  Studying the nature of various types of supernovae (SNe) is important for our
understanding of stellar evolution. Observations of atomic and molecular gas in
the host galaxies of gamma-ray bursts (GRBs) and SNe have recently been used to
learn about the nature of the explosions themselves and the star formation
events during which their progenitors were born. Based on archival data for
M74, which previously has not been investigated in the context of SN positions,
we report the gas properties in the environment of the broad-lined type Ic
(Ic-BL) SN 2002ap and the type II SNe 2003gd, 2013ej, and 2019krl. The SN
2002ap is located at the end of an off-centre, asymmetric, 55 kpc-long HI
extension containing 7.5% of the total atomic gas in M74, interpreted as a
signature of external gas accretion. It is the fourth known case of an
explosion of a presumably massive star located close to a concentration of
atomic gas (after GRBs 980425, 060505, and SN 2009bb). It is unlikely that all
these associations are random (at a 3sigma significance), so the case of SN
2002ap adds to the evidence that the birth of the progenitors of type Ic-BL SNe
and GRBs is connected with the accretion of atomic gas from the intergalactic
medium. The HI extension could come from tidally disrupted companions of M74,
or be a remnant of a galaxy or a gas cloud that accreted entirely from the
intragroup medium. The other (type II) SNe in M74 are located at the outside
edge of a spiral arm. This suggests that either their progenitors were born
when gas was piling up there or that the SN progenitors moved away from the arm
due to their orbital motions. These type II SNe do not seem to be related to
gas accretion.
