Probing protoneutron stars with gamma-ray axionscopes

TL;DR

This paper explores how gamma-ray observations from supernovae can reveal properties of protoneutron stars and axion-like particles, providing a new way to probe SN core processes and particle physics.

Contribution

It introduces a method to use gamma-ray spectra from supernovae to investigate axion production channels and PNS core conditions, including pion abundance.

Findings

Gamma-ray spectra can distinguish axion production mechanisms.

Detection of spectral components reveals PNS temperature and pion content.

Gamma-ray telescopes can probe fundamental particle interactions in supernovae.

Abstract

Axion-like particles (ALPs) coupled to nucleons can be efficiently produced in the interior of protoneutron stars (PNS) during supernova (SN) explosions. If these ALPs are also coupled to photons they can convert into gamma rays in the Galactic magnetic field. This SN-induced gamma-ray burst can be observable by gamma-ray telescopes like ${\textit Fermi}$-LAT if the SN is in the field of view of the detector. We show that the observable gamma-ray spectrum is sensitive to the production processes in the SN core. In particular, if the nucleon-nucleon bremsstrahlung is the dominant axion production channel, one expects a thermal spectrum with average energy $E_a \simeq 50$ MeV. In this case the gamma-ray spectrum observation allows for the reconstruction of the PNS temperature. In case of a sizable pion abundance in the SN core, one expects a second spectral component peaked at $E_a\simeq 200$ MeV due to axion pionic processes. We demonstrate that, through a dedicated LAT analysis, we can detect the presence of this pionic contribution, showing that the detection of the spectral shape of the gamma-ray signal represents a unique probe of the pion abundance in the PNS.