Extragalactic jets: the high energy view

I review the current knowledge of high-energy emission from extragalctic jets. First I discuss gamma-ray emission from blazars, which provides us numerous precious information on the innermost portions of the relativistic jets. I describe the constraints on the dynamics of the jet from the subpc to the pc scale provided by recent VLBI studies of TeV sources, together with the modelling of the emission from the blazar jet. Finally I discuss high energy emission from large scale jets as seen by Chandra and I report on the expected gamma-ray emission from large-scale regions of jets.Comment: 17 pages, 10 figures. Invited review at the Xth Marcel Grossmann Meeting on General Relativity, Rio de Janeiro, Brazil, July 200

Jets from subpc to kpc scale

The Chandra discovery of bright X-ray emission from kpc-scale jets provides us unprecedented insights into the physical state of the plasma in the flow. In particular it is possible to get good constraints on the power and pressure in bright knots. For a group of selected sources with blazar-type cores it is also possible to constrain the physical quantities of the jet at sub-pc scale. We discuss how these results can help us to connect the properties of the jet at different scales.Comment: 4 pages, Proceedings of the conference "The Physics of Relativistic Jets in the CHANDRA and XMM Era", 23-27 September 2002, Bologn

An emerging population of BL Lacs with extreme properties: towards a class of EBL and cosmic magnetic field probes?

High energy observations of extreme BL Lac objects, such as 1ES 0229+200 or 1ES 0347-121, recently focused interest both for blazar and jet physics and for the implication on the extragalactic background light and intergalactic magnetic field estimate. However, the number of these extreme highly peaked BL Lac objects (EHBL) is still rather small. Aiming at increase their number, we selected a group of EHBL candidates starting from the BL Lac sample of Plotkin et al. (2011), considering those undetected (or only barely detected) by the Large Area Telescope onboard Fermi and characterized by a high X-ray vs. radio flux ratio. We assembled the multi-wavelength spectral energy distribution of the resulting 9 sources, profiting of publicly available archival observations performed by the Swift, Galex and Fermi satellites, confirming their nature. Through a simple one-zone synchrotron self-Compton model we estimate the expected VHE flux, finding that in the majority of cases it is within the reach of present generation of Cherenkov arrays or of the forthcoming Cherenkov Telescope Array (CTA).Comment: 12 pages, 5 figures, accepted for publication in MNRA

Very-high-energy quasars hint at ALPs

One of the mysteries of very-high-energy (VHE) astrophysics is the observation of flat spectrum radio quasars (FSRQs) above about 30 GeV, because at those energies their broad line region should prevent photons produced by the central engine to escape. Although a few astrophysical explanations have been put forward, they are totally ad hoc. We show that a natural explanation emerges within the conventional models of FSRQs provided that photon-ALP oscillations take place inside the source for the model parameters within an allowed range.Comment: 4 pages, 3 figures. Proceeding of the workshop "9th Patras Workshop on Axions, WIMPs and WISPs", 24 - 28 June 2013, Schloss Waldhausen, Mainz, Germany (to be published in the Proceedings