Molecular Clouds Surrounding Supernova Remnant G43.9+1.6: Associated and
  Non-associated
  Many supernova remnants (SNRs) are considered to evolve in molecular
environments, but the associations between SNRs and molecular clouds (MCs) are
often unclear. Being aware of such ambiguous case, we report our study on the
molecular environment towards the SNR G43.9+1.6 by CO line observations. We
investigated the correlations between the SNR and MCs at different velocities,
and found two velocity components, i.e. $\sim$5 km s$^{-1}$ and $\sim$50 km
s$^{-1}$ velocity components, showing spatial correlations with the remnant.
However, no dynamical evidence of disturbance was found for the $\sim$5 km
s$^{-1}$ velocity component. At the distance of the $\sim$5 km s$^{-1}$
velocity component, either near or far distance, the derived physical
parameters are unreasonable too. We conclude that the SNR is not associated
with the $\sim$5 km s$^{-1}$ velocity component, and their spatial correlation
is just a chance correlation. For the $\sim$50 km s$^{-1}$ velocity component,
dynamical evidence of disturbances, as well as the spatial correlation,
indicate that it is associated with the SNR. We found that all the CO spectra
extracted from the molecular clumps distributed along the border of the remnant
are with broadened components presented, which can be fitted by Gaussian
functions. By further analysis, we suggest that the SNR is at a near kinematic
distance of about 3.1 kpc.
