Ultra High Energy Protons Research Articles

The remarkable microquasar S26: A super-Eddington PeVatron

S26 is an extragalactic microquasar with the most powerful jets ever discovered. They have a kinetic luminosity of $L_ j $. This implies that the accretion power to the black hole should be super-Eddington, of the order of $L_ acc j $. However, the observed X-ray flux of this system indicates an apparent very sub-Eddington accretion luminosity of $L_ X We aim to characterize the nature of S26, explain the system emission, and study the feasibility of super-Eddington microquasars as potential PeVatron sources. We first analyze multi-epoch X-ray observations of S26 obtained with XMM-Newton and model the super-Eddington disk and its wind. We then develop a jet model and study the particle acceleration and radiative processes that occur in shocks generated near the base of the jet and in its terminal region. We find that the discrepancy between the jet and the apparent disk luminosities in S26 is caused by the complete absorption of the disk radiation by the wind ejected from the super-Eddington disk. The non-thermal X-rays are produced near the base of the jet, and the thermal X-rays are emitted in the terminal regions. The radio emission observed with the Australia Telescope Compact Array can be explained as synchrotron radiation produced at the reverse shock in the lobes. We also find that S26 can accelerate protons to PeV energies in both the inner jet and the lobes. The ultra-high energy protons accelerated in the lobes of S26 are injected into the interstellar medium with a total power of $ We conclude that S26 is a super-Eddington microquasar with a dense disk-driven wind that obscures the X-ray emission from the inner disk, and that the supercritical nature of the system allows the acceleration of cosmic rays to PeV energies.

Constraints on the proton fraction of cosmic rays at the highest energies and the consequences for cosmogenic neutrinos and photons

Over the last decade, observations have shown that the mean mass of ultra-high-energy cosmic rays (UHECRs) increases progressively toward the highest energies. However, the precise composition is still unknown and several theoretical studies hint at the existence of a subdominant proton component up to the highest energies. Motivated by the exciting prospect of performing charged-particle astronomy with ultra-high-energy (UHE) protons we quantify the level of UHE-proton flux that is compatible with present multimessenger observations and the associated fluxes of neutral messengers produced in the interactions of the protons. We study this scenario with numerical simulations of two independent populations of extragalactic sources and perform a fit to the combined UHECR energy spectrum and composition observables, constrained by diffuse gamma-ray and neutrino observations. We find that up to of order 10% of the cosmic rays at the highest energies can be UHE protons, although the result depends critically on the selected hadronic interaction model for the air showers. Depending on the maximum proton energy (E max p) and the redshift evolution of sources, the associated flux of cosmogenic neutrinos and UHE gamma rays can significantly exceed the multimessenger signal of the mixed-mass cosmic rays. Moreover, if E max p is above the GZK limit, we predict a large flux of UHE neutrinos above EeV energies that is absent in alternate scenarios for the origin of UHECRs. We present the implications and opportunities afforded by these UHE proton, neutrino and photon fluxes for future multimessenger observations.

Exploring the Emission Mechanisms of Mrk 180 with Long-term X-Ray and γ-Ray Data

Markarian (Mrk) 180 is a BL Lacertae object located at a redshift of 0.045 and is a potential candidate for high-energy cosmic-ray acceleration. We have analyzed the Fermi Large Area Telescope (Fermi-LAT) γ-ray data of Mrk 180 collected over a period of 12.8 yr and found no significant enhancement in the flux from the long-term γ-ray light curve. We have also analyzed Swift X-ray, ultraviolet, and optical, and X-ray Multi-Mirror Mission (XMM-Newton) data to construct the multiwavelength spectral energy distribution (SED). The SED has been modeled with one-zone pure leptonic and lepto-hadronic scenarios to explain the underlying physics of multiwavelength emission. The pure leptonic model and the two lepto-hadronic models, viz., (i) line-of-sight interactions of ultrahigh-energy cosmic rays (UHECRs; E ≳ 1017 eV) with the cosmic background radiation and (ii) the interactions of relativistic protons with the cold protons in the jet, have been compared in our work. Moreover, an earlier study has associated Mrk 180 with the Telescope Array (TA) hotspot of UHECRs at E > 57 EeV. This speculation motivates us to check whether ultrahigh-energy protons and iron nuclei can reach the Earth from Mrk 180. After comparing the results of our simulation with the current observational data, we find that Mrk 180 is unlikely to be a source of the UHECR events contributing to the TA hotspot for conservative strengths of extragalactic magnetic fields.

