Radio observation of the transient CSS161010

The inferred initial kinetic energy of CSS161010 (Ek>~1051erg) is comparable to that of long gamma-ray bursts, but the ejecta mass that is coupled to the mildly relativistic outflow is significantly larger (~0.01-0.1M{odot}). This is consistent with the lack of observed {gamma}-rays. The luminous X-rays were produced by a different emission component to the synchrotron radio emission.

CSS161010 is located at ~150Mpc in a dwarf galaxy with stellar mass M*~107M{sun} and specific star formation rate sSFR~0.3/Gyr. This mass is among the lowest inferred for host galaxies of explosive transients from massive stars. Our observations of CSS161010 are consistent with an engine-driven aspherical explosion from a rare evolutionary path of a H-rich stellar progenitor, but we cannot rule out a stellar tidal disruption event on a centrally located intermediate-mass black hole.

Regardless of the physical mechanism, CSS161010 establishes the existence of a new class of rare (rate<0.4% of the local core-collapse supernova rate) H-rich transients that can launch mildly relativistic outflows.