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 and 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 (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 (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 and 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.