The interaction of high-energy particles affected by quantum gravity is argued from the experimental viewpoint of raising a question, "our detection method for high-energy gamma-rays supplies ...trustworthy observation data and we are now seeing the true image of the universe through high-energy gamma-rays?" The modified dispersion relation (MDR) for particles' energy and momentum is applied to the equation of energy-momentum conservation in particle reactions, to study the restriction imposed on the kinematic state of high-energy particles by the Lorentz invariance violation (LIV) due to quantum gravity, as a function of the incident particle energy of the reaction. The result suggests that the interaction utilized for gamma-ray detection is not free from the effect of quantum gravity when gamma-ray energy is higher than 10 super(13) ~ 10 super(17) eV depending on models of MDR. Discussion is presented on the prospect of finding clear evidence of the LIV effect from gamma-ray observations, as well as on the radiation and propagation mechanism of gamma-rays under the influence of the LIV effect.
Protons with energies up to ∼1015 eV are the main component of cosmic rays, but evidence for the specific locations where they could have been accelerated to these energies has been lacking. ...Electrons are known to be accelerated to cosmic-ray energies in supernova remnants, and the shock waves associated with such remnants, when they hit the surrounding interstellar medium, could also provide the energy to accelerate protons. The signature of such a process would be the decay of pions (π0), which are generated when the protons collide with atoms and molecules in an interstellar cloud: pion decay results in γ-rays with a particular spectral-energy distribution. Here we report the observation of cascade showers of optical photons resulting from γ-rays at energies of ∼1012 eV hitting Earth's upper atmosphere, in the direction of the supernova remnant RX J1713.7-3946. The spectrum is a good match to that predicted by pion decay, and cannot be explained by other mechanisms.
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Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The fluxes of the inverse Compton γ-rays expected from synchrotron X-ray nebulae are calculated and the observability of this radiation is discussed. The main emphasis is given to the pulsar driven ...nebulae (plerions), although the results and conclusions are equally applicable to the extended non-thermal X-ray sources produced by shock-accelerated electrons in the shell-type supernovae remnants. The existence of the non-thermal (synchrotron) component of X-radiation in these objects implies an effective acceleration of electrons up to energies Ee ~ 100B1/2−5€keV TeV (B −5 = B/ 10−5 G; € keV = €/1keV). The inverse Compton scattering of the same electrons on the ambient photon fields may result in observable TeV γ-radiation as well. The 2.7-K microwave background radiation is, as a rule, the dominant target photon field for production of γ-rays. This provides a direct relation, for the given magnetic field, between the typical energies of the synchrotron (€) and inverse Compton (E) photons produced by the same electrons: €keV ≃ 0.07 (E/1 TeV)B − 5. The ratio of relevant energy fluxes at these energies is about fγ( ≥ E)/fx( ≥ € ) ≃ 0.1B −5−2 ξ, where the fx ( ≥ € ) is the energy flux of soft X-rays corrected for absorption, and the factor ξ ≃ 1 is introduced in order to take into account possible differences in the source sizes responsible for the fluxes observed by X-ray and γ-ray detectors. Since the fluxes of X-ray nebulae with angular size less than a few arcmin are typically at the level of fx ≤ 10−11 erg cm−2 s−1, then the detectability of these objects in TeV γ-rays, by current atmospheric Cherenkov telescopes with sensitivities a few times 10 −12 erg cm−2 s−1, would significantly depend on the ambient magnetic field. In particular, the γ-ray observability of these X-ray nebulae becomes problematic even for the lowest possible magnetic field, i.e. B ~ BISM ≃ 3–5 μG. Otherwise, the detection of γ-rays from such sources would require ξ ≫ 1, which implies that in fact the relativistic electrons occupy a significantly larger region around the accelerator than the ≥ 1 arcmin X-ray nebulae resolved by the ROSAT and ASCA satellites. We argue that the invocation of such an hypothesis allows us to explain satisfactorily the flux of TeV γ-rays detected from the direction of the recently discovered faint X-ray nebula around the pulsar PSR B1706 − 44.
Because accretion and merger shocks in clusters of galaxies may accelerate particles to high energies, clusters are candidate sites for the origin of ultra-high-energy (UHE) cosmic rays. A prediction ...was presented for gamma-ray emission from a cluster of galaxies at a detectable level with the current generation of imaging atmospheric Cherenkov telescopes. The gamma-ray emission was produced via inverse Compton upscattering of cosmic microwave background photons by electron-positron pairs generated by collisions of UHE cosmic rays in the cluster. We observed two clusters of galaxies, Abell 3667 and Abell 4038, searching for very high energy gamma-ray emission with the CANGAROO-III atmospheric Cherenkov telescope system in 2006. The analysis showed no significant excess around these clusters, yielding upper limits on the gamma-ray emission. From a comparison of the upper limit for the northwest radio relic region of Abell 3667 with a model prediction, we derive a lower limit for the magnetic field of the region of ~0.1 Delta *mG. This shows the potential of gamma-ray observations in studies of the cluster environment. We also discuss the flux upper limit from cluster center regions using a model of gamma-ray emission from neutral pions produced in hadronic collisions of cosmic-ray protons with the intracluster medium. The derived upper limit of the cosmic-ray energy density within this framework is an order of magnitude higher than that of our Galaxy.
Sub-TeV gamma-ray emission from the northwest rim of the supernova remnant RX J0852.0-4622 was detected with the CANGAROO II telescope and recently confirmed by the HESS group. In addition, the HESS ...data revealed a very wide (up to 2 in diameter), shell-like profile of the gamma-ray emission. We carried out CANGAROO III observations in 2005 January and February with three telescopes and show here the results of threefold coincidence data. We confirm the HESS results about the morphology and the energy spectrum and find that the energy spectrum in the NW rim is consistent with that of the whole remnant.
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