2009A&A...505..265L

We study a thermonuclear supernova (SN), emphasizing very late phases. An extensive dataset for SN 2003hv that covers the flux evolution from maximum light to day +786 is presented. This includes 82 epochs of optical imaging, 24 epochs of near-infrared (NIR) imaging, and 10 epochs of optical spectroscopy. These data are combined with published nebular-phase IR spectra, and the observations are compared to model light curves and synthetic nebular spectra. SN 2003hv is a normal Type Ia supernova (SN Ia) with photometric and spectroscopic properties consistent with its rarely observed B-band decline-rate parameter, Δm₁₅(B)=1.61±0.02. The blueshift of the most isolated [FeII] lines in the nebular-phase optical spectrum appears consistent with those observed in the IR at similar epochs. At late times there is a prevalent color evolution from the optical toward the NIR bands. We present the latest-ever detection of a SN Ia in the NIR in Hubble Space Telescope images. The study of the ultraviolet/optical/infrared (UVOIR) light curve reveals that a substantial fraction of the flux is ``missing'' at late times. Between 300 and 700 days past maximum brightness, the UVOIR light curve declines linearly following the decay of radioactive ⁵⁶Co, assuming full and instantaneous positron trapping. At 700 days we detect a possible slowdown of the decline in optical-bands, mainly in the V-band. The data are incompatible with a dramatic infrared catastrophe (IRC). However, the idea that an IRC occurred in the densest regions before 350 days can explain the missing flux from the UVOIR wavelengths and the flat-topped profiles in the NIR. We argue that such a scenario is possible if the ejecta are clumpy. The observations suggest that positrons are most likely trapped in the ejecta.