6 cm, and becomes muchsteeper (alpha=-2.0) between 6 and 2 cm. The spectral index does not varysignificantly along the length of the Northern Thread, which implies eitherthat the diffusion timescale for the emitting electrons is less than theirsynchrotron lifetime, or that the emitting electrons are reacceleratedcontinuously at multiple positions along the filament. Because of the lack ofspectral index variation, we have not located the source of relativisticelectrons. Polarization observations at 6 and 3.6 cm confirm the non-thermalnature of the emission from the Northern Thread. The fractional polarization inthe Northern Thread reaches 70% in some regions, although the polarizedemission is patchy. Large rotation measures (RM > 2000 rad/m2) have beenobserved with irregular variations across the filament.The intrinsic magneticfield in the Northern Thread is predominantly aligned along its long axis.Comment: 19 pages, incl. 24 figs; to appear in the Astrophysical Journa