We propose a new method for the estimation of ultra-high energy cosmic ray (UHECR) mass composition from a distribution of their arrival directions. The method employs a test statistic (TS) based on a characteristic deflection of UHECR events with respect to the distribution of luminous matter in the local Universe. Making realistic simulations of the mock UHECR sets, we show that this TS is robust to the presence of galactic and non-extreme extra-galactic magnetic fields and sensitive to the mass composition of events in a set. This allows one to constrain the UHECR mass composition by comparing the TS distribution of a composition model in question with the data TS, and to discriminate between different composition models. While the statistical power of the method depends somewhat on the MF parameters, this dependence decreases with the growth of statistics. The method shows good performance even at GZK energies where the estimation of UHCER mass composition with traditional methods is complicated by a low statistics.
This paper presents a search for correlation in the arrival directions of 2190 neutrino candidate events detected in 2007-2008 by the ANTARES telescope, and 69 ultra-high energy cosmic rays (UHECRs) observed by the Pierre Auger Observatory between January 1st 2004 and December 31st 2009. No significant correlation was found. The corresponding 90% C.L. upper limit on the neutrino flux from each observed UHECR direction (assuming an equal flux from all of them and for $E^{-2}$ energy spectrum) is 4.99$\times10{^{-8}}$ GeV cm$^{-2}$ s$^{-1}$.
The data on arrival directions of ultra-high energy cosmic rays (UHECRs) detected with the Yakutsk array are analyzed. The work is induced by the recent claim of the Pierre Auger collaboration for the significant correlation found between UHECRs and positions of nearby Active Galactic Nuclei (AGN) on the celestial sphere; and no correlation the HiRes collaboration stands for. Conflicting data of four giant arrays concern possible extragalactic sources of UHECRs and appeal to the profound analysis and to the future data from the Telescope Array/Northern Auger Observatory.
The study of ultra-high energy cosmic rays (UHECRs) has recently experienced a jump in statistics as well as improved instrumentation. This has allowed a better sensitivity in searching for anisotropies in the arrival directions of cosmic rays. In this written version of the presentation given by the inter-collaborative "Anisotropy Working Group" at the International Symposium on Future Directions in UHECR physics at CERN in February 2012, we report on the current status for anisotropy searches in the arrival directions of UHECRs.
Modern observatories of ultra-high energy cosmic rays (UHECR) have collected over 10^4 events with energies above 10 EeV, whose arrival directions appear to be nearly isotropically distributed. On the other hand, the distribution of matter in the nearby Universe -- and, therefore, presumably also that of UHECR sources -- is not homogeneous. This is expected to leave an imprint on the angular distribution of UHECR arrival directions, though deflections by cosmic magnetic fields can confound the picture. In this work, we investigate quantitatively this apparent inconsistency. To this end we stud…
We present results of elaborate four-dimensional simulations of the propagation of ultra-high-energy cosmic rays (UHECR), which are based on a realistic astrophysical scenario. The distribution of the arrival directions of the UHECR is found to have a pronounced dipolar anisotropy and rather weak higher-order contributions to the angular power spectrum. This finding agrees well with the recent observation of a dipolar anisotropy for UHECR with arrival energies above 8 EeV by the Pierre Auger Observatory and constitutes an important prediction for other energy ranges and higher-order angular co…
We study the anisotropy in the arrival directions of PAO UHECRs, using the point source correlational angular distance distribution. The result shows that the anisotropy is characterized by one prominent excess region and one void region. The excess region is located near the Centaurus A direction, supporting that the Centaurus A is a promising UHECR source. The void region near the south pole direction may be used to limit the diffuse isotropic background contribution.
