The γ-ray deposition histories of calcium-rich supernovae

Calcium-rich supernovae (Ca-rich SNe) are faint, rapidly evolving transients whose progenitor system is yet to be determined. We derive the γ-ray deposition histories of five Ca-rich SNe from the literature in order to place constraints on possible progenitor systems. We find that the γ-ray escape time, t₀, of the Ca-rich SNe sample is ≈ 35-65 d, within the unoccupied region between Type Ia SNe and stripped-envelope supernovae (SESNe). The t₀−M_Ni56 distribution of these SNe, where M_Ni56 is the synthesized ⁵⁶Ni mass in the explosion, creates a continuum between the Type Ia and SESNe t₀−M_Ni56 distribution, hinting at a possible connection between all the events. By comparing our results to models from the literature, we were able to determine that helium shell detonation models and core-collapse models of ultra-stripped stars are unlikely to explain Ca-rich SNe since the gamma-ray escape time in these models is smaller than the observed values. Models that agree with the observed t₀−M_Ni56 distribution are explosions of low mass, M ≈ 0.75-0.8 M⊙, white dwarfs and core-collapse models of stripped stars with an ejecta mass of M ≈ 1-3 M⊙.