High energy electromagnetic cascades in extragalactic space: physics and features

Using the analytic modeling of the electromagnetic cascades compared with more precise numerical simulations we describe the physical properties of electromagnetic cascades developing in the universe on CMB and EBL background radiations. A cascade is initiated by very high energy photon or electron and the remnant photons at large distance have two-component energy spectrum, ∝E⁻² (∝E^−1.9 in numerical simulations) produced at cascade multiplication stage, and ∝E^−3/2 from Inverse Compton electron cooling at low energies. The most noticeable property of the cascade spectrum in analytic modeling is 'strong universality', which includes the standard energy spectrum and the energy density of the cascade ωcas as its only numerical parameter. Using numerical simulations of the cascade spectrum and comparing it with recent Fermi LAT spectrum we obtained the upper limit on ω_cas stronger than in previous works. The new feature of the analysis is "E_max rule". We investigate the dependence of ω_cas on the distribution of sources, distinguishing two cases of universality: the strong and weak ones.

CRPropa 3 - a Public Astrophysical Simulation Framework for Propagating Extraterrestrial Ultra-High Energy Particles

We present the simulation framework CRPropa version 3 designed for efficient development of astrophysical predictions for ultra-high energy particles. Users can assemble modules of the most relevant propagation effects in galactic and extragalactic space, include their own physics modules with new features, and receive on output primary and secondary cosmic messengers including nuclei, neutrinos and photons. In extension to the propagation physics contained in a previous CRPropa version, the new version facilitates high-performance computing and comprises new physical features such as an interface for galactic propagation using lensing techniques, an improved photonuclear interaction calculation, and propagation in time dependent environments to take into account cosmic evolution effects in anisotropy studies and variable sources. First applications using highlighted features are presented as well.

Ultra High Energy Cosmic Rays and Neutrinos

We discuss the production of ultra high energy neutrinos coming from the propagation of ultra high energy cosmic rays and in the framework of top-down models for the production of these extremely energetic particles. We show the importance of the detection of ultra high energy neutrinos that can be a fundamental diagnostic tool to solve the discrepancy in the observed chemical composition of ultra high energy cosmic rays and, at the extreme energies, can unveil new physics in connection with the recent cosmological observations of the possible presence of tensor modes in the fluctuation pattern of the cosmic microwave background.

[arXiv:1603.05886]

Characteristics of Four Upward-pointing Cosmic-ray-like Events Observed with ANITA

First Upper Limits on the Radar Cross Section of Cosmic-Ray Induced Extensive Air Showers

TARA (Telescope Array Radar) is a cosmic ray radar detection experiment colocated with Telescope Array, the conventional surface scintillation detector (SD) and fluorescence telescope detector (FD) near Delta, Utah, U.S.A. The TARA detector combines a 40 kW, 54.1 MHz VHF transmitter and high-gain transmitting antenna which broadcasts the radar carrier over the SD array and within the FD field of view, towards a 250 MS/s DAQ receiver. TARA has been collecting data since 2013 with the primary goal of observing the radar signatures of extensive air showers (EAS). Simulations indicate that echoes are expected to be short in duration (~10 microseconds) and exhibit rapidly changing frequency, with rates on the order of 1 MHz/microsecond. The EAS radar cross-section (RCS) is currently unknown although it is the subject of over 70 years of speculation. A novel signal search technique is described in which the expected radar echo of a particular air shower is used as a matched filter template and compared to waveforms obtained by triggering the radar DAQ using the Telescope Array fluorescence detector. No evidence for the scattering of radio frequency radiation by EAS is obtained to date. We report the first quantitative RCS upper limits using EAS that triggered the Telescope Array Fluorescence Detector.

