Abstract
The core-collapse of a hydrogen rich massive star most often results in
a supernova (SN) with a plateau phase in its light curve. However, in
some cases we do not observe this plateau. We present observations of
the unusually luminous supernova 2016gsd that displays little evidence
of the expected drop from the optically thick phase to the radioactively
powered tail. With a peak absolute magnitude of V=$-$19.95$\pm$0.08,
this object is one of the brightest type II SNe, and lies in the gap of
magnitudes between the majority of type II SNe and the superluminous
SNe. The velocities derived from the absorption in H are also unusually
high with the blue edge tracing the fastest moving gas initially at
20000 kms$^{-1}$ and then declining approximately linearly to 15000
kms$^{-1}$ over ~100 days. The dwarf host galaxy of the SN indicates a
low metallicity progenitor which may also contribute to the weakness of
the metal lines in its spectra. We examine SN 2016gsd with reference to
similarly luminous, linear type II SNe such as SNe 1979C and 1998S, and
discuss the interpretation of its observational characteristics. We
compare the observations with a model produced by the JEKYLL code and
find that a massive star with a depleted and inflated hydrogen envelope
struggles to reproduce the high luminosity and extreme linearity of SN
2016gsd. Instead, we suggest that the influence of interaction between
the SN ejecta and circumstellar material can explain the majority of the
observed properties of the SN. The high velocities and strong H$\alpha$
absorption present throughout the evolution of the SN may imply a CSM
configured in an asymmetric geometry.
Original language | English |
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Journal | Monthly Notices of the Royal Astronomical Society |
Early online date | 10 Feb 2020 |
Publication status | Early online date - 10 Feb 2020 |
Keywords
- Astrophysics - High Energy Astrophysical Phenomena
- Astrophysics - Astrophysics of Galaxies
- Astrophysics - Solar and Stellar Astrophysics