PTF10ops - a subluminous, normal-width lightcurve Type Ia supernova in the middle of nowhere

TL;DR

PTF10ops is a unique Type Ia supernova with subluminous spectral features but a normal-width lightcurve, found in an unusual environment with no nearby host galaxy, challenging existing supernova classification models.

Contribution

This paper reports the discovery and detailed analysis of PTF10ops, a supernova that defies current classification by combining subluminous spectral features with a normal-width lightcurve.

Findings

Spectral features typical of subluminous SNe Ia

Normal-width lightcurve with long rise-time

Host environment with no nearby galaxy detected

Abstract

PTF10ops is a Type Ia supernova (SN Ia), whose lightcurve and spectral properties place it outside the current SN Ia subtype classifications. Its spectra display the characteristic lines of subluminous SNe Ia, but it has a normal-width lightcurve with a long rise-time, typical of normal luminosity SNe Ia. The early-time optical spectra of PTF10ops were modelled using a spectral fitting code and found to have all the lines typically seen in subluminous SNe Ia, without the need to invoke more uncommon elements. The host galaxy environment of PTF10ops is also unusual with no galaxy detected at the position of the SN down to an absolute limiting magnitude of r \geq -12.0 mag, but a very massive galaxy is present at a separation of ~148 kpc and at the same redshift as suggested by the SN spectral features. The progenitor of PTF10ops is most likely a very old star, possibly in a low metallicity environment, which affects its explosion mechanism and observational characteristics. PTF10ops does not easily fit into any of the current models of either subluminous or normal SN Ia progenitor channels.