  The results of a study of the short gamma-ray burst GRB 231115A in the X-ray
and gamma-ray ranges are presented, based on data from the INTEGRAL and Fermi
space observatories. The source of the burst is localized by the IBIS/ISGRI
telescope of INTEGRAL observatory with an accuracy of $\leq$ 1.5 arcmin, it is
located in the Cigar Galaxy (M 82). Early follow-up observations of the burst
localization region were carried out in the optical range with the 36-cm
telescope of the ISON-Kitab observatory and the 70-cm telescope AS-32 of the
Abastumani Astrophysical Observatory, the optical emission has not been
detected. The proximity of the host galaxy ($D_L \simeq 3.5$ Mpc) significantly
limits energetics of the event ($E_{iso}\ \sim\ 10^{45}$ erg) and allows us to
interpret the burst as a giant flare of a previously unknown soft gamma
repeater (SGR) which is an extreme manifestation of the activity of a highly
magnetized neutron star (magnetar). This conclusion is confirmed by the energy
spectrum atypically hard for cosmological gamma-ray bursts, as well as the
absence of optical afterglow and gravitational wave signal, which should have
been detected in the LIGO/Virgo/KAGRA experiments if the burst was caused by a
merger of binary neutron stars. The location of the burst in the $E_{p,i}$ --
$E_{iso}$ and $T_{90,i}$ -- $EH$ diagrams also suggests that GRB 231115A was a
magnetar giant flare. This is the first well-localized giant flare of an
extragalactic SGR.
