# Using Gamma Ray Monitoring to Avoid Missing the Next Milky Way Type Ia Supernova

## TL;DR

Monitoring gamma-ray emissions from radioactive decay in supernovae can provide early detection of Milky Way Type Ia supernovae, enabling prompt multi-wavelength follow-up despite optical and radio dimness.

## Contribution

This paper demonstrates that gamma-ray observatories like Fermi/GBM and Swift/BAT can serve as effective early warning systems for Galactic Type Ia supernovae through simulation of their gamma-ray signals.

## Key findings

- GBM and BAT can confirm a Galactic SNIa explosion within days.
- Early detection depends on the distribution of $^{56}$Ni, especially surface presence.
- Simulations show potential for prompt multi-wavelength follow-up.

## Abstract

A Milky-Way Type Ia Supernova (SNIa) could be unidentified or even initially unnoticed, being dim in radio, X-rays, and neutrinos, and suffering large optical/IR extinction in the Galactic plane. But SNIa emit nuclear gamma-ray lines from $^{56}{\rm Ni}\to ^{56}{\rm Co}\to ^{56}{\rm Fe}$ radioactive decays. These lines fall within the Fermi/GBM energy range, and the $^{56}{\rm Ni}$ 158 keV line is detectable by Swift/BAT. Both instruments frequently monitor the Galactic plane, which is transparent to gamma rays. Thus GBM and BAT are ideal Galactic SNIa early warning systems. We simulate SNIa MeV light curves and spectra to show that GBM and BAT could confirm a Galactic SNIa explosion, followed by Swift localization and observation in X-rays and UVOIR band. The time of detection depends sensitively on the $^{56}{\rm Ni}$ distribution, and can be as early as a few days if $\gtrsim$ 10% of the $^{56}{\rm Ni}$ is present in the surface as suggested by SN2014J gamma data.