X-ray and ultraviolet (XUV) radiation from pre-main-sequence
stars is a key factor to control the gas evolution in protoplanetary disks
through photoevaporation and ionization. Among the XUV sources in the
system, stellar flares serve as a unique emitter of hard X-ray photons (≳
10 keV) which drive various chemical reactions in the disk. While previous
observation has reported that the time- variability in stellar X-ray
luminosity has a non-negligible effect on disk ionization, theoretical work
has still lacked precise modeling of X-ray flares, such as the nature of
individual flares and hard X-ray emission.

Given the necessity to incorporate the previously overlooked factors for
elucidating the role of flares in disk evolution, we develop a model of
time-varying X-ray emission in pre-main-sequence stars based on theories
and observations of stellar flares. This model enables us to generate X-ray
light curves of flares and their spectral energy distributions, including
their temporal evolution. Using our X-ray model, we also conduct the
radiative transfer calculation to investigate how X-ray flares affect the
disk ionization. Our findings indicate that photons with ≳ 10 keV play a
critical role in disk ionization, underscoring the essential contribution
of stellar flares to disk chemistry.