2021MNRAS.505.4106M

The properties of the broad-lined Type Ic supernova (SN) 2013dx, associated with the long gamma-ray burst GRB 130702A at a redshift z = 0.145, are derived via spectral modelling. SN 2013dx was similar in luminosity to other GRB/SNe, with a derived value of the mass of ⁵⁶Ni ejected in the explosion of ≃0.4 M_☉. However, its spectral properties suggest a smaller explosion kinetic energy. Radiation transport models were used to derive a plausible mass and density distribution of the SN ejecta in a one-dimensional approximation. While the mass ejected in the explosion that is obtained from the modelling (M_ej ≃ 9 M_☉) is similar to that of all other well-studied GRB/SNe, the kinetic energy is significantly smaller (E_K ∼ 10⁵² erg). This leads to a smaller E_K/M_ej ratio, ≃10⁵¹ erg/M_☉, which is reflected in the narrower appearance of the spectral lines. While the low E_K does not represent a problem for the scenario in which magnetar energy aids powering the explosion and the nucleosynthesis, it is nevertheless highly unusual. SNe Ic with similar E_K have never been seen in coincidence with a GRB, and no well-observed GRB/SN has shown similarly low E_K and E_K/M_ej.