  Gravitational-wave radiometry is a powerful tool by which weak signals with
unknown signal morphologies are recovered through a process of cross
correlation. Radiometry has been used, e.g., to search for persistent signals
from known neutron stars such as Scorpius X-1. In this paper, we demonstrate
how a more ambitious search--for persistent signals from unknown neutron
stars--can be efficiently carried out using folded data, in which an entire
~year-long observing run is represented as a single sidereal day. The all-sky,
narrowband radiometer search described here will provide a computationally
tractable means to uncover gravitational-wave signals from unknown, nearby
neutron stars in binary systems, which can have modulation depths of ~0.1-2 Hz.
It will simultaneously provide a sensitive search algorithm for other
persistent, narrowband signals from unexpected sources.