High-energy neutrinos are expected to be produced by the interaction of accelerated particles near the acceleration sites. For this reason, it is interesting to search for correlation in the arrival directions of ultra-high energy cosmic rays (UHECRs) and HE neutrinos. We present here the results of a search for correlations between UHECR events measured by the Pierre Auger Observatory and Telescope Array and high-energy neutrino candidate events from IceCube and ANTARES. We perform a cross-correlation analysis, where the angular separation between the arrival directions of UHECRs and neutrino…
The distribution of ultra-high-energy cosmic-ray arrival directions appears to be nearly isotropic except for a dipole moment of order $6 \times (E/10~\mathrm{EeV})$ per cent. Nonetheless, at the highest energies, as the number of possible candidate sources within the propagation horizon and the magnetic deflections both shrink, smaller-scale anisotropies might be expected to emerge. On the other hand, the flux suppression reduces the statistics available for searching for such anisotropies. In this work, we consider two different lists of candidate sources: a sample of nearby starburst galaxi…
Active galactic nuclei (AGN) are considered as one of the most appropriate sources of cosmic rays with energy exceeding $\sim 10^{18}$ 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 car…
Ultrahigh energy cosmic rays (UHECRs) are believed to originate from astrophysical sources, which should trace the large scale structure (LSS) of the universe. On the other hand, the magnetic field in the intergalactic space (IGMF), which also traces the LSS of the universe, deflects the trajectories of the charged UHECRs and spoils the positional correlation of the observed UHECR events with their true sources. To explore this problem, we studied a simulation of the propagation of UHE protons through the magnetized LSS of the universe, reported earlier in Das et al. (2008), in which the IGMF …
We predict the arrival direction distribution of cosmic rays including their deflection in the Galactic magnetic field, for several combinations of source and composition hypotheses: the sources are hard X-ray AGNs or uniformly sample the matter distribution of galaxies, and the composition at the source is pure proton or is the Galactic cosmic ray composition measured by CREAM. We use the regular component of the Jansson-Farrar 2012 model for the GMF and allow for rigidities as low as 2 EeV. We report the correlations of published UHECRs, rescaling event energies so as to reconcile the spectr…
We study the possibility that the $γ$-ray loud active galactic nuclei (AGN) are the sources of ultra-high energy cosmic rays (UHECR), through the correlation analysis of their locations and the arrival directions of UHECR. We use the $γ$-ray loud AGN with $d\le 100 {\rm Mpc}$ from the second Fermi Large Area Telescope AGN catalog and the UHECR data with $E\ge 55 {\rm EeV}$ observed by Pierre Auger Observatory. The distribution of arrival directions expected from the $γ$-ray loud AGN is compared with that of the observed UHECR using the correlational angular distance distribution and the Kolmog…
The arrival directions of ultra-high-energy cosmic rays appear to be approximately isotropically distributed over the whole sky, but the last-generation UHECR detector arrays, the Pierre Auger Observatory (Auger) and the Telescope Array (TA), have detected thousands of events, allowing us to study small deviations from isotropy. So far, Auger has detected a large-scale anisotropy consistent with a $\sim 6.5\%$ dipole moment in the distribution of cosmic rays with $E > 8$~EeV, and both collaborations have reported indications for smaller-scale anisotropies at higher energies. On the other hand,…
The sources of ultrahigh-energy cosmic rays (UHECRs) have been difficult to catch. It was recently pointed out that while sources of UHECR protons exhibit anisotropy patterns that become denser and compressed with rising energy, nucleus-emitting-sources give rise to a cepa stratis (onion-like) structure with layers that become more distant from the source position with rising energy. The peculiar shape of the hot spots from nucleus-accelerators is steered by the competition between energy loss during propagation and deflection on the Galactic magnetic field (GMF). Here, we run a full-blown sim…
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 fiel…
We explore the potential of a future, ultra-high energy cosmic ray (UHECR) experiment, that is able to overcome the limitation of low statistics, to detect anisotropy in the arrival directions of UHECRs. We concentrate on the lower energy range of future instruments (E > 50 EeV), where, if the UHECR source number density is not too low, the sources should be numerous enough to imprint a clustering pattern in the sky, and thus possibly in the UHECR arrival directions. Under these limits, the anisotropy signal should be dominated by the clustering of astrophysical sources per-se in the large-sca…
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 v…
We investigate several aspects of the correlations reported by the Pierre Auger Observatory between the highest energy cosmic rays (UHECRs) and galaxies in the Veron-Cetty Veron (VCV) catalog of AGNs. First, we quantify the extent of the inhomogeneity and impurity of the VCV catalog. Second, we determine how the correlation between the highest energy Auger UHECRs and VCV galaxies is modified when only optically-identified AGNs are used. Finally, we measure the correlation between the published Auger UHECRs and the distribution of matter. Our most important finding is that the correlation betwe…
The propagation trajectories of ultra-high-energy cosmic rays (UHECRs) are inevitably affected by Galactic magnetic field (GMF). Because of the inevitability, the importance of the studies of the propagation in GMF have increased to interpret the results of recent UHECR experiments. This article reviews the effects of GMF to the propagation and arrival directions of UHECRs and introduces recent studies to constrain UHECR sources.
