The nature of supernovae 2010O and 2010P in Arp 299 - II. Radio emission

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 {\tilde}1 to {\tilde}3 yr 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 towards SN 2010P probe the dense circumstellar envelope of this SN, and imply dot$\{$M$\}$ [ $\{$M\_$\{${\sun}$\}$ yr\^{}$\{$-1$\}$$\}$] / v\_$\{$wind$\}$ [10 km s\^{}$\{$-1$\}$] =(3.0-5.1) {\times} 10$^{-5}$, with a 5 GHz peak luminosity of {\tilde}1.2 {\times} 10$^{27}$ erg s$^{- 1}$ Hz$^{- 1}$ on day {\tilde}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.