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The JEM-EUSO program

JEM-EUSO is an international collaboration for the development of space--based Ultra High Energy Cosmic Ray (UHECR) detectors. The instrument consists of a wide Field Of View (FOV) camera for the detection of the UV light emitted by Extensive Air Showers (EAS) in the atmosphere. Within the JEM-EUSO framework several pathfinders have been developed or are in course of development: EUSO-TA, EUSO-Balloon, EUSO-SPB and Mini-EUSO. For the near future the K-EUSO detector is foreseen to detect cosmic rays from space. In this paper we present the JEM-EUSO project and give an overview of the pathfinders and of their results.

[arXiv:1703.01875]

07.03.2017 Francesco Fenu Arxiv.org (Submitted on 6 Mar 2017)

20.01.2017

A study of photons at ultra high energy using Auger surface detector

We present a new method to derive an upper limit on the ultra-high-energy (UHE) photon flux above a given energy, using the Auger SD events. As previous studies, it takes advantage of the fundamental differences between showers induced by hadrons and showers induced by photons (signal rise time, slope of the Lateral Distribution Function, radius of curvature), but it uses photon shower simulations adapted to the actually observed SD events, on an event-by-event basis. In particular, we find that a limited number of simulations per event allows to reach an upper limit that is very close to the ideal case that would be obtained with an infinite number of simulations. For instance, 10 simulated showers per event are sufficient to reach an upper limit only 10 percent higher than the ideal one. As an illustration, we apply this method to the SD events reconstructed above 55 EeV, which provides an optimized upper limit on the photon flux above 150 EeV, and indicate how this can be easily extended to the lower-energy events, to constrain the photon flux down to much lower energies.

[arXiv:1610.04566]

17.10.2016 Guillaume Decerprit, N. G. Busca, E. Parizot Arxiv.org (Submitted on 14 Oct 2016)

A new method to test the hypothesis of isotropy of the ultrahigh energy cosmic ray flux

We developed a new method in order to detect and quantify a potential anisotropy in the ultrahigh energy cosmic ray flux. The proposed method is a new statistical tool based upon the percolation process that is used in physics to describe the formation of long-range connectivity in random systems. Specifically, we investigate the dynamic of the arrangement of cosmic rays into clusters as a function of the maximum angular separation between the arrival directions of a pair of events. In a first step, we characterize the percolation process and extract the most sensitive observable through Monte-Carlo simulations. We then apply the algorithm to the data taken by the array of surface detectors of the Pierre Auger Observatory up to January 2010. The strongest signal appears at an energy threshold of 56.74 EeV and an angular scale of 4 for which the hypothesis of isotropy of the arrival directions of the highest-energy cosmic rays is rejected at a nearly 90% C.L.

[arXiv:1610.04561]

17.10.2016 Guillaume Decerprit, Benjamin Rouillé d'Orfeuil, Cyril Lachaud Arxiv.org (Submitted on 14 Oct 2016)

Cosmic ray composition measurements and cosmic ray background free gamma-ray observations with Cherenkov telescopes

Muon component of extensive air showers (EAS) initiated by cosmic ray particles carries information on the primary particle identity. We show that the muon content of EAS could be measured in a broad energy range from 10-100 TeV up to ultra-high-energy cosmic ray range using wide field-of-view imaging atmospheric Cherenkov telescopes observing strongly inclined or nearly horizontal EAS from the ground of from high altitude. Cherenkov emission from muons in such EAS forms a distinct component (halo or tail) of the EAS image in the telescope camera. We show that detection of the muon signal could be used to measure composition of the cosmic ray spectrum in the energy ranges of the knee, the ankle and of the Galactic-to-extragalactic transition. It could also be used to veto the cosmic ray background in gamma-ray observations. This technique provides a possibility for up to two orders of magnitude improvement of sensitivity for gamma-ray flux in the energy band above 10 PeV, compared to KASCADE-Grande, and an order-of-magnitude improvement of sensitivity in the multi-EeV energy band, compared to Pierre Auger Observatory.

