X-Ray Spectral Variability of the Seyfert Galaxy NGC4593

Abstract

X-ray (0.1-10 keV) spectra of NGC 4593 were obtained with EXOSAT on seven epochs between 1984 and 1986 using the low and medium energy detectors. Detailed results of the spectral analysis of the seven spectra (obtained from the EXOSAT database) of this galaxy are presented here. Power-law, two power-law, thermal bremsstrahlung and broken power- law models with fixed absorption (fixed with the galactic column density value) were used to fit the data. Broken power-law + fixed absorption model describes the best fit to the spectra than that obtained from other models. However this model cannot completely fit the soft excess emission present in the spectra of NGC 4593, which leads to the suggestion that, most probably, two soft emission components are present in this galaxy. A highly significant (>99.9%) emission line feature was detected which could be the redshifted 6.4 keV fluorescent Fe-K line. Detected soft excess variability and the Fe-K emission line is reported here for the first time for NGC 4593. The significance of these results is discussed.