Multifrequency Radio Studies of G359.1-00.2

Abstract

The Molonglo Observatory Synthesis Telescope, the Australia Telescope Compact Array, and the Very Large Array have been used to carry out imaging and polarimetry experiments on the unusual Galactic center filamentary object G359.1-00.2, also known as "the Snake." The observations were carried out at 843, 1446, 4790, 5840, and 8640 MHz, with resolutions as fine as 2″. The images reveal intricate internal structure in the object and physical properties similar to previously recognized filamentary features in the region. Several models of the source are discussed, with some form of electrodynamic activity being favored at present. It is not possible, however, to rule out all other models discussed - a jet or ejectum from a supernova event, a star wake or trail, a shock front, a phenomenon related to a cosmic string or the nearby "Great Annihilator," 1E1740.7-2942, a morphologically unusual supernova remnant - conclusively. Several models do predict observable changes in the source on timescales of years, so further observations will help clarify this issue. A fractional linear polarization as high as ∼50% was found for part of the Snake, although some regions of the source are completely depolarized. The frequency dependence of the observed polarization properties suggests a model of the source as a twisted ribbon embedded in a thermal medium giving rise to an external rotation measure of at least 5500 rad m-2, with strong depolarization due to an internal Faraday depth of up to 1400 rad m-2. The derived properties of the thermal medium in this model require a thermal electron density of 10 cm-3 with a line-of-sight magnetic field strength of 7 μG along a path of length ∼100 pc. These parameters are consistent with material in a nuclear disk in the Galactic center.