Can superbubbles accelerate ultrahigh energy protons?

ABSTRACT 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 protons above peta-electronvolt (PeV) energies can be expected. While the external forward shock of the superbubble may account for acceleration of particles up to 100 TeV, internal primary shocks such as supernova remnants expanding in the low density medium or the collective wind termination shock which forms around a young compact cluster provide more favourable channels to accelerate protons up to 1 PeV, and possibly beyond. Under reasonable conditions, clustered supernovae launching powerful shocks into the magnetized wind of a young and compact massive star cluster are found to be the most promising systems to accelerate protons above 10 PeV. On the other hand, stochastic re-acceleration in the strongly turbulent plasma is found to be much less effective than claimed in previous works, with a maximum proton energy of at most a few hundred TeV.

Neutrino beams at ultra high energy proton colliders on the basis of focusing single crystals

The problem of creation of high energy neutrino beams on the basis of modern and future circular proton accelerators with the help of traditional technology seems to be expensive and difficult. In our previous article we proposed a new method for generation of neutrino beams for 6.5 TeV protons at the LHC based on the use of focusing bent single crystals. However, in last years there have been publications devoted to proton colliders with an energy of 50 TeV. This encouraged us to study the possibility of applying of the proposed method to generate neutrino beams at these colliders. In addition, we present some new information for proton energy 6.5 TeV.

Efficiency of centrifugal mechanism in producing PeV neutrinos from active galactic nuclei

A several-step theoretical model is constructed to trace the origin of ultra high energy (UHE) [1−2] PeV neutrinos detected, recently, by the IceCube collaboration. Protons in the AGN magnetosphere, experiencing different gravitational centrifugal force, provide free energy for the parametric excitation of Langmuir waves via a generalized two-stream instability. Landau damping of these waves, outside the AGN magnetosphere, can accelerate protons to ultra high energies. The ultimate source for this mechanism, the Langmuir-Landau-Centrifugal-Drive (LLCD), is the gravitational energy of the compact object. The LLCD generated UHE protons provide the essential ingredient in the creation of UHE neutrinos via appropriate hadronic reactions; protons of energy 1017 eV can be generated in the plasmas surrounding AGN with bolometric luminosities of the order of 1043 ergs s−1. By estimating the diffusive energy flux of extragalactic neutrinos in the energy interval [1−2] PeV, we find that an acceptably small fraction 0.003% of the total bolometric luminosity will suffice to create the observed fluxes of extragalactic ultra-high energy neutrinos.

High Energy electron and proton acceleration by circularly polarized laser pulse from near critical density hydrogen gas target

Relativistic electron rings hold the possibility of very high accelerating rates, and hopefully a relatively cheap and compact accelerator/collimator for ultrahigh energy proton source. In this work, we investigate the generation of helical shaped quasi-monoenergetic relativistic electron beam and high-energy proton beam from near critical density plasmas driven by petawatt-circularly polarized-short laser pulses. We numerically observe the efficient proton acceleration from magnetic vortex acceleration mechanism by using the three dimensional particle-in-cell simulations; proton beam with peak energy 350 MeV, charge ~10nC and conversion efficiency more than 6% (which implies 2.4 J proton beam out of the 40 J incident laser energy) is reported. We detailed the microphysics involved in the ion acceleration mechanism, which requires investigating the role of self-generated plasma electric and magnetic fields. The concept of efficient generation of quasi-monoenergetic electron and proton beam from near critical density gas targets may be verified experimentally at advanced high power – high repetition rate laser facilities e.g. ELI-ALPS. Such study should be an important step towards the development of high quality electron and proton beam.

Constraints on Physical Conditions for the Acceleration on Ultra-high-energy Cosmic Rays in Nearby Active Galactic Nuclei (AGNs) Observed with the Fermi Large Area Telescope

Abstract We investigated the possibility of acceleration of ultra-high-energy cosmic rays (UHECRs) in nearby active galactic nuclei (AGNs) using archival multi-wavelength observational data, and then we constrained their physical conditions, i.e., the luminosity of the synchrotron radiation and the size of the acceleration site. First, we investigated the spatial correlation between the arrival directions of UHECRs and the positions of nearby AGNs in the Fermi third gamma-ray source catalog. We selected 27 AGNs as candidates of accelerators of UHECRs. Then, we evaluated the physical conditions in the acceleration regions of these AGNs via the Pe’er and Loeb method, which uses the peak luminosity of synchrotron radiation and the peak flux ratio of inverse Compton scattering to synchrotron radiation. From the evaluation, we found that six AGNs have the ability to accelerate ultra-high-energy (UHE) protons in the AGN cores. Furthermore, we found that the minimum acceleration size must be more than a few kpc for acceleration of UHE protons in the AGN lobes.

