The late-time light curve of the type Ia supernova 2000cx

Abstract

Abstract.We have conducted a systematic and comprehensive monitoring programme of the type Ia supernova 2000cx at late phases using the VLT and HST. The VLT observations cover phases 360 to 480 days past maximum brightness and include photometry in the BVRIJH bands, together with a single epoch in each of U and K s . While the optical bands decay by about 1.4 mag per 100 days, we find that the near-IR magnitudes stay virtually constant during the observed period. This means that the importance of the near-IR to the bolometric light curve increases with time. The finding is also in agreement with our detailed modeling of a type Ia supernova in the nebular phase. In these models, the increased importance of the near-IR is a temperature effect. We note that this complicates late-time studies where often only the V band is well monitored. In particular, it is not correct to assume that any optical band follows the bolometric light curve at these phases, and any conclusions based on such assumptions, e.g., regarding positron-escape, must be regarded as premature. A very simple model where all positrons are trapped can reasonably well account for the observations. The nickel mass deduced from the positron tail of this light curve is lower than found from the peak brightness, providing an estimate of the fraction of late-time emission that is outside of the observed wavelength range. Our detailed models show the signature of an infrared catastrophe at these epochs, which is not supported by the observations.

Late light curves of normally luminous Type Ia supernovae

“…These results suggest that a slower I-band decline rate is a general feature of the late light curves of normal/super-luminous SNe Ia, and is possibly suggesting a shift in the late emission to longer wavelengths. A major result of Sollerman et al (2004) was the constant late time emission seen in the NIR curves of SN 2000cx, which supports the idea that the emission is moving into the NIR and eventually into the IR resulting in an IRC. Our results from the analysis of these SNe reinforce the need for more observations of SNe Ia in the NIR in an attempt to reproduce what was seen in SN 2000cx and also in SN 1998bu Figure 2 shows the combined light curves of the six SNe plotted on the radiation transport models of Sollerman et al (2004).…”

“…A major result of Sollerman et al (2004) was the constant late time emission seen in the NIR curves of SN 2000cx, which supports the idea that the emission is moving into the NIR and eventually into the IR resulting in an IRC. Our results from the analysis of these SNe reinforce the need for more observations of SNe Ia in the NIR in an attempt to reproduce what was seen in SN 2000cx and also in SN 1998bu Figure 2 shows the combined light curves of the six SNe plotted on the radiation transport models of Sollerman et al (2004). The V-band model light curve has been normalized to be zero magnitude at 200d along with the data.…”

“…The combined light curves can be seen in Figures 2 & 3, where they are normalized to be zero magnitude at 200days past explosion assuming an 18d rise time to peak light. The data set for SN 2000E includes photometry from Valentini et al (2003), and the data set for SN 2000cx includes data from Li et al (2001), Jha (2002), Candia et al (2003), and Sollerman et al (2004), where the data from our observations are plotted as the filled symbols. …”

SN 2003du: 480 days in the life of a normal type Ia supernova

“…14c we compare the uvoir "bolometric" LC of SN 2003du with the two models presented by Sollerman et al (2004). The models are in the form of broadband U-to-H magnitudes.…”

“…The models are generic, and have not been tuned to any particular SN. They have been computed with 0.6 M 56 Ni and assume full positron trapping, and differ only in the treatment of the photoionization representing two extreme cases that the UV photons either escape or are fully redistributed to lower energies (for more details see Sollerman et al 2004 and references therein). For a comparison with SN 2003du the models were only re-scaled to a distance modulus µ = 32.79 mag, and yet they fit the absolute flux level of the LC of SN 2003du quite well.…”