In this work we evaluate the physical acceptability of relativistic anisotropic spheres modeled b... more In this work we evaluate the physical acceptability of relativistic anisotropic spheres modeled by two polytropic equations of state-with the same newtonian limit-commonly used to describe compact objects in General Relativity. We integrate numerically the corresponding Lane-Emden equation in order to get density, mass and pressure profiles. An ansatz is used for the anisotropic pressure allowing us to have material configurations slightly deviated from isotropic condition. Numerical models are classified in a parameter space according to the number of physical acceptability conditions that they fulfil. We found that the polytropes considering total energy density are more stable than the second type of polytropic EoS.
This paper explored the physical acceptability conditions for anisotropic matter configurations i... more This paper explored the physical acceptability conditions for anisotropic matter configurations in General Relativity. The study considered a generalized polytropic equation of state P = κρ γ +αρ−β for a heuristic anisotropy. We integrated the corresponding Lane-Emden equation for several hundred models and found the parameter-space portion ensuring the physical acceptability of the configurations. Polytropes based on the total energy density are more viable than those with baryonic density, and small positive local anisotropies produce acceptable models. We also found that polytropic configurations where tangential pressures are greater than radial ones are also more acceptable. Finally, convective disturbances do not generate cracking instabilities. Several models emerging from our simulations could represent candidates of astrophysical compact objects.
We sketch an algorithm to generate exact anisotropic solutions starting from a barotropic EoS and... more We sketch an algorithm to generate exact anisotropic solutions starting from a barotropic EoS and setting an ansatz on the metric functions. To illustrate the method, we use a generalization of the polytropic equation of state consisting of a combination of a polytrope plus a linear term. Based on this generalization, we develop two models which are not deprived of physical meaning as well as fulfilling the stringent criteria of physical acceptability conditions. We also show that some relativistic anisotropic polytropic models may have singular tangential sound velocity for polytropic indexes greater than one. This happens in anisotropic matter configurations when the polytropic equation of state is implemented together with an ansatz on the metric functions. The generalized polytropic equation of state is free from this pathology in the tangential sound velocity.
ARTI is a complete framework designed to simulate the signals produced by the secondary particles... more ARTI is a complete framework designed to simulate