2007A&A...470L...1S

To elucidate the nature of the late-phase emission of the normal type Ia supernova SN 2001el. 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±0.14, 1.43±0.06, 1.48±0.06, 1.45±0.07, and 1.03±0.07 magnitudes (per hundred days) in the U, B, V, R, and I bands, respectively. In contrast, in the near-infrared (JHK_s) 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±0.10 and 0.17±0.11 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 result does not favor the prediction of a weak and/or radially combed magnetic field configuration.