The X-ray emission of 3C 273.
Koyama, K.; Nandra, K.; Tanaka, Y.; Hayashida, K.; Makishima, K.; Pounds, K. A.; Turner, M. J. L.; Makino, F.; Ohashi, T.; Stewart, G. C.; Inoue, H.; Williams, O. R.; Kii, T.; Courvoisier, T. J. L.; Takano, S.
United Kingdom, Switzerland
Abstract
The X-ray emission of 3C273 in the 0.2-35 keV band has been studied, with EXOSAT and Ginga, over the period 1983 December to 1985 December. The overall flux is variable on a time-scale of weeks by a factor of 2. The spectral index in the 2-10 keV band (α ~0.5) is significantly different from the 'canonical' AGN index of α = 0.7. There are small but significant variations with time in the spectral index which are not statistically correlated with the overall X-ray flux level. Iron emission with an equivalent width of ~50 eV is detected in one of the Ginga observations. Although evidence for the line is weaker in the other observations, the absence of significant variability in the iron line flux suggests that it is independent of the variations in the 2-10 keV flux. There is a soft excess present in all the EXOSAT (ME and LE) observations, which varies independently of the 2-10 keV flux, but on similar time- scales. This implies an origin close to, but separate from, the source of the harder X-rays.