K.P. Singh, N.J. Westergaard, H.W. Schnopper, H. Awaki, and Y. Tawara

Abstract

The X-ray light curves and X-ray spectra of Markarian (Mrk) 509 from two observations with the Ginga satellite are presented. A continuously varying X-ray intensity on hourly time scales was observed on both the occasions. The observed variability is the fastest reported so far from Mrk 509. The X-ray intensity was observed to increase almost linearly before saturating at the maximum on October 8, 1988, and thus showing a quadratic trend. About five days later, it was observed to decrease linearly. The maximum variation observed is 30 percent. The X-ray spectra accumulated for different intensity levels were analyzed separately. It is found that the 1-30 keV spectra are best explained by (1) a variable power law with the photon index Gamma in the range of 1.6-1.7 over the energy bandwidth of 3-30 keV and showing a steepening with increase in the intensity, (2) a variable low-energy excess below 3 keV with a very steep spectrum, (3) a Gaussian line feature near 6 keV best observed during the peak brightness level and having an equivalent width of 150 + or - 49 eV, and (4) good evidence for a flatter spectrum above 10 keV during the maximum brightness.