PTF 13efv - An outburst 500 days prior to the SNHunt 275 explosion and its radiative efficiency

TL;DR

This paper reports the detection of a precursor outburst 500 days before SNHunt 275's explosion, analyzing its radiative efficiency and discussing implications for supernova progenitor behavior.

Contribution

It presents the first pre-explosion observations of SNHunt 275, including a precursor event, and estimates the radiative efficiency of the outburst relative to kinetic energy.

Findings

Precursor detected 500 days before the main explosion.

Radiative efficiency ratio estimated between 0.04 and 3400.

Low velocities suggest uncertain connection to final disruption.

Abstract

The progenitors of some supernovae (SNe) exhibit outbursts with super-Eddington luminosities prior to their final explosions. This behavior is common among Type IIn SNe, but the driving mechanisms of these precursors are not yet well understood. SNHunt 275 was announced as a possible new SN during May 2015. Here we report on pre-explosion observations of the location of this event by the Palomar Transient Factory (PTF) and report the detection of a precursor about 500 days prior to the 2015 May activity (PTF 13efv). The observed velocities in the 2015 transient and its 2013 precursor absorption spectra are low (1000-2000 km/s), so it is not clear yet if the recent activity indeed marks the final disruption of the progenitor. Regardless of the nature of this event, we use the PTF photometric and spectral observations, as well as Swift-UVOT observations, to constrain the efficiency of the radiated energy relative to the total kinetic energy of the precursor. We find that, using an order-of-magnitude estimate and under the assumption of spherical symmetry, the ratio of the radiated energy to the kinetic energy is in the range of 0.04 to 3400.