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

Abstract

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 ${}^{57}$Co powered 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 - $M_{\mathrm{Cr}}\sim 1.9\times 10^{-2}{\mathrm{M}}_{\odot }$ - in transients initiated by explosive helium burning ($\hat{I}\pm$-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 $0.45M_{\odot }$ surrounded by a thick helium layer of mass $0.21M_{\odot }$. We present observational limits on the presence of ${}^{48}$V in nearby SNe Ia 2014J using the \textit{INTEGRAL} space telescope, excluding a ${}^{48}$Cr production on the surface of more than $0.1{\mathrm{M}}_{\odot }$. 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 $3\ddot{I}ƒ$ detection by the gamma-ray telescopes \textit{INTEGRAL}/SPI, COSI and AMEGO.

9 pages, 3 figures, submitted to MNRAS, minor revisions Sept 2021