ar X iv : a st ro - p h / 03 04 11 2 v 1 7 A pr 2 00 3 Optical Light Curves of Supernovae ⋆

Photometry is the most easily acquired information about supernovae. The light curves constructed from regular imaging provide signatures not only for the energy input, the radiation escape, the local environment and the progenitor stars, but also for the intervening dust. They are the main tool for the use of supernovae as distance indicators through the determination of the luminosity. The light curve of SN1987A still is the richest and longest observed example for a core-collapse supernova. Despite the peculiar nature of this object, as explosion of a blue supergiant, it displayed all the characteristics of type II supernovae. The light curves of type Ib/c supernovae are more homogeneous, but still display the signatures of explosions in massive stars, among them early interaction with their circumstellar material. Wrinkles in the near-uniform appearance of thermonuclear (type Ia) supernovae have emerged during the past decade. Subtle differences have been observed especially at near infrared (NIR) wavelengths. Interestingly, the light curve shapes appear to correlate with a variety of other characteristics of these supernovae. The construction of bolometric light curves provides the most direct link to theoretical predictions and can yield sorely needed constraints for the models. First steps in this direction have been already made. 1 Physics of Supernova Light Curves The temporal evolution of the energy release by supernovae (SNe) is one of the major sources of information about the nature of these events. The brightness information is relatively easy to obtain and, hence, light curves have been one of the main stays of supernova research. It is not only the light curves themselves, but also the absolute luminosity and the color evolution that have provided major insights into the supernova phenomenon. Through light curves it has been possible to distinguish between progenitor models, infer some aspects of the progenitor evolution, measure the power sources, detail the explosion models, and probe the local environment of the supernova explosions. The observational data have been substantially increased over the last decade (for a status before 1990 see [51]). In particular, there are now large databases with light curve data for type Ia supernovae (SNIa). The data on type II supernovae has been extensively expanded as well, but there is still a clear lack of light curves for peculiar objects. Over the last decade the supernova family has ⋆ to be published in: ”Supernovae and Gamma Ray Bursters”, Lecture Notes in Physics (http://link.springer.de/series/lnpp) 2 Leibundgut and Suntzeff further acquired new members and subclassifications (see the chapter by Turatto in this volume). The energetic display of a supernova can have several different input sources. The most important power comes in almost all cases from the radioactive decay of material newly synthesized in the explosion. The major contributor is Ni, the main product of burning to nuclear statistical equilibrium at the temperatures and densities encountered in supernovae. This nucleus is unstable and decays with a half-life of 6.1 days due to electron capture to Co emitting γ-photons with energies of 750 keV, 812 keV, and 158 keV. The cobalt isotope is also unstable and decays with a half-life of 77.1 days through electron capture (81%) and β-decay (19%) to Fe. In this process γ-photons with energies of 1.238 MeV and 847 keV are emitted. The kinetic energy of the electrons is about 600 keV (for more details on the radioactive decays see [3,26,78]). The γ-rays are downscattered or thermalized in the ejecta until they emerge as optical or NIR photons [2,48,85]. The light curves depend on the size and mass of the progenitor star and the strength of the explosion. Additional energy input, which results in modulations of the emerging radiation, comes from shock cooling, recombination of the ionized ejecta, collision of the shock with circumstellar medium (CSM) and possible accretion onto a compact remnant. Light curves are further shaped by the time-variable escape fraction of γ-rays, dust formation and absorption in the interstellar medium. In some cases, forward scattered light can change the light curves, e.g., through light echos and fluorescence of nearby gas ionized by the X-ray/UV shock breakout of the explosion. With this panoply of different energy contributors and modulators, light curve displays are very rich indeed. Despite the plethora of possibilities, light curves of different supernova types are rather distinct, although not sufficiently so for a solid classification. They are, however, important tools to learn about the physics of supernovae. Light curves are discussed in [37,51,56,80,81]. Reviews concentrating more specifically on SNIa light curves can be found in [57,58,73,107], while the light curves of core-collapse supernovae have mostly been summarized in relation to SN1987A [4,72]. Additional well-sampled data sets are available for SN1993J, SN1998S and SN1999em (see references below). The following sections give a brief overview of observational data sources (§2), describe the light curves of the main supernova types (core-collapse supernovae in §3 and thermonuclear supernovae in §4) and the physics behind the light curve shapes. We will discuss bolometric light curves in §5 before we summarize in §6.