Modeling of Transverse Momentum Spectra for Charged Particles in Proton–Proton Collisions Based on Soft Computing Approaches

ABSTRACTThe transverse momentum (pT) distributions (or spectra) of charged particles produced in high and ultra-high energy proton–proton (pp) collisions are studied by the neuro-fuzzy model. The objective of the present work is developing an Adaptive Neuro-Fuzzy Inference System (ANFIS) for calculating and predicting the transverse momentum spectra of charged particles as a function of pT and the center-of-mass energy (), as well as the modeling of the average transverse momentum ⟨pT⟩ as a function of , i.e., we have proposed and developed two models. The ANFIS models were designed based on available experimental data for = 53 GeV, 200 GeV, 546 GeV, 900 GeV, 1800 GeV, 2360 GeV and 7 TeV. The empirical results from the developed ANFIS models for pT distributions, as well as ⟨pT⟩ for pp collisions are compared with the theoretical ones which are obtained from other models. The comparison results show a great deal of agreement between the available experimental data (up to 7 TeV) and the theoretical ones. At full large hadron collider (LHC) energy ( = 14 TeV), we have predicted the pT spectra and ⟨pT⟩ which also, show a good agreement with different models.

Recent Ultra High Energy neutrino bounds and multimessenger observations with the Pierre Auger Observatory

The overall picture of the highest energy particles produced in the Universe is changing because of measurements made with the Pierre Auger Observatory. Composition studies of cosmic rays point towards an unexpected mixed composition of intermediate mass nuclei, more isotropic than anticipated, which is reshaping the future of the field and underlining the priority to understand composition at the highest energies. The Observatory is competitive in the search for neutrinos of all flavors above about 100 PeV by looking for very inclined showers produced deep in the atmosphere by neutrinos interacting either in the atmosphere or in the Earth’s crust. It covers a large field of view between −85◦ and 60◦ declination in equatorial coordinates. Neutrinos are expected because of the existence of ultra high energy cosmic rays. They provide valuable complementary information, their fluxes being sensitive to the primary cosmic ray masses and their directions reflecting the source positions. We report the results of the neutrino search providing competitive bounds to neutrino production and strong constraints to a number of production models including cosmogenic neutrinos due to ultra high energy protons. We also report on two recent contributions of the Observatory to multimessenger studies by searching for correlations of neutrinos both with cosmic rays and with gravitational waves. The correlations of the directions of the highest energy astrophysical neutrinos discovered with IceCube with the highest energy cosmic rays detected with the Auger Observatory and the Telescope Array revealed an excess that is not statistically significant and is being monitored. The targeted search for neutrinos correlated with the discovery of the gravitational wave events GW150914 and GW151226 with advanced LIGO has led to the first bounds on the energy emitted by black hole mergers in Ultra-High Energy Neutrinos.

Modeling a Kolmogorov-Type Magnetic Field in the Galaxy and its Effect on an Extragalactic Isotropic Flux of Ultra High Energy Cosmic Rays

A model of turbulent galactic magnetic fields was developed in which, the type of turbulence were considered to be Kolmogorov. We tested the effect of this model on an isotropically distributed flux of ultra high energy cosmic ray in the extragalactic space. To do this, a giant Galactic halo (radius of ∼⃒ 100Mpc) was considered. Regular and random components of the Galactic Magnetic Fields were considered to have the mean observed relevant values and also satisfy a Kolmogorov field type. The deviation from isotropy then were calculated considering the propagation of ultra high energy protons in such a magnetic field and results were discussed to show how isotropic is the flux of ultra high energy cosmic rays in the extragalactic space. It is seen that considering an isotropic flux of ultra high energy cosmic rays in the intergalactic space for different choices of galactic magnetic field is not consistence with the distribution of observed ultra high energy events.

