April 2, 1997
Active galaxies and gamma ray bursts are the sources of the highest energy photons detected by astronomical telescopes. We speculate that they may be the sources of the highest energy cosmic rays. This makes them true proton accelerators, where the highest energy photons are the decay products of neutral pions photoproduced when the proton beams interacts with ambient radiation. Neutrinos from the decay of charged pions represent an incontrovertible signature for proton acceleration. A main theme of this talk is that their fluxes can be estimated from the measured gamma ray luminosity by model-independent methods, based on dimensional analysis and textbook particle physics.
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June 17, 2002
We introduce neutrino astronomy from the observational fact that Nature accelerates protons and photons to energies in excess of 10^{20} and 10^{13} eV, respectively. Although the discovery of cosmic rays dates back close to a century, we do not know how and where they are accelerated. We review the facts as well as the speculations about the sources. Among these gamma ray bursts and active galaxies represent well-motivated speculations because these are also the sources of t...
January 22, 2011
The origin of the highest energy cosmic rays is still unknown. The discovery of their sources will reveal the workings of the most energetic astrophysical accelerators in the universe. Current observations show a spectrum consistent with an origin in extragalactic astrophysical sources. Candidate sources range from the birth of compact objects to explosions related to gamma-ray bursts or to events in active galaxies. We discuss the main effects of propagation from cosmologica...
August 28, 1996
We present the theoretical arguments and describe the accumulating experimental evidence that jets, powered by supermassive black holes, are true cosmic accelerators. They produce photons of TeV energy, possible higher, and may be the enigmatic source of the highest energy cosmic rays. The features of the multi-wavelength emission spectrum are dictated by the interactions of electrons and protons, accelerated in the vicinity of the black hole, with the ambient light in the ga...
November 4, 2011
Identifying the accelerators that produce the Galactic and extragalactic cosmic rays has been a priority mission of several generations of high energy gamma ray and neutrino telescopes; success has been elusive so far. Detecting the gamma-ray and neutrino fluxes associated with cosmic rays reaches a new watershed with the completion of IceCube, the first neutrino detector with sensitivity to the anticipated fluxes, and the construction of CTA, a ground-based gamma ray detecto...
February 21, 1997
There are tantalizing hints that jets, powered by supermassive black holes at the center of active galaxies, are true cosmic proton accelerators. They produce photons of TeV energy, possible higher, and may be the enigmatic source of the highest energy cosmic rays. Photoproduction of neutral pions by accelerated protons on UV light is the source of the highest energy photons, in which most of the bolometric luminosity of the galaxy may be emitted. The case that proton beams p...
August 28, 2002
I discuss recent advances being made in the physics and astrophysics of cosmic rays and cosmic gamma-rays at the highest observed energies as well as the related physics and astrophysics of very high energy cosmic neutrinos. I also discuss the connections between these topics.
February 14, 2023
Understanding the acceleration of Ultra High Energy Cosmic Rays is one of the great challenges of contemporary astrophysics. In this short review, we summarize the general observational constraints on their composition, spectrum and isotropy which indicate that nuclei heavier than single protons dominate their spectra above $\sim 5\,{\rm EeV}$, that they are strongly suppressed above energies $\sim50\,{\rm EeV}$, and that the only significant departure from isotropy is a dipo...
June 3, 2004
It has been speculated earlier that Gamma Ray Bursts are sources of ultrahigh energy cosmic rays. Recently, the search for high energy photons from Gamma Ray Bursts by Milagro group has put limits on the isotropic luminosity of these transient sources in very high energy photons. The implications of the results obtained by Milagro to our understanding of the ultrahigh energy cosmic ray spectrum from these sources have been discussed in the present work.
November 5, 2008
Astrophysical neutrinos can be produced in proton interactions of charged cosmic rays with ambient photon or baryonic fields. Cosmic rays are observed in balloon, satellite and air shower experiments every day, from below 1e9 eV up to macroscopic energies of 1e21 eV. The observation of different photon fields has been done ever since, today with detections ranging from radio wavelengths up to very high-energy photons in the TeV range. The leading question for neutrino astrono...
December 23, 2014
We will review the main channels of gamma ray emission due to the acceleration and propagation of cosmic rays, discussing the cases of both galactic and extra-galactic cosmic rays and their connection with gamma rays observations.