اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدScience with the new generation high energy gamma- ray experiments
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This Conference is the fifth of a series of Workshops on High Energy Gamma- ray Experiments, following the Conferences held in Perugia 2003, Bari 2004, Cividale del Friuli 2005, Elba Island 2006. This year the focus was on the use of gamma-ray to study the Dark Matter component of the Universe, the origin and propagation of Cosmic Rays, Extra Large Spatial Dimensions and Tests of Lorentz Invariance.
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Previous researches on high-energy neutrino events from gamma-ray bursters (GRBs) suggest a neutrino speed variation $v(E)=c(1pm E/E^{ u}_{mathrm{LV}})$ with ${E}^{ u}_{rm LV}=(6.4pm 1.5)times10^{17}~{ rm GeV}$, together with an intrinsic time differ
ence ${Delta {t}_{rm in}=(-2.8pm 0.7)times10^2~{rm s}}$, which means that high-energy neutrinos come out about 300~s earlier than low-energy photons in the source reference system. Considering the possibility that pre-bursts of neutrinos may be accompanied by high-energy photons, in this work we search for high-energy photon events with earlier emission time from 100 to 1000~s before low-energy photons at source by analyzing Fermi Gamma-ray Space Telescope (FGST) data. We perform the searching of photon events with energies larger than 100~MeV, and find 14 events from 48 GRBs with known redshifts. Combining these events with a $1.07~rm{TeV}$ photon event observed by the Major Atmospheric Gamma Imaging Cherenkov telescopes (MAGIC), we suggest a pre-burst stage with a long duration period of several minutes of high energy neutrino emissions accompanied by high energy photons at the GRB source.
We consider the recent results on UHECR (Ultra High Energy Cosmic Ray) composition and their distribution in the sky from ten EeV energy (the dipole anisotropy) up to the highest UHECR energies and their clustering maps: UHECR have been found mostly
made by light and lightest nuclei. We summarized the arguments that favor a few localized nearby extragalactic sources for most UHECR as CenA, NG 253, M82. We comment also on the possible partial role of a few remarkable galactic UHECR sources. Finally we revive the eventual role of a relic neutrino eV mass in dark hot halo (hit by ZeV neutrinos) to explain the new UHECR clustering events centered around a very far cosmic AGN sources as 3C 454.
We investigate prolonged engine activities of short gamma-ray bursts (SGRBs), such as extended and/or plateau emissions, as high-energy gamma-ray counterparts to gravitational waves (GWs). Binary neutron-star mergers lead to relativistic jets and mer
ger ejecta with $r$-process nucleosynthesis, which are observed as SGRBs and kilonovae/macronovae, respectively. Long-term relativistic jets may be launched by the merger remnant as hinted in X-ray light curves of some SGRBs. The prolonged jets may dissipate their kinetic energy within the radius of the cocoon formed by the jet-ejecta interaction. Then the cocoon supplies seed photons to non-thermal electrons accelerated at the dissipation region, causing high-energy gamma-ray production through the inverse Compton scattering process. We numerically calculate high-energy gamma-ray spectra in such a system using a one-zone and steady-state approximation, and show that GeV--TeV gamma-rays are produced with a duration of $10^2-10^5$ seconds. They can be detected by {it Fermi}/LAT or CTA as gamma-ray counterparts to GWs.
The observed multi-GeV gamma-ray emission from the solar disk --- sourced by hadronic cosmic rays interacting with gas, and affected by complex magnetic fields --- is not understood. Utilizing an improved analysis of the Fermi-LAT data that includes
the first resolved imaging of the disk, we find strong evidence that this emission is produced by two separate mechanisms. Between 2010-2017 (the rise to and fall from solar maximum), the gamma-ray emission is dominated by a polar component. Between 2008-2009 (solar minimum) this component remains present, but the total emission is instead dominated by a new equatorial component with a brighter flux and harder spectrum. Most strikingly, although 6 gamma rays above 100 GeV are observed during the 1.4 years of solar minimum, none are observed during the next 7.8 years. These features, along with a 30-50 GeV spectral dip which will be discussed in a companion paper, were not anticipated by theory. To understand the underlying physics, Fermi and HAWC observations of the imminent Cycle 25 solar minimum are crucial.
We report the detection of two new gamma-ray sources in the Fermi-LAT sky (Pass 8) at energies higher than 20 GeV, and confirmed at lower energies, using a source detection tool based on the Minimum Spanning Tree algorithm. One of these sources, at a
Galactic latitude of about -4{deg}, is a new discovery, while the other was previously reported above 50 GeV in the 2FHL catalogue. We searched for archival multi-wavelength data of possible counterparts and found interesting candidates. Both objects are radio sources and their WISE infrared colours are typical of blazars. While for the former source no optical spectra are available, for the latter a puzzling optical spectrum corresponding to a white dwarf star is found in the 6dF database. We discuss the spectral energy distributions of both sources and possible interpretations.
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