Discovery of hard X-ray emission from supernova 1987A

We report the discovery of hard X-rays from the region of the supernova SN1987A in the Large Magellanic Cloud. The observations were made from the Mir-Kvant observatory 'Rontgen'. Hard X-rays were first observed on 10 August 1987 and SN1987A then became the main target of the observatory. Up to 15 September 1987, a total of 115 pointings on 21 days were made. 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 ˜1.4. At low energies the spectrum becomes even flatter and there is indication of a cutoff between 10 and 25keV. The luminosity over the energy range 20–300 keV is ˜2x1038 erg s–1 (assuming a distance of 55 kpc). The error box for the hard source has a (2σ) radius of 10 arc min and contains SN1987A. The results have important implications for current models of SN1987A.