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Session 54 - Star Clusters, Kinematics and the Galactic Center.
Display session, Wednesday, June 10
Multifrequency, polarimetric observations were made with the VLA of two of the Galactic Center non-thermal radio filaments, G0.08+0.15, and G359.96+0.09, also known as the Northern and Southern Threads (Morris amp; Yusef-Zadeh, 1985). Observations were made at 20, 6, 3.6 and 2 cm and had high enough resolution to resolve the Threads for the first time. The 20 cm image reveals a wealth of new detail in sources within the inner 60 pc of the Galaxy. The Southern Thread shows a significant split along its length, similar to what has been observed in the G359.54+0.018 filament (Yusef-Zadeh et al. 1997). With a resolution of 2\arcsec, the 6 cm image reveals little substructure along its length, although there is a gradual broadening along its length and it becomes markedly diffuse at its NE extent. The spectrum of the Northern Thread has been fit with two components, \alpha=-0.7, and \alpha=-2.0, where S_\nu \propto \nu^\alpha. The spectral index does not vary signigicantly along its length, which prevents us from locating the source of the acceleration of the electrons. Polarization measures at 6 and 3.6 cm confirm that the Northern Thread is non-thermal. The fractional polarization in the NTF is as high as 50% in some regions, although the polarized emission has a very patchy distribution. The RM varies irregularly across the filament, and its value ranges from 200-3000 rad m^-2. The lack of any apparent pattern in the distribution of RM suggests that the Faraday rotating medium is not intimately assocated with the filament since it is so highly ordered. The Faraday corrected polarization vectors reveal that the intrinsic magnetic field direction of the Northern Thread is predominantely aligned along its long axis. At 6 and 3.6 cm, the total intensity of the Southern Thread does not stand out, but the polarized emission at 3.6 cm has been imaged and shows that the NTF is bifurcated, similar to the substructure seen at 20 cm.
Program listing for Wednesday