Propagation of UHECRs in the Universe

The origin, propagation, and mechanisms of acceleration of the ultra-high energy cosmic rays (UHECRs) are not yet well understood. Aiming for a better interpretation of the available experimental data, these data have to be confronted with theoretical models. A realistic simulation of the propagation of UHECRs in the universe should take into account all the relevant energy loss processes due to the interaction with astrophysical backgrounds, as well as the intervening cosmic magnetic fields. Cosmological effects, such as the redshift dependence of the photon backgrounds and the adiabatic expansion of the universe can play an important role in the aforementioned processes. Here we present results of simulations of the propagation of UHECR through the large scale structure of the universe considering cosmological and magnetic field effects simultaneously.Comment: Proceedings of RICAP 2013; 4 pages, 5 figure

Amplification of the Signal-to-Noise Ratio in Cosmic Ray Maps Using the Mexican Hat Wavelet Family

In this work we analyze the effect of smoothing maps containing arrival directions of cosmic rays with a gaussian kernel and kernels of the mexican hat wavelets of orders 1, 2 and 3. The analysis is performed by calculating the amplification of the signal-to-noise ratio for several background patterns (noise) and different number of events coming from a simulated source (signal) for an ideal detector capable of observing the full sky with uniform coverage. We extend this analysis for a virtual observatory with two sites, one in the northern hemisphere, the other in the southern, considering an acceptance law.Comment: Contributions to the 32nd International Cosmic Ray Conference, Beijing, China, August 201

On the Measurement of the Helicity of Intergalactic Magnetic Fields Using Ultra-High-Energy Cosmic Rays

The origin of the first magnetic fields in the Universe is a standing problem in cosmology. Intergalactic magnetic fields (IGMFs) may be an untapped window to the primeval Universe, providing further constrains on magnetogenesis. We demonstrate the feasibility of using ultra-high-energy cosmic rays (UHECRs) to constrain the helicity of IGMFs by performing simulations of cosmic-ray propagation in simple magnetic field configurations. We show that the first harmonic moments of the arrival distribution of UHECRs may be used to measure the absolute value of the helicity and its sign.Comment: 25 pages, 11 figures; published versio

Morphological properties of blazar-induced gamma-ray haloes

At TeV energies and above gamma rays can induce electromagnetic cascades, whose charged component is sensitive to intervening intergalactic magnetic fields (IGMFs). When interpreting gamma-ray measurements in the energy range between a few GeV and hundreds of TeV, one has to carefully account for effects due to IGMFs, which depend on their strength and power spectrum. Therefore, gamma-ray-induced electromagnetic cascades can be used as probes of cosmic magnetism, since their arrival distribution as well as spectral and temporal properties can provide unique information about IGMFs, whose origin and properties are currently poorly understood. In this contribution we present an efficient three-dimensional Monte Carlo code for simulations of gamma-ray propagation. We focus on the effects of different configurations of IGMFs, in particular magnetic helicity and the power spectrum of stochastic fields, on the morphology of the arrival directions of gamma rays, and discuss the prospects for detecting pair haloes around distant blazars.Comment: 8 pages, 7 figures. Proceedings of the 35th International Cosmic Ray Conference (ICRC 2017), Bexco, Busan, South Kore

Detection of Point Sources in Cosmic Ray Maps using the Mexican Hat Wavelet Family

An analysis of the sensitivity of gaussian and mexican hat wavelet family filters to the detection of point sources of ultra-high energy cosmic rays was performed. A source embedded in a background was simulated and the number of events and amplitude of this source was varied aiming to check the sensitivity of the method to detect faint sources with low statistic of events.Comment: Proceedings of the Second International Symposium on Strong Electromagnetic Fields and Neutron Stars (Havana, Cuba, 2011). 6 pages, 4 figure

Cosmogenic gamma-rays and neutrinos constrain UHECR source models

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, the detectable fraction of protons present at the highest energies in UHECRs, for experiments with sensitivities to the single-flavor neutrino flux at $\sim1$ EeV in the range of $\sim 10^{-8}$ - $10^{-10}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$, is shown as a function of the evolution of UHECR sources. Experiments that reach this sensitivity will be able to significantly constrain the proton fraction for realistic source evolution models.Comment: Proc. 35th ICRC, Busan, South Korea, PoS(ICRC2017)56

