  In this work we present the photometric and spectroscopic observations of
Type IIb Supernova 2017gpn. This supernova was discovered in the error-box of
LIGO/Virgo G299232 gravitational-wave event. We obtained the light curves in B
and R passbands and modelled them numerically using the one-dimensional
radiation hydrocode STELLA. The best-fit model has the following parameters:
the pre-SN star mass and the radius are 3.5 Msun and 50 Rsun, respectively; the
explosion energy is Eexp = 1.2 * 10^51 erg; the mass of radioactive nickel is
M56Ni =0.11 Msun, which is totally mixed through the ejecta, the mass of the
hydrogen envelope 0.06 Msun. Moreover, SN 2017gpn is a confirmed SN IIb that is
located at the farthest distance from the center of its host galaxy NGC 1343
(i.e. the projected distance is about 21 kpc). This challenges the scenario of
the origin of Type IIb Supernovae from massive stars.
