Detection of Another Molecular Bubble in the Galactic Center
  The $l=-1.2^{\circ}$ region in the Galactic center has a high CO
$J$=3-2/$J$=1-0 intensity ratio and extremely broad velocity width. This paper
reports the detection of five expanding shells in the $l=-1.2^{\circ}$ region
based on the CO $J$=1-0, $^{13}$CO $J$=1-0, CO $J$=3-2, and SiO $J$=8-7 line
data sets obtained with the Nobeyama Radio Observatory 45 m telescope and James
Clerk Maxwell Telescope. The kinetic energy and expansion time of the expanding
shells are estimated to be $10^{48.3-50.8}$ erg and $10^{4.7-5.0}$ yr,
respectively. The origin of these expanding shells is discussed. The total
kinetic energy of $10^{51}$ erg and the typical expansion time of ${\sim}10^5$
yr correspond to multiple supernova explosions at a rate of $10^{-5}$-$10^{-4}$
yr$^{-1}$. This indicates that the $l=-1.2^{\circ}$ region may be a molecular
bubble associated with an embedded massive star cluster, although the absence
of an infrared counterpart makes this interpretation somewhat controversial.
The expansion time of the shells increases as the Galactic longitude decreases,
suggesting that the massive star cluster is moving from Galactic west to east
with respect to the interacting molecular gas. We propose a model wherein the
cluster is moving along the innermost x1 orbit and the interacting gas collides
with it from the Galactic eastern side.
