  P/2013 P5 PANSTARRS was discovered in Aug. 2013, displaying a cometary tail,
but with orbital elements typical for a member of the inner asteroid Main Belt.
  We monitored the object from 2013 Aug. 30 until Oct. 05 using the CFHT, NTT,
CA 1.23m, Perkins 1.8m (Lowell), and the 0.6m TRAPPIST telescopes. We measured
its nuclear radius to be r < 0.25-0.29km, and its colours g-r = 0.58+/-0.05 and
r-i = 0.23+/-0.06, typical for an S-class asteroid. We failed to detect any
rotational light curve, with an amplitude < 0.05mag and a double-peaked
rotation period < 20h. A detailed Finson-Probstein analysis of deep NTT and
CFHT images indicated that the object was active since at least late January
2013 until the time of the latest observations in 2013 September, with at least
two peaks of activity around 2013 June 14+/-10d and 2013 July 22+/-3d. The
changes of activity level and the activity peaks were extremely sharp and
short, shorter than the temporal resolution of our observations (about 1d). The
dust distribution was similar during these two events, with dust grains
covering at least the 1-1000{\mu}m range. The total mass ejected in grains <1mm
was estimated to be 3.0 10$^6$kg and 2.6 10$^7$kg around the two activity
peaks.
  Rotational disruption cannot be ruled out as the cause of the dust ejection.
We also propose that the components of a contact binary might gently rub and
produce the observed emission. Volatile sublimation might also explain what
appears as cometary activity over a period of 8 months. However, while Main
Belt comets best explained by ice sublimation are found in the outskirts of the
Main Belt, where water ice is believed to be able to survive buried in
moderately large objects for the age of the solar system deeply, the presence
of volatiles in an object smaller than 300m in radius would be very surprising
in the inner asteroid belt.
