  We present the physical and dynamical properties of the recently discovered
active asteroid (248370) 2005 QN173 (aka 433P). From our observations, we
derived two possible rotation period solutions of 2.7 and 4.1 hours. The
corresponding light curve amplitudes computed after correcting for the effect
of coma are 0.28 and 0.58 mag, respectively. Both period solutions are shorter
than the critical rotation limit computed for a strengthless triaxial
ellipsoid, suggesting that rotation mass shedding should at least partly be
responsible for the observed activity. We confirm that the activity level is
fading further, but at a very modest rate of only 0.006 mag/day, still also
compatible with sublimation-driven activity. We found that 248370 likely
belongs to the Themis asteroid family, making it a fourth main-belt comet
associated with this group. Orbital characteristics of 248370 are also
consistent with its origin in the young 288P cluster of asteroids. The 288P
cluster is associated with its namesake main-belt comet, providing an exciting
possibility for a comparative analysis of intriguing main-belt comets 248370
and 288P.
