High energy gamma ray counterparts of astrophysical sources of ultra-high energy cosmic rays (original) (raw)
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Cosmic-ray world with gamma-ray astronomy: a wealth on information, an even more open issue
EPJ Web of Conferences, 2015
Since from their discovery in 1912, Cosmic-Rays (CRs) are one of the most debated issues of the high energy astrophysics. Their origin is still a fundamental problem and is the subject of very intense research. Until now, the best candidate sources of Galactic CR component are Supernova Remnants (SNRs) but final proof for the origin of CRs up to the knee can only be obtained through two fundamental signatures, the detection of a clear gamma-ray signature of π 0 decay in Galactic sources and the identification of sources emitting a photon spectrum up to PeV energies. Both indications are quite difficult to obtain. The two gamma-ray satellites, AGILE and Fermi, together with ground telescopes operating in the TeV energy range (HESS, VERITAS and MAGIC), collected a great amount of data from SNRs. In spite of the recent discovery of the neutral pion spectral signature in the SNR W44 spectrum by AGILE (and confirmed by Fermi-LAT), all gamma-ray data collected at GeV and TeV energies for several young and middle-aged SNRs provide interesting challenges to current theoretical models. The emerging view from gamma-ray and particle detection is intriguing and lead to revisit the CR-SNR paradigm, considering also the contribution of other kind of sources.
Galactic and extragalactic sources of very high energy gamma rays
The European Physical Journal Special Topics, 2022
Very high energy γ-rays are one of the most important messengers of the non-thermal Universe. The major motivation of very high energy γ-ray astronomy is to find sources of high energy cosmic rays. Several astrophysical sources are known to accelerate cosmic rays to very high energies under extreme conditions. Very high energy γ-rays are produced at these astrophysical sites or near through interactions of cosmic rays in the surrounding medium close to the sources. Gamma-rays, being neutral, travel in a straight line and thus give us valuable information about the cosmic ray sources and their surroundings. Additionally, very high energy γ-ray astronomy can probe many fundamental physics questions. Ground-based γ-ray astronomy began its journey in 1989 when Whipple telescope detected TeV γ-rays from the Crab, a pulsar wind nebula in the Milky Way. In the last two decades, technological improvements have facilitated the development of the latest generation of very high energy detectors and telescopes which have delivered exciting new results. Until now over two hundred very high energy γ-ray sources, both galactic and extra-galactic has been detected. These observations have provided a deeper insight into a large number of important questions in high energy astrophysics and astroparticle physics. This review article is an attempt to enumerate the most important results in the exciting and rapidly developing field of very high energy γ-ray astronomy.
Astrophysical origins of ultrahigh energy cosmic rays
Reports on Progress in Physics, 2004
In the first part of this review we discuss the basic observational features at the end of the cosmic ray energy spectrum. We also present there the main characteristics of each of the experiments involved in the detection of these particles. We then briefly discuss the status of the chemical composition and the distribution of arrival directions of cosmic rays. After that, we examine the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin (GZK) cutoff, and discuss the level of confidence with which each experiment have detected particles beyond the GZK energy limit. In the second part of the review, we discuss astrophysical environments able to accelerate particles up to such high energies, including active galactic nuclei, large scale galactic wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding galaxies, and gamma ray burst fireballs. In the third part of the review we provide a brief summary of scenarios which try to explain the super-GZK events with the help of new physics beyond the standard model. In the last section, we give an overview on neutrino telescopes and existing limits on the energy spectrum and discuss some of the prospects for a new (multi-particle) astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used to probe new physics beyond the electroweak scale.
PeV gamma rays from interactions of ultra high energy cosmic rays in the Milky Way
Astroparticle Physics, 2012
The PeV gamma ray background produced in the interactions of ultra high energy cosmic rays with the ambient matter and radiations during their propagation in the Milky Way has been calculated in this paper. If the primary ultra high energy cosmic rays are produced from Galactic point sources then those point sources are also emitting PeV gamma rays. We discuss that the detection of galactocentric PeV gamma rays in the future would be a signature of the presence of EeV cosmic accelerators in the Milky Way.
Ultra High Energy Cosmic Rays: Origin and Propagation
Modern Physics Letters A, 2010
We introduce the highest energy cosmic rays and briefly review the powerful astrophysical objects where they could be accelerated. We then introduce the interactions of different cosmic ray particles with the photon fields of the Universe and the formation of the cosmic ray spectra observed at Earth. The last topic is the production of secondary gamma rays and neutrinos in the interactions of the ultrahigh energy cosmic rays.
Secondary nuclear production physics is receiving increased attention given the high-quality measurements of the gamma-ray emissivity of local interstellar gas between ~50 MeV and ~40 GeV, obtained with the Large Area Telescope on board the Fermi space observatory. More than 90% of the gas-related emissivity above 1 GeV is attributed to gamma-rays from the decay of neutral pions formed in collisions between cosmic rays and interstellar matter, with lepton-induced processes becoming increasingly important below 1 GeV. The elementary kinematics of neutral pion production and decay are re-examined in light of two physics questions: does isobaric production follow a scaling behavior? and what is the minimum proton kinetic energy needed to make a gamma-ray of a certain energy formed through intermediate pi0 production? The emissivity spectrum will allow the interstellar cosmic-ray spectrum to be determined reliably, providing a reference for origin and propagation studies as well as inpu...
ON THE ORIGIN OF VERY HIGH ENERGY COSMIC RAYS
Modern Physics Letters A, 2005
We discuss the most recent developments in our understanding of the acceleration and propagation of cosmic rays up to the highest energies. In particular we specialize our discussion to three issues: 1) developments in the theory of particle acceleration at shock waves; 2) the transition from galactic to extragalactic cosmic rays; 3) implications of up-to-date observations for the origin of ultra high energy cosmic rays (UHECRs).
Galactic diffuse γ-ray emission at TeV energies and the ultra-high energy cosmic rays
AIP Conference Proceedings, 1997
Using the cosmic ray (CR) data available in the energy interval (10 − 2 × 10 7 ) GeV/particle, we have calculated the profile of the primary γ-ray spectrum produced by the interaction of these CR with thermal nuclei of the ISM. Normalized to the EGRET measurements, this allows an estimate of the galactic diffuse γ-ray background due to intermediate and high energy CR at TeV energies. On the other hand, over the last few years, several particles with energies above 10 20 eV (beyond the Greisen-Zatsepin-Kuzmin cut-off) have been detected. These particles are very likely extragalactic protons originated at distances not greater than 30 − 50 Mpc [e.g., 1]. The propagation of these ultra-high energy protons (UHEP) through the intergalactic medium leads to the development of γ-ray cascades and an ultimate signature at TeV energies. To assess the statistical significance of this γ-ray signature by the UHEP, we have also simulated the development of electromagnetic cascades triggered by the decay of a 10 19 eV π o in the intergalactic medium after an UHEP collision with a cosmic microwave background photon.
Constraints on the local sources of ultra high-energy cosmic rays
Journal of Cosmology and Astroparticle Physics, 2009
Ultra high-energy cosmic rays (UHECRs) are believed to be protons accelerated in magnetized plasma outflows of extra-Galactic sources. The acceleration of protons to ∼ 10 20 eV requires a source power L > 10 47 erg s −1 . The absence of steady sources of sufficient power within the GZK horizon of 100 Mpc, implies that UHECR sources are transient. We show that UHECR "flares" should be accompanied by strong X-ray and γ-ray emission, and that X-ray and γ-ray surveys constrain flares which last less than a decade to satisfy at least one of the following conditions: (i) L > 10 50 erg s −1 ; (ii) the power carried by accelerated electrons is lower by a factor > 10 2 than the power carried by magnetic fields or by > 10 3 than the power in accelerated protons; or (iii) the sources exist only at low redshifts, z ≪ 1. The implausibility of requirements (ii) and (iii) argue in favor of transient sources with L > 10 50 erg s −1 .
High-energy gamma -ray emission from gamma-ray bursts
Astronomy and Astrophysics, 2000
GRBs are nowadays a rather well understood phenomenon in the soft (KeV-MeV) γ-ray energy band, while only a few GRBs have been observed at high photon energies (E γ > ∼ 1 GeV). It is also widely recognized that GRBs accelerate protons to relativistic energies and that dense media are often present nearby the sources. Within this framework and by further adopting Totani's suggestion that GRB events release an amount of energy ∼ 10 54 ∆Ω erg, we compute in detail the high-energy γray flux from the decay of neutral pions produced through the interaction of accelerate protons with nucleons in the surrounding medium. We also take into account the local and intergalactic γ-ray absorption. The presence of magnetic fields around the GRB sources causes the deflection of the accelerated protons and so a temporal spread of the produced high-energy γ-rays with respect to the signal in the soft γ-ray band. Moreover, we analyze the possibility to detect the γ-ray signal in the GeV-TeV energy range by the ARGO detector under construction in Tibet.