We present a Bayesian hierarchical model which enables a joint fit of the ultra-high-energy cosmic ray (UHECR) energy spectrum and arrival directions within the context of a physical model for the UHECR phenomenology. In this way, possible associations with astrophysical source populations can be assessed in a physically and statistically principled manner. The importance of including the UHECR energy data and detection effects is demonstrated through simulation studies, showing that the effective GZK horizon is significantly extended for typical reconstruction uncertainties. We also verify th…
Observations of cosmic ray arrival directions made with the Pierre Auger Observatory have previously provided evidence of anisotropy at the 99% CL using the correlation of ultra high energy cosmic rays (UHECRs) with objects drawn from the Veron-Cetty Veron catalog. In this paper we report on the use of three catalog independent methods to search for anisotropy. The 2pt-L, 2pt+ and 3pt methods, each giving a different measure of self-clustering in arrival directions, were tested on mock cosmic ray data sets to study the impacts of sample size and magnetic smearing on their results, accounting f…
It is possible that ultra-high energy cosmic rays (UHECRs) are generated by active galactic nuclei (AGNs), but there is currently no conclusive evidence for this hypothesis. Several reports of correlations between the arrival directions of UHECRs and the positions of nearby AGNs have been made, the strongest detection coming from a sample of 27 UHECRs detected by the Pierre Auger Observatory (PAO). However, the PAO results were based on a statistical methodology that not only ignored some relevant information (most obviously the UHECR arrival energies but also some of the information in the ar…
A consequence of Liouville's theorem indicates that the recently observed large scale anisotropy in the arrival direction of Ultra-High-Energy Cosmic Rays (UHECRs) cannot be produced by the Galactic magnetic field, thus this anisotropy already needs to be present outside our Galaxy. But in this case, the observed energy spectrum and composition of UHECRs differs from the one outside of the Milky Way, due to the suppression or the amplification of the UHECR flux from certain directions by the Galactic magnetic field. In this work, we investigate this effect for the case of a dipole and a quadru…
Numerous authors have suggested that the ultra-high energy cosmic rays (UHECR) detected by the Pierre Auger Observatory and other cosmic-ray telescopes may be accelerated in the nuclei, jets or lobes of radio galaxies. Here I focus on stochastic acceleration in the lobes. I show that the requirement that they accelerate protons to the highest observed energies places constraints on the observable properties of radio lobes that are satisfied by a relatively small number of objects within the Greisen-Zat'sepin-Kuzmin (GZK) cutoff; if UHECR are protons and are accelerated within radio lobes, thei…
We report results of the first comprehensive, high resolution study of the deflections of UHECRs using a realistic model of the Galactic magnetic field and extending to sufficiently low rigidities, R = E/Z = 10^18 V, to describe Fe in the UHE energy range or the mixed composition reported by the Pierre Auger Collaboration at the energy of the observed dipole anisotropy. We use the Jansson-Farrar (JF12) model, which has both large scale coherent and a structured random components, and determine deflections for fifteen rigidities from 10^18.0 to 10^20.0 V, for L_coh = 30 pc and 100 pc. We check …
