6. The SED
In Fig. 6 we show the overall spectral energy distributions of PKS 0528+134 at different epochs, as indicated by the labels. Data have been dereddened assuming cm-2, corresponding to . We have reported the minimum and maximum values of the radio and optical data obtained during our campaign.
The not simultaneous data shown in Fig. 6 have been taken from Wall & Peacock 1985; Bloom et al. 1994; Edelson 1987; Reuter et al. 1997; Rieke et al. 1982; Condon et al. 1977; Collmar et al. 1997; McNaron-Brown et al., 1995 and Mukherjee et al. 1996. We also show some simultaneous sets of data: the 1991 Comptel and EGRET spectrum (Collmar et al. 1997); the 1994 and 1995 X-ray (ASCA) and EGRET data (we also have an optical point during the 1994 campaign; data for these two campaigns are presented in Sambruna et al. 1997 and references therein); our 1997 IR, optical, X-ray data together with the EGRET point from Mukherjee et al. 1997b and the radio data from the GBI archive (see Fig. 1).
As all other -ray bright blazars, also the SED of PKS 0528+134 is characterized by two peaks, one between the far IR and optical spectral bands, and the other at MeV energies. As discussed in Sambruna et al. (1997), the dereddened (using ) optical spectrum is inverted (), and thus indicative of the presence of a `blue bump' component. This is not easy to reconcile with the very large and rapid optical variability. We also note that due to the presence of molecular clouds along the line of sight the gas to dust ratio may be anomalous and the value of may be larger than the one adopted above. Further spectral observations in the IR optical range could help clarifying this issue.
As can be seen, the MeV-GeV emission dominates the bolometric output by a large amount, reaching an (isotropic) luminosity in excess of 1049 erg s-1 (with km s-1 Mpc-1 and ).
© European Southern Observatory (ESO) 1999
Online publication: July 16, 1999