2021MNRAS.508.1590P

Detection of gamma-rays emitted by radioactive isotopes synthesized in stellar 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 ⁵⁷Co powered the late-time evolution of SN1987A's light curve, and conclusive evidence that ⁵⁶Ni 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 ⁴⁸V, the daughter nucleus of ⁴⁸Cr, which is expected to be synthesized in large quantities - M_Cr ∼1.9×10^–2 M_☉ - in transients initiated by explosive helium burning (α-capture) of a thick helium shell. We calculate emergent gamma-ray line fluxes for a simulated explosion model of a thermonuclear explosion of carbon-oxygen white dwarf core of mass 0.45 M_☉ surrounded by a thick helium layer of mass 0.21 M_☉. We present observational limits on the presence of ⁴⁸V in nearby SNe Ia 2014J using the INTEGRAL space telescope, excluding a ⁴⁸Cr production on the surface of more than 0.1 M_☉. We find that the future gamma-ray mission the All-Sky Medium Energy Gamma-Ray Observatory (AMEGO) will have an approximately 5 per cent chance of observing ⁴⁸V 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 3σ detection by the gamma-ray telescopes INTEGRAL/SPI, Compton Spectrometer and Imager (COSI), and AMEGO.