Whimper of a Bang: Documenting the Final Days of the Nearby Type Ia Supernova 2011fe

Abstract

Using the Hubble Space Telescope (HST) and the Large Binocular Telescope, we followed the evolution of the Type Ia supernova (SN Ia) 2011fe for an unprecedented 1840 days past B-band maximum light and over a factor of 7 million in flux. At 1840 days, the 4000 -17000 Å quasi-bolometric luminosity is just (420 ± 20) L . By measuring the late-time quasi-bolometric light curve, we present the first confident detection of 57 Co decay in a SN Ia light curve and estimate a mass ratio of log( 57 Co/ 56 Co) = −1.59 +0.06 −0.07 . We do not have a clean detection of 55 Fe, but find a limit of 55 Fe/ 57 Co < 0.22 with 99% confidence. These abundance ratios provide unique constraints on the progenitor system because the central density of the exploding white dwarf(s) dictates these nucleosynthetic yields. The observed ratios strongly prefer the lower central densities of doubledegenerate models ( 55 Fe/ 57 Co = 0.27) over the higher central densities of near-Chandrasekhar-mass singledegenerate models ( 55 Fe/ 57 Co = 0.68). However, additional theoretical studies predicting isotopic yields from a broader range of progenitor systems are motivated by these unique observations. We will continue to observe SN 2011fe for another ∼ 600 days with HST and possibly beyond.

Wait for It: Post-Supernova Winds Driven by Delayed Radioactive Decays

“…The observed quasi-bolometric late-time light curve of the best observed SN Ia to date, SN 2011fe, is shown as bullets (Nugent et al 2011;Tsvetkov et al 2013;Kerzendorf et al 2014;Shappee et al 2016). The late-time flattening of SN 2011fe and other SNe Ia above simple predictions for 56 Co decay within the SN ejecta has been attributed to light echoes and the decay of long-lived radioactive isotopes such as 57 Co and 55 Fe (Seitenzahl et al 2009;Röpke et al 2012;Kerzendorf et al 2014;Graur et al 2016;Shappee et al 2016).…”

“…The late-time flattening of SN 2011fe and other SNe Ia above simple predictions for 56 Co decay within the SN ejecta has been attributed to light echoes and the decay of long-lived radioactive isotopes such as 57 Co and 55 Fe (Seitenzahl et al 2009;Röpke et al 2012;Kerzendorf et al 2014;Graur et al 2016;Shappee et al 2016). Our models represent an additional contribution to the total luminosity, and thus the observed light curve represents an upper limit to the luminosity for our wind models.…”

Constraints on the density distribution of type Ia supernovae ejecta inferred from late-time light-curve flattening

“…The best Type Ia supernova for late-time studies is SN 2011fe (see discussion in Shappee, et al 2017), which was observed over a wide range of wavelengths at late time. However, even in this case, a significant fraction of the flux is predicted to be emitted outside of the observed wavelength range (Fransson & Jerkstrand 2015), complicating the comparison to models.…”

“…In the last few years, a few Ia SNe were observed to late times with a more complete spectral coverage, and were found to exhibit a late-time flattening of the light curve (Graur, et al 2016;Dimitriadis, et al 2017;Kerzendorf, et al 2017;Shappee, et al 2017;Yang, et al 2018;Graur, et al 2018a,b;Graur 2019;Li, et al 2019). Assuming that the observed flattening is due to heating by 57 Co and 55 Fe decays, and ignoring delayed deposition, abundances of 57 Co and 55 Fe were derived, typically assuming fully trapped positrons.…”

A year-long plateau in the late-time near-infrared light curves of type Ia supernovae

“…To date, this so-called "IR catastrophe" has not been observed in the optical. In fact, several recent studies have shown that the decline of the optical light curves begins to slow down at ∼ 800 days (Cappellaro et al 1997;Leloudas et al 2009;Fransson & Jerkstrand 2015;Graur et al 2016Graur et al , 2018bGraur 2019;Shappee et al 2017;Yang et al 2018;Dimitriadis et al 2017;Kerzendorf et al 2017;Li et al 2019). 2012ht, 2013dy, 2017erp, 2018gv, and 2019np in their host galaxies.…”