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

TL;DR

This study maps an ultra-high-velocity gas feature near the W44 supernova remnant, revealing its physical properties and proposing formation scenarios involving an inactive black hole.

Contribution

It provides detailed observations of the Bullet feature and introduces new formation hypotheses involving an isolated black hole.

Findings

Bullet has a compact size of 0.5x0.8 pc^2 and broad velocity width (~100 km/s).

Bullet exhibits higher density and temperature than surrounding shell.

Kinetic energy of Bullet is approximately 10^48 erg.

Abstract

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 ${\it J}$=1-0, CO ${\it J}$=3-2, CO ${\it J}$=4-3, and HCO$^+$ ${\it J}$=1-0 maps with a compact appearance ($0.5\times 0.8$ pc$^2$) and an extremely broad velocity width ($\Delta V\!\simeq\!100 \ \rm km \, s ^{-1}$). 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 $10^{48.0} \ {\rm erg}$ 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.