  The majority of massive stars are members of binary systems, a fraction of
which is expected to remain bound after the first star goes off as a supernova.
When the second star also explodes, the SN ejecta are bound to interact with
the compact object companion. We explore the consequences of this interaction
in the case of a black hole (BH) companion. We show that accretion of the SN
ejecta by the BH generally occurs with highly super-Eddington rates, which can
be strongly modulated if the ejecta are clumpy, as typically observed in
supernova remnants. This late accretion produces transient flaring activity
with a time delay from the SN explosion of days to months, depending on the
orbital separation and the velocity of the ejecta. The flares are expected to
have a non-thermal, broad band spectrum, but their high-frequency emission (UV
and X-rays) would be absorbed within the remnant. Observed flares should
therefore be in the optical and near-infrared. We propose this model as an
explanation to the late-time flaring activity observed in the fast blue optical
transient AT2022tsd.
