The Evolution of Temperature and Bolometric Luminosity in Type-II Supernovae

TL;DR

This study analyzes the temperature evolution and bolometric luminosity of 29 type-II supernovae using multi-band photometry, revealing signatures of hydrogen recombination and clarifying the timing of optical plateau onset.

Contribution

It provides a uniform analysis of supernova temperature and luminosity evolution, highlighting the observable effects of hydrogen recombination and refining the understanding of optical plateau timing.

Findings

Strong evidence for hydrogen recombination signatures.

Optical plateau onset correlates with black body peak reaching filter wavelength.

Recombination affects the light curve after initial fast decline.

Abstract

In this work we present a uniform analysis of the temperature evolution and bolometric luminosity of a sample of 29 type-II supernovae (SNe), by fitting a black body model to their multi-band photometry. Our sample includes only SNe with high quality multi-band data and relatively well sampled time coverage. Most of the SNe in our sample were detected less than a week after explosion so their light curves cover the evolution both before and after recombination starts playing a role. We use this sample to study the signature of hydrogen recombination, which is expected to appear once the observed temperature drops to $\approx 7,000$K. Theory predicts that before recombination starts affecting the light curve, both the luminosity and the temperature should drop relatively fast, following a power-law in time. Once the recombination front reaches inner parts of the outflow, it sets the observed temperature to be nearly constant, and slows the decline of the luminosity (or even leads to a re-brightening). We compare our data to analytic studies and find strong evidence for the signature of recombination. We also find that the onset of the optical plateau in a given filter, is effectively the time at which the black body peak reaches the central wavelength of the filter, as it cools, and it does not correspond to the time at which recombination starts affecting the emission.