[arXiv:1610.01794]

10.10.2016 A. Neronov, D.V. Semikoz, Ie.Vovk, R. Mirzoyan Arxiv.org (Submitted on 6 Oct 2016)

The Nature and Origin of Ultra-High Energy Cosmic Ray Particles

We outline two concepts to explain Ultra High Energy Cosmic Rays (UHECRs), one based on radio galaxies and their relativistic jets and terminal hot spots, and one based on relativistic Super-Novae (SNe) or Gamma Ray Bursts (GRBs) in starburst galaxies, one matching the arrival direction data in the South (the radio galaxy Cen A) and one in the North (the starburst galaxy M82). Ubiquitous neutrino emission follows accompanied by compact TeV photon emission, detectable more easily if the direction is towards Earth. The ejection of UHECRs is last. We have observed particles up to ZeV, neutrinos up to PeV, photons up to TeV, 30 - 300 Hz GW events, and hope to detect soon of order Hz to mHz GW events. Energy turnover in single low frequency GW events may be of order 10^63 erg. How can we further test these concepts? First of all by associating individual UHECR events, or directional groups of events, with chemical composition in both the Telescope Array (TA) Coll. and the Auger Coll. data. Second by identifying more TeV to PeV neutrinos with recent SMBH mergers. Third by detecting the order < mHz GW events of SMBH binaries, and identifying the galaxies host to the stellar BH mergers and their GW events in the range up to 300 Hz. Fourth by finally detecting the formation of the first generation of SMBHs and their mergers, surely a spectacular discovery.

[arXiv:1610.00944]

10.10.2016 Peter L. Biermann, Laurentiu I. Caramete, Federico Fraschetti, Laszlo A. Gergely, Benjamin C. Harms, Emma Kun, Jon Paul Lundquist, Athina Meli, Biman B. Nath, Eun-Suk Seo, Todor Stanev, Julia Becker Tjus Arxiv.org (Submitted on 4 Oct 2016)

LIC and LID considerations in the design and implementation of the MEMS laser pointing mechanism for the EUSO UV laser altimeter

The EUSO (Extreme Universe Space Observatory) project is developing a new mission concept for the scientific research of Ultra High Energy Cosmic Rays (UHECRs) from space. The EUSO wide-field telescope will look down from space onto the Earth night sky to detect UV photons emitted from air showers generated by UHECRs in our atmosphere. In this article we concentrate on the mitigation strategies agreed so far, and in particular on the implementation of a careful early selection and testing of subsystem materials (including optics), design and interfaces of the subsystem and an optimization of the instrument operational concept.

[arXiv:1609.03771]

15.09.2016 Enrico Bozzo, Thomas Burch, Alessandra Ciapponi, Clemens Heese, Arno Hoogerwerf, Nicholas Lan, Andrii Neronov, Vincent Revol, Ross Stanley Arxiv.org (Submitted on 13 Sep 2016)

Air Shower Radio Emission with Energy E0≥1019 eV by Yakutsk Array Data

The paper presents short technical description of Yakutsk Radio Array and some preliminary results obtained from measurements of radio emission at 32 MHz frequency induced by air shower particles with energy E11019 eV. The data obtained at Yakutsk array in 1987-1989 (first set of measurements) and 2009-2014 (new set of measurements). For the first time, at Yakutsk array radio emission from air shower with energy > 1019 eV was registered including the shower with highest energy ever registered at Yakutsk array with energy 21020 eV.

[arXiv:1609.03273]

15.09.2016 S. P. Knurenko, I. S. Petrov Arxiv.org (Submitted on 12 Sep 2016)

Cosmogenic photons strongly constrain UHECR source models

With the newest version of our Monte Carlo code for ultra-high-energy cosmic ray (UHECR) propagation, CRPropa 3, the flux of neutrinos and photons due to interactions of UHECRs with extragalactic background light can be predicted. Together with the recently updated data for the isotropic diffuse gamma-ray background (IGRB) by Fermi LAT, it is now possible to severely constrain UHECR source models. The evolution of the UHECR sources especially plays an important role in the determination of the expected secondary photon spectrum. Pure proton UHECR models are already strongly constrained, primarily by the highest energy bins of Fermi LAT's IGRB, as long as their number density is not strongly peaked at recent times.

