  Outbursts are known to begin with a sudden appearance and steep brightening
of a "stellar nucleus" --- an unresolved image of a plume of material on its
way from the comet's surface and an initial stage of an expanding halo of
ejecta. Since the brightness of this feature is routinely reported, together
with astrometry, by most comet observers as the "nuclear magnitude," it is
straightforward to determine the onset time, a fundamental parameter of any
outburst, by inspecting the chronological lists of such observations for a
major jump in the nuclear brightness. Although it is inadmissible to mix
nuclear magnitudes by different observers without first carefully examining
their compatibility, the time constraints obtained from data sets reported by
different observers can readily be combined. The intersection of these sets
provides the tightest possible constraint on the outburst's onset time. Applied
to comet 168P/Hergenrother during its 2012 return to perihelion, three
outbursts were detected and their timing determined with good to excellent
accuracy. Six fragmentation events experienced by the comet are shown to have
occurred in the same period of time as the outbursts. Three companions are
likely to have broken off from the primary in the first outburst, two
companions in the second outburst, and one companion in the last outburst. All
companions were short-lived, belonging to the class of excessively brittle
fragments. Yet, the results suggest that most of the mass lost in the first
outburst remained relatively intact during the liftoff, while the opposite was
the case in the last outburst.
