Related papers: Diffuse Gamma Rays from the Galactic Plane: Probin…
The region around the Galactic center (GC) is now well established to be brighter at energies of a few GeV than expected from conventional models of diffuse gamma-ray emission and catalogs of known gamma-ray sources. We study the GeV excess…
The double humped SED (Spectral Energy Distribution) of blazars, and their flaring phenomena can be explained by various leptonic and hadronic models. However, accurate modeling of the high frequency component and clear identification of…
The extended gamma ray source MGRO J1908+06, discovered by the Milagro air shower detector in 2007, has been observed for about 4 years by the ARGO-YBJ experiment at TeV energies, with a statistical significance of 6.2 standard deviations.…
The launch of the Fermi gamma-ray space telescope and the imaging air Cerenkov telescopes H.E.S.S., MAGIC, and VERITAS have substantially transformed our knowledge of gamma-ray sources in the last decade. The extragalactic gamma-ray sky is…
Recent measurements of cosmic ray electrons and positrons by PAMELA, ATIC, Fermi and HESS have revealed interesting excesses and features in the GeV-TeV range. Many possible explanations have been suggested, invoking one or more nearby…
Identification of the cosmic-ray (CR) `PeVatrons', which are sources capable of accelerating particles to $\sim10^{15}$ eV energies and higher, may lead to resolving the long-standing question of the origin of the spectral feature in the…
Ultra-high energy cosmic ray protons accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds. We show that such cascades can contribute between ~1%…
The Fermi Collaboration has recently updated their analysis of gamma rays from the center of the Galaxy. They reconfirm the presence of an unexplained emission feature which is most prominent in the region of $1-10$ GeV, known as the…
In the last few years the Fermi-LAT instrument has detected GeV gamma-ray emission from several novae. Such GeV emission can be interpreted in terms of inverse Compton emission from electrons accelerated in the shock or in terms of emission…
The latest results from PAMELA and FERMI experiments confirm the necessity to improve theoretical models of production and propagation of galactic electrons and positrons. There are many possible explanations for the positron excess…
A survey of the inner Galaxy region of Galactic longitude l in [+15, +50] degree and latitude b in [-4,+4] degree is performed using one-third of the High Altitude Water Cherenkov (HAWC) Observatory operated during its construction phase.…
Observations of TeV--PeV-energy cosmic neutrinos by the IceCube observatory have suggested that extragalactic cosmic-ray sources should have an optical depth greater than $\sim$0.01 and contribute to more than 10\% of the observed bulk of…
We simulate the neutrino and $\gamma$-ray emissions of the Galaxy which are originated from the hadronic scattering of cosmic rays (CR) with the interstellar medium (ISM). Rather than assuming a uniform CR density, we estimate the spatial…
High-energetic gamma rays from astrophysical targets constitute a unique probe for annihilation or decay of heavy particle dark matter (DM). After several decades, diverse null detections have resulted in strong constraints for DM particle…
Radiatively inefficient accretion flows (RIAFs) in low-luminosity active galactic nuclei (LLAGNs) have been suggested as cosmic-ray and neutrino sources that may largely contribute to the observed diffuse neutrino intensity. We show that…
Photons with very high energy up to TeV (VHE) emitted from active galactic nuclei (AGNs) provide some invaluable information of the origin of $\gam$-ray emission. Although 66 blazars have been detected by {\it EGRET}, only three low…
The recent detection of TeV gamma-radiation from the direction of the Galactic Center within several arc-minutes around Sgr A* is the first model-independent evidence of existence of high energy particle accelerator(s) in the central 10 pc…
Atmospheric Cerenkov Telescopes, including HESS and MAGIC, have detected a spectrum of gamma-rays from the galactic center region which extends from $\sim$200 GeV or lower, to at least $\sim$10 TeV. Although the source of this radiation is…
Motivated by the gamma-ray excess observed from the region surrounding the Galactic Center, we explore particle dark matter models that could potentially account for the spectrum and normalization of this signal. Taking a model-independent…
More than 90% of the Galactic gas-related gamma-ray emissivity above 1 GeV is attributed to the decay of neutral pions formed in collisions between cosmic rays and interstellar matter, with lepton-induced processes becoming increasingly…