[arXiv:1609.03336]

15.09.2016 Arjen van Vliet Arxiv.org (Submitted on 12 Sep 2016)

Measurement of the Muon Production Depths at the Pierre Auger Observatory

The muon content of extensive air showers is an observable sensitive to the primary composition and to the hadronic interaction properties. The Pierre Auger Observatory uses water-Cherenkov detectors to measure particle densities at the ground and therefore is sensitive to the muon content of air showers. We present here a method which allows us to estimate the muon production depths by exploiting the measurement of the muon arrival times at the ground recorded with the Surface Detector of the Pierre Auger Observatory. The analysis is performed in a large range of zenith angles, thanks to the capability of estimating and subtracting the electromagnetic component, and for energies between 1019.2 and 1020 eV.

[arXiv:1609.02498]

09.09.2016 Laura Collica (for the Pierre Auger Collaboration) Arxiv.org (Submitted on 8 Sep 2016)

Results and Perspectives of the Auger Engineering Radio Array

The Auger Engineering Radio Array (AERA) is an extension of the Pierre Auger Cosmic-Ray Observatory. It is used to detect radio emission from extensive air showers with energies beyond 1017 eV in the 3080 MHz frequency band. After three phases of deployment, AERA now consists of more than 150 autonomous radio stations with different spacings, covering an area of about 17 km2. It is located at the same site as other Auger low-energy detector extensions enabling combinations with various other measurement techniques. The radio array allows different technical schemes to be explored as well as cross-calibration of our measurements with the established baseline detectors of the Auger Observatory. We report on the most recent technological developments and give an overview of the experimental results obtained with AERA. In particular, we will present the measurement of the radiation energy, i.e., the amount of energy that is emitted by the air shower in the form of radio emission, and its dependence on the cosmic-ray energy by comparing with the measurement of the the well-calibrated Auger surface detector. Furthermore, we outline the relevance of this result for the absolute calibration of the energy scale of cosmic-ray observatories.

[arXiv:1609.01513]

09.09.2016 Christian Glaser (for the Pierre Auger Collaboration) Arxiv.org (Submitted on 6 Sep 2016)

A roadmap for searching cosmic rays correlated with the extraterrestrial neutrinos seen at IceCube

We have built regions in a Sky map where it should be expected the arrival of 120 EeV ultrahigh energy cosmic rays (UHECR) directionally correlated with the latest astrophysical neutrino tracks observed at IceCube, which are taken as point sources. In order to calculate these arrival directions we have considered contributions to the cosmic rays deflections originated by the galactic and the extragalactic magnetic field, and a UHECR composition compatible with the current expectations. We have used the Jansson-Farrar JF12 model for the Galactic magnetic field and an extragalactic magnetic field strength of 1nG and coherence length of 1Mpc. We observe that the regions outside of the Galactic plane are more strongly correlated with the neutrino tracks than those adjacent to or in it, with the former regions being good candidates to search for excesses, or anisotropies, in the UHECR flux. Additionally, we have focused, as an example, on the region of 150 EeV UHECR arrival directions correlated with the IceCube event 37 located at (l,b)=(137.1,65.8) in the Northern Hemisphere, far away from the Galactic plane, obtaining an angular size 5, being 3 for 200 EeV, and 8 for 120 EeV. The results presented in this paper represent a useful UHECR excess search Sky map guide.

