Fireball in Fast Radio Bursts

Fast radio bursts (FRBs) are the brightest radio transients in the universe. Since the unexpected discovery in the 21st century, their extreme nature is one of the biggest mysteries of astrophysics. FRBs are also unique probes of the universe, opening a new field of FRB cosmology. In 2020, Galactic FRBs were detected from magnetar bursts, pinning down one of the origins of FRBs. In this talk, I will ask how to transfer the energy from the surface of a neutron star to the emission site of FRBs. If thermal energy is released near the surface, a fireball is created and expands under its own pressure along magnetic field lines. We show that a fireball that emits X-rays similar to the magnetar bursts can also accelerate the outflow to the high Lorentz factor with sufficient kinetic energy to power FRBs, thanks to baryon or resonant cyclotron scattering. Additionally, if Alfven waves are launched from the surface, they could decay into sound (slow MHD) waves and backward-propagating Alfven waves, and eventually boost the fireball. We show that the parametric decay occurs even for high sigma (ratio of the magnetic to matter energy density) but with the rate suppressed by sigma^{-1/2}. If time permits, I will also present binary models for periodic FRBs.