The changing X-ray period of the Seyfert galaxy IRAS18325-5926

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  • 7 March 1998
Abstract
We report on two observations of the Seyfert galaxy IRAS18325-5926 made in 1997 December and 1998 February with the Rossi X-ray Timing Explorer (RXTE). We find evidence for periodicities in the resulting X-ray lightcurves which are shorter than the 58 ks period found from data of the source taken in 1997 March with the imaging satellite ASCA. It is therefore likely that IRAS18325-5926 has a quasi-periodic oscillation (QPO) similar to, but at a much longer period than, the QPO seen in some Galactic Black Hole Candidates. The power spectrum of the February data has several peaks. If we select the highest peak in the February power spectrum, the variation of the period is consistent with that expected from two massive black holes spiralling together due to the emission of gravitational radiation. The a priori probability of finding such an event could be as high as 1/1000.

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