Due to the action of the intervening cosmic magnetic fields, ultra-high energy cosmic rays (UHECRs) can be deflected in such a way as to create clustered energy-ordered filamentary structures in the arrival direction of these particles, the so-called multiplets. In this work we propose a new method based on the spherical wavelet transform to identify multiplets in sky maps containing arrival directions of UHECRs. The method is illustrated in simulations with a multiplet embedded in isotropic backgrounds with different numbers of events. The efficiency of the algorithm is assessed through the c…
We develop the statistical methods for comparing two sets of arrival directions of cosmic rays in which the two-dimensional distribution of arrival directions is reduced to the one-dimensional distributions so that the standard one-dimensional Kolmogorov-Smirnov test can be applied. Then we apply them to the analysis of correlation between the ultra-high energy cosmic rays (UHECR) with energies above $5.7\times10^{19}$ eV, observed by Pierre Auger Observatory (PAO) and Akeno Giant Air Shower Array (AGASA), and the active galactic nuclei (AGN) within the distance 100 Mpc. For statistical test, …
From deflections in galactic and extragalactic magnetic fields energy dependent structures in the arrival directions of ultra-high energy cosmic rays (UHECR) are expected. We propose to characterize these structures by the strength of collimation of energy along the principal axes in selected regions in the sky. While the strength of collimation are indicators of anisotropy in the arrival distribution of UHECR, the orientation of the principal system holds information about the direction of the deflections of UHECR. We discuss the method and present expected limits on the strength of deflectio…
Centaurus B (Cen B) is one of the closest and brightest radio-loud galaxy in the southern sky. This radio galaxy, proposed as a plausible candidate for accelerating ultra-high-energy cosmic rays (UHECRs), is near the highest-energy neutrino event reported (IC35) in the High-Energy Starting Events catalog. Pierre Auger observatory reported the highest energy comic rays during 10 years of collecting data with some of them around this source. In this paper, the analysis of the gamma-ray spectrum and the light curve above 200 MeV is presented with nine years of cumulative Fermi-LAT data around Cen…
Auger data show evidence for a correlation between ultrahigh-energy cosmic rays (UHECRs) and nearby starburst galaxies. This intriguing correlation is consistent with data collected by the Telescope Array, which have revealed a much more pronounced directional ``hot spot'' in arrival directions not far from the starburst galaxy M82. In this work, we assume starbursts are sources of UHECRs and investigate the prospects to use the observed distribution of UHECR arrival directions to constrain Galactic magnetic field models. We show that if the Telescope Array hot spot indeed originates from M82,…
Ultra-high energy cosmic rays (UHECR) above an energy threshold of tens of EeV might undergo only small deflections due to interstellar magnetic fields. Their arrival directions would then point to regions of possible hadronic acceleration processes, which are likely to be also sources of high energy neutrinos. To search for such cosmic accelerators, we present here the first high statistics analysis of directional correlations between neutrino candidates from the IceCube Observatory and UHECR events. Data taken with IceCube in a configuration of 22 strings provided the basis for using publish…
Arrival directions of ultra-high energy cosmic rays (UHECRs) exhibit mainly an isotropic distribution with some small deviations in particular energy bins. In this paper, the Yakutsk array data are tested for circular uniformity of arrival directions in right ascension using 2 methods appropriate for the energy ranges below and above $10^{18}$ eV. No statistically significant deviation from uniformity is found in the arrival directions of cosmic rays (CRs) detected within the observation period 1974--2000.