[arXiv:1608.05099]

20.08.2016 J.A. Carpio, A.M. Gago Arxiv.org (Submitted on 17 Aug 2016)

Propagation of Ultra High Energy Cosmic Rays in Extragalactic Magnetic Fields: A view from cosmological simulations

We use the CRPropa code to simulate the propagation of ultra high energy cosmic rays (with energy 1018eV and pure proton composition) through extragalactic magnetic fields that have been simulated with the cosmological ENZO code.We test both primordial and astrophysical magnetogenesis scenarios in order to investigate the impact of different magnetic field strengths in clusters, filaments and voids on the deflection of cosmic rays propagating across cosmological distances. We also study the effect of different source distributions of cosmic rays around simulated Milky-Way like observers. Our analysis shows that the arrival spectra and anisotropy of events are rather insensitive to the distribution of extragalactic magnetic fields, while they are more affected by the clustering of sources within a 50 Mpc distance to observers. Finally, we find that in order to reproduce the observed degree of isotropy of cosmic rays at  EeV energies, the average magnetic fields in cosmic voids must be 0.1 nG, providing limits on the strength of primordial seed fields.

[arXiv:1607.08872]

01.08.2016 Stefan Hackstein, Franco Vazza, Marcus Brueggen, Guenter Sigl, Andrej Dundovic Arxiv.org (Submitted on 29 Jul 2016)

Radio detection of Cosmic-Ray Air Showers and High-Energy Neutrinos

This review provides an introduction to the radio emission by particle cascades, an overview on the various experiments, and explains methods for the radio measurement of air-shower properties. Furthermore, potential applications of the radio technique in high-energy astroparticle physics are discussed. Due to the successful operation of digital radio experiments and due to the improved quantitative understanding of the emission, radio detection is back on the list of promising techniques for extensive air showers. With a threshold of about 100 PeV radio detectors are particularly useful to study the highest-energy galactic cosmic rays and ultra-high-energy extragalactic particles of all types. Various antenna arrays like LOPES, CODALEMA, AERA, LOFAR, and Tunka-Rex have shown that radio measurements can compete in precision with other techniques, in particular for the arrival direction, the energy, and the position of the shower maximum. The scientific potential of the radio technique seems to be maximum in combination with particle detectors, which increases the total accuracy for air-shower measurements. This is crucial for a better separation of different primary particles, like gamma-ray photons, neutrinos, or different types of nuclei. In addition to air-showers the radio technique can be used for particle cascades in dense media. Several pioneering experiments like ARA, ARIANNA, and ANITA are currently searching for cascades induced by ultra-high-energy neutrinos in ice. Moreover, several future projects aim at both, high-energy cosmic-rays and neutrinos. SKA will search for neutrino and cosmic-ray initiated cascades in the lunar regolith and provide unprecedented detail for air-shower measurements. Finally, radio detectors with huge exposure like GRAND, SWORD, or EVA are being considered to study the highest energy cosmic rays and neutrinos.

[arXiv:1607.08781]

01.08.2016 Frank G. Schröder Arxiv.org (Submitted on 29 Jul 2016)

Nuclear Physics Meets the Sources of the Ultra-High Energy Cosmic Rays

We study the implications of nuclear data and models for cosmic-ray astrophysics, which involves the photodisintegration of nuclei up to iron in astrophysical environments. We demonstrate that data on photo-absorption cross sections are sparse in that mass range by screening nuclear databases, such as EXFOR; these cross sections are needed to compute the photodisintegration rates. We also test the prediction power of models, such as TALYS, and find uncertainties of the order of a factor two. If however the radiation fields are strong enough such that the nuclear cascade in the astrophysical source can develop, we find that differences among different models average out -- unless there is a systematic offset in the interaction model. We conclude with an isotope chart describing which information is in principle necessary to describe nuclear interactions, supported by simulating the entire disintegration chain in a gamma-ray burst. We also point out that a first consistency check may be the measurement of the absorption cross section for different isobars.

[arXiv:1607.07989]

29.07.2016 Denise Boncioli, Anatoli Fedynitch, Walter Winter Arxiv.org (Submitted on 27 Jul 2016)

Constraints on ultra-high-energy cosmic ray sources from a search for neutrinos above 10 PeV with IceCube