On ultra high energy cosmic rays and their resultant gamma rays

The Fermi Large Area Telescope (Fermi LAT) collaboration has recently reported on 50 months of measurements of the isotropic Extragalactic Gamma Ray Background (EGRB) spectrum between 100MeV and 820GeV. Ultrahigh Energy Cosmic Ray (UHECR) protons interact with the Cosmic Microwave Background (CMB) photons and produce cascade photons of energies 10MeV-1TeV that contribute to the EGRB flux. We examine seven possible evolution models for UHECRs and find that UHECR sources that evolve as the Star Formation Rate (SFR), medium low luminosity active galactic nuclei type-1 (L=10^43.5erg sec^(−1) in the [0.5-2]KeV band), and BL Lacertae objects (BL Lacs) are the most acceptable given the constraints imposed by the observed EGRB. Other possibilities produce too much secondary γ-radiation. In all cases, the decaying dark matter contribution improves the fit at high energy, but the contribution of still unresolved blazars, which would leave the smallest role for decaying dark matter, may yet provide an alternative improvement. 
The possibility that the entire EGRB can be fitted with resolvable but not-yet-resolved blazars, as recently claimed by Ajello et al. (2015), would leave little room in the EGRB to accommodate γ-rays from extragalactic UHECR production, even for many source evolution rates that would otherwise be acceptable. We find that, under the assumption of UHECRs being mostly protons, there is not enough room for producing extragalactic UHECRs with AGN, GRB, or even SFR source evolution. Sources that evolve as BL Lacs on the other hand, would produce much less secondary γ-radiation and would remain a viable source of UHECRs, provided that they dominate.

[arXiv:1603.04074]

Evidence for a Local "Fog" of Sub-Ankle UHECR

During their propagation through intergalactic space, ultrahigh energy cosmic rays (UHECRs) interact with the background radiation fields. These interactions give rise to energetic electron/positron pairs and photons which in turn feed electromagnetic cascades, resulting in a diffuse gamma-ray background radiation. The gamma-ray flux level generated in this way highly depends upon the UHECR propagation distance, as well as the evolution of their sources with redshift. Recently, the \fermi collaboration has reported that the majority of the total extragalactic gamma-ray flux originates from extragalactic point sources. This posits a stringent upper limit on the diffuse gamma-ray flux generated via UHECR propagation, and subsequently constrains their abundance in the distant Universe. Focusing on the contribution of UHECR at energies below the ankle within a narrow energy band ((1−4)×10^18eV), we calculate the diffuse gamma-ray flux generated through UHECR propagation, normalizing the total cosmic ray energy budget in this band to the measured flux. We find that in order to not overproduce the cascade gamma-ray flux, a local "fog" of UHECR produced by nearby sources must exist, with a possible non-negligible contribution from our Galaxy. Following the assumption that a given fraction of the observed IGRB at 820GeV originates from UHECR, we obtain a constraint on the maximum distance for the majority of their sources. With UHECR above the ankle invariably also contributing to the diffuse gamma-ray backgound, the results presented here are conservative.

Ultrahigh Energy Cosmic Rays and Black Hole Mergers

The recent detection of the gravitational wave source GW150914 by the LIGO collaboration motivates a speculative source for the origin of ultrahigh energy cosmic rays as a possible byproduct of the immense energies achieved in black hole mergers, provided that the black holes have spin as seems inevitable and there are relic magnetic fields and disk debris remaining from the formation of the black holes or from their accretion history. We argue that given the modest efficiency <0.01 required per event per unit of gravitational wave energy release, merging black holes potentially provide an environment for accelerating cosmic rays to ultrahigh energies.

[arXiv:1602.06961]

Energy and flux measurements of ultra-high energy cosmic rays observed during the first ANITA flight

The first flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment recorded 16 radio signals that were emitted by cosmic-ray induced air showers. The dominant contribution to the radiation comes from the deflection of positrons and electrons in the geomagnetic field, which is beamed in the direction of motion of the air shower. For 14 of these events, this radiation is reflected from the ice and subsequently detected by the ANITA experiment at a flight altitude of ∼36 km. In this paper, we estimate the energy of the 14 individual events and find that the mean energy of the cosmic-ray sample is 2.9 × 10¹⁸ eV, which is significantly lower than the previous estimate. By simulating the ANITA flight, we calculate its exposure for ultra-high energy cosmic rays. We estimate for the first time the cosmic-ray flux derived only from radio observations and find agreement with measurements performed at other observatories. In addition, we find that the ANITA data set is consistent with Monte Carlo simulations for the total number of observed events and with the properties of those events.