The Impact of Plasma Instabilities on the Spectra of TeV Blazars

Relativistic jets from blazars are known to be sources of very-high-energy gamma rays (VHEGRs). During their propagation in the intergalactic space, VHEGRs interact with pervasive cosmological photon fields such as the extragalactic background light (EBL) and the cosmic microwave background (CMB), producing electron-positron pairs. These pairs can upscatter CMB/EBL photons to high energies via inverse Compton scattering, thereby continuing the cascade process. This is often used to set limits on intergalactic magnetic fields (IGMFs). However, the picture may change if plasma instabilities, arising due to the interaction of the pairs with the intergalactic medium (IGM), cool down the electrons/positrons faster than inverse Compton scattering. As a consequence, the kinetic energy lost by the pairs to the IGM could cause a hardening in the observed gamma-ray spectrum at energies below $\sim$100 GeV. Here we study several types and models of instabilities and assess their impact for interpreting observations of distant blazars. Our results suggest that plasma instabilities can describe the spectra of some blazars and mimic the effects of IGMFs, depending on parameters such as intrinsic spectrum of the object, the density and temperature of the IGM, and the luminosity of the beam. On the other hand, we find that for our fiducial set of parameters plasma instabilities do not have a major impact on the spectra of some of the blazars studied. Therefore, they may be used for constraining IGMFs.Comment: 14 pages, 8 figures; minor changes to match published versio

Extragalactic Sources and Propagation of UHECRs

With the publicly available astrophysical simulation framework for propagating extraterrestrial UHE particles, CRPropa 3, it is now possible to study realistic UHECR source scenarios including deflections in Galactic and extragalactic magnetic fields in an efficient way. Here we discuss three recent studies that have already been done in that direction. The first one investigates what can be expected in the case of maximum allowed intergalactic magnetic fields. Here is shown that, even if voids contain strong magnetic fields, deflections of protons with energies $\gtrsim 60 \; \text{EeV}$ from nearby sources might be small enough to allow for UHECR astronomy. The second study looks into several scenarios with a smaller magnetization focusing on large-scale anisotropies. Here is shown that the local source distribution can have a more significant effect on the large-scale anisotropy than the EGMF model. A significant dipole component could, for instance, be explained by a dominant source within 5 Mpc distance. The third study looks into whether UHECRs can come from local radio galaxies. If this is the case it is difficult to reproduce the observed low level of anisotropy. Therefore is concluded that the magnetic field strength in voids in the EGMF model used here is too low and/or there are additional sources of UHECRs that were not taken into account in these simulations.Comment: UHECR2016 conference proceedin

VHE Emission from Magnetic Reconnection in the RIAF of SgrA*

The cosmic-ray (CR) accelerator at the galactic centre (GC) is not yet established by current observations. Here we investigate the radiative-inefficient accretion flow (RIAF) of Sagittarius A* (SgrA*) as a CR accelerator assuming acceleration by turbulent magnetic reconnection, and derive possible emission fluxes of CRs interacting within the RIAF (the central $\sim10^{13}$cm). The target environment of the RIAF is modelled with numerical, general relativistic magneto-hydrodynamics (GRMHD) together with leptonic radiative transfer simulations. The acceleration of the CRs is not computed here. Instead, we inject CRs constrained by the magnetic reconnection power of the accretion flow and compute the emission/absorption of $\gamma$-rays due to these CRs interacting with the RIAF, through Monte Carlo simulations employing the {\tt CRPropa 3} code. The resulting very-high-energy (VHE) fluxes are not expected to reproduce the point source HESS J1745-290 as the emission of this source is most likely produced at pc scales. The emission profiles derived here intend to trace the VHE signatures of the RIAF as a CR accelerator and provide predictions for observations of the GC with improved angular resolution and differential flux sensitivity as those of the forthcoming Cherenkov Telescope Array (CTA). Within the scenario presented here, we find that for mass accretion rates $\gtrsim 10^{-7}$M$_\odot$yr$^{-1}$, the RIAF of SgrA* produces VHE fluxes which are consistent with the H.E.S.S. upper limits for the GC and potentially observable by the future CTA. The associated neutrino fluxes are negligible compared with the diffuse neutrino emission measured by the IceCube.Comment: Accepted for publication in the Ap