PTF11mnb: First analog of supernova 2005bf

Long-rising, double-peaked supernova Ic from a massive progenitor^⋆

¹ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
e-mail: francesco.taddia@astro.su.se
² Department of Astronomy, San Diego State University, San Diego, CA 92182, USA
³ Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, 277-8583 Chiba, Japan
⁴ Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel
⁵ Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
⁶ Astronomy Department, University of California at Berkeley, Berkeley, CA 94720, USA
⁷ Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50B-4206, Berkeley, CA 94720, USA
⁸ Université de Lyon 1, Villeurbanne; CNRS/IN2P3, Institut de Physique Nucléaire de Lyon, 69622 Lyon, France
⁹ Tsinghua Center for Astrophysics, Tsinghua University, 100084 Beijing, PR China
¹⁰ Centre de Physique des Particules de Marseille, Aix-Marseille Université, CNRS/IN2P3, 163 avenue de Luminy, Case 902, 13288 Marseille Cedex 09, France

Received: 10 October 2016
Accepted: 12 October 2017

Abstract

Aims. We study PTF11mnb, a He-poor supernova (SN) whose light curves resemble those of SN 2005bf, a peculiar double-peaked stripped-envelope (SE) SN, until the declining phase after the main peak. We investigate the mechanism powering its light curve and the nature of its progenitor star.

Methods. Optical photometry and spectroscopy of PTF11mnb are presented. We compared light curves, colors and spectral properties to those of SN 2005bf and normal SE SNe. We built a bolometric light curve and modeled this light curve with the SuperNova Explosion Code (SNEC) hydrodynamical code explosion of a MESA progenitor star and semi-analytic models.

Results. The light curve of PTF11mnb turns out to be similar to that of SN 2005bf until ~50 d when the main (secondary) peaks occur at −18.5 mag. The early peak occurs at ~20 d and is about 1.0 mag fainter. After the main peak, the decline rate of PTF11mnb is remarkably slower than what was observed in SN 2005bf, and it traces well the ⁵⁶Co decay rate. The spectra of PTF11mnb reveal a SN Ic and have no traces of He unlike in the case of SN Ib 2005bf, although they have velocities comparable to those of SN 2005bf. The whole evolution of the bolometric light curve is well reproduced by the explosion of a massive (M_ej = 7.8 M_⊙), He-poor star characterized by a double-peaked ⁵⁶Ni distribution, a total ⁵⁶Ni mass of 0.59 M_⊙, and an explosion energy of 2.2 × 10⁵¹ erg. Alternatively, a normal SN Ib/c explosion (M(⁵⁶Ni) = 0.11 M_⊙, E_K = 0.2 × 10⁵¹ erg, M_ej = 1 M_⊙) can power the first peak while a magnetar, with a magnetic field characterized by B = 5.0 × 10¹⁴ G, and a rotation period of P = 18.1 ms, provides energy for the main peak. The early g-band light curve can be fit with a shock-breakout cooling tail or an extended envelope model from which a radius of at least 30 R_⊙ is obtained.

Conclusions. We presented a scenario where PTF11mnb was the explosion of a massive, He-poor star, characterized by a double-peaked ⁵⁶Ni distribution. In this case, the ejecta mass and the absence of He imply a large ZAMS mass (~85 M_⊙) for the progenitor, which most likely was a Wolf-Rayet star, surrounded by an extended envelope formed either by a pre-SN eruption or due to a binary configuration. Alternatively, PTF11mnb could be powered by a SE SN with a less massive progenitor during the first peak and by a magnetar afterward.