  Centaurs are small Solar System objects on chaotic orbits in the giant planet
region, forming an evolutionary continuum with the Kuiper belt objects and
Jupiter-family comets. Some Centaurs are known to exhibit cometary activity,
though unlike comets this activity tends not to correlate with heliocentric
distance and the mechanism behind it is currently poorly understood. We utilize
serendipitous observations from the Asteroid Terrestrial-impact Last Alert
System (ATLAS), Zwicky Transient Facility (ZTF), Panoramic Survey Telescope and
Rapid Response System (Pan-STARRS), Dark Energy Survey (DES), and Gaia in
addition to targeted follow-up observations from the Las Cumbres Observatory,
TRAnsiting Planets and PlanetesImals Small Telescope South (TRAPPIST-South),
and Gemini North telescope to analyze an unexpected brightening exhibited by
the known active Centaur (2060) Chiron in 2021. This is highly indicative of a
cometary outburst. As of 2023 February, Chiron has still not returned to its
pre-brightening magnitude. We find Chiron's rotational lightcurve, phase curve
effects, and possible high-albedo surface features to be unlikely causes of
this observed brightening. We consider the most likely cause to be an epoch of
either new or increased cometary activity, though we cannot rule out a possible
contribution from Chiron's reported ring system, such as a collision of as-yet
unseen satellites shepherding the rings. We find no evidence for coma in our
Gemini or TRAPPIST-South observations, though this does not preclude the
possibility that Chiron is exhibiting a coma that is too faint for observation
or constrained to the immediate vicinity of the nucleus.
