Light curves of hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory

TL;DR

This study analyzes the light-curve properties of 26 hydrogen-poor superluminous supernovae from the Palomar Transient Factory, revealing their distinct photometric features, decay behaviors, and potential powering mechanisms, with implications for their use in cosmology.

Contribution

First comprehensive analysis of SLSNe-I light curves from PTF, demonstrating their unique photometric properties and evaluating models for their luminosity sources.

Findings

SLSNe-I are brighter and have longer rise times than normal SNe Ib/c.

Late-time light curves are consistent with radioactive decay or magnetar models.

Sample analysis does not support SLSNe-I as reliable cosmological distance indicators.

Abstract

We investigate the light-curve properties of a sample of 26 spectroscopically confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar Transient Factory (PTF) survey. These events are brighter than SNe Ib/c and SNe Ic-BL, on average, by about 4 and 2~mag, respectively. The peak absolute magnitudes of SLSNe-I in rest-frame $g$ band span $-22\lesssim M_g \lesssim-20$~mag, and these peaks are not powered by radioactive $^{56}$Ni, unless strong asymmetries are at play. The rise timescales are longer for SLSNe than for normal SNe Ib/c, by roughly 10 days, for events with similar decay times. Thus, SLSNe-I can be considered as a separate population based on photometric properties. After peak, SLSNe-I decay with a wide range of slopes, with no obvious gap between rapidly declining and slowly declining events. The latter events show more irregularities (bumps) in the light curves at all times. At late times, the SLSN-I light curves slow down and cluster around the $^{56}$Co radioactive decay rate. Powering the late-time light curves with radioactive decay would require between 1 and 10${\rm M}_\odot$ of Ni masses. Alternatively, a simple magnetar model can reasonably fit the majority of SLSNe-I light curves, with four exceptions, and can mimic the radioactive decay of $^{56}$Co, up to $\sim400$ days from explosion. The resulting spin values do not correlate with the host-galaxy metallicities. Finally, the analysis of our sample cannot strengthen the case for using SLSNe-I for cosmology.