Sagittarius A* as an Origin of the Galactic PeV Cosmic Rays?
  Supernova remnants (SNRs) have commonly been considered as a source of the
observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator
("Pevatron"). In this work, we study Sagittarius A* (Sgr A*), which is the
low-luminosity active galactic nucleus of the Milky Way Galaxy, as another
possible canditate of the Pevatron, because it sometimes became very active in
the past. We assume that a large number of PeV CRs were injected by Sgr A* at
the outburst about 10^7 yr ago when the Fermi bubbles were created. We
constrain the diffusion coefficient for the CRs in the Galactic halo on the
condition that the CRs have arrived on the Earth by now, while a fairly large
fraction of them have escaped from the halo. Based on a diffusion-halo model,
we solve a diffusion equation for the CRs and compare the results with the CR
spectrum on the Earth. The observed small anisotropy of the arrival directions
of CRs may be explained if the diffusion coefficient in the Galactic disk is
smaller than that in the halo. Our model predicts that a boron-to-carbon ratio
should be energy-independent around the knee, where the CRs from Sgr A* become
dominant. It is unlikely that the spectrum of the CRs accelerated at the
outburst is represented by a power-law similar to the one for those responsible
for the gamma-ray emission from the central molecular zone (CMZ) around the
Galactic center.
