  We propose magnetically arrested disks (MADs) in quiescent black-hole (BH)
binaries as the origin of the multiwavelength emission, and argue that this
class of sources can dominate the cosmic-ray spectrum around the knee. X-ray
luminosities of Galactic BH binaries in the quiescent state are far below the
Eddington luminosity, and thus, radiatively inefficient accretion flows (RIAFs)
are formed in the inner region. Strong thermal and turbulent pressures in RIAFs
produce outflows, which can create large-scale poloidal magnetic fields. These
fields are carried to the vicinity of the BH by the rapid inflow motion,
forming a MAD. Inside the MAD, non-thermal protons and electrons are naturally
accelerated by magnetic reconnections or stochastic acceleration by turbulence.
Both thermal and non-thermal electrons emit broadband photons via synchrotron
emission, which are broadly consistent with the optical and X-ray data of the
quiescent BH X-ray binaries. Moreover, protons are accelerated up to PeV
energies and diffusively escape from these MADs, which can account for the
cosmic-ray intensity around the knee energy.
