Rapidly Decaying Supernova 2010X: A Candidate ".Ia" Explosion

TL;DR

SN 2010X is a rapidly decaying supernova, likely a .Ia explosion, with unique properties that challenge existing models and suggest a new class of fast, helium-rich thermonuclear events.

Contribution

This paper reports the discovery and detailed analysis of SN 2010X, proposing it as a candidate .Ia supernova and providing insights into its explosion mechanism and composition.

Findings

SN 2010X decays exponentially with a 5-day timescale.

Spectral analysis suggests presence of Aluminum or Helium.

The supernova's properties are consistent with a helium shell detonation.

Abstract

We present the discovery, photometric and spectroscopic follow-up observations of SN 2010X (PTF 10bhp). This supernova decays exponentially with tau_d=5 days, and rivals the current recordholder in speed, SN 2002bj. SN 2010X peaks at M_r=-17mag and has mean velocities of 10,000 km/s. Our light curve modeling suggests a radioactivity powered event and an ejecta mass of 0.16 Msun. If powered by Nickel, we show that the Nickel mass must be very small (0.02 Msun) and that the supernova quickly becomes optically thin to gamma-rays. Our spectral modeling suggests that SN 2010X and SN 2002bj have similar chemical compositions and that one of Aluminum or Helium is present. If Aluminum is present, we speculate that this may be an accretion induced collapse of an O-Ne-Mg white dwarf. If Helium is present, all observables of SN 2010X are consistent with being a thermonuclear Helium shell detonation on a white dwarf, a ".Ia" explosion. With the 1-day dynamic-cadence experiment on the Palomar Transient Factory, we expect to annually discover a few such events.