Observational Validation of Cosmic Ray Acceleration Hypothesis

Physica Scripta

Some general features of cosmic ray acceleration are summarized along with some inferences that can be drawn concerning the origin of the UHE component. The UHE luminosity density is found to be similar to that derived for GeV cosmic rays and its slope suggests a distinct origin. Reports of clustering on small angular scale, if confirmed, would rule out most proposed source models. More generally, it is argued that the highest energy particles can only be accelerated in sites that can induce an EMF E > ∼ 3 × 10 20 V and an associated power L min > ∼ E 2 /Z ∼ 10 39 W, where Z is the characteristic, electrical impedance, typically < ∼ 100Ω. Shock acceleration, unipolar induction and magnetic flares are the three most potent, observed, acceleration mechanisms and radio jet termination shocks, γ-ray blast waves, dormant black holes in galactic nuclei and magnetars are the least implausible, "conventional" manifestations of these mechanisms that have been invoked to explain the UHE cosmic rays. Each of these models presents problems and deciding between these and "exotic" origins for UHE cosmic rays, including those involving new particles or defects will require improved statistical information on the energies, arrival times and directions, as should be provided by the Auger project.

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019), 2019

Physics Reports, 2013

The accelerating expansion of the universe is the most surprising cosmological discovery in many decades, implying that the universe is dominated by some form of "dark energy" with exotic physical properties, or that Einstein's theory of gravity breaks down on cosmological scales. The profound implications of cosmic acceleration have inspired ambitious experimental efforts to measure the history of expansion and growth of structure with percent-level precision or higher. We review in detail the four most well established methods for making such measurements: Type Ia supernovae, baryon acoustic oscillations (BAO), weak gravitational lensing, and galaxy clusters. We pay particular attention to the systematic uncertainties in these techniques and to strategies for controlling them at the level needed to exploit "Stage IV" dark energy facilities such as BigBOSS, LSST, Euclid, and WFIRST. We briefly review a number of other approaches including redshift-space distortions, the Alcock-Paczynski test, and direct measurements of H_0. We present extensive forecasts for constraints on the dark energy equation of state and parameterized deviations from GR, achievable with Stage III and Stage IV experimental programs that incorporate supernovae, BAO, weak lensing, and CMB data. We also show the level of precision required for other methods to provide constraints competitive with those of these fiducial programs. We emphasize the value of a balanced program that employs several of the most powerful methods in combination, both to cross-check systematic uncertainties and to take advantage of complementary information. Surveys to probe cosmic acceleration produce data sets with broad applications, and they continue the longstanding astronomical tradition of mapping the universe in ever greater detail over ever larger scales.

Reports on Progress in Physics, 2009

Theoretical approaches to explaining the observed acceleration of the universe are reviewed. We briefly discuss the evidence for cosmic acceleration, and the implications for standard General Relativity coupled to conventional sources of energy-momentum. We then address three broad methods of addressing an accelerating universe: the introduction of a cosmological constant, its problems and origins; the possibility of dark energy, and the associated challenges for fundamental physics; and the option that an infrared modification of general relativity may be responsible for the large-scale behavior of the universe.

2009

We discuss recent observations of high energy cosmic ray positrons and electrons in the context of hadronic interactions in supernova remnants, the suspected accelerators of galactic cosmic rays. Diffusive shock acceleration can harden the energy spectrum of secondary positrons relative to that of the primary protons and electrons and thus explain the rise in the positron fraction observed by PAMELA above 10 GeV. We normalize the hadronic interaction rate by holding pion decay to be responsible for the gamma-rays detected by HESS from some SNRs. By simulating the spatial and temporal distribution of SNRs in the Galaxy according to their known statistics, we are able to then fit the electron (plus positron) energy spectrum measured by Fermi. It appears that IceCube has good prospects for detecting the hadronic neutrino fluxes expected from nearby SNRs. PACS numbers: 98.70.Sa, 96.50.sb, 98.58.Mj arXiv:0909.4060v2 [astro-ph.HE]

Annual Review of Nuclear and Particle Science, 2009

The discovery that the cosmic expansion is accelerating has been followed by an intense theoretical and experimental response in physics and astronomy. The discovery implies that our most basic notions about how gravity work are violated on cosmological distance scales.

