Intermediate-luminosity red transients: Spectrophotometric properties and connection to electron-capture supernova explosions

Cai, YZ, Pastorello, A, Fraser, M, Botticella, MT, Elias-Rosa, N, Wang, LZ, Kotak, R, Benetti, S, Cappellaro, E, Turatto, M, Reguitti, A, Mattila, S, Smartt, SJ, Ashall, C, Benitez, S, Chen, TW, Harutyunyan, A, Kankare, E, Lundqvist, P, Mazzali, PA et al (2021) Intermediate-luminosity red transients: Spectrophotometric properties and connection to electron-capture supernova explosions. Astronomy and Astrophysics, 654. ISSN 0004-6361

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Abstract

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 × 1040 erg s-1 and their total radiated energies are on the order of (0.3-3) × 1047 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 56Co decay. If the late-time power source is indeed radioactive decay, these transients produce 56Ni masses on the order of 10-4 to 10-3 M⊙. 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] λ7291,7324 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.

Item Type:	Article
Uncontrolled Keywords:	0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	EDP Sciences
Date of acceptance:	29 July 2021
Date Deposited:	02 Nov 2022 10:40
Last Modified:	02 Nov 2022 10:40
DOI or ID number:	10.1051/0004-6361/202141078
URI:	https://ljmu-9.eprints-hosting.org/id/eprint/17990

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