Small Progenitors, Large Couplings: Type Ic Supernova Constraints on Radiatively Decaying Particles

Abstract

Supernova (SN) 1987A is a celebrated laboratory in searches for gamma-ray flashes produced by the radiative decay of sub-GeV particles such as axion-like particles (ALPs), sterile neutrinos, and novel gauge bosons. At large couplings, however, particles decay rapidly inside the stellar envelope, which results in a suppression of the signal. Focusing on the prototypical example of ALPs with a photon coupling, we show that core-collapse SNe of Type Ic are much less affected by this attenuation, thanks to the compactness of their progenitors ensuing from the loss of their envelope. While Fermi-LAT may miss the brief gamma-ray flash from a single Type Ic SN, their high rate allows for a statistical approach: by stacking many events, we can obtain constraints that significantly surpass those from SN 1987A at large couplings. Our approach can be extended to any feebly interacting particle featuring a decay channel into photons.

Figures (7)

• Figure 1: Novel constraints on ALP-photon coupling from Type Ic SNe at 90% confidence level (CL) using a typical value of the progenior star radius of $R_{\mathrm{prog}} = 1.0 \times 10^{10}$ cm. Existing constraints include low-energy SNe Caputo:2022mahFiorillo:2025yzf, neutron star mergers Diamond:2023ctoDev:2023hax, gamma-ray and X-ray signals at the Solar Maximum Mission and the Pioneer Venus Observatory Jaeckel:2017tudCaputo:2021ruxHoof:2022xbeDiamond:2023scc, and Big-Bang nucleosynthesis Depta:2020wmr.
• Figure 2: Expected number of signal events for SN2020oi as a function of $g_{a\gamma}$ for different masses. The horizontal dashed black line corresponds to the expected average background in the signal window $v_1$. The vertical lines correspond to a decay length $\ell_a$ for an ALP with energy $300$ MeV equal to the progenitor radius.
• Figure S1: Decay bounds from SNe as a cosmic beam dump: sketch of the geometry (left) and resulting constraints (right).
• Figure S2: Number of emitted ALPs per unit energy, for varying ALP mass (listed in the legend), using the cold SN model introduced in the main text. We fix the coupling $g_{a\gamma}=10^{-10}\,\mathrm{GeV}^{-1}$, with the overall number of events scaling as $g_{a\gamma}^2$ in the free-streaming regime.
• Figure S3: Regions in the parameter space where pair production and bremsstrahlung are rapid enough to thermalize. In the intersection of the two regions (marked by a black line), a fireball is formed with consequent reprocessing of the gamma-ray energy in the 100-keV range.