  In 1981, a faint radio source (G') was detected near the center of the
lensing galaxy of the famous "twin quasar" Q0957+561. It is still unknown
whether this central radio source is a third quasar image or an active nucleus
of the lensing galaxy, or a combination of both. In an attempt to resolve this
ambiguity, we observed Q0957+561 at radio wavelengths of 13cm, 18cm, and 21cm,
using the Very Long Baseline Array in combination with the phased Very Large
Array and the Green Bank Telescope. We measured the spectrum of G' for the
first time and found it to be significantly different from the spectra of the
two bright quasar images. This finding suggests that the central component is
primarily or entirely emission from the foreground lens galaxy, but the
spectrum is also consistent with the hypothesis of a central quasar image
suffering free-free absorption. In addition, we confirm the previously-reported
VLBI position of G' just north of the optical center of the lens galaxy. The
position slightly favors the hypothesis that G' originates in the lens, but is
not conclusive. We discuss the prospects for further clarification of this
issue.
