  In eclipsing X-ray binary systems, the direct X-ray emission is blocked by
the companion star during the eclipse. We observe only reprocessed emission
that contains clues about the environment of the compact object and its
chemical composition, ionization levels, etc. We have found flares in some
X-ray binaries during their eclipses. The study of eclipse flares provides
additional clues regarding the size of the reprocessing region and helps
distinguish between different components of the X-ray spectrum observed during
the eclipse. In the archival data, we searched for flares during eclipses of
high-mass X-ray binaries and found flares in three sources: Vela X-1, LMC X-4,
and 4U 1700-37. Comparing spectral properties of the eclipse flare and
non-flare data, we found changes in the power-law photon index in all three
sources and multiple emission lines in Vela X-1 and 4U 1700-37. The fluxes of
prominent emission lines showed a similar increase as the overall X-ray flux
during the eclipse flare, suggesting the lines originate in the binary
environment and not in the interstellar medium. We also observed a soft excess
in 4U 1700-37 that remains unchanged during both eclipse flare and non-flare
states. Our analysis suggests that this emission originates from the extremely
thin shell of the stellar wind surrounding the photosphere of its companion
star. The detection of short (100-200 seconds) count-rate doubling timescale in
4U 1700-37 and LMC X-4 indicates that the eclipse reprocessing occurs in a
region larger than, but comparable to the size of the companion star.
