The long-lived Type IIn SN 2015da: Infrared echoes and strong interaction within an extended massive shell^★,★★

¹ Department of Astronomy and the Oskar Klein Centre, Stockholm University, AlbaNova, Roslagstullsbacken 21, 114 21 Stockholm, Sweden
e-mail: leonardo.tartaglia@astro.su.se
² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ Tuorla Observatory, Department of Physics and Astronomy, 20014, University of Turku, Turku, Finland
⁴ School of Physics, O’Brien Centre for Science North, University College Dublin, Belfield Dublin 4, Ireland
⁵ Department of Applied Physics, Universidad de Cádiz, campus of Puerto Real, 11510 Cádiz, Spain
⁶ Institute of Space Sciences (ICE, CSIC), Campus UAB, Camí de Can Magrans s/n, 08193, Cerdanyola del Vallès, Barcelona, Spain
⁷ Institut d’Estudis Espacials de Catalunya (IEEC), c/Gran Capità 2–4, Edif. Nexus 201, 08034 Barcelona, Spain
⁸ Benoziyo Center for Astrophysics and the Helen Kimmel center for planetary science, Weizmann Institute of Science, 76100 Rehovot, Israel
⁹ Xinjiang Astronomical Observatory, 150 Science 1–Street, Urumqi, Xinjiang 830011, PR China
¹⁰ Xingming Observatory, Mountain Nanshan, Urumqi, Xinjiang 830011, PR China
¹¹ Graduate Institute of Astronomy, National Central University, 300 Zhongda Rd., Zhongli District, Taoyuan City 32001, Taiwan, PR China
¹² Department of Astronomy/Steward Observatory, 933 North Cherry Avenue, Rm. N204, Tucson, AZ 85721-0065, USA
¹³ Osservatorio Astronomico di Monte Agliale, Via Cune Motrone, 55023 Borgo a Mozzano, Lucca, Italy
¹⁴ Physics Department and Tsinghua Center for Astrophysics, Tsinghua University, Beijing 100084, PR China
¹⁵ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, PR China
¹⁶ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650216, PR China
¹⁷ Department of Astronomy, School of Physics and Astronomy, Shanghai Jiaotong Univeristy, Shanghai 200240, PR China
¹⁸ Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 10101 Beijing, PR China
¹⁹ School of Astronomy and Space Science, University of Chinese Academy of Sciences, 101408 Beijing, PR China
²⁰ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138-1516, USA
²¹ Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117-5575, USA
²² Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
²³ Department of Physics, University of California, Davis, CA 95616, USA
²⁴ The Oskar Klein Centre, Physics Department, Stockholm University, AlbaNova, Roslagstullsbacken 21, 21 Stockholm, Sweden
²⁵ Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
²⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁷ European Southern Observatory Karl – Schwarzschild – Str 2 85748, Garching bei München, Germany
²⁸ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA

Received: 22 August 2019
Accepted: 29 December 2019

Abstract

In this paper we report the results of the first ~four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy ≳ 10⁵¹ erg. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be ≃ 8 M_⊙, with an extreme mass-loss rate for the progenitor star ≃0.6 M_⊙ yr⁻¹, suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a fluxexcess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass ≳ 0.4 × 10⁻³ M_⊙ for the dust.