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11th of November 2022
Flux density evolution of a supernova remnant
by Bietenholz et al.
Supernova (SN) 1996cr, in the nearby Circinus Galaxy had the highest radio flux density ever observed for opticallyidentified radio supernova (163 mJy at 8.3 GHz; Bauer 2007b; Bauer et al. 2008), as well as being one of only a handful of supernovae which can still be observed in radio more than 20 yr after the explosion. It was only firmly identified as a SN in 2008, well after the explosion, so the explosion date, t0, is not accurately known. SN 1996cr has remained unusually bright in both radio and X-ray for more than two decades, and is one of only a small number of long-lived core-collapse SNe (CCSNe) whose evolution can be studied over more than a decade. Bietenholz et al. present broadband radio flux-density measurements supernova (SN) 1996cr, made with MeerKAT, ATCA and ALMA, and images made from Very Long Baseline Interferometry (VLBI) observations with the Southern Hemisphere Long Baseline Array. The image above shows the radio light curves of SN 1996cr at 8.6 and 1.4 GHz, including earlier measurements from a 2013 paper by Meunier et al. The red points and dashed line show the 1.4 GHz light curve, while the blue points and solid line show the 8.6 GHz one. Since 2010 (t = 5370 d), the flux density has declined rapidly. The spectrum was initially inverted, with higher flux densities at higher frequencies, but gradually flattened after several years and now has a relatively steep spectrum (with higher flux densities at lower frequencies) The spectral energy distribution of SN 1996cr in 2020, at age, t ∼8700 d, is a power-law with a spectral index of -0.6 between 1 and 34 GHz, but may steepen further at higher frequencies. SN 1996cr's rise in the radio and X-rays is attributed to the SN shock interacting with a dense region of the circum-steller medium.

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