A Cold and Diffuse Giant Molecular Filament in the Region of
  $l=41^\circ$, $b=-1^\circ$
  Data of $^{12}$CO/$^{13}$CO/C$^{18}$O $J=1\to0$ emission toward the Galactic
plane region of $l=35^\circ$ to $45^\circ$ and $b= -5^\circ$ to $+5^\circ$ are
available with the Milky Way Imaging Scroll Painting (MWISP) project. Using the
data, we found a giant molecular filament (GMF) around
$l\approx38\sim42^\circ$, $b\approx-3.5\sim0^\circ$, $V_{LSR} \approx 27 \sim
40$ km~s$^{-1}$, named the GMF MWISP G041-01. At a distance of 1.7 kpc, the GMF
is about 160 pc long. With a median excitation temperature about 7.5 K and a
median column density about $10^{21}$ cm$^{-2}$, this GMF is very cold and very
diffuse compared to known GMFs. Using the morphology in the data cube, the GMF
is divided into four components among which three show filamentary structure.
Masses of the components are $ 10^3 \sim 10^4 M_\odot$, with a total mass for
the whole filament being about $7\times10^4 M_\odot$ from the LTE method.
$^{13}$CO cores inside each component are searched. Virial parameters are about
2.5 for these cores and have a power-law index of -0.34 against the mass. The
mass fraction of dense cores traced by $^{13}$CO to the diffuse clouds traced
by $^{12}$CO are about 7% for all components of the GMF. We found signatures of
possible large scale filament-filament collision in the GMF.
