  We report radio observations of two stripped-envelope supernovae (SNe), 2010O
and 2010P, which exploded within a few days of each other in the luminous
infrared galaxy Arp 299. Whilst SN 2010O remains undetected at radio
frequencies, SN 2010P was detected (with an astrometric accuracy better than 1
milli arcsec in position) in its optically thin phase in epochs ranging from ~1
to ~3yr after its explosion date, indicating a very slow radio evolution and a
strong interaction of the SN ejecta with the circumstellar medium. Our
late-time radio observations toward SN 2010P probe the dense circumstellar
envelope of this SN, and imply a mass-loss rate (Msun/yr) to wind velocity (in
units of 10 km/s) ratio of (3.0-5.1)E-05, with a 5 GHz peak luminosity of
~1.2E+27 erg/s/Hz on day ~464 after explosion. This is consistent with a Type
IIb classification for SN 2010P, making it the most distant and most slowly
evolving Type IIb radio SN detected to date.
