Long-rising Type II supernovae from Palomar Transient Factory and Caltech Core-Collapse Project

Abstract

Context. Supernova (SN) 1987A was a peculiar hydrogen-rich event with a long-rising (∼84 d) light curve, stemming from the explosion of a compact blue supergiant star. Only a few similar events have been presented in the literature in recent decades. Aims. We present new data for a sample of six long-rising Type II SNe (SNe II), three of which were discovered and observed by the Palomar Transient Factory (PTF) and three observed by the Caltech Core-Collapse Project (CCCP). Our aim is to enlarge this small family of long-rising SNe II, characterizing their differences in terms of progenitor and explosion parameters. We also study the metallicity of their environments. Methods. Optical light curves, spectra, and host-galaxy properties of these SNe are presented and analyzed. Detailed comparisons with known SN 1987A-like events in the literature are shown, with particular emphasis on the absolute magnitudes, colors, expansion velocities, and host-galaxy metallicities. Bolometric properties are derived from the multiband light curves. By modeling the earlytime emission with scaling relations derived from the SuperNova Explosion Code (SNEC) models of MESA progenitor stars, we estimate the progenitor radii of these transients. The modeling of the bolometric light curves also allows us to estimate other progenitor and explosion parameters, such as the ejected 56 Ni mass, the explosion energy, and the ejecta mass. Results. We present PTF12kso, a long-rising SN II that is estimated to have the largest amount of ejected 56 Ni mass measured for this class. PTF09gpn and PTF12kso are found at the lowest host metallicities observed for this SN group. The variety of early lightcurve luminosities depends on the wide range of progenitor radii of these SNe, from a few tens of R (SN 2005ci) up to thousands (SN 2004ek) with some intermediate cases between 100 R (PTF09gpn) and 300 R (SN 2004em). Conclusions. We confirm that long-rising SNe II with light-curve shapes closely resembling that of SN 1987A generally arise from blue supergiant (BSG) stars. However, some of them, such as SN 2004em, likely have progenitors with larger radii (∼300 R , typical of yellow supergiants) and can thus be regarded as intermediate cases between normal SNe IIP and SN 1987A-like SNe. Some extended red supergiant (RSG) stars such as the progenitor of SN 2004ek can also produce long-rising SNe II if they synthesized a large amount of 56 Ni in the explosion. Low host metallicity is confirmed as a characteristic of the SNe arising from compact BSG stars.

SN 2018hna: 1987A-like Supernova with a Signature of Shock Breakout

“…The cooling envelope phase in 1987A-like events shows a steep rise in colors as seen in the evolution of U-V and B-V colors (Figures 5B and C and SN 2006V are bluer compared to SN 1987A. This agrees with the fact that 1987A-like events with bluer colors tend to be brighter at maximum (Taddia et al 2016). SN 2018hna is bluer in U-V by ∼ 1.6 mag and in B-V by ∼ 0.4 mag.…”

“…It is seen that the progenitors of 1987A-like events produce higher amount of 56 Ni in comparison to normal Type II SNe as majority of them have higher ejecta masses (Taddia et al 2016). The degree of 56 Ni-mixing and the net amount of 56 Ni synthesized helps change the rise to the maximum.…”

“…These will be referred to as 1987A-like events, whereas, Type II events with an RSG progenitor will be referred to as normal Type II SNe. Analysis of 1987A-like events have shown that these arise from rather compact progenitors (BSG, R < 100 R ) with a higher ZAMS mass, higher explosion energies (> 10 51 erg) and higher synthesized 56 Ni (∼ 0.1 M ) when compared to normal Type II SNe (Pastorello et al 2012;Taddia et al 2016).…”

The Matter Beyond the Ring: The Recent Evolution of SN 1987A Observed by the Hubble Space Telescope

“…Specifically, the relatively compact nature of the BSG progenitor resulted in a 56 Ni dominated peak in the light curve rather than a plateau. A number of other SN 1987A-like events have been observed and the rate has been estimated to 1-3% of the core collapse rate (Pastorello et al 2012;Taddia et al 2016). There is observational evidence that these SNe preferentially occur in low-metallicity environments (Pastorello et al 2012;Taddia et al 2013), which may explain explosions in the BSG stage (Arnett et al 1989).…”

Comparison of the optical light curves of hydrogen-rich and hydrogen-poor type II supernovae

“…A number of further sub-classifications exists, such as those SNe II showing similar properties to SN 1987A (with particularly long-rising light curves, see e.g. Pastorello et al 2012, Taddia et al 2016 and references therein), and those displaying narrow emission features in their spectra, the Type IIn (Schlegel 1990). However, both of these groups show characteristics sufficiently distinct from hydrogen-rich SNe II (as defined above) that we do not consider them in this work (see Arcavi 2017 and references therein for additional discussion on hydrogen-rich CCSNe).…”