Axionlike Particles from Hypernovae

It was recently pointed out that very energetic subclasses of supernovae (SNe), like hypernovae and superluminous SNe, might host ultrastrong magnetic fields in their core. Such fields may catalyze the production of feebly interacting particles, changing the predicted emission rates. Here we consider the case of axionlike particles (ALPs) and show that the predicted large scale magnetic fields in the core contribute significantly to the ALP production, via a coherent conversion of thermal photons. Using recent state-of-the-art supernova (SN) simulations, including magnetohydrodynamics, we find that, if ALPs have masses $m_a\sim \mathcal{O}(10)\mathrm{MeV}$, their emissivity in such rare but exciting conditions via magnetic conversions would be over 2 orders of magnitude larger than previously estimated. Moreover, the radiative decay of these massive ALPs would lead to a peculiar delay in the arrival times of the daughter photons. Therefore, high-statistics gamma-ray satellites can potentially discover MeV ALPs in an unprobed region of the parameter space and shed light on the magnetohydrodynamical nature of the SN explosion.

Figure 1

Angle-averaged radial profile for the temperature $T$ (blue), plasma frequency ${\omega }_{\mathrm{pl}}$ (orange), screening scale ${\kappa }_s$ (black), and magnetic field strength $B$ (dashed red) at $t_{\mathrm{pb}}=370\mathrm{ms}$.

Figure 2

Differential ALP production rate for the Primakoff (orange) and the $B$-conversion (blue) processes, for $m_a=2$, 5, 13 MeV (dashed, solid, and dotted lines, respectively) and $g_{a\gamma }={10}^{-11}{\mathrm{GeV}}^{-1}$, at $t_{\mathrm{pb}}=370\mathrm{ms}$. In the case of $m_a=2$, 5 MeV, at $\omega \gtrsim 10\mathrm{MeV}$, we notice a small peak due to the presence—in a very narrow energy range—of longitudinal modes conversion.

Figure 3

Number of events per unit time with $2\sigma$ Poissonian fluctuation contours expected to be observed by Fermi LAT, as a function of the time delay, obtained considering only Primakoff (blue), and both Primakoff and $B$ conversions (orange), for $m_a=5\mathrm{MeV}$ and $g_{a\gamma }={10}^{-11}{\mathrm{GeV}}^{-1}$. On the upper $x$ axis, the ALP energy corresponding to each delay time $\tau$ is shown.