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 45m 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 Δ V ≃ 100kms^-1 and a size of 9pc × 12pc. It seems to consist of two expanding shells with sizes of ∼ 10 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 ∼ 6 × 10⁴ yr. No association of a nonthermal radio continuum source suggests a strong magnetic field (B ≳ 0.4mG) in the vicinity of CO 1.27+0.01.