[doi:10.1016/j.astropartphys.2016.01.001]

The Influence of Magnetic Fields on UHECR Propagation from Virgo A

Active galactic nuclei (AGN) are considered as one of the most appropriate sources of cosmic rays with energy exceeding ∼10¹⁸ eV. Virgo A (M87 or NGC 4486) is the second closest to the Milky Way active galaxy. According to existing estimations it can be a prominent source of ultra high energy cosmic rays (UHECR). However not many events have been registered in the sky region near Virgo A, possibly due to magnetic field influence. In the present work we check UHECR events from the recent sets of data (AUGER, Telescope Array etc.) for possibility of their origination in this AGN. We carried out the simulation of UHECR motion from Virgo A taking into account their deflections in galactic (GMF) as well as extragalactic (EGMF) magnetic fields according to the several latest models. The maps of expected UHECR arrival directions were obtained as a result. It has been found the following: 1) UHECR deflection caused by EGMF is comparable with GMF one, moreover the influence of EGMF sometimes is dominating; 2) effect of EGMF demonstrates obvious asymmetry in the final distribution of expected UHECR arrival directions; 3) the results of simulations depend on chosen GMF model and are still open for the discussion.

[arXiv:1602.01683]

Detection prospects of the TA hotspot by space observatories

n the present-day cosmic ray data, the strongest indication of anisotropy of the ultra-high energy cosmic rays (UHECRs) is the 20-degree hotspot observed by the Telescope Array with the statistical significance of 3.4{\sigma}. In this work, we study the possibility of detection of such a spot by space-based all-sky observatories. We show that if the detected luminosity of the hotspot is attributed to a physical effect and not a statistical fluctuation, the KLYPVE and JEM-EUSO experiments would need to collect ~300 events with E>57 EeV in order to detect the hotspot at the 5{\sigma} confidence level with the 68% probability. We also study the dependence of the detection prospects on the hotspot luminosity.

[arXiv:1601.06363]

An All-Sky Search for Three Flavors of Neutrinos from Gamma-Ray Bursts with the IceCube Neutrino Observatory

We present the results and methodology of a search for neutrinos produced in the decay of charged pions created in interactions between protons and gamma-rays during the prompt emission of 807 gamma-ray bursts (GRBs) over the entire sky. This three-year search is the first in IceCube for shower-like Cherenkov light patterns from electron, muon, and tau neutrinos correlated with GRBs. We detect five low-significance events correlated with five GRBs. These events are consistent with the background expectation from atmospheric muons and neutrinos. The results of this search in combination with those of IceCube's four years of searches for track-like Cherenkov light patterns from muon neutrinos correlated with Northern-Hemisphere GRBs produce limits that tightly constrain current models of neutrino and ultra high energy cosmic ray production in GRB fireballs.

[arXiv:1601.06484]

Constraining pion interactions at very high energies by cosmic ray data

We demonstrate that a substantial part of the present uncertainties in model predictions for the average maximum depth of cosmic ray-induced extensive air showers is related to very high energy pion-air collisions. Our analysis shows that the position of the maximum of the muon production profile in air showers is strongly sensitive to the properties of such interactions. Therefore, the measurements of the maximal muon production depth by cosmic ray experiments provide a unique opportunity to constrain the treatment of pion-air interactions at very high energies and to reduce thereby model-related uncertainties for the shower maximum depth.

[arXiv:1601.06567]

Ultrahigh-Energy Cosmic Rays from the "En Caul" Birth of Magnetars

Rapidly-spinning magnetars can potentially form by the accretion induced collapse of a white dwarf or by neutron star mergers if the equation of state of nuclear density matter is such that two low mass neutron stars can sometimes form a massive neutron star rather than a black hole. In either case, the newly born magnetar is an attractive site for producing ultrahigh-energy cosmic rays (particles with individual energies exceeding 10¹⁸eV; UHECRs). The short-period spin and strong magnetic field are able to accelerate particles up to the appropriate energies, and the composition of material on and around the magnetar may naturally explain recent inferences of heavy elements in UHECRs. We explore whether the small amount of natal debris surrounding these magnetars allows the UHECRs to easily escape. We also investigate the impact on the UHECRs of the unique environment around the magnetar, which consists of a bubble of relativistic particles and magnetic field within the debris. Rates and energetics of UHECRs are consistent with such an origin even though the rates of events that produce rapidly-spinning magnetars remain very uncertain. The low ejecta mass also helps limit the high-energy neutrino background associated with this scenario to be below current IceCube constraints over most of the magnetar parameter space. A unique prediction is that UHECRs may be generated in old stellar environments without strong star formation in contrast to what would be expected for other UHECR scenarios, such as active galactic nuclei or long gamma-ray bursts.

