Discovery of hard X-ray emission from supernova 1987A.

The discovery of hard X-rays from the region of the SN1987A in the LMC is reported. The observations were made from the Mir-Kvant observatory Roentgen. Hard X-rays were first observed on August 10, 1987; a total of 115 pointings on 21 days were made up to September 15, 1987. The flux showed little variation during the observation period. The measured spectrum extends from 20 keV to 300 keV and is extremely hard, having a photon power-law index of about 1.4. At low energies, the spectrum becomes even flatter, and there is indication of a cutoff between 10 and 25 keV. The luminosity over the energy range 20-300 keV is about 2 x 120 to the 38th erg/s, assuming a distance of 55 kpc. The error box for the hard source has a 2-sigma radius of 10 arcmin and contains SN1987A.