What sparks the radio-loud phase of nearby quasars?
  To better constrain the hypotheses proposed to explain why only a few quasars
are radio loud (RL), we compare the characteristics of 1958 nearby $(z\le 0.3)$
SDSS quasars, covered by the FIRST and NVSS radio surveys. Only 22\% are RL
with $\log(L_{1.4{\rm GHz}}) \ge 22.5$ W Hz$^{-1}$, the majority being compact
(C), weak radio sources (WRS), with $\log(L_{1.4{\rm GHz}}) < 24.5$ W
Hz$^{-1}$. 15\% of the RL quasars have extended radio morphologies: 3\% have a
core and a jet (J), 2\% have a core with one lobe (L), and 10\% have a core
with two lobes (T), the majority being powerful radio sources (PRS), with
$\log(L_{1.4{\rm GHz}}) \ge 24.5$ W Hz$^{-1}$. In general, RL quasars have
higher bolometric luminosities and ionisation powers than radio quiet (RQ)
quasars. The WRS have comparable black hole (BH) masses as the RQ quasars, but
higher accretion rates or radiative efficiencies. The PRS have higher BH masses
than the WRS, but comparable accretion rates or radiative efficiencies. The WRS
also have higher $FWHM_{\rm [OIII]}$ than the PRS, consistent with a coupling
of the spectral characteristics of the quasars with their radio morphologies.
Inspecting the SDSS images and applying a neighbour search algorithm reveal no
difference between the RQ and RL quasars of their host galaxies, environments,
and interaction. Our results prompt the conjecture that the phenomenon that
sparks the radio-loud phase in quasars is transient, intrinsic to the AGN, and
stochastic, due to the chaotic nature of the accretion process of matter onto
the BHs.