[arXiv:1601.02625]

Proposal of the Electrically Charged Stellar Black Holes as Accelerators of Ultra High Energy Cosmic Rays

A new mechanism for the acceleration of ultra high energy cosmic rays (UHECR) is presented here. It is based on the tunnel-ionization of neutral atoms approaching electrically charged stellar black holes and on the repulsion of the resulting positively charged atomic part by huge, long-range electric fields. Energies above 10¹⁸ eV for these particles are calculated in a simple way by means of this single-shot, all-electrical model. When this acceleration mechanism is combined with the supernova explosions in the galactic halo of the massive runaway stars expelled from the galactic disk, this model predicts nearly the correct values of the measured top energy of the UHECRs and their flux in a specified EeV energy range. It also explains the near isotropy of the arrivals of these energetic particles to Earth, as has been recently measured by the Auger Observatory.

[arXiv:1601.02916]

The sensitivity of past and near-future lunar radio experiments to ultra-high-energy cosmic rays and neutrinos

Various experiments have been conducted to search for the radio emission from ultra-high-energy particles interacting in the lunar regolith. Although they have not yielded any detections, they have been successful in establishing upper limits on the flux of these particles. I present a review of these experiments in which I re-evaluate their sensitivity to radio pulses, accounting for effects which were neglected in the original reports, and compare them with prospective near-future experiments. In several cases, I find that past experiments were substantially less sensitive than previously believed. I apply existing analytic models to determine the resulting limits on the fluxes of ultra-high-energy neutrinos and cosmic rays. In the latter case, I amend the model to accurately reflect the fraction of the primary particle energy which manifests in the resulting particle cascade, resulting in a substantial improvement in the estimated sensitivity to cosmic rays. Although these models are in need of further refinement, in particular to incorporate the effects of small-scale lunar surface roughness, their application here indicates that a proposed experiment with the LOFAR telescope would test predictions of the neutrino flux from exotic-physics models, and an experiment with a phased-array feed on a large single-dish telescope such as the Parkes radio telescope would allow the first detection of cosmic rays with this technique, with an expected rate of one detection per 140 hours.

[arXiv:1601.02980]

A Bayesian analysis of the 69 highest energy cosmic rays detected by the Pierre Auger Observatory

The origins of ultra-high energy cosmic rays (UHECRs) remain an open question. Several attempts have been made to cross-correlate the arrival directions of the UHECRs with catalogs of potential sources, but no definite conclusion has been reached. We report a Bayesian analysis of the 69 events from the Pierre Auger Observatory (PAO), that aims to determine the fraction of the UHECRs that originate from known AGNs in the Veron-Cety & Veron (VCV) catalog, as well as AGNs detected with the Swift Burst Alert Telescope (Swift-BAT), galaxies from the 2MASS Redshift Survey (2MRS), and an additional volume-limited sample of 17 nearby AGNs. The study makes use of a multi-level Bayesian model of UHECR injection, propagation and detection. We find that for reasonable ranges of prior parameters, the Bayes factors disfavour a purely isotropic model. For fiducial values of the model parameters, we report 68% credible intervals for the fraction of source originating UHECRs of 0.09+0.05-0.04, 0.25+0.09-0.08, 0.24+0.12-0.10, and 0.08+0.04-0.03 for the VCV, Swift-BAT and 2MRS catalogs, and the sample of 17 AGNs, respectively.

[arXiv:1601.02305]

Radio detection of high-energy cosmic rays with the Auger Engineering Radio Array (PISA 2015)

The Auger Engineering Radio Array (AERA) is an enhancement of the Pierre Auger Observatory in Argentina. Covering about View the 17km², AERA is the world-largest antenna array for cosmic-ray observation. It consists of more than 150 antenna stations detecting the radio signal emitted by air showers, i.e., cascades of secondary particles caused by primary cosmic rays hitting the atmosphere. At the beginning, technical goals had been in focus: first of all, the successful demonstration that a large-scale antenna array consisting of autonomous stations is feasible. Moreover, techniques for calibration of the antennas and time calibration of the array have been developed, as well as special software for the data analysis. Meanwhile physics goals come into focus. At the Pierre Auger Observatory air showers are simultaneously detected by several detector systems, in particular water-Cherenkov detectors at the surface, underground muon detectors, and fluorescence telescopes, which enables cross-calibration of different detection techniques. For the direction and energy of air showers, the precision achieved by AERA is already competitive; for the type of primary particle, several methods are tested and optimized. By combining AERA with the particle detectors we aim for a better understanding of cosmic rays in the energy range from approximately 0.3 to 10EeV, i.e., significantly higher energies than preceding radio arrays.

