Exploring Quantum Gravity with Very-High-Energy Gamma-Ray Instruments - Prospects and Limitations

Some models for quantum gravity (QG) violate Lorentz invariance and predict an energy dependence of the speed of light, leading to a dispersion of high-energy gamma-ray signals that travel over cosmological distances. Limits on the dispersion from short-duration substructures observed in gamma-rays emitted by gamma-ray bursts (GRBs) at cosmological distances have provided interesting bounds on Lorentz invariance violation (LIV). Recent observations of unprecedentedly fast flares in the very-high energy gamma-ray emission of the active galactic nuclei (AGNs) Mkn 501 in 2005 and PKS 2155-304 in 2006 resulted in the most constraining limits on LIV from light-travel observations, approaching the Planck mass scale, at which QG effects are assumed to become important. I review the current status of LIV searches using GRBs and AGN flare events, and discuss limitations of light-travel time analyses and prospects for future instruments in the gamma-ray domain.Comment: 11 pages, 4 figures, proceedings of "Science with the New Generation of High Energy Gamma-Ray Experiments", Euganean Spa Area, Padova: October 8-10, 200

First results of the two square meters multilayer glass composite mirror design proposed for the Cherenkov Telescope Array developed at INFN

The Cherenkov Telescope Array (CTA) is a future ground-based gamma-ray astronomy detector that will consist of more than 100 Imaging Atmospheric Cherenkov Telescopes of different sizes. The total reflective surface of roughly 10 000 m$^2$ requires unprecedented technological efforts towards a cost-efficient production of light-weight and reliable mirror substrates at high production rate. We report on a new mirror concept proposed for CTA developed by INFN, which is based on the replication from a spherical convex mold under low pressure. The mirror substrate is an open structure design made by thin glass layers at the mirror's front and rear interspaced by steel cylinders. A first series of nominal size mirrors has been produced, for which we discuss the optical properties in terms of radius of curvature and focusing power

The hunt for cosmic neutrino sources with IceCube

IceCube is a cubic-kilometer neutrino telescope under construction at the geographic South Pole. Once completed it will comprise 4800 optical sensors deployed on 80 vertical strings at depths in the ice between 1450 and 2450 meters. Part of the array is already operational and data was recorded in the configurations with 9 (year 2006/2007), 22 (year 2007/2008) and 40-strings (year 2008/2009) respectively. Here we report preliminary results on the search for point-like neutrino sources using data collected with the first 22 strings (IC-22).Comment: 10 pages, 3 figures, prepared for the Scineghe08 Conference, Padova/Italy (2008

Status and recent results of MAGIC

MAGIC is a single-dish Cherenkov telescope located on La Palma (Spain), hence with an optimal view on the Northern sky. Sensitive in the 30 GeV-30 TeV energy band, it is nowadays the only ground-based instrument being able to measure high-energy gamma-rays below 100 GeV. We review the most recent experimental results obtained using MAGIC.Comment: Contribution to the Proceedings of "Science with the new generation of high energy gamma-ray experiments", Abano Terme, Italy, 8-10 October 200

Fermi Gamma-ray Space Telescope Observations of Gamma-ray Pulsars

The Large Area Telescope on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST), with its large field of view and effective area, combined with its excellent timing capabilities, is poised to revolutionize the field of gamma-ray astrophysics. The large improvement in sensitivity over EGRET is expected to result in the discovery of many new gamma-ray pulsars, which in turn should lead to fundamental advances in our understanding of pulsar physics and the role of neutron stars in the Galaxy. Almost immediately after launch, Fermi clearly detected all previously known gamma-ray pulsars and is producing high precision results on these. An extensive radio and X-ray timing campaign of known (primarily radio) pulsars is being carried out in order to facilitate the discovery of new gamma-ray pulsars. In addition, a highly efficient time-differencing technique is being used to conduct blind searches for radio-quiet pulsars, which has already resulted in new discoveries. I present some recent results from searches for pulsars carried out on Fermi data, both blind searches, and using contemporaneous timing of known radio pulsars.Comment: To appear in the Proceedings of the 6th Workshop on Science with the New Generation of High Energy Gamma-Ray Experiments (SciNeGHE '08), held in Padova, 8-10 October 2008, Eds. D. Bastieri, R. Rand

Gamma-ray burst observations with new generation imaging atmospheric Cerenkov Telescopes in the FERMI era

After the launch and successful beginning of operations of the FERMI satellite, the topics related to high-energy observations of gamma-ray bursts have obtained a considerable attention by the scientific community. Undoubtedly, the diagnostic power of high-energy observations in constraining the emission processes and the physical conditions of gamma-ray burst is relevant. We briefly discuss how gamma-ray burst observations with ground-based imaging array Cerenkov telescopes, in the GeV-TeV range, can compete and cooperate with FERMI observations, in the MeV-GeV range, to allow researchers to obtain a more detailed and complete picture of the prompt and afterglow phases of gamma-ray bursts.Comment: 9 pages, two figures. Proceeding for the 6th "Science with the New Generation of High Energy Gamma-Ray Experiments" worksho

High energy emission from galaxy clusters and particle acceleration due to MHD turbulence

In the next years the FERMI gamma ray telescope and the Cherenkov telescopes will put very stringent constraints to models of gamma ray emission from galaxy clusters providing crucial information on relativistic particles in the inter-galactic-medium. We derive the broad band non-thermal spectrum of galaxy clusters in the context of general calculations in which relativistic particles (protons and secondary electrons due to proton-proton collisions) interact with MHD turbulence generated in the cluster volume during cluster mergers, and discuss the importance of future gamma ray observations.Comment: 9 pages, 2 figures, in proceedings of "Science with the new generation of high energy gamma ray experiments", AIP Conf. Proc. Series, D.Bastieri and R.Rando ed

The GeV to TeV view of SNR IC443: predictions for Fermi

We present a theoretical model that explains the high energy phenomenology of the neighborhood of SNR IC 443, as observed with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope and the Energetic Gamma-Ray Experiment Telescope (EGRET). We also discuss how the model can be tested with observations by the Fermi Gamma-ray Large Area Space Telescope. We interpret MAGIC J0616+225 as delayed TeV emission of cosmic-rays diffusing from IC 443 and interacting with a known cloud located at a distance of about 20 pc in the foreground of the remnant. This scenario naturally explains the displacement between EGRET and MAGIC sources, their fluxes, and their spectra. Finally, we predict how this context can be observed by Fermi.Comment: To appear in the Proceedings of the 6th Workshop on Science with the New Generation of High Energy Gamma-Ray Experiments (SciNeGHE '08), held in Padova October 200

Lithium ion-induced damage in silicon detectors

Silicon diodes processed by CNM on standard and oxygenated silicon substrates have been irradiated by 58 MeV lithium ions. The radiation-induced effects are very similar to the one observed after proton irradiation: substrate space charge sign inversion (SCSI), lower increase of the effective substrate doping concentration after SCSI for the oxygenated devices. The experimental radiation hardness factor has been determined to be 45.01, within 8.2% with the expected value. These results suggest that 58 MeV Li ions are a suitable radiation source for radiation hardness studies by ions heavier than protons for the future very high luminosity hadron colliders