We report constraints on the sources of ultra-high-energy cosmic ray (UHECR) above 109 GeV, based on an analysis of seven years of IceCube data. This analysis efficiently selects very high energy neutrino-induced events which have deposited energies from 106 GeV to above 1011 GeV. Two neutrino-induced events with an estimated deposited energy of (2.6±0.3)×106 GeV, the highest neutrino energies observed so far, and (7.7±2.0)×105 GeV were detected. The atmospheric background-only hypothesis of detecting these events is rejected at 3.6σ. The hypothesis that the observed events are of cosmogenic origin is also rejected at >99% CL because of the limited deposited energy and the non-observation of events at higher energy, while their observation is consistent with an astrophysical origin. Our limits on cosmogenic neutrino fluxes disfavor the UHECR sources having cosmological evolution stronger than the star formation rate, e.g., active galactic nuclei and γ-ray bursts, assuming proton-dominated UHECRs. Constraints on UHECR sources including mixed and heavy UHECR compositions are obtained for models of neutrino production within UHECR sources. Our limit disfavors a significant part of parameter space for active galactic nuclei and new-born pulsar models.

[arXiv:1607.05886]

21.07.2016 IceCube Collaboration Arxiv.org (Submitted on 20 Jul 2016)

Neutrino, γ-ray and cosmic ray fluxes from the core of the closest radio galaxies

The closest radio galaxies; Centaurus A, M87 and NGC 1275, have been detected from radio wavelengths to TeV γ-rays, and also studied as high-energy neutrino and ultra-high-energy cosmic ray potential emitters. Their spectral energy distributions show a double-peak feature, which is explained by synchrotron self-Compton model. However, TeV γ-ray measured spectra could suggest that very-high-energy γ-rays might have a hadronic origin. We introduce a lepto-hadronic model to describe the broadband spectral energy distribution; from radio to sub GeV photons as synchrotron self-Compton emission and TeV γ-ray photons as neutral pion decay resulting from pγ interactions occurring close to the core. These photo-hadronic interactions take place when Fermi-accelerated protons interact with the seed photons around synchrotron self-Compton peaks. Obtaining a good description of the TeV γ-ray fluxes, firstly, we compute neutrino fluxes and events expected in IceCube detector and secondly, we estimate ultra-high-energy cosmic ray fluxes and event rate expected in Telescope Array, Pierre Auger and HiRes observatories. Within this scenario we show that the expected high-energy neutrinos cannot explain the astrophysical flux observed by IceCube, and the connection with ultra-high-energy cosmic rays observed by Auger experiment around Centaurus A, might be possible only considering a heavy nuclei composition in the observed events.

[arXiv:1607.04633]

20.07.2016 Nissim Fraija, Antonio Marinelli Arxiv.org (Submitted on 15 Jul 2016)

Sensitivity of the space-based CHerenkov from Astrophysical Neutrinos Telescope (CHANT)

Neutrinos with energies in the PeV to EeV range produce upgoing extensive air showers when they interact underground close enough to the surface of the Earth. We study the possibility for detection of such showers with a system of very wide field-of-view imaging atmospheric Cherenkov telescopes, named CHANT for CHerenkov from Astrophysical Neutrinos Telescope, pointing down to a strip below the Earth's horizon from space. We find that CHANT provides sufficient sensitivity for the study of the astrophysical neutrino flux in a wide energy range, from 10~PeV to 10~EeV. A space-based CHANT system can discover and study in detail the cosmogenic neutrino flux originating from interactions of ultra-high-energy cosmic rays in the intergalactic medium.

[arXiv:1606.03629]

14.06.2016 A.Neronov, D.V.Semikoz, L.A.Anchordoqui, J.Adams, A.V.Olinto Arxiv.org (Submitted on 11 Jun 2016)

Multi-PeV Signals from a New Astrophysical Neutrino Flux Beyond the Glashow Resonance

The IceCube neutrino discovery was punctuated by three showers with Eν ~ 1-2 PeV. Interest is intense in possible fluxes at higher energies, though a marked lack of Eν ~ 6 PeV Glashow resonance events implies a spectrum that is soft and/or cutoff below ~few PeV. However, IceCube recently reported a through-going track event depositing 2.6 ± 0.3 PeV. A muon depositing so much energy can imply Eνμ 10 PeV. We show that extending the soft Eν2.6 spectral fit from TeV-PeV data is unlikely to yield such an event. Alternatively, a tau can deposit this much energy, though requiring Eντ ~10x higher. We find that either scenario hints at a new flux, with the hierarchy of νμ and ντ energies suggesting a window into astrophysical neutrinos at Eν~ 100 PeV if a tau. We address implications, including for ultrahigh-energy cosmic-ray and neutrino origins.