Pierre Auger observatory reported the distribution of arrival directions of the highest energy cosmic rays. These events were collected in 10 years of operations with declinations between -90$^\circ$ and +45$^\circ$. The IceCube neutrino telescope reported the detection of 82 extraterrestrial neutrinos in the High-Energy Starting Events catalog. The highest-energy neutrino event (IC35) reported in this catalog had an energy of 2004$^{+236}_{-262}$ TeV and its reconstruction was centered at RA=$208.4^\circ$ and DEC=$-55.8^\circ$ (J2000). Being Centaurus A the nearest radio-loud active Galactic …
We studied how the intergalactic magnetic field (IGMF) affects the propagation of super-GZK protons that originate from extragalactic sources within the local GZK sphere. Toward this end, we set up hypothetical sources of ultra-high-energy cosmic-rays (UHECRs), virtual observers, and the magnetized cosmic web in a model universe constructed from cosmological structure formation simulations. We then arranged a set of reference objects mimicking active galactic nuclei (AGNs) in the local universe, with which correlations of simulated UHECR events are analyzed. With our model IGMF, the deflection…
We demonstrate that the UHECRs produced in the nuclear cascade in the jet of Low-Luminosity Gamma-Ray Bursts (LL-GRBs) can describe the UHECR spectrum and composition and, at the same time, the diffuse neutrino flux at the highest energies. The radiation density in the source simultaneously controls the neutrino production and the development of the nuclear cascade, leading to a flux of nucleons and light nuclei describing even the cosmic-ray ankle at $5 \times 10^{18}$ eV. The derived source parameters are consistent with population studies, indicating a baryonic loading factor of about ten. …
We consider the synchrotron emission from electrons out in the Galactic halo bubble region where the Fermi bubble structures reside. Utilising a simple analytical expression for the non-thermal electron distribution and a toy magnetic field model, we simulate polarised synchrotron emission maps at a frequency of 30~GHz. Comparing these maps with observational data, we obtain constraints on the parameters of our toy Galactic halo bubble magnetic field model. Utilising this parameter value range for the toy magnetic field model, we determine the corresponding range of arrival directions and supp…
We present the results of simulations of the ultra-high energy cosmic ray (UHECR) propagation in the Galactic magnetic field (GMF). Different assumptions on the large-scale GMF structure and/or primary particle lead to distinctly different deflection patterns of the highest energy cosmic rays (CR). The GMF modifies the exposure of an UHECR experiment to the extragalactic sky. We estimated these effects for the Pierre Auger experiment. Further forward-tracking studies under plausible UHECR sources scenarios will allow for direct comparison with the observed correlation between the nearby active…
In light of the increasingly heavy UHECR composition at the highest energies, as observed by the Pierre Auger Observatory, the implications of these results on the actual source composition and spectra are investigated. Depending on the maximum energy of the particles accelerated, sources producing hard spectra and/or containing a considerably enhanced heavy component appear a necessary requirement. Consideration is made of two archetypal models compatible with these results. The secondary signatures expected , following the propagation of the nuclear species from source to Earth, are determin…
We use CRPropa 3 to show how the expected cosmogenic neutrino and gamma-ray spectra depend on the maximum energy of ultra-high energy cosmic rays (UHECRs) at their sources, on the spectral index at injection and on the chemical composition of UHECRs. The isotropic diffuse gamma-ray background measured by Fermi/LAT is already close to touching upon a model with co-moving source evolution and with the chemical composition, spectral index and maximum acceleration energy optimized to provide the best fit to the UHECR spectrum and composition measured by the Pierre Auger Collaboration. Additionally…
Telescope Array (TA) has recently published results of nearly nine years of $X_{\mathrm{max}}$ observations providing its highest statistics measurement of ultra high energy cosmic ray (UHECR) mass composition to date for energies exceeding $10^{18.2}$ eV. This analysis measured agreement of observed data with results expected for four different single elements. Instead of relying only on the first and second moments of $X_{\mathrm{max}}$ distributions, we employ a morphological test of agreement between data and Monte Carlo to allow for systematic uncertainties in data and in current UHECR ha…
