Intermediate-luminosity red transients: Spectrophotometric properties and connection to electron-capture supernova explosions
Creators: name: Cai, Y. -Z.
name: Pastorello, A.
name: Fraser, M.
name: Botticella, M. T.
name: Elias-Rosa, N.
name: Wang, L. -Z.
name: Kotak, R.
name: Benetti, S.
name: Cappellaro, E.
name: Turatto, M.
name: Reguitti, A.
name: Mattila, S.
name: Smartt, S. J.
name: Ashall, C.
name: Benitez, S.
name: Chen, T. -W.
name: Harutyunyan, A.
name: Kankare, E.
name: Lundqvist, P.
name: Mazzali, P. A.
name: Morales-Garoffolo, A.
name: Ochner, P.
name: Pignata, G.
name: Prentice, S. J.
name: Reynolds, T. M.
name: Shu, X. -W.
name: Stritzinger, M. D.
name: Tartaglia, L.
name: Terreran, G.
name: Tomasella, L.
name: Valenti, S.
name: Valerin, G.
name: Wang, G. -J.
name: Wang, X. -F.
name: Borsato, L.
name: Callis, E.
name: Cannizzaro, G.
name: Chen, S.
name: Congiu, E.
name: Ergon, M.
name: Galbany, L.
name: Gal-Yam, A.
name: Gao, X.
name: Gromadzki, M.
name: Holmbo, S.
name: Huang, F.
name: Inserra, C.
name: Itagaki, K.
name: Kostrzewa-Rutkowska, Z.
name: Maguire, K.
name: Margheim, S.
name: Moran, S.
name: Onori, F.
name: Carracedo, A. Sagués
name: Smith, K. W.
name: Sollerman, J.
name: Somero, A.
name: Wang, B.
name: Young, D. R.
Publisher: name: arXiv
Year: 2021
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present the spectroscopic and photometric study of five intermediate-luminosity red transients (ILRTs), namely AT 2010dn, AT 2012jc, AT 2013la, AT 2013lb, and AT 2018aes. They share common observational properties and belong to a family of objects similar to the prototypical ILRT SN~2008S. These events have a rise time that is less than 15 days and absolute peak magnitudes of between $-11.5$ and $-14.5$ mag. Their pseudo-bolometric light curves peak in the range $0.5$ - $9.0 \times10^{40}~\mathrm{erg~s}^{-1}$ and their total radiated energies are on the order of (0.3 - 3) $\times$~10$^{47}$~erg. After maximum brightness, the light curves show a monotonic decline or a plateau, resembling those of faint supernovae IIL or IIP, respectively. At late phases, the light curves flatten, roughly following the slope of the $^{56}$Co decay. If the late-time power source is indeed radioactive decay, these transients produce $^{56}$Ni masses on the order of $10^{-4}$ to $10^{-3}$~\msun. The spectral energy distribution of our ILRT sample, extending from the optical to the mid-infrared (MIR) domain, reveals a clear IR excess soon after explosion and non-negligible MIR emission at very late phases. The spectra show prominent H lines in emission with a typical velocity of a few hundred km~s$^{-1}$, along with Ca~II features. In particular, the [Ca~II] $λ$7291,7324 doublet is visible at all times, which is a characteristic feature for this family of transients. The identified progenitor of SN~2008S, which is luminous in archival Spitzer MIR images, suggests an intermediate-mass precursor star embedded in a dusty cocoon. We propose the explosion of a super-asymptotic giant branch star forming an electron-capture supernova as a plausible explanation for these events.
description: 31 pages, 17 figures; accepted for publication in Astronomy and Astrophysics