The Enigmatic Compact Radio Source Coincident with the Energetic X-Ray Pulsar PSR J1813-1749 and HESS J1813-178

New Very Large Array (VLA) detections of the variable radio continuum source VLA J181335.1-174957, associated with the energetic X-ray pulsar PSR J1813-1749 and the TeV source HESS J1813-178, are presented. The radio source has a right circular polarization of ∼50% and a negative spectral index of -1.3 ± 0.1, which show that it is nonthermal. The radio pulses of the pulsar are not detected from additional Effelsberg observations at 1.4 GHz made within one week of a VLA detection. This result would appear to support the idea that the continuum radio emission detected with the VLA does not trace the time-averaged emission pulses, as had previously been suggested. We discuss other possible origins for the radio source, such as a pulsar wind, magnetospheric emission, and a low-mass star companion. However, observations made at higher frequencies by Camilo et al. show that the VLA source is in fact the time-averaged pulsed emission and that the detection of the pulses had not been achieved because this is the most scattered pulsar known.