In this letter, we present an update of a method for analysing arrival directions of ultra-high-energy cosmic rays (UHECRs) above the Greisen--Zatsepin--Kuz'min cut-off with a deep convolutional neural network developed originally in Kalashev, Pshirkov, Zotov (2020). Namely, we introduce energy as another variable employed in the analysis. This allows us to take into account the intrinsic uncertainties in energy of primary cosmic rays present in any experiment, which were not taken into account in the previous study, without any loss of quality of the classifier. We present the architecture of…
In this paper we investigate the possible existence of multi-point correlation in the arrival direction of the UHECR events detected by the High Resolution Fly's Eye (HiRes) stereo detector. Multi-point correlations could result from the deflection of UHECRs by galactic and intergalactic magnetic fields, and the subsequent dispersion of arrival directions from point like sources. The search is performed by calculating the solid angle subtended by the polygon between triplets and quadruplets of events in the HiRes data. The resulting distribution of solid angles is then compared to the cumulati…
Extensive simulations of the ultra-high energy cosmic ray (UHECR) propagation in the Galactic magnetic field (GMF) have been performed, and the results are presented. The use of different available models of the large-scale GMF and/or primary particle assumptions leads to distinctly different deflection patterns of the highest energy cosmic rays (CR). The lensing effects of the Galactic field modify the exposure of an UHECR experiment to the extragalactic sky. To quantify these effects for the Pierre Auger experiment, we performed a correlation analysis of the simulated cosmic ray event sample…
Cosmic rays (CRs) are protons and atomic nuclei that flow into our Solar system and reach the Earth with energies of up to ~10^21 eV. The sources of ultra-high energy cosmic rays (UHECRs) with E >~ 10^19 eV remain unknown, although there are theoretical reasons to think that at least some come from active galactic nuclei (AGNs). One way to assess the different hypotheses is by analysing the arrival directions of UHECRs, in particular their self-clustering. We have developed a fully Bayesian approach to analyzing the self-clustering of points on the sphere, which we apply to the UHECR arrival d…
Radio galaxies are intensively discussed as the sources of cosmic rays observed above about 3 EeV, called ultra-high-energy cosmic rays (UHECRs). Here, the key issues from a recent investigation are summed up, where the individual characteristics of radio galaxies, as well as the impact by the extragalactic magnetic-field structures up to a distance of 120 Mpc has been taken into account. It is shown that the average contribution of radio galaxies taken over a very large volume cannot explain the observed features of UHECRs measured at Earth. However, we obtain excellent agreement with the spe…
We analyze the correlation of the positions of gamma-ray sources in the Fermi Large Area Telescope First Source Catalog (1FGL) and the First LAT Active Galactic Nuclei (AGN) Catalog (1LAC) with the arrival directions of ultra-high-energy cosmic rays (UHECRs) observed with the Pierre Auger Observatory, in order to investigate the origin of UHECRs. We find that Galactic sources and blazars identified in the 1FGL are not significantly correlated with UHECRs, while the 1LAC sources display a mild correlation (2.6 sigma level) on a ~2.4 degree angular scale. When selecting only the 1LAC AGNs closer…
Understanding the origins of ultrahigh energy cosmic rays (UHECRs) - which reach energies in excess of $10^{20}~{\rm eV}$ - stretches particle acceleration physics to its very limits. In this review, we discuss how such energies can be reached, using general arguments that can often be derived on the back of an envelope. We explore possible particle acceleration mechanisms, with special attention paid to shock acceleration. Informed by the arguments derived, we discuss where UHECRs might come from and which classes of powerful astrophysical objects could be UHECR sources; generally, we favour …
The Pierre Auger Observatory is the world's largest operating detection system for the observation of ultra high energy cosmic rays (UHECRs). The detector allows detailed measurements of their energy spectrum, mass composition and arrival directions of primary cosmic rays in the energy range above $10^{17}$ eV. The data collected at the Observatory over the last decade show the suppression of the cosmic ray flux at energies above $4\times10^{19}$ eV. However, it is still unclear if this suppression is caused by the propagation of cosmic rays or rather by energy limitation of their sources. The…
Active galactic nuclei (AGNs) are considered to be one of the most appropriate sources of ultra high energy cosmic rays (UHECRs, $E \gtrsim 10^{18} \mathrm{~eV}$). Radiogalaxy Virgo A (M87) in the centre of a cluster of galaxies Virgo Cluster (VC) can be a prominent source of UHECRs. We investigate the possible contribution of Virgo A and the VC to the flux of events with trans-GZK energies - extremely high energy cosmic rays (EHECRs) - from the recent Auger and Telescope Array (TA) data sets ($E > 52 \mathrm{~EeV}$ and $E > 57 \mathrm{~EeV}$, respectively). We simulate EHECR propagation from …