[arXiv:1601.00462]

Molecular Bremsstrahlung Radiation at GHz Frequencies in Air

A detection technique for ultra-high energy cosmic rays, complementary to the fluorescence technique, would be the use of the molecular Bremsstrahlung radiation emitted by low-energy ionization electrons left after the passage of the showers in the atmosphere. In this article, a detailed estimate of the spectral intensity of photons at ground level originating from this radiation is presented. The spectral intensity expected from the passage of the high-energy electrons of the cascade is also estimated. The absorption of the photons in the plasma of electrons/neutral molecules is shown to be negligible. The obtained spectral intensity is shown to be 2×10⁻²¹W cm⁻² GHz⁻¹ at 10 km from the shower core for a vertical shower induced by a proton of 10^17.5 eV. In addition, a recent measurement of Bremsstrahlung radiation in air at gigahertz frequencies from a beam of electrons produced at 95 keV by an electron gun is also discussed and reasonably reproduced by the model.

[arXiv:1601.00551]

Maximum entropy analysis of cosmic ray composition

We focus on the primary composition of cosmic rays with the highest energies that cause extensive air showers in the Earth's atmosphere. A way of examining the two lowest order moments of the sample distribution of the depth of shower maximum is presented. The aim is to show that useful information about the composition of the primary beam can be inferred with limited knowledge we have about processes underlying these observations. In order to describe how the moments of the depth of shower maximum depend on the type of primary particles and their energies, we utilize a superposition model. Using the principle of maximum entropy, we are able to determine what trends in the primary composition are consistent with the input data, while relying on a limited amount of information from shower physics. Some capabilities and limitations of the proposed method are discussed. In order to achieve a realistic description of the primary mass composition, we pay special attention to the choice of the parameters of the superposition model. We present two examples that demonstrate what consequences can be drawn for energy dependent changes in the primary composition.

[arXiv:1512.09248]

Ultra-high-energy-cosmic-ray hot spots from tidal disruption events

We consider the possibility that tidal disruption events (TDEs) caused by supermassive black holes (SMBHs) in nearby galaxies can account for the ultra-high-energy cosmic-ray (UHECR) hot spot reported recently by the Telescope Array (TA) and the warm spot by Pierre Auger Observatory (PAO). We describe the expected cosmic-ray signal from a TDE and derive the constraints set by the timescale for dispersion due to intergalactic magnetic fields and the accretion time of the SMBH. We demonstrate that TDEs in M82 can explain the hot spot detected by the TA. Based on data-driven assumptions regarding the SMBH mass function, the luminosity scaling of the TDEs and the mass dependence of their rate, we then analyze the full parameter space of the model to search for consistency with the full-sky isotropic signal. Doing so, we show that TDEs can account for both the TA hot spot and full-sky UHECR observations. Using our model we show that the warm spot in the PAO data in the direction of Centaurus A (Cen A) can also be explained by TDEs. Finally, we show that although both hydrogen and iron nuclei are viable candidates for UHECRs, iron nuclei require smaller intergalactic magnetic fields and are therefore more feasible if TDEs explain the TA and PAO results.

[arXiv:1512.04959]

Extreme BL Lacs: probes for cosmology and UHECR candidates

High-energy observations of extreme BL Lac objects, such as 1ES0229+200 or 1ES 0347-121, recently focused interest both for blazar and jet physics and for the implication on the extragalactic background light and intergalactic magnetic field estimate. Moreover, their enigmatic properties have been interpreted in a scenario in which their primary high- energy output is through a beam of high-energy hadrons. However, despite their possible important role in all these topics, the number of these extreme highly peaked BL Lac objects (EHBL) is still rather small. Aiming at increase their number, we selected a group of EHBL candidates considering those undetected (or only barely detected) by the LAT onboard Fermi and characterized by a high X-ray versus radio flux ratio. We assembled the multi-wavelength spectral energy distribution of the resulting 9 sources, using available archival data of Swift, GALEX, and Fermi satellites, confirming their nature. Through a simple one-zone synchrotron self-Compton model we estimate the expected very high energy flux, finding that in the majority of cases it is within the reach of present generation of Cherenkov arrays or of the forthcoming CTA.