[arXiv:1605.08781]

31.05.2016 Matthew D. Kistler, Ranjan Laha (KIPAC, Stanford, SLAC) Arxiv.org (Submitted on 27 May 2016)

Evidence that the maximum electron energy in hotspots of FR II galaxies is not determined by synchrotron cooling

It has been suggested that relativistic shocks in extragalactic sources may accelerate the highest energy cosmic rays. The maximum energy to which cosmic rays can be accelerated depends on the structure of magnetic turbulence near the shock but recent theoretical advances indicate that relativistic shocks are probably unable to accelerate particles to energies much larger than a PeV. We study the hotspots of powerful radiogalaxies, where electrons accelerated at the termination shock emit synchrotron radiation. The turnover of the synchrotron spectrum is typically observed between infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the shock is < TeV for a canonical magnetic field of ~100 micro Gauss. Based on theoretical considerations we show that this maximum energy cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonably large and most of the jet upstream energy goes to non-thermal particles. We test this result by considering a sample of hotspots observed with high spatial resolution at radio, infrared and optical wavelengths.

[arXiv:1605.05125]

18.05.2016 Anabella T. Araudo, Anthony R. Bell, Aidan Crilly, Katherine M. Blundell Arxiv.org (Submitted on 17 May 2016)

Uncertainty from Extrapolation of Cosmic Ray Air Shower Parameters

Recent measurements at the LHC of the p-p total cross section have reduced the uncertainty in simulations of cosmic ray air showers. In particular of the depth of shower maximum, called Xmax. However, uncertainties of other important parameters, in particular the multiplicity and elasticity of high energy interactions, have not improved, and there is a remaining uncertainty due to the total cross section. Uncertainties due to extrapolations from accelerator data, at a maximum energy of  one TeV in the p-p center of mass, to 250 TeV (3×1019 eV in a cosmic ray proton's lab frame) introduce significant uncertainties in predictions of <Xmax>. In this paper we estimate a lower limit on these uncertainties. The result is that the uncertainty in <Xmax> is larger than the difference among the modern models being used in the field. At the full energy of the LHC, which is equivalent to 1×1017 eV in the cosmic ray lab frame, the extrapolation is not as extreme, and the uncertainty is approximately equal to the difference among the models.

[arXiv:1605.05241]

18.05.2016 R.U. Abbasi, G.B. Thomson Arxiv.org (Submitted on 17 May 2016)

New Limits on Extragalactic Magnetic Fields from Rotation Measures

We take advantage of the wealth of rotation measures data contained in the NRAO VLA Sky Survey catalog to derive new, statistically robust, upper limits on the strength of extragalactic magnetic fields. We simulate the extragalactic magnetic field contribution to the rotation measures for a given field strength and correlation length, by assuming that the electron density follows the distribution of Lyman-α clouds. Based on the observation that rotation measures from distant radio sources do not exhibit any trend with redshift, while the extragalactic contribution instead grows with distance, we constrain fields with Jeans’ length coherence length to be below 1.7 nG at the 2σ level, and fields coherent across the entire observable Universe below 0.65 nG. These limits do not depend on the particular origin of these cosmological fields.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.191302

18.05.2016 M. S. Pshirkov, P. G. Tinyakov, and F. R. Urban Phys. Rev. Lett. 116, 191302 – Published 12 May 2016

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 ±0.7 (stat) ± 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.

[arXiv:1605.02564]

11.05.2016 The Pierre Auger Collaboration Arxiv.org (Submitted on 9 May 2016)

Ultrahigh Energy Cosmic Rays: A Galactic Origin?

