3.4. X and gamma-ray emission
[Bowyer et al. 1970] have reported the first convincing evidence for X-ray emission from 3C 273 using a collimator instrument on a sounding rocket. This result was confirmed by Uhuru measurements reported by [Kellog et al. 1971]. In a 1977 review [Gursky & Schwartz 1977] state that 3C 273 is still the only quasar reliably associated with an X-ray source and that it is not certain that X-ray emission is a characteristic of active galactic nuclei in general. This has changed since then, X-ray emission is one of the important emission components of all classes of AGN. 3C 273 has thus been observed, often many times, by all X-ray satellites. We present here the X-ray data to about 10 keV obtained by EINSTEIN [Wilkes & Elvis 1987], EXOSAT, GINGA (both reported in [Turner et al. 1990]), ROSAT [Leach McHardy & Papadakis 1995] and [Walter et al. 1994], ASCA [Yaqoob et al. 1994] and SAX [Grandi et al. 1997] and higher energy data as discussed in [Maisack et al. 1992] for HEXE data, [Bassani et al. 1992] for SIGMA data and [McNaron-Brown et al. 1995] for OSSE data.
This emission has 4 features (see Fig. 7): A steep low energy component that emerges from the interstellar absorption called the soft excess, a straight power law that extends to about 1MeV (which we will call the medium energy component) on which a weak Fe line appears and a steeper power law above about 1MeV (called the high energy component in the following).