Prospects of direct detection of $^{48}$V gamma-rays from thermonuclear supernovae

Abstract

Detection of gamma-rays emitted by radioactive isotopes synthesized in stellar outbursts or explosions can give important insights into the processes that power transients such as supernovae, as well as providing a detailed census of the abundance of different isotope species relevant to the chemical evolution of the Universe. Observations of nearby supernovae have yielded observational proof that 57 Co drove the late-time evolution of SN1987A's lightcurve, and conclusive evidence that 56 Ni and its daughter nuclei power the light curves of Type Ia supernovae. In this paper we describe the prospects for detecting nuclear decay lines associated with the decay of 48 V, the daughter nucleus of 48 Cr, which is expected to be synthesised in large quantities in transients initiated by explosive helium burning ( -capture) of a thick helium shell. We investigate these prospects using results for the emergent gamma-ray line fluxes from a radiative transfer simulation performed for a simulated explosion model of a thermonuclear explosion of carbon-oxygen white dwarf core of mass 0.45 ⊙ surrounded by a thick helium layer of mass 0.21 ⊙ . We find that the future gamma-ray mission AMEGO will have an approximately 5 per cent chance of observing 48 V gamma-rays from such events during the currently-planned operational lifetime, based on our birthrate predictions of faint thermonuclear transients. We describe the conditions for a 3 detection by the gamma-ray instruments INTEGRAL/SPI, COSI and AMEGO.