Optical and spectral observations and hydrodynamic modelling of type IIb supernova 2017gpn

In this work we present the photometric and spectroscopic observations of type IIb supernova 2017gpn. This supernova was discovered in the error-box of the LIGO/Virgo G299232 gravitational-wave event. We obtained the light curves in the B and R passbands and modelled them numerically using the one-dimensional radiation hydrocode stella. The best-fitting model has the following parameters: the pre-SN star mass and the radius are M ≈ 3.5 M⊙ and R ≈ 50 R⊙, respectively; the explosion energy is Eₑₓₚ ≈ 1.2× 10⁵¹ erg; the mass of radioactive nickel is M_ ⁵⁶Ni ≈ 0.11 M⊙, which is completely mixed throughout the ejecta; and the mass of the hydrogen envelope M_ Hₑₙᵥ ≈ 0.06 M⊙. Moreover, SN 2017gpn is a confirmed SN IIb that is located at the farthest distance from the centre of its host galaxy NGC 1343 (i.e. the projected distance is ∼21 kpc). This challenges the scenario of the origin of type IIb supernovae from massive stars.