The evolution of superluminous supernova LSQ14mo and its interacting host galaxy system ^⋆

¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany
e-mail: jchen@mpe.mpg.de
² Argelander Institute for Astronomy, University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
⁴ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
⁵ Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁶ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching-bei-München, Germany
⁷ Division of Theoretical Astronomy, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan
⁸ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
⁹ Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), 3941 Pittsburgh, USA
¹⁰ Physics and Astronomy Department, University of Pittsburgh, Pittsburgh, PA 15260, USA
¹¹ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel
¹² ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching-bei-München, Germany
¹³ Institut d’Astrophysique de Paris, CNRS, and Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
¹⁴ Physics Department, Yale University, 217 Prospect Street, New Haven, CT 06511-8499, USA
¹⁵ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
¹⁶ Department of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK

Received: 29 November 2016
Accepted: 25 January 2017

Abstract

We present and analyse an extensive dataset of the superluminous supernova (SLSN) LSQ14mo (z = 0.256), consisting of a multi-colour light curve from −30 d to +70 d in the rest-frame (relative to maximum light) and a series of six spectra from PESSTO covering −7 d to +50 d. This is among the densest spectroscopic coverage, and best-constrained rising light curve, for a fast-declining hydrogen-poor SLSN. The bolometric light curve can be reproduced with a millisecond magnetar model with ~ 4 M_⊙ ejecta mass, and the temperature and velocity evolution is also suggestive of a magnetar as the power source. Spectral modelling indicates that the SN ejected ~ 6 M_⊙ of CO-rich material with a kinetic energy of ~7 × 10⁵¹ erg, and suggests a partially thermalised additional source of luminosity between −2 d and +22 d. This may be due to interaction with a shell of material originating from pre-explosion mass loss. We further present a detailed analysis of the host galaxy system of LSQ14mo. PESSTO and GROND imaging show three spatially resolved bright regions, and we used the VLT and FORS2 to obtain a deep (five-hour exposure) spectra of the SN position and the three star-forming regions, which are at a similar redshift. The FORS2 spectrum at + 300 days shows no trace of SN emission lines and we place limits on the strength of [O i] from comparisons with other Ic supernovae. The deep spectra provides a unique chance to investigate spatial variations in the host star-formation activity and metallicity. The specific star-formation rate is similar in all three components,as is the presence of a young stellar population. However, the position of LSQ14mo exhibits a lower metallicity, with 12 + log (O/H) = 8.2 in both the R₂₃ and N2 scales (corresponding to ~0.3 Z_⊙ ). We propose that the three bright regions in the host system are interacting, which could induce gas flows triggering star formation in low-metallicity regions.