2010ApJ...714L.295W

The radio-quiet quasar (RQQ) SDSS J1536+0441A shows two broad-line emission systems, recently interpreted as a binary black hole (BBH) system with a subparsec separation; as a double-peaked emitter; or as both types of systems. The NRAO Very Long Baseline Array was used to search for 8.4 GHz emission from SDSS J1536+0441A, focusing on the optical localization region for the broad-line emission, of area 5400 mas² (0.15 kpc²). One source was detected, with a diameter of less than 1.63 mas (8.5 pc) and a brightness temperature T_b>1.2x10⁷ K. New NRAO Very Large Array photometry at 22.5 GHz, and earlier photometry at 8.5 GHz, gives a rising spectral slope of α = 0.35±0.08. The slope implies an optically thick synchrotron source, with a radius of about 0.04 pc, and thus T_b∼ 5x10¹⁰ K. The implied radio sphere at the rest frequency 31.2 GHz has a radius of 800 gravitational radii, just below the size of the broad-line region in this object. Observations at higher frequencies can probe whether or not the radio sphere is as compact as expected from the coronal framework for the radio emission of RQQs.