It is suggested that essentially all of the UHECRs we detect, including those at the highest energy, originate in our Galaxy. It is shown that even if the density of sources decreases with Galactic radius, then the anisotropy and composition can be understood. Inward anisotropy, as recently reported by the Auger collaboration can be understood as drift along the current sheet of UHECRs originating outside the solar circle, as predicted in Kumar and Eichler (2014), while those originating within the solar circle exit the Galaxy at high latitudes.

[arXiv:1604.05721]

22.04.2016 David Eichler, Noemie Globus, Rahul Kumar, Eyal Gavish Arxiv.org (Submitted on 19 Apr 2016)

Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory

The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects related to the angles of incidence of the particles into the detectors. The magnitude of the effect depends upon the zenith angle and state of development of the shower and thus provides a novel observable, (secθ)max, sensitive to the mass composition of cosmic rays above 3×1018 eV. By comparing measurements with predictions from shower simulations, we find for both of our adopted models of hadronic physics (QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass increases slowly with energy, as has been inferred from other studies. However, the mass estimates are dependent on the shower model and on the range of distance from the shower core selected. Thus the method has uncovered further deficiencies in our understanding of shower modelling that must be resolved before the mass composition can be inferred from (secθ)max.

15.04.2016

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, E2 (E1.9 in numerical simulations) produced at cascade multiplication stage, and E3/2 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 ωcas stronger than in previous works. The new feature of the analysis is "Emax rule". We investigate the dependence of ωcas on the distribution of sources, distinguishing two cases of universality: the strong and weak ones.

01.04.2016 V. Berezinsky, O. Kalashev Arxiv.org (Submitted on 13 Mar 2016)

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.

25.03.2016 Rafael Alves Batista, Andrej Dundovic, Martin Erdmann, Karl-Heinz Kampert, Daniel Kuempel, Gero Müller, Guenter Sigl, Arjen van Vliet, David Walz, Tobias Winchen Arxiv.org (Submitted on 23 Mar 2016)

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]

23.03.2016 Roberto Aloisio Arxiv.org (Submitted on 18 Mar 2016)

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

18.03.2016 P.W.Gorham, J.Nam, A.Romero-Wolf, et. al. Arxiv.org (Submitted on 16 Mar 2016)

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.

18.03.2016 R.U. Abbasi, M. Abe, M. Abou Bakr Othman et. al. Arxiv.org (Submitted on 16 Mar 2016)

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]

15.03.2016 Eyal Gavish, David Eichler Arxiv.org (Submitted on 13 Mar 2016)

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 ((14)×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.

14.03.2016 Ruo-Yu Liu, Andrew M. Taylor, Xiang-Yu Wang, Felix A. Aharonian Arxiv.org (Submitted on 10 March 2016)

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]

25.02.2016 Kumiko Kotera, Joseph Silk Arxiv.org (Submitted on 22 Feb 2016)

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]

09.02.2016 H. Schoorlemmer, K. Belov, A. Romero-Wolf, et al. Astroparticle Physics (14 January 2016)

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]

05.02.2016 Oleh Kobzar, Olexandr Sushchov, Bohdan Hnatyk, Volodymyr Marchenko Arxiv.org (Submitted on 4 Feb 2016)

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]

26.01.2016 D. Semikoz, P. Tinyakov, M. Zotov Arxiv.org (Submitted on 24 Jan 2016)

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]

26.01.2016 IceCube Collaboration Submitted to the Astrophysical Journal

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]

26.01.2016 Sergey Ostapchenko, Marcus Bleicher Arxiv.org (Submitted on 25 Jan 2016)

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]

14.01.2016 Anthony L. Piro (Carnegie Observatories), Juna A. Kollmeier (Carnegie Observatories, IAS) submitted for publication in The Astrophysical Journal

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]

14.01.2016 Jose Soto-Manriquez Arxiv.org (Submitted on 12 Jan 2016)

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]

14.01.2016 Justin Bray Arxiv.org (Submitted on 12 Jan 2016)

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]

14.01.2016 Alexander Khanin, Daniel J. Mortlock arXiv.org, Submitted on 11 Jan 2016

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]

