ALMA CO Observations of the Gamma-Ray Supernova Remnant RX J1713.7-3946:
  Discovery of Shocked Molecular Cloudlets and Filaments at 0.01 pc scales
  RX J1713.7-3946 is a unique core-collapse SNR that emits bright TeV
gamma-rays and synchrotron X-rays caused by cosmic rays, in addition to
interactions with interstellar gas clouds. We report here on results of ALMA
$^{12}$CO($J$ = 1-0) observations toward the northwestern shell of the SNR. We
newly found three molecular complexes consisting of dozens of shocked molecular
cloudlets and filaments with typical radii of $\sim$0.03-0.05 pc and densities
of $\sim$$10^4$ cm$^{-3}$. These cloudlets and filaments are located not only
along synchrotron X-ray filaments, but also in the vicinity of X-ray hotspots
with month or year-scale time variations. We argue that X-ray hotspots were
generated by shock-cloudlet interactions through magnetic-field amplification
up to mG. The ISM density contrast of $\sim$$10^5$, coexistence of molecular
cloudlets and low-density diffuse medium of $\sim$0.1 cm$^{-3}$, is consistent
with such a magnetic field amplification as well as a wind-bubble scenario. The
small-scale cloud structures also affect hadronic gamma-ray spectra considering
the magnetic field amplification on surface and inside clouds.
