High energy X-ray observations of NGC 5506

We have a continuing programme of spectral and temporal studies of a variety of galactic and extragalactic sources in the 20–200 keV band using a large area scintillation counter telescope. The observations of NGC 5506, a Seyfert type 2 galaxy, taken on three occasions during the 1998–2000 period suggest that not only source luminosity varies by a factor of ∼10, but also there is a marked change in the spectral index. The data is consistent with a systematic long-term periodic variation. Our analysis of the all sky monitor light curve suggests a 41.12-day period in the source intensity. This paper presents the spectral parameters in the hard X-ray region and proposes that the observed behaviour of the source can be explained on the basis of a binary black hole model for the core activity of the source.