Ultra-bright optical transients are linked with type Ic supernovae

TL;DR

This paper presents detailed observations of an ultra-bright optical transient, SN 2010gx, revealing that such transients are likely linked to type Ic supernovae, challenging existing explosion models and understanding of progenitors.

Contribution

It provides the first detailed photometric and spectral analysis of an ultra-bright transient, suggesting a connection to type Ic supernovae and raising new questions about explosion physics.

Findings

SN 2010gx shows early blue spectra with O II lines

Spectra develop type Ic features about 25 days post-discovery

Late-time data suggest large ejected masses and non-standard luminosity sources

Abstract

Recent searches by unbiased, wide-field surveys have uncovered a group of extremely luminous optical transients. The initial discoveries of SN 2005ap by the Texas Supernova Search and SCP-06F6 in a deep Hubble pencil beam survey were followed by the Palomar Transient Factory confirmation of host redshifts for other similar transients. The transients share the common properties of high optical luminosities (peak magnitudes ~ -21 to -23), blue colors, and a lack of H or He spectral features. The physical mechanism that produces the luminosity is uncertain, with suggestions ranging from jet-driven explosion to pulsational pair-instability. Here we report the most detailed photometric and spectral coverage of an ultra-bright transient (SN 2010gx) detected in the Pan-STARRS 1 sky survey. In common with other transients in this family, early-time spectra show a blue continuum, and prominent broad absorption lines of O II. However, about 25d after discovery, the spectra developed type Ic supernova features, showing the characteristic broad Fe II and Si II absorption lines. Detailed, post-maximum follow-up may show that all SN 2005ap and SCP-06F6 type transients are linked to supernovae Ic. This poses problems in understanding the physics of the explosions: there is no indication from late-time photometry that the luminosity is powered by 56Ni, the broad lightcurves suggest very large ejected masses, and the slow spectral evolution is quite different from typical Ic timescales. The nature of the progenitor stars and the origin of the luminosity are intriguing and open questions.