Cosmic absorption of ultra high energy particles

This paper summarizes the limits on propagation of ultra high energy particles in the Universe, set up by their interactions with cosmic background of photons and neutrinos. By taking into account cosmic evolution of these backgrounds and considering appropriate interactions we derive the mean free path for ultra high energy photons, protons and neutrinos. For photons the relevant processes are the Breit-Wheeler process as well as the double pair production process. For protons the relevant reactions are the photopion production and the Bethe-Heitler process. We discuss the interplay between the energy loss length and mean free path for the Bethe-Heitler process. Neutrino opacity is determined by its scattering off the cosmic background neutrino. We compute for the first time the high energy neutrino horizon as a function of its energy.

Energy reconstruction of hadron-initiated showers of ultra-high energy cosmic rays

The current methods to determine the primary energy of ultra-high energy cosmic rays (UHECRs) are different when dealing with hadron or photon primaries. The current experiments combine two different techniques, an array of surface detectors and fluorescence telescopes. The latter allow an almost calorimetric measurement of the primary energy. Thus, hadron-initiated showers detected by both type of detectors are used to calibrate the energy estimator from the surface array (usually the interpolated signal at a certain distance from the shower core S(r0)) with the primary energy. On the other hand, this calibration is not feasible when searching for photon primaries since no high energy photon has been unambiguously detected so far. Therefore, pure Monte Carlo parametrizations are used instead.In this work, we present a new method to determine the primary energy of hadron-induced showers in a hybrid experiment based on a technique previously developed for photon primaries. It consists on a set of calibration curves that relate the surface energy estimator, S(r0), and the depth of maximum development of the shower, Xmax, obtained from the fluorescence telescopes. Then, the primary energy can be determined from pure surface information since S(r0) and the zenith angle of the incoming shower are only needed. Considering a mixed sample of ultra-high energy proton and iron primaries and taking into account the reconstruction uncertainties and shower to shower fluctuations, we demonstrate that the primary energy may be determined with a systematic uncertainty below 1% and resolution around 16% in the energy range from 1018.5 to 1019.6eV. Several array geometries, the shape of the energy error distributions and the uncertainties due to the unknown composition of the primary flux have been analyzed as well.

A self-consistent interpretation of the GeV–TeV emission from a distant blazar PKS 1424+240

We propose a scenario for self-consistent interpretation of GeV - TeV spectrum of a distant blazar PKS 1424+240. In this scenario, ultra-high energy (UHE) protons are assumed to exist in the blazar jet and produce gamma rays through synchrotron emission emitted by relativistic protons and pair cascades (resulted from $p\gamma$ interaction); meanwhile, some of these UHE protons may escape from the jet and are injected into intergalactic space. Therefore, we assume that UHE cosmic rays (CR) originate from relativistic protons in the jet and use energy-independent escape timescale to obtain UHECR injection spectrum. Both contributions of gamma rays injected by the source and secondary gamma rays produced in interactions of UHECRs emitted by the blazar with photon background during their propagation through intergalactic space are calculated. Our results show that this scenario is able to reproduce the GeV-TeV spectrum of PKS 1424+240 self-consistently in a broad range of redshifts $0.6<z<1.3$. The required relativistic jet power $L_p\simeq3\times10^{46}\ \rm erg\ s^{-1}$ only moderately depends on the assumed source redshift, while the proton escape timescale (and the injected UHECR luminosity) strongly depends on $z$. We compare the integral TeV fluxes predicted in our scenario with the sensitivity of the planned Cherenkov Telescope Array (CTA), and discuss the implications to future observations.

Near-Threshold Production ofW±,Z0, andH0at a Fixed-Target Experiment at the Future Ultrahigh-Energy Proton Colliders

We outline the opportunities to study the production of the Standard Model bosons,W±,Z0, andH0, at “low” energies at fixed-target experiments based on possible future ultrahigh-energy proton colliders, that is, the High-Energy LHC, the Super proton-proton Collider, and the Future Circular Collider hadron-hadron. These can be indeed made in conjunction with the proposed future colliders designed to reach up tos=100 TeV by using bent crystals to extract part of the halo of the beam which would then impinge on a fixed target. Without disturbing the collider operation, this technique allows for the extraction of a substantial amount of particles in addition to serving for a beam-cleaning purpose. With this method, high-luminosity fixed-target studies at centre-of-mass energies above theW±,Z0, andH0masses,s≃170–300 GeV, are possible. We also discuss the possibility offered by an internal gas target, which can also be used as luminosity monitor by studying the beam transverse shape.

