Type IIn supernova light-curve properties measured from an untargeted survey sample

Abstract

The evolution of a Type IIn supernova (SN IIn) is governed by the interaction between the SN ejecta and a hydrogen-rich circumstellar medium (CSM). SNe IIn thus allow us to probe the late-time mass-loss history of their progenitor stars. We present a sample of SNe IIn from the untargeted, magnitude-limited surveys of the Palomar Transient Factory (PTF) and its successor, the intermediate PTF (iPTF). To date, statistics on SN IIn optical light curve properties have generally been based on small ( 10 SNe) samples from targeted SN surveys. SNe IIn found and followed by the PTF/iPTF were used to select a sample of 42 events with useful constraints on the rise times as well as with available post-peak photometry. The SNe were discovered in 2009-2016 and have at least one low-resolution classification spectrum, as well as photometry from the P48 and P60 telescopes at Palomar Observatory. We study the light-curve properties of these SNe IIn using spline fits (for the peak and the declining portion) and template matching (for the rising portion). We study the peak-magnitude distribution, rise times, decline rates, colour evolution, host galaxies, and K-corrections of the SNe in our sample. We find that the typical rise times are divided into fast and slow risers as 20 ± 8 d and 50 ± 15 d, respectively. The decline rates could possibly be divided into two groups (with slopes 0.013 ± 0.008 mag d −1 and 0.040 ± 0.014 mag d −1 ), but this division has weak statistical significance. We find no significant correlation between the peak luminosity of SNe IIn and their rise times, but the more luminous SNe IIn are generally found to be more durable and the slowly rising SNe IIn are generally found to be slowly declining. The SNe in our sample were hosted by galaxies of absolute magnitude −22 Mg −13 mag. The K-corrections at light-curve peak of the SNe in our sample are found to be within 0.2 mag for the observer's frame r-band, for SNe IIn at redshifts z < 0.25. Applying K-corrections and including also ostensibly "superluminous" SNe IIn, we find that the peak magnitudes are M r peak = −19.18 ± 1.32 mag. We conclude that the occurrence of conspicuous light-curve bumps in SNe IIn, such as in iPTF13z, is limited to 1.4 +14.6 −1.0 % of the SNe IIn. We also investigate a possible subtype of SNe IIn with a fast rise to a 50 d plateau followed by a slow, linear decline. iPTF13agz, iPTF13aki, iPTF13asr, iPTF13cuf, iPTF14bcw, iPTF14bpa, iPTF15aym, iPTF15bky, iPTF15blp, iPTF15eqr, iPTF16fb. ⋆ Based in part on observations made with the Palomar Transient Factory and intermediate Palomar Transient Factory surveys.

Bright, Months-long Stellar Outbursts Announce the Explosion of Interaction-powered Supernovae

“…Most observed precursors develop quite slowly as pointed out in Section 6.1.1. Nyholm et al (2020) measured the rise and decline rates for ∼30 Type IIn SNe from the PTF/iPTF sample and the precursors we detect rise more slowly than any Type IIn SNe in their sample. A possible explanation could be that the precursor shock front propagates with a substantially lower velocity compared to the SN ejecta.…”

“…With rise times of 4-25 days, all SNe with detected precursors are part of the fast-rising subgroup identified by Nyholm et al (2020) 26 which includes approximately twothirds of the Type IIn SNe in their sample. A likely explanation is that fast-rising SNe IIn are typically fainter (Nyholm et al 2020) and our precursor search is most sensitive to nearby, faint SNe (see Figure 12). We here assume that energetic precursors eject more material and search for a correlation between the radiative precursor energy and the estimated SN rise time.…”

The Zwicky Transient Facility Bright Transient Survey. II. A Public Statistical Sample for Exploring Supernova Demographics*

“…SNe IIn (which for this purpose we take to include all events classified as SLSN-II on TNS, most but not all of which show SN IIn-like narrow features) obey the opposite correlation: more slowly declining events are on average more luminous, in agreement with Ofek et al (2014) and Nyholm et al (2020). This relation may turn over toward the short-timescale end of the diagram: Type Ibn SNe form a small cluster of luminous CSM-interacting hydrogen-poor transients, of which the shortest events are generally more luminous than the longer ones, but the sample is small and the trend is not significant.…”

The Carnegie Supernova Project II

“…The narrow Hα P Cygni feature is measured to have a blue velocity at zero intensity (BVZI) of 106 ± 6 km s −1 and a P Cygni minimum velocity of 66 ± 6 km s −1 . This line component is observed in many SNe IIn and is thought to be formed from outer unshocked circumstellar material (CSM) that is excited by the emission originating from the shock region (see, e.g., Kiewe et al 2012;Taddia et al 2013;Nyholm et al 2020). As a result, the BVZI value of this component provides a measure of the CSM velocity.…”