[arXiv:1512.05080]

Surprises from extragalactic propagation of UHECRs

Ultra-high energy cosmic ray experimental data are now of very good statistical significance even in the region of the expected GZK feature. The identification of their sources requires sophisticate analysis of their propagation in the extragalactic space. When looking at the details of this propagation some unforeseen features emerge. We will discuss some of these "surprises".

[arXiv:1512.02314]

A Uniformly Selected, All-Sky Optical AGN catalog, for UHECR Correlation

Studies discerning whether there is a significant correlation between UHECR arrival directions and optical AGN are hampered by the lack of a uniformly selected and complete all-sky optical AGN catalog. To remedy this, we are preparing such a catalog based on the 2MASS Redshift Survey (2MRS), a spectroscopic sample of ∼44,500 galaxies complete to a K magnitude of 11.75 over 91% of the sky. We have analyzed the available optical spectra of these 2MRS galaxies (∼80% of the galaxies), in order to identify the AGN amongst them with uniform criteria. We present a first-stage release of the AGN catalog for the southern sky, based on spectra from the 6dF Galaxy survey and CTIO telescope. Providing a comparably uniform and complete catalog for the northern sky is more challenging because the spectra for the northern galaxies were taken with different instruments.

[arXiv:1512.00688]

Origin of the ankle in the ultra-high energy cosmic ray spectrum and of the extragalactic protons below it

The sharp change in slope of the ultra-high energy cosmic ray (UHECR) spectrum around 10^18.6 eV (the ankle), combined with evidence of a light but extragalactic component near and below the ankle which evolves to intermediate composition above, has proved exceedingly challenging to understand theoretically. We show that for a range of source conditions, photo-disintegration of ultra-high energy nuclei in the region surrounding a UHECR accelerator naturally accounts for the observed spectrum and composition of the entire extragalactic component, which dominates above about 10^17.5 eV. The mechanism has a clear signature in the spectrum and flavors of neutrinos.

[arXiv:1512.00484]

The Galactic magnetic field and its lensing of ultrahigh energy and Galactic cosmic rays

It has long been recognized that magnetic fields play an important role in many astrophysical environments, yet the strength and structure of magnetic fields beyond our solar system have been at best only qualitatively constrained. The Galactic magnetic field in particular is crucial for modeling the transport of Galactic CRs, for calculating the background to dark matter and CMB-cosmology studies, and for determining the sources of UHECRs. This report gives a brief overview of recent major advances in our understanding of the Galactic magnetic field (GMF) and its lensing of Galactic and ultrahigh energy cosmic rays.

[arXiv:1512.00051]

IceCube Constraints on Fast-Spinning Pulsars as High-Energy Neutrino Sources

Relativistic winds of fast-spinning pulsars have been proposed as a potential site for cosmic-ray acceleration from very high energies (VHE) to ultrahigh energies (UHE). We re-examine conditions for high-energy neutrino production, considering the interaction of accelerated particles with baryons of the expanding supernova ejecta and the radiation fields in the wind nebula. We make use of the current IceCube sensitivity in diffusive high-energy neutrino background, in order to constrain the parameter space of the most extreme neutron stars as sources of VHE and UHE cosmic rays. We demonstrate that the current non-observation of 10¹⁸ eV neutrinos put stringent constraints on the pulsar scenario. For a given model, birthrates, ejecta mass and acceleration efficiency of the magnetar sources can be constrained. When we assume a proton cosmic-ray composition and spherical supernovae ejecta, we find that the IceCube limits almost exclude their significant contribution to the observed UHE cosmic ray flux. Furthermore, we consider scenarios where a fraction of cosmic rays can escape from jet-like structures piercing the ejecta, without significant interactions. Such scenarios would enable the production of UHE cosmic rays and help remove the tension between their EeV neutrino production and the observational data.

[arXiv:1511.08518]

Sensitivity of the JEM-EUSO telescope to gravity effects in neutrino-induced air showers

We examine the JEM-EUSO sensitivity to gravity effects in the context of Randall-Sundrum (RS) model with a single extra dimension and small curvature of the metric. Exchanges of reggeized Kaluza-Klein gravitons in the t-channel contribute to the inelastic cross-section for scattering of ultra-high-energy neutrinos off nucleons. Such effects can be detected in deeply penetrating quasi-horizontal air showers induced by interactions of cosmic neutrinos with atmospheric nucleons. For this reason, we calculate the expected number of quasi-horizontal air showers at the JEM-EUSO observatory as a function of two parameters of the RS model.

