SN 1999ga: a low-luminosity linear type II supernova?

¹ Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK e-mail: a.pastorello@qub.ac.uk
² Perth Observatory, 337 Walnut Road, Bickley 6076, Perth, Australia
³ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁴ INAF – Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, 35122 Padova, Italy
⁵ Tuorla Observatory, Department of Physics & Astronomy, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁶ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Julian Maries Vej 30, 2100 Copenhagen, Denmark
⁷ Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia
⁸ Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo and Siding Spring Observatories Cotter Road, Weston Creek, ACT 2611, Australia
⁹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching bei München, Germany
¹⁰ INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy

Received: 6 March 2009
Accepted: 28 March 2009

Abstract

Context. Type II-linear supernovae are thought to arise from progenitors that have lost most of their H envelope by the time of the explosion, and they are poorly understood because they are only occasionally discovered. It is possible that they are intrinsically rare, but selection effects due to their rapid luminosity evolution may also play an important role in limiting the number of detections. In this context, the discovery of a subluminous type II-linear event is even more interesting.

Aims. We investigate the physical properties and characterise the explosion site of the type II SN 1999ga, which exploded in the nearby spiral galaxy NGC 2442.

Methods. Spectroscopic and photometric observations of SN 1999ga allow us to constrain the energetics of the explosion and to estimate the mass of the ejected material, shedding light on the nature of the progenitor star in the final stages of its life. The study of the environment in the vicinity of the explosion site provides information on a possible relation between these unusual supernovae and the properties of the galaxies hosting them.

Results. Despite the lack of early-time observations, we provide reasonable evidence that SN 1999ga was probably a type II-linear supernova that ejected a few solar masses of material, with a very small amount of radioactive elements of the order of 0.01 .