3 research outputs found
VLBI detection of an AGN pair in the binary black hole candidate SDSS J1536+0441
We present first pc-scale radio imaging of the radio-quiet candidate binary
black hole system SDSS J1536+0441. The observations were carried out by the
European VLBI Network at the frequency of 5 GHz and allowed to image SDSS
J1536+0441 with a resolution of about 10 mas (50 pc). Two compact radio cores
are detected at the position of the kpc-scale components VLA-A and VLA-B,
proving the presence of two compact active nuclei with radio luminosity about
10^{40} erg/s, thus ruling out the possibility that the two radio sources are
both powered by one 0.1 pc binary black hole. From a comparison with published
8.5 GHz flux densities we derived an estimate of the radio spectral index of
the two pc-scale cores. Both cores have flat or inverted spectral index and, at
least for the case of VLA-A, we can rule out the possibility that synchrotron
self-absorption is responsible for the inverted radio spectrum. We suggest that
thermal free-free emission from an X-ray heated disk wind may be powering the
radio emission in VLA-A.Comment: Accepted for publication in ApJ Letters
Parsec-Scale Localization of the Quasar SDSS J1536+0441A, a Candidate Binary Black Hole System
The radio-quiet quasar 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 VLBA 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 mas^2 (0.15 kpc^2). One source was detected, with a diameter of less
than 1.63 mas (8.5 pc) and a brightness temperature T_b > 1.2 x 10^7 K. New
NRAO VLA photometry at 22.5 GHz, and earlier photometry at 8.5 GHz, gives a
rising spectral slope of alpha = 0.35+/-0.08. The slope implies an optically
thick synchrotron source, with a radius of about 0.04 pc, and thus T_b ~ 5 x
10^10 K. The implied radio-sphere at rest frame 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 radio-quiet quasars.Comment: 6 pages; 2 figures; emulateapj.cls; to appear in ApJ
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.Comment: 5 pages; 1 figure; emulateapj.cls; to appear in ApJ