SN 2009E: a faint clone of SN 1987A ^⋆,⋆⋆

¹ INAF - Osservatorio Astronomico di Padova, Vicolo dell’ Osservatorio 5, 35122 Padova, Italy
e-mail: andrea.pastorello@oapd.inaf.it
² Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
³ Dipartimento di Astronomia, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁴ INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁵ INAF - Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
⁶ Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, 10691 Stockholm, Sweden
⁷ Tuorla Observatory, Department of Physics & Astronomy, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁸ Les Mauruches Observatoire, 364 Chemin de Notre Dame, 06220 Vallauris, France
⁹ Osservatorio Astronomico di Castelmartini, IAU 160, via Bartolini 1317, 51036 Larciano, Pistoia, Italy
¹⁰ Observatorio El Gujio, Onice 21, 28260 Galapagar, Madrid, Spain
¹¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching bei München, Germany
¹² Coddenham Astronomical Observatory, Suffolk, UK
¹³ Osservatorio Astronomico di Tavolaia, Piazza della Vittoria 41, 56020 Santa Maria a Monte, Pisa, Italy
¹⁴ Private address, 105 Glen Pine Trail, Dawnsonville, GA 30543, USA
¹⁵ Osservatorio Astronomico Polse di Cougnes, Zuglio, 33020 Udine, Italy
¹⁶ Center for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
¹⁷ Fundación Galileo Galilei - INAF, Telescopio Nazionale Galileo, 38700 Santa Cruz de la Palma, Tenerife, Spain
¹⁸ Private address, 1401 South A, Arkansas City, KS 67005, USA
¹⁹ The Astronomer, 16 Westminster Close, Basingstoke, Hants, RG22 4PP, UK
²⁰ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
²¹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
²² Department of Physics and Astronomy, Western Kentucky University, 1906 College Heights Blvd., Bowling Green, KY 42101-1077, USA
²³ University of Oklahoma, Health Science Center, 1100 N. Lindsay, Oklahoma City, OK 73104, USA

Received: 16 September 2011
Accepted: 3 November 2011

Abstract

Context.1987A-like events form a rare sub-group of hydrogen-rich core-collapse supernovae that are thought to originate from the explosion of blue supergiant stars. Although SN 1987A is the best known supernova, very few objects of this group have been discovered and, hence, studied.

Aims. In this paper we investigate the properties of SN 2009E, which exploded in a relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest 1987A-like supernova discovered so far. We also attempt to characterize this subgroup of core-collapse supernovae with the help of the literature and present new data for a few additional objects.

Methods. The lack of early-time observations from professional telescopes is compensated by frequent follow-up observations performed by a number of amateur astronomers. This allows us to reconstruct a well-sampled light curve for SN 2009E. Spectroscopic observations which started about 2 months after the supernova explosion, highlight significant differences between SN 2009E and the prototypical SN 1987A. Modelling the data of SN 2009E allows us to constrain the explosion parameters and the properties of the progenitor star, and compare the inferred estimates with those available for the similar SNe 1987A and 1998A.

Results. The light curve of SN 2009E is less luminous than that of SN 1987A and the other members of this class, and the maximum light curve peak is reached at a slightly later epoch than in SN 1987A. Late-time photometric observations suggest that SN 2009E ejected about 0.04 M_⊙ of ⁵⁶Ni, which is the smallest ⁵⁶Ni mass in our sample of 1987A-like events. Modelling the observations with a radiation hydrodynamics code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an initial radius of  ~7 × 10¹² cm and an ejected mass of  ~19 M_⊙. The photospheric spectra show a number of narrow (v ≈ 1800 km s^-1) metal lines, with unusually strong Ba II lines. The nebular spectrum displays narrow emission lines of H, Na I, [Ca II] and [O I], with the [O I] feature being relatively strong compared to the [Ca II] doublet. The overall spectroscopic evolution is reminiscent of that of the faint ⁵⁶Ni-poor type II-plateau supernovae. This suggests that SN 2009E belongs to the low-luminosity, low ⁵⁶Ni mass, low-energy tail in the distribution of the 1987A-like objects in the same manner as SN 1997D and similar events represent the faint tail in the distribution of physical properties for normal type II-plateau supernovae.