Discovery of Radio Emission from the Quasar SDSS J1536+0441, a Candidate
  Binary Black-Hole System
  The radio-quiet quasar SDSS J1536+0441 shows two broad-line emission systems
that Boroson & Lauer interpret as a candidate binary black-hole system with a
separation of 0.1 pc (0.02 mas). From new VLA imaging at 8.5 GHz, two faint
sources, separated by 0.97 arcsec (5.1 kpc), have been discovered within the
quasar's optical localization region. Each radio source is unresolved, with a
diameter of less than 0.37 arcsec (1.9 kpc). A double radio structure is seen
in some other radio-quiet quasars, and the double may be energized here by the
candidate 0.1-pc binary black-hole system. Alternatively, the radio emission
may arise from a binary system of quasars with a projected separation of 5.1
kpc, and the two quasars may produce the two observed broad-line emission
systems. Binary active galactic nuclei with a kpc scale separation are known
from radio and X-ray observations, and a few such system are expected in the
Boroson & Lauer sample based on the observed clustering of quasars down to the
10 kpc scale. Future observations designed to distinguish between the 0.1 pc
and 5 kpc scales for the binary system are suggested.
