arXiv subjects

G. Setti

Publications and source records attributed to G. Setti.

42 records · Page 3Linked to original sources

arXiv1999

X-ray emission from FRII's radio lobes and the relativistic particle content

It is pointed out that copius X-rays from the lobes of FRII radio galaxies are expected as a natural consequence of the unification linking FRIIs and radio-loud quasars. The detection of extended X-ray emission from 3C 219, likely due to Inverse Compton scattering of the IR photons from a hidden quasar with the relativistic electrons in the lobes, provides the first observational evidence supporting this conjecture. The X-ray fluxes detected in the directions of other five pwerful FRIIs with large redshifts may be similarly accounted for (an alternative to a thermal origin from hot intracluster gas). Much less energetic electrons than those producing the synchrotron radio emission are involved in the process. Then the equipartition conditions imply stronger fields, and significantly stronger internal pressures of the relativic plasmas, than those derived with conventional equipartition equations. The importance of this effect in the pressure balance with the confining intergalactic gas is pointed out.

astro-ph↗

arXiv1999

The contribution of AGN to the X-ray background: the effect of iron features

The contribution of the iron emission line, commonly detected in the X-ray spectra of Seyfert (Sey) galaxies, to the cosmic X-ray background (XRB) spectrum is evaluated in the framework of the XRB synthesis models based on AGN unification schemes. To derive the mean line properties, we have carried out a search in the literature covering a sample of about 70 AGN. When adopting line parameters in agreement with the observations, it turns out that the maximum contribution of the iron line to the XRB is less than 7% at a few keV. This is still below the present uncertainties in the XRB spectrum measurements.

astro-ph↗

arXiv1998

Evidence for inverse Compton emission in the powerful radio galaxy 3C 219

Spectral analysis of ROSAT PSPC and ASCA archive data and a recent ROSAT HRI observation of the powerful FRII radio galaxy 3C 219 reveal an absorbed point-like source, coincident with the nucleus, and a non-thermal extended component aligned with the radio structure. The point-like source can be readily interpreted as a hidden quasar in the nucleus, giving further support to the unification scheme of FRII radio galaxies and radio loud quasars. The coincidence between the X-ray (0.1-10 keV) and radio spectral index suggest that most of the emission associated with the extended component is due to the inverse Compton process in the radio lobes. The extended circumnuclear emission can be understood as Compton scattering of the IR-optical radiation emitted by the hidden quasar and surrounding dusty/molecular torus. This is the first observational evidence supporting the existence of this effect, which also probes the relativistic electron spectrum at energies much lower than those involved in the synchrotron radio emission. The observed X-ray flux can be matched by assuming that the energy density of the relativistic particles exceed the equipartition value by about a factor of 10. At larger distances from the nucleus ($\geq 70$kpc) the inverse Compton scattering with the cosmic microwave background photons becomes more important and may explain the observed X-ray features if positive fluctuations in the column densities of relativistic electrons are present. Alternatively, one cannot exclude with the present data a thermal contribution by hot clumpy gas surrounding the radio lobes.

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arXiv1997

Inverse Compton X-rays from strong FRII radio-galaxies

In the framework of the quasar-radio galaxies unification the radio emitting lobes of FRII radio galaxies are pervaded by an intense quasar radiation field.Inverse Compton (IC) scattering between the relativistic electrons and the IR-optical photons from a hidden quasar may provide an important contribution to the X-ray emission of these radio galaxies. The soft X-ray emission properties of six strong, high redshift FRIIs (3C 277.2, 280, 294, 324, 356, 368) are compared with our model expectations,taking into account also the contribution from the IC-scattering of the CMB photons with the radio electrons. We find that the soft X-ray luminosities and spectra of five out six sources can be satisfactorily explained by our model with the exception of 3C 324 whose X-ray emission is probably dwarfed by that of the galaxies'cluster of which this sources is a member. One important effect is the prediction that the observed X-ray emission associated with the two radio lobes would be asymmetric if the radio axis is inclined with respect to the plane of the sky, the far-away lobe being the more luminous.The ratio between the X-ray luminosities of the two lobes is derived for several values of the inclination of the radio axis.However, the predicted angular sizes of these distant radio galaxies are small and difficult to be resolved with present X-ray facilities.

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arXiv1996

Can Flat Spectrum Radio Quasars make most of the overall gamma--ray background ?

The contribution of discrete sources to the gamma--ray background is modeled. Flat spectrum radio quasars are known to make a substantial contribution to the hard (E > 100 MeV) background. The so called ``MeV bump", however, cannot be accounted for in terms of known classes of sources even taking into account the newly discovered class of objects with a broad band spectrum sharply peaked in the MeV range (``MeV blazars"). Even in the most optimistic case the predicted intensity falls short of at least a factor three.

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arXiv1994

The contribution of AGNs to the X-ray background

We report the results of a detailed analysis of the contribution of various classes of AGNs to the extragalactic X-ray background (XRB). The model is based on the unification schemes of AGNs and on their related X-ray spectral properties in the light of recent observational results. The integrated emission from AGNs, when folded with an appropriate cosmological evolution law, can provide a good fit to the XRB over a wide energy range, from several to $\sim$ 100 keV, while it contributes only about 74\% of the ROSAT soft XRB. The model predictions have been checked against all available observational constraints from both hard and soft X-ray surveys (counts, redshift distributions and average X-ray source spectral properties).

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