The Mid-Infrared and Optical Decay of SN 2011fe

Abstract

We measure the decay rate of the mid-IR luminosity from type Ia supernova 2011fe between six months and one year after explosion using Spitzer/IRAC observations. The fading in the 3.6 micron channel is 1.48+/-0.02 mag/100d, which is similar to that seen in blue optical bands. The supernova brightness fades at 0.78+/-0.02 mag/100d in the 4.5 micron channel which is close to that observed in the near-IR. We argue that the difference is a result of doubly ionized iron-peak elements dominating the bluer IRAC band while singly ionized species are controlling the longer wavelength channel. To test this, we use Large Binocular Telescope spectra taken during the same phases to show that doubly ionized emission lines do fade more slowly than their singly ionized cousins. We also find that [Co III] emission fades at more than twice the radioactive decay rate due to the combination of decreasing excitation in the nebula, recombination and cobalt decaying to iron. The nebular emission velocities of [Fe III] and [Co III] lines show a smaller blue-shift than emission from singly ionized atoms. The Si II velocity gradient near maximum light combined with our nebular velocity measurements suggest SN 2011fe was a typical member of the `low velocity gradient' class of type Ia. Analyzing IRAC photometry from other supernovae we find that mid-IR color of type Ia events is correlated with the early light curve width and can be used as an indicator of the radioactive nickel yield.

11 pages, 6 figures, 3 tables

References in corpus (5)

• BVRI lightcurves of supernovae SN 2011fe in M101, SN 2012aw in M95, and SN 2012cg in NGC 4424
• No Stripped Hydrogen in the Nebular Spectra of Nearby Type Ia Supernova 2011fe
• Analysis of the Early-Time Optical Spectra of SN 2011fe in M101
• Late Light Curves of Normal Type Ia Supernovae
• Testing SNe Ia distance measurement methods with SN 2011fe

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• Measuring nickel masses in Type Ia supernovae using cobalt emission in nebular phase spectra
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• A Systematic Study of Mid-Infrared Emission from Core-Collapse Supernovae with SPIRITS
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• Whimper of a Bang: Documenting the Final Days of the Nearby Type Ia Supernova 2011fe
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• Twins for life? A comparative analysis of the Type Ia supernovae 2011fe and 2011by
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• A JWST Near- and Mid-Infrared Nebular Spectrum of the Type Ia Supernova 2021aefx
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• The Whisper of a Whimper of a Bang: 2400 Days of the Type Ia SN 2011fe Reveals the Decay of ${}^{55}$Fe
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