[arXiv:1511.07196]

Cosmic ray transport and anisotropies to high energies

A model is introduced, in which the irregularity spectrum of the Galactic magnetic field beyond the dissipation length scale is first a Kolmogorov spectrum k^−5/3 at small scales λ=2π/k with k the wave-number, then a saturation spectrum k⁻¹, and finally a shock-dominated spectrum k⁻² mostly in the halo/wind outside the Cosmic Ray disk. In an isotropic approximation such a model is consistent with the Interstellar Medium (ISM) data. With this model we discuss the Galactic Cosmic Ray (GCR) spectrum, as well as the extragalactic Ultra High Energy Cosmic Rays (UHECRs), their chemical abundances and anisotropies. UHECRs may include a proton component from many radio galaxies integrated over vast distances, visible already below 3 EeV.

[arXiv:1511.04229]

The IceCube Neutrino Observatory, the Pierre Auger Observatory and the Telescope Array: Joint Contribution to the 34th International Cosmic Ray Conference (ICRC 2015)

We have conducted three searches for correlations between ultra-high energy cosmic rays detected by the Telescope Array and the Pierre Auger Observatory, and high-energy neutrino candidate events from IceCube. Two cross-correlation analyses with UHECRs are done: one with 39 cascades from the IceCube `high-energy starting events' sample and the other with 16 high-energy `track events'. The angular separation between the arrival directions of neutrinos and UHECRs is scanned over. The same events are also used in a separate search using a maximum likelihood approach, after the neutrino arrival directions are stacked. To estimate the significance we assume UHECR magnetic deflections to be inversely proportional to their energy, with values 3^?, 6^? and 9^? at 100 EeV to allow for the uncertainties on the magnetic field strength and UHECR charge. A similar analysis is performed on stacked UHECR arrival directions and the IceCube sample of through-going muon track events which were optimized for neutrino point-source searches.

[arXiv:1511.02109]

Pierre Auger Observatory and Telescope Array: Joint Contributions to the 34th International Cosmic Ray Conference (ICRC 2015)

Joint contributions of the Pierre Auger Collaboration and the Telescope Array Collaboration to the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands.

[arXiv:1511.02103]

Luminosity of ultrahigh energy cosmic rays and bounds on magnetic luminosity of radio-loud active galactic nuclei

We investigate the production of magnetic flux from rotating black holes in active galactic nuclei (AGNs) and compare it with the upper limit of ultrahigh energy cosmic ray (UHECR) luminosities, calculated from observed integral flux of GeV-TeV gamma rays for nine UHECR AGN sources. We find that, for the expected range of black hole rotations (0.44<a<0.80), the corresponding bounds of theoretical magnetic luminosities from AGNs coincides with the calculated UHECR luminosity. We argue that such result possibly can contribute to constrain AGN magnetic and dynamic properties as phenomenological tools to explain the requisite conditions to proper accelerate the highest energy cosmic rays.

[arXiv:1511.01003]

The origin of IceCube's neutrinos: Cosmic ray accelerators embedded in star forming calorimeters

The IceCube collaboration reports a detection of extra-terrestrial neutrinos. The isotropy and flavor content of the signal, and the coincidence, within current uncertainties, of the 50 TeV to 2 PeV flux and the spectrum with the Waxman-Bahcall bound, suggest a cosmological origin of the neutrinos, related to the sources of ultra-high energy, >10¹⁰ GeV, cosmic-rays (UHECR). The most natural explanation of the UHECR and neutrino signals is that both are produced by the same population of cosmological sources, producing CRs (likely protons) at a similar rate, E²dn/dE∝E⁰, over the [1 PeV,10¹¹ GeV] energy range, and residing in "calorimetric" environments, like galaxies with high star formation rate, in which E/Z<100 PeV CRs lose much of their energy to pion production. A tenfold increase in the effective mass of the detector at ?100 TeV is required in order to significantly improve the accuracy of current measurements, to enable the detection of a few bright nearby starburst "calorimeters", and to open the possibility of identifying the CR sources embedded within the calorimeters, by associating neutrinos with photons accompanying transient events responsible for their generation. Source identification and a large neutrino sample may enable one to use astrophysical neutrinos to constrain new physics models.

