SN 1986J VLBI. IV. The Nature of the Central Component

Abstract

We report on VLA measurements between 1 and 45 GHz of the evolving radio spectral energy distribution (SED) of SN 1986J, made in conjunction with VLBI imaging. The SED of SN 1986J is unique among supernovae, and shows an inversion point and a high-frequency turnover. Both are due to the central component seen in the VLBI images, and both are progressing downward in frequency with time. The optically-thin spectral index of the central component is almost the same as that of the shell. We fit a simple model to the evolving SED consisting of an optically-thin shell and a partly-absorbed central component. The evolution of the SED is consistent with that of a homologously expanding system. Both components are fading, but the shell more rapidly. We conclude that the central component is physically inside the expanding shell, and not a surface hot-spot central only in projection. Our observations are consistent with the central component being due to interaction of the shock with the dense and highly-structured circumstellar medium that resulted from a period of common-envelope evolution of the progenitor. However a young pulsar-wind nebula or emission from an accreting black hole can also not be ruled out at this point.

Recent VLBI Results on SN 1986J and the Possibility of FRBs Originating from Inside the Expanding Ejecta of Supernovae

“…We describe our observations briefly here. More detail can be found in our series of papers [4,5,6,7]. We have observed SN 1986J with the Jansky Very Large Array (VLA), to measure the evolving total flux density at a wide range of frequencies.…”

“…For details of the fitted values, and other results, please see [7,12]. Of interest in our context of FRB signals propagating through the ejecta is the solution for EM: EM = (1.64 ± 0.21) × 10 9 (t/ 20 yr) −2.72±0.26 cm −6 pc.…”

“…It is relatively nearby, in the galaxy NGC 891, at a distance of 10 Mpc (NASA/IPAC Extragalactic Database, NED). SN 1986J is bright in the radio, and we have been observing it with very long baseline interferometry (VLBI) since 1987 and can resolve the expanding ejecta [4,5,6,7,8]. We show a dual-frequency VLBI image of SN 1986J in Figure 1.…”

“…It may, however, also represent shock interaction with a very aspherical circumstellar medium distribution left over from a binary progenitor which had undergone a period of common-envelope evolution. We discuss the various hypotheses in [7]. However, for the present purpose, the physical nature of the central component is not important, the important thing is only that it resides within the expanding cloud of SN ejecta.…”

The search for high-energy neutrinos coincident with fast radio bursts with the ANTARES neutrino telescope

“…Several models have been proposed such as neutron star mergers (Totani, 2013;Wang et al, 2016) possibly associated to short Gamma-Ray Bursts (GRBs) (Zhang, 2014;Palaniswamy et al, 2014;Murase et al, 2017) or supramassive neutron star collapses (Falcke & Rezzolla, 2014;Ravi & Lasky, 2014;Li et al, 2014). Non-destructive flaring models including giant pulses from young and rapidly rotating neutron stars (Pen & Connor, 2015;Cordes & Wasserman, 2016), magnetar giant flares (Popov & Postnov, 2013;Lyubarsky, 2014), hyperflares from soft gamma-repeaters (Popov & Postnov, 2010), a young neutron star embeded in a wind bubble (Murase et al, 2016) or maybe from the interior of young supernovae (Bietenholz & Bartel, 2017) are however good astrophysical candidates to explain both types of repeating and non repeating FRBs. More exotic models have also been proposed such as radio burst radiation of superconducting cosmic strings (Cao & Yu, 2018;Ye et al, 2017).…”