Hard X-ray observation of NGC 4151 with the MIFRASO telescope

During a balloon flight on July 29, 1986 of the Mifraso telescope, a region of the sky containing the Seyfert galaxy NGC 4151 was studied over the photon energy range 15-300 keV. A 5.5 sigma excess, interpreted as originating from the direction of NGC 4151, was detected in the energy band 27-80 keV. The corresponding emission spectrum may be represented by a single power law with a photon spectral index of alpha = 1.5 + or - 0.6. The result is compared to previous hard X-ray observations of this source. Apart from this measurement, an observation of the Crab Nebula as an in-flight calibration source of the telescope is described. 33 refs.