Late-time emission of type Ia supernovae: optical and near-infrared observations of SN 2001el

TL;DR

This study presents detailed optical and near-infrared observations of SN 2001el at late times, revealing decay rates, the significance of near-infrared emission, and implications for positron trapping in type Ia supernovae.

Contribution

First comprehensive late-time optical and near-infrared light curves of a normal type Ia supernova, confirming the importance of near-infrared emission and positron trapping.

Findings

Optical light curves decay linearly with specific time scales.

Near-infrared flux remains nearly constant at late epochs.

Late-time luminosity decay consistent with positron energy deposition.

Abstract

We present optical and near-infrared light curves of SN 2001el from 310 to 445 days past maximum light, obtained with the Very Large Telescope. The late-time optical (UBVRI) light curves decay in a nearly linear fashion with decay time scales of 1.43\pm0.14, 1.43\pm0.06, 1.48\pm0.06, 1.45\pm0.07, and 1.03\pm0.07 magnitudes (per hundred days) in the U, B, V, R and I bands, respectively. In contrast, in the near-infrared (JHKs) bands the time evolution of the flux appears to be nearly constant at these epochs. We measure decline rates (per hundred days) of 0.19\pm0.10 and 0.17\pm0.11 magnitudes in the J and H bands, respectively. We construct a UVOIR light curve, and find that the late-time luminosity has a decay time scale nearly consistent with complete depostion of positron kinetic energy. The late-time light curves of the normal type Ia SN 2001el demonstrate the increased importance of the near-infrared contribution. This was previously observed in the peculiar SN 2000cx, and the results for SN 2001el thus ensure that the conclusions previously based on a single peculiar event are applicable to normal type Ia supernovae. The measured late-time UVOIR decline rate suggests that a majority of the positrons are trapped within the ejecta. This results does not favor the predictions of a weak and/or radially combed magnetic field configuration.