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We present Hubble Space Telescope observations and photometric measurements of the Type Ia supernova (SN Ia) SN 2013aa 1500 days after explosion. At this epoch, the luminosity is primarily dictated by the amounts of radioactive ${}^{57}textrm{Co}$ and ${}^{55}textrm{Fe}$, while at earlier epochs, the luminosity depends on the amount of radioactive ${}^{56}textrm{Co}$. The ratio of odd-numbered to even-numbered isotopes depends significantly on the density of the progenitor white dwarf during the SN explosion, which, in turn, depends on the details of the progenitor system at the time of ignition. From a comprehensive analysis of the entire light curve of SN 2013aa, we measure a $M({}^{57}textrm{Co})/M({}^{56}textrm{Co})$ ratio of $0.02^{+0.01}_{-0.02}$, which indicates a relatively low central density for the progenitor white dwarf at the time of explosion, consistent with double-degenerate progenitor channels. We estimate $M({}^{56}textrm{Ni}) = 0.732 pm 0.151:mathrm{M_{odot}}$, and place an upper limit on the abundance of ${}^{55}textrm{Fe}$. A recent study reported a possible correlation between $M({}^{57}textrm{Co})/M({}^{56}textrm{Co})$ and stretch for four SNe Ia. SN 2013aa, however, does not fit this trend, indicating either SN 2013aa is an extreme outlier or the correlation does not hold up with a larger sample. The $M({}^{57}textrm{Co})/M({}^{56}textrm{Co})$ measured for the expanded sample of SNe Ia with photometry at extremely late times has a much larger range than that of explosion models, perhaps limiting conclusions about SN Ia progenitors drawn from extremely late-time photometry.
We present late-time optical $R$-band imaging data from the Palomar Transient Factory (PTF) for the nearby type Ia supernova SN 2011fe. The stacked PTF light curve provides densely sampled coverage down to $Rsimeq22$ mag over 200 to 620 days past exp
We present early-time Swift and Chandra X-ray data along with late-time optical and near-infrared observations of SN 2013by, a Type IIL supernova (SN) that occurred in the nearby spiral galaxy ESO 138$-$G10 (D $sim 14.8$ Mpc). Optical and NIR photome
In this work we analyse late-time (t > 100 d) optical spectra of low-redshift (z < 0.1) Type Ia supernovae (SNe Ia) which come mostly from the Berkeley Supernova Ia Program dataset. We also present spectra of SN 2011by for the first time. The BSNIP s
The very nearby Type Ia supernova 2014J in M82 offers a rare opportunity to study the physics of thermonuclear supernovae at extremely late phases ($gtrsim$800 days). Using the Hubble Space Telescope (HST), we obtained six epochs of high precision ph
We present early phase observations in optical and near-infrared wavelengths for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate of the light curve is $Delta m_{15}(B)=0.65pm 0.03$, which is one of the slowest among SNe Ia.