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 et al. 1987), EXOSAT, GINGA (both reported in (Turner et al. 1990)), ROSAT (Leach et al. 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 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 1 MeV (called the high energy component in the following).

Figure 7. The average X and gamma-ray spectrum. Data from Fig. 1. Panels as in Fig. 4.