Kinematics of Ultra-High-Velocity Gas in the Expanding Molecular Shell adjacent to the W44 Supernova Remnant

We mapped the ultra-high-velocity feature (the “Bullet”) detected in the expanding molecular shell associated with the W44 supernova remnant using the Nobeyama Radio Observatory 45-m telescope and the ASTE 10-m telescope. The Bullet clearly appears in the CO $J$=1-0, CO $J$=3-2, CO ${\it J}$=4-3,andHCO$^+$ $J$=1-0 maps with a compact appearance ($0.5\times 0.8$pc$^2$)andanextremelybroadvelocitywidth($\Delta V!\simeq!100
\rm km , s ^{-1}$). The line intensities indicate that the Bullet has a higher density and temperature than those in the expanding molecular shell. The kinetic energy of the Bullet amounts to ${10}^{48.0}\mathrm{e}\mathrm{r}\mathrm{g}$ which is approximately 1.5 orders of magnitude greater than the kinetic energy shared to the small solid angle of it. Two possible formation scenarios with an inactive isolated black hole (BH) are presented.