arXiv: High Energy Astrophysical Phenomena, 2020

We present six case studies from a broad mass range ($1 - 10^9$ $M_\odot$) of astrophysical objects, each of which exhibit signs of jets and emit intense high energy gamma rays ($&gt;10$ GeV). Many of these objects also emit spatially identifiable ultra high energy cosmic rays (UHECRs). In all cases it is found that wakefield acceleration (WFA) explains both the global properties and details. For blazars, we also explain the temporal structure of these signals, which includes neutrinos, and the correlations in their &quot;bursts&quot; and anti-correlation in flux and index. Blazars ($\sim 10^9$ $M_\odot$), radio galaxies ($\sim 10^8\, M_{\odot}$), Seyfert galaxies ($\sim 10^6 \,M_{\odot}$), starburst galaxies ($\sim 10^{3}\, M_{\odot}$), down to microquasars ($1 \sim 10$ $M_\odot$) interestingly exhibit the same physics since the nature of the accretion and acceleration is independent of the mass, aside from maximum values. It is possible to accelerate electrons to energies much gre...

Astronomy & Astrophysics, 2013

Context. Observation of Balmer lines from the region around the forward shock of supernova remnants may provide precious information on the shock dynamics and on the efficiency of particle acceleration at the shock. Aims. We calculate the Balmer line emission and the shape of the broad Balmer line for parameter values suitable for SNR 0509-67.5, as a function of the cosmic ray acceleration efficiency and of the level of thermal equilibrium between electrons and protons behind the shock. This calculation aims to use the width of the broad Balmer line emission to infer the cosmic ray acceleration efficiency in this remnant. Methods. We use the recently developed nonlinear theory of diffusive shock acceleration in the presence of neutrals. The semianalytical approach that we developed includes a description of magnetic field amplification as due to resonant streaming instability, the dynamical reaction of both accelerated particles and turbulent magnetic field on the shock, and all channels of interaction between neutral atoms and background plasma that change the shock dynamics. Results. We achieve a quantitative assessment of the CR acceleration efficiency in SNR 0509-67.5 as a function of the shock velocity and different levels of electron-proton thermalization in the shock region. If the shock moves faster than ∼4500 km s -1 , one can conclude that particle acceleration must be taking place with an efficiency of several tens of percent. For lower shock velocity the evidence of particle acceleration becomes less clear because of the uncertainty in the electron-ion equilibrium downstream. We also discuss the role of future measurements of the narrow Balmer line.

The non-linear back reaction of accelerated cosmic rays at the shock fronts, leads to the formation of a smooth precursor with a length scale corresponding to the diffusive scale of the energetic particles. Past works claimed that shocklets could be created in the precursor region of a specific shock width, which might energize few thermal particles to sufficient acceleration and furthermore this precursor region may act as confining large angle scatterer for very high energy cosmic rays. On the other hand, it has been shown that the smoothing of the shock front could lower the acceleration efficiency. These controversies motivated us to investigate numerically by Monte Carlo simulations the particle acceleration efficiency in oblique modified shocks. The results show flatter spectra compared to the spectra of the pressumed sharp discontinuity shock fronts. The findings are in accordance with theoretical predictions, since the scattering inside the precursor confines high energy par...

The Advanced Composition Explorer Mission, 1998

We summarize our model of galactic cosmic-ray (GCR) origin and acceleration, wherein a mixture of interstellar and/or circumstellar gas and dust is accelerated by a supernova remnant (SNR) blast wave. A detailed analysis of observed GCR abundances , combined with the knowledge that many refractory elements known to be locked in grains in the interstellar medium (ISM) are abundant in cosmic rays, has lead us to revive an old suggestion (Epstein, 1980) that charged dust grains can be shock accelerated. Here, we outline results (presented more completely in Ellison et al., 1997) from a nonlinear shock model which includes (i) the direct acceleration of interstellar gas-phase ions, (ii) a simplified model for the direct acceleration of weakly charged grains to ∼100 keV amu −1 energies, simultaneously with the acceleration of the gas ions, (iii) the energy losses of grains colliding with the ambient gas, (iv) the sputtering of grains, and (v) the simultaneous acceleration of the sputtered ions to TeV energies. We show that the model produces GCR source abundance enhancements of the volatile, gas-phase elements, which are an increasing function of mass, as well as a net, mass independent, enhancement of the refractory, grain elements over protons, consistent with cosmic-ray observations. The GCR 22 Ne and C excesses may also be accounted for in terms of the acceleration of 22 Ne-C-enriched pre-SN Wolf-Rayet star wind material surrounding the most massive supernovae. The O excess seen in cosmic rays probably cannot be interpreted in terms of W-R star nucleosynthesis, but is easily accounted for in our model since 15 to 20% of O is trapped in grain cores and this O will be preferentially accelerated. We have expanded the parameter range explored in to lower shock speeds and higher maximum cosmic-ray energies and find similar fits to the H/He ratio and the cosmic-ray source spectra.