High Energy Phenomena in Blazars

Advances in the capabilities of X-ray, gamma-ray and TeV telescopes have brought new information on the physics of relativistic jets, which are responsible for the blazar "phenomenon". In particular the broad band sensitivity of the BeppoSAX satellite, extending up to 100 KeV has allowed unprecedented studies of their hard X-ray spectra. I summarize here some basic results and present a unified view of the blazar population, whereby all sources contain essentially similar jets despite diversities in other properties, like the presence or absence of emission lines in their optical spectra. Blazars with emission lines are of particular interest in that it is possible to estimate both the luminosity of the jet and the luminosity of the accretion disk. Implications for the origin of the power carried by relativistic jets, possibly involving rapidly spinning supermassive black holes are discussed. We suggest that emission line blazars are accreting at near critical rates, while BL lacs, where emission lines are weak or absent are highly subcritical.Comment: 11 pages, 7 figures, presented at the 20th Texas Symposium, 10-15 Dec. 200

A Model for the X-Ray and UV Emission from Seyfert Galaxies and Galactic Black Holes

We propose that the X--ray emission from radio quiet AGN and galactic black holes is due to Comptonization of soft thermal photons emitted by the underlying accretion disk in localized structures (blobs). The power per unit area produced by the blobs, impinging on the disk, can easily dominate the radiation internally produced by the disk. In this case the electron temperature and the high energy spectrum can be determined in a similar way as in the previously studied homogeneous model (Haardt \& Maraschi 1991). However in the present model: a) the emitted spectrum is largely independent of the {\it fraction} of gravitational power dissipated in the blobs; b) the X--ray spectrum can be harder depending on a form factor of the blobs; c) the UV (or soft X--ray for galactic objects) luminosity that is not intercepted by the blobs can be larger than the X--ray luminosity. In the framework of a simplified accretion disk $\alpha-\Omega$ dynamo model, we make order of magnitude estimates of the number of active blobs, their size, luminosity and hence their compactness, finding values in agreement with what is observed. The expected UV to X--ray spectra and correlations of X--ray and UV light curves are discussed.Comment: 10 pages. Plain Tex. Accepted in ApJ Letter

X-rays from Radio-Galaxies: BeppoSAX Observations

We briefly review BeppoSAX observations of X-ray bright radio-galaxies. Their X-ray spectra are quite varied, and perhaps surprisingly, any similarity between radio-loud AGN and Seyfert galaxies is the exception rather than the rule. When detected, reprocessing features (iron line and reflection) are generally weak, suggesting two possible scenarios: either: (1) non-thermal (jet?) radiation dilutes the X-ray emission from the disk in radio-loud objects, or (2) the solid angle subtended by the X-ray reprocessing material is smaller in radio-loud than in radio-quiet AGN due to different characteristics of the accretion disk itself.Comment: 6 pages, to appear in `Life Cycles of Radio Galaxies', ed. J. Biretta et al., New Astronomy Review

Progress in understanding Blazars from BeppoSAX observations

Results obtained with BeppoSAX observations of blazars within various collaborative programs are presented. The spectral similarity "paradigm", whereby the spectral energy distributions of blazars follow a sequence, leading to a unified view of the whole population, is briefly illustrated. We concentrate on recent observations of flares and associated spectral variability for three objects at the "blue" end of the spectral sequence, namely PKS 2155-304, Mkn 421 and Mkn 501. The results are discussed in terms of a general analytic synchrotron self-Compton interpretation of the overall spectrum. The physical parameters of the quasi-stationary emission region can be derived with some confidence, while the variability mechanism(s) must be complex.Comment: 10 pages, 8 figures, to be published in the Proceedings of the 32nd COSPAR Meeting, Nagoya, 12-19 July 199

There is More than Meets the Eye. Undead, Ghosts and Spirits in the Decretum of Burchard of Worms

The Corrector, that is, the nineteenth book of Burchard of Worms’s Decretum, is widely recognized as one of the essential sources for the study of pagan survivals around the year 1000 A.D. in Germany – more specifically, in the Rhenish Hesse. The Decretum is in itself an important collection of canon law of its time, but the Corrector in particular has drawn the attention of scholars because of its peculiarities. Most interestingly, despite being partially based on previous penitentials and council canons, book nineteen of the Decretum was also partly written originally by the Bishop of Worms himself, and thus turns out to be a fundamental penitential text for the understanding of pagan survivals at the time and in the place of its composition. The source proves all the more useful for scholars interested in beliefs concerning death, the “undead”, and the likes, even though terminology can be deceptive: for this reason, modern and anachronistic taxonomies such as “ghost”, “undead”, “revenant”, etc. will be discarded, in favour of an emic approach which aims at respecting the text and imposing as fewer filters as possible. As a matter of fact, Burchard mentions many kinds of otherworldly entities which recall our modern notions of “ghosts”, “spirits” and “undead”, but often does not attach further details to identify them – either because he did not deem them worthy of his attention, or because he might have not known folk beliefs in detail. In any case, Burchard’s Germany appears to be densely populated: people share their space with hordes of “spectres”, seem to be aware of it, and often believe to be able to join them. The aim of the present contribution is then to analyze those folk beliefs which involve otherworldly entities, in order to critically discuss their characteristics and understand their implications among the people of Hesse around the year 1000. Attention will be specifically focused on the relationship between the living and the dead/undead, and will cast light on a series of related aspects such as: 1) the bias against women – who were held naturally predisposed to credulity; 2) positive/negative interactions between man and otherworldly entities; 3) attributes associated to said entities (persistent, wicked, benevolent/malevolent, etc.); 4) the fear of the darkness due to the supposed activity of evil spirits in the night hours; 5) the role of otherwordly entities at the service of the living; 6) the fear that the dead may rise again and harm the living