  We report results of a deep all-sky search for periodic gravitational waves
from isolated neutron stars in data from the first Advanced LIGO observing run.
This search investigates the low frequency range of Advanced LIGO data, between
20 and 100 Hz, much of which was not explored in initial LIGO. The search was
made possible by the computing power provided by the volunteers of the
Einstein@Home project. We find no significant signal candidate and set the most
stringent upper limits to date on the amplitude of gravitational wave signals
from the target population, corresponding to a sensitivity depth of 48.7
[1/$\sqrt{{\textrm{Hz}}}$]. At the frequency of best strain sensitivity, near
100 Hz, we set 90% confidence upper limits of $1.8 \times 10^{-25}$. At the low
end of our frequency range, 20 Hz, we achieve upper limits of $3.9 \times
10^{-24}$. At 55 Hz we can exclude sources with ellipticities greater than
$10^{-5}$ within 100 pc of Earth with fiducial value of the principal moment of
inertia of $10^{38} \textrm{kg m}^2$.
