  We present a search for Galactic transient gamma-ray sources using 13 years
of the Fermi Large Area Telescope data. The search is based on a recently
developed variable-size sliding-time-window (VSSTW) analysis and aimed at
studying variable gamma-ray emission from binary systems, including novae,
gamma-ray binaries, and microquasars. Compared to the previous search for
transient sources at random positions in the sky with 11.5 years of data, we
included gamma rays with energies down to 500 MeV, increased a number of test
positions, and extended the data set by adding data collected between February
2020 and July 2021. These refinements allowed us to detect an additional three
novae, V1324 Sco, V5855 Sgr, V357 Mus, and one gamma-ray binary, PSR B1259-63,
with the VSSTW method. Our search revealed a gamma-ray flare from the
microquasar, Cygnus X-3, occurred in 2020. When applied to equal quarters of
the data, the analysis provided us with detections of repeating signals from
PSR B1259-63, LS I +61 303, PSR J2021+4026, and Cygnus X-3. While the Cygnus
X-3 was bright in gamma rays in mid-2020, it was in a soft X-ray state and we
found that its gamma-ray emission was modulated with the orbital period.