Cosmic PeV neutrinos and the sources of ultrahigh energy protons

The IceCube experiment recently detected the first flux of high-energy neutrinos in excess of atmospheric backgrounds. We examine whether these neutrinos originate from within the same extragalactic sources as ultrahigh-energy cosmic rays. Starting from rather general assumptions about spectra and flavors, we find that producing a neutrino flux at the requisite level through pion photoproduction leads to a flux of protons well below the cosmic-ray data at ~10^18 eV, where the composition is light, unless pions/muons cool before decaying. This suggests a dominant class of accelerator that allows for cosmic rays to escape without significant neutrino yields.

An analysis of Fermi-LAT observations of the outskirts of the Coma cluster of galaxies

We analyse the data from the Fermi-Large Area Telescope in order to search for a ring-like gamma-ray structure around the Coma cluster. The ring-like structure has recently been suggested to be detected with VERITAS at energies higher than 220 GeV and could possibly be associated with an accretion shock. Our analysis of the Fermi data is performed at energies > 100 MeV and we find no detection of this structure in the Fermi data. We derive the 95 per cent upper limit on the flux from the region covering the proposed ring-like structure. The derived upper limit on the flux at > 100 MeV cannot be incorporated with the detection of an accretion shock wave around Coma at the significance of 4.5 sigma by VERITAS at very high energies, if the production mechanism of the gamma-ray emission generates a photon spectrum with a power index of 2 in the broad energy band. The model of gamma-ray emission induced by ultrahigh-energy protons can reconcile the results of the VERITAS and Fermi observations.

Cosmogenic neutrinos and gamma rays

Abstract We describe the photoproduction interactions of ultrahigh energy protons on the universal photon backgrounds and the production of very high-energy neutrinos and γ-rays in such interactions. We compare the production in propagation in the microwave background to that in the extragalactic background light. The propagation of heavy nuclei is discussed only briefly. We show the extreme models for cosmogenic neutrino production and the limits set on them by different experiments.

NEUTRINO AND UHECR SPECTRA FROM MRK 421

We present the neutrino and UHECR spectra obtained from a detailed fitting of the spectral energy distribution (SED) of Mrk 421 (March 2001) using two variations of the leptohadronic model. In particular, while the low-energy component (optical to X-rays) of the SED is fitted by synchrotron emission of primary electrons in both models, the high-energy one (GeV-TeV gamma-rays) is synchrotron emission attributed either to ultra-high energy protons (LHs model) or to secondary electrons produced by the decay of charged pions (LHπ model). In the LHπ case we find that the produced neutrino spectra are sharply peaked at Eν ~ 30 PeV with a peak flux slightly below the IC-40 sensitivity limit for Mrk 421. In the LHs model, on the other hand, the neutrino spectra fall well outside the PeV energy range, but the calculated E ~ 30 EeV — UHECR flux at earth is close to that observed by HiresI, Telescope Array and Pierre Augere experiments.

Long-lived PeV–EeV neutrinos from gamma-ray burst blastwave

Long duration gamma-ray bursts are powerful sources that can accelerate particles to ultrahigh energies. Acceleration of protons in the forward shock of the highly relativistic gamma-ray burst (GRB) blastwave allows PeV-EeV neutrino production by photopion interactions of ultrahigh energy protons with x-ray to optical photons of the GRB afterglow emission. Four different blastwave evolution scenarios are considered: adiabatic and fully radiative blastwaves in a constant density circumburst medium and in a wind environment with the particle density in the wind decreasing inversely proportional to the square of the radius from the center of the burst. The duration of the neutrino flux depends on the evolution of the blastwave and can last up to a day in the case of an adiabatic blastwave in a constant density medium. Neutrino fluxes from the three other blastwave evolution scenarios are also calculated. Diffuse neutrino fluxes calculated using the observed rate of long-duration GRBs are consistent with the recent IceCube upper limit on the prompt GRB neutrino flux below PeV. The diffuse neutrino flux needed to explain the two neutrino events at PeV energies recently detected by IceCube can partially come from the presented GRB blastwave diffuse fluxes. Future observations by IceCube and upcoming huge radio Askaryan experiments will be able to probe the flux models presented here or constrain the GRB blastwave properties.