DOI: 10.1016/j.nima.2015.08.047
07.01.2016 Frank G. Schröder, for the Pierre Auger Collaboration Nucl. Instr. Meth A

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 2×1021W cm2 GHz1 at 10 km from the shower core for a vertical shower induced by a proton of 1017.5 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]

07.01.2016 I. Al Samarai, C. Berat, O. Deligny, A. Letessier-Selvon, F. Montanet, M. Settimo, P. Stassi submitted to Phys. Rev. D

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]

07.01.2016 Dalibor Nosek, Jan Ebr, Jakub Vícha, Petr Trávníček, Jana Nosková Accepted for publication in Astroparticle Physics

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]

18.12.2015 Daniel N. Pfeffer, Ely D. Kovetz, Marc Kamionkowski ArXiv.org (Submitted on 15 Dec 2015)

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]

18.12.2015 F. Tavecchio, G. Bonnoli Proceedings of the Conference "High-Energy Phenomena and Relativistic Outflows V", held in La Plata, 5-8 October 2015

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]

10.12.2015 Denise Boncioli, Armando di Matteo, Aurelio Grillo, for the Pierre Auger Collaboration Cosmic Ray International Seminar, 14-16 September 2015, Gallipoli, Italy; to be published in Nucl. Phys. B Proc. Suppl

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]

03.12.2015 Ingyin Zaw, Yanping Chen, Glennys R. Farrar Proceedings of The 34th International Cosmic Ray Conference

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 1018.6 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 1017.5 eV. The mechanism has a clear signature in the spectrum and flavors of neutrinos.

[arXiv:1512.00484]

03.12.2015 Glennys R. Farrar, Michael Unger, Luis A. Anchordoqui Contribution to ICRC 2015; Phys. Rev. D 92, 123001 – Published 1 December 2015

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]

02.12.2015 Glennys R. Farrar Invited talk at the Focus Meeting on Scale Free Phenomena at the Honolulu IAU, Aug. 2015.

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]

30.11.2015 Ke Fang, Kumiko Kotera, Kohta Murase, Angela V. Olinto http://arxiv.org/, to be submitted to JCAP

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]

24.11.2015 Stefan Mladenov, Galina Vankova, Roumen Tsenov, Mario Bertaina, Andrea Santangelo for the JEM-EUSO Collaboration http://arxiv.org/

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 k5/3 at small scales λ=2π/k with k the wave-number, then a saturation spectrum k1, and finally a shock-dominated spectrum k2 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]

16.11.2015 P. L. Biermann, L. I. Caramete, A. Meli, B. N. Nath, E.-S. Seo, V. de Souza, J. Becker Tjus proceedings for the "Cosmic Ray Anisotropies" conference, 26-30 January 2015, Bad Honnef, Germany

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 36 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]

11.11.2015 IceCube Collaboration, Pierre Auger Collaboration, Telescope Array Collaboration http://arxiv.org/

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]

11.11.2015 Telescope Array Collaboration, Pierre Auger Collaboration http://arxiv.org/

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]

09.11.2015 C. H. Coimbra-Araújo, R. C. Anjos Phys. Rev. D 92, 103001, Published 2 November 2015

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/dEE0, 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]

09.11.2015 E. Waxman To appear in "Neutrino Astronomy- Current status, future prospects", Eds. T. Gaisser & A. Karle (World Scientific)

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+ϵ), where we take the limit ϵ0+. 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 η1/ϵ. 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 ξ2M/robs 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]

29.10.2015 Mandar Patil, Tomohiro Harada Arxiv.org (Submitted on 28 Oct 2015)

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]

28.10.2015 Justin Vandenbroucke, Silvia Bravo, Peter Karn, Matthew Meehan, Matthew Plewa, Tyler Ruggles, David Schultz, Jeffrey Peacock, Ariel Levi Simons ICRC2015, #691

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]

13.10.2015 Radomír Šmída, Ralph Engel

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.

29.09.2015 Olga Kambeitz for the Pierre Auger Collaboration

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.

24.09.2015 Alexander E. Hervé, for the NA61 Collaboration

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