[arXiv:1511.00815v1]

Infinite efficiency of collisional Penrose process: Can over-spinning Kerr geometry be the source of ultra-high-energy cosmic rays and neutrinos?

The origin of the ultra-high-energy particles we receive on the Earth from the outer space such as EeV cosmic rays and PeV neutrinos remains an enigma. All mechanisms known to us currently make use of electromagnetic interaction to accelerate charged particles. In this paper we propose a mechanism exclusively based on gravity rather than electromagnetic interaction. We show that it is possible to generate ultra-high-energy particles starting from particles with moderate energies using the collisional Penrose process in an overspinning Kerr spacetime transcending the Kerr bound only by an infinitesimal amount, i.e., with the Kerr parameter a=M(1+?), where we take the limit ?→0⁺. We consider two massive particles starting from rest at infinity that collide at r=M with divergent center-of-mass energy and produce two massless particles. We show that massless particles produced in the collision can escape to infinity with the ultra-high energies exploiting the collisional Penrose process with the divergent efficiency η∼1/√?→∞. Assuming the isotropic emission of massless particles in the center-of-mass frame of the colliding particles, we show that half of the particles created in the collisions escape to infinity with the divergent energies. To a distant observer, ultra-high-energy particles appear to originate from a bright spot which is at the angular location ξ∼2M/r_obs with respect to the singularity on the side which is rotating towards the observer. We show that the anisotropy in emission in the center-of-mass frame, which is dictated by the differential cross-section of underlying particle physics process, leaves a district signature on the spectrum of ultra-high-energy massless particles. Thus, it provides a unique probe into fundamental particle physics.

[arXiv:1510.08205]

Detecting particles with cell phones: the Distributed Electronic Cosmic-ray Observatory

In 2014 the number of active cell phones worldwide for the first time surpassed the number of humans. Cell phone camera quality and onboard processing power (both CPU and GPU) continue to improve rapidly. In addition to their primary purpose of detecting photons, camera image sensors on cell phones and other ubiquitous devices such as tablets, laptops and digital cameras can detect ionizing radiation produced by cosmic rays and radioactive decays. While cosmic rays have long been understood and characterized as a nuisance in astronomical cameras, they can also be identified as a signal in idle camera image sensors. We present the Distributed Electronic Cosmic-ray Observatory (DECO), a platform for outreach and education as well as for citizen science. Consisting of an app and associated database and web site, DECO harnesses the power of distributed camera image sensors for cosmic-ray detection.

[arXiv:1510.07665]

The ultra-high energy cosmic rays image of Virgo A

Arrival directions of ultra-high energy cosmic rays from the direction of ten brightest radio sources lying within 50 Mpc from our Galaxy were studied by using recent models of the largescale Galactic magnetic field. A detailed study, where also small-scale turbulent magnetic field component was implemented, is presented for the radiogalaxy Virgo A. This radiogalaxy is located far from the Galactic plane which leads to a unique image of this UHECR source candidate, if the flux is composed from a mixture of intermediate mass nuclei. We present a method suitable for identifying cosmic rays arriving from this close-by radiogalaxy.

 [arXiv:1509.09033]

Radio Detection of Horizontal Extensive Air Showers with AERA

AERA, the Auger Engineering Radio Array, located at the Pierre Auger Observatory in Malargüe, Argentina measures the radio emission of extensive air showers in the 30-80 MHz frequency range and is optimized for the detection of air showers up to 60° zenith angle. In this contribution the motivation, the status, and first results of the analysis of horizontal air showers with AERA will be presented.

Results from Pion-Carbon Interactions Measured by NA61/SHINE for Improved Understanding of Extensive Air Showers

The interpretation of extensive air shower measurements, produced by ultra-high energy cosmic rays, relies on the correct modeling of the hadron-air interactions that occur during the shower development. The majority of hadronic particles are produced at equivalent beam energies below the TeV range. NA61/SHINE is a fixed target experiment using secondary beams produced at CERN at the SPS. Hadron-hadron interactions have been recorded at beam momenta between 13 and 350 GeV/c with a wide-acceptance spectrometer. In this contribution we present measurements of the spectra of charged pions and the ρ⁰ production in pion-carbon interactions, which are essential for modeling of air showers.