Related papers: Acceleration of petaelectronvolt protons in the Ga…
The nearby radio galaxy Centaurus A belongs to a class of Active Galaxies that are very luminous at radio wavelengths. The majority of these galaxies show collimated relativistic outflows known as jets, that extend over hundreds of…
Jets associated with Active Galactic Nuclei (AGN) have been observed for almost a century, initially at optical and radio wavelengths. They are now widely accepted as "exhausts" produced electromagnetically by the central, spinning, massive…
The central region of our Galaxy is a very peculiar environment, containing magnetic fields in excess of 100 mG and gas densities reaching ~ 10^4cm^-3. This region was observed as a strong source of GeV and TeVs gammas, what suggests that a…
The observational progress in the $\gamma$-ray astronomy in the last few years has led to the discovery of more than a thousand sources at GeV energies and more than a hundred sources at TeV energies. A few different classes of compact…
We critically assess limits on the maximum energy of protons accelerated within superbubbles around massive stellar clusters, considering a number of different scenarios. In particular, we derive under which circumstances acceleration of…
The origin of Galactic cosmic rays (CRs), particularly around the knee region ($\sim$3 PeV), remains a major unsolved question. Recent observations by LHAAASO suggest that the knee is shaped mainly by protons, with a transition to heavier…
Imaging Atmospheric Cherenkov Telescopes have revealed more than 100 TeV sources along the Galactic Plane, around 45% of them remain unidentified. However, radio observations revealed that dense molecular clumps are associated with 67% of…
Supernova remnants are one potential source class considered a PeVatron (i.e. capable of accelerating cosmic rays above PeV energies). The shock fronts produced after the explosion of the supernova are ideal regions for particle…
Recent cosmic-ray measurements have found an anomaly in the cosmic-ray energy spectrum at GeV-TeV energies. Although the origin of the anomaly is not clearly understood, suggested explanations include effect of cosmic-ray source spectrum,…
It has long been speculated that supernova remnants represent a major source of cosmic rays in the Galaxy. Observations over the past decade have ceremoniously unveiled direct evidence of particle acceleration in SNRs to energies…
The measurement of diffuse PeV gamma-ray emission from the Galactic plane would provide information about the energy spectrum and propagation of Galactic cosmic rays, and the detection of a point-like source of PeV gamma rays would be…
We analyze the conditions that enable acceleration of particles to ultra-high energies, ~10^{20} eV (UHECRs). We show that broad band photon data recently provided by WMAP, ISOCAM, Swift and Fermi satellites, yield constraints on the…
Observations of the Milky Way at TeV-PeV energies reveal a bright diffuse flux of hadronic cosmic rays and also bright point sources of gamma rays. If the gamma-ray sources are hadronic cosmic-ray accelerators, then they must also be…
Cherenkov telescopes play a major role in the growth of the TeV Astronomy which, in 20 years, has reached the status of an important branch of Astrophysics, because of the observations of the violent, non thermal processes in the extreme…
Supernova remnants are often presented as the most probable sources of Galactic cosmic rays. This idea is supported by the accumulation of evidence that particle acceleration is happening at supernova remnant shocks. Observations in the TeV…
Microquasars are laboratories for the study of jets of relativistic particles produced by accretion onto a spinning black hole. Microquasars are near enough to allow detailed imaging of spatial features across the multiwavelength spectrum.…
The observations of high energy $\gamma$-ray emission from the Galactic center (GC) by HESS, and recently by Fermi, suggest the cosmic ray acceleration in the GC and possibly around the supermassive black hole. In this work we propose a…
One of the major scientific objectives of the future Cherenkov Telescope Array (CTA) Observatory is the search for PeVatrons. PeVatrons are cosmic-ray factories able to accelerate nuclei at least up to the knee feature seen in the spectrum…
Based on the collective linear and nonlinear processes in a magnetized plasma surrounding the black hole at the galactic center (GC), an acceleration mechanism is proposed to explain the recent detection/discovery of PeV protons. In a two…
Some recent experiments detecting very high energy (VHE) gamma-rays above 10-20 TeV independently reported VHE bursts for some of bright gamma-ray bursts (GRBs). If these signals are truly from GRBs, these GRBs must emit a much larger…