X-ray luminosity and spectral variability in the Seyfert type I galaxy : PG 2130+099

Abstract

We present broad-band (0.1-10 keY) X-ray observations of a bright Seyfert I galaxy, PG 2130+099, using the low-energy (LE) and the medium-energy (ME) detectors of the EXOSAT Observatory. The observations were carried out on two occasions separated by a year (in 1984 and 1985), and the X-ray flux was found to have increased by ~35% in the 1.5-6 keY band and by a factor of ~2 in the low energies (0.1-2.0 keV). We have carried out a spectral fit to the combined LE and ME data and found that a two-component spectral model is required to explain the data on both the occasions. The two-component model consists of a hard power-law component and a steep power law (Γ ⋍ 6.0) or a blackbody emission (kT = 30 eV) in the low energy. The intensity of the low component and the spectral index of the hard component were found to be significantly different on the two occasions. The photon spectral index of the hard component was ~1.6 in 1984 and increased to 2.0 in 1985 when the source was brighter.