A Hyperenergetic CO Shell in the Galactic Center Molecular Cloud Complex

We report on the detection of a high-velocity feature, CO 1.27 $+$ 0.01, in the Galactic-center molecular-cloud complex. In our 12CO images taken with the NRO 45 m telescope, CO 1.27 $+$ 0.01 appears as the second prominent high-velocity feature, next to CO 0.02–0.02, having a velocity width of $\Delta V \simeq 100 \,\mathrm{km} \,\mathrm{s}^{-1}$ and a size of $9 \,\mathrm{pc} \times 12 \,\mathrm{pc}$ . It seems to consist of two expanding shells with sizes of $\sim 10 \,\mathrm{pc}$ . The major shell has a kinetic energy of about an order of magnitude larger than the gravitational energy, indicating that the shell is apparently gravitationally unbound. We propose that CO 1.27 $+$ 0.01 may have been accelerated by a series of supernova explosions which occurred within the last $\sim 6 \times 10^4 \,\mathrm{yr}$ . No association of a nonthermal radio continuum source suggests a strong magnetic field ( $B \gtrsim 0.4 \,\mathrm{mG}$ ) in the vicinity of CO 1.27 $+$ 0.01.