VLF observations of magnetar flares.

I review VLF observations of magnetar flares and their numerical simulations. First, I present a brief observational summary of magnetars from the viewpoint of high-energy astrophysics. What I would like to stress here is that peak spectra of giant flares from magnetars are poorly understood due to saturation problems of X-ray and gamma-ray instruments in space, because the peak flux is very huge. VLF amplitude and phase observations enables us to estimate the peak spectra. Second, I present Monte Carlo simulations which are needed to estimate the altitude profile of electron number density when gamma-rays are directed onto the ionosphere. After that, Finite-Difference Time-Domain (FDTD) simulations are shown which simulate VLF wave propagation. Finally, summary and future perspectives are presented. [ABSTRACT FROM AUTHOR]