706 research outputs found
Physics from Time Variability of the VHE Blazar PKS 2155-304
Blazars are the principal extragalactic sources of very high energy gamma-ray emission in the Universe. These objects constitute a sub-class of Active Galactic Nuclei whose
emission is dominated by Doppler boosted non-thermal radiation from plasma outflowing at relativistic speeds from the central engine. This plasma outflow happens in the
form of large-scale collimated structures called jets, which can extend for Mpc in length and transport energy from the central engine of the galaxy to the larger scale intergalac-
tic medium. Over thirty such sources have been discovered to date by ground-based gamma-ray telescopes such as H.E.S.S., and PKS 2155-304 is the prototypical southern-hemisphere representative of this population of objects.
In this thesis I have studied in detail some aspects of the temporal variability of the jet emission from PKS 2155-304, combining coordinated observations across the electromagnetic spectrum, from optical polarimetric measurements to X-ray and ground-based gamma-ray data. The temporal properties of the dataset allowed us to derive important physical information about the structure and emission mechanisms of the source and put constraints to the location of the sites of VHE emission and particle acceleration within the jet. We have also derived a sensitive statistical measure, called Kolmogorov distance,
which we applied to the large outburst observed from PKS 2155-304 in July 2006, to derive the most stringent constraints to date on limits for the violation of Lorentz invariance induced by quantum-gravity effects from AGN measurements
Future developments in ground-based gamma-ray astronomy
Ground-based gamma-ray astronomy is a powerful tool to study cosmic-ray
physics, providing a diagnostic of the high-energy processes at work in the
most extreme astrophysical accelerators of the universe. Ground-based gamma-ray
detectors apply a number of experimental techniques to measure the products of
air showers induced by the primary gamma-rays over a wide energy range, from
about 30 GeV to few PeV. These are based either on the measurement of the
atmospheric Cherenkov light induced by the air showers, or the direct detection
of the shower's secondary particles at ground level. Thanks to the recent
development of new and highly sensitive ground-based gamma-ray detectors,
important scientific results are emerging which motivate new experimental
proposals, at various stages of implementation. In this chapter we will present
the current expectations for future experiments in the field.Comment: To appear in "Handbook of X-ray and Gamma-ray Astrophysics" by
Springer (Eds. C. Bambi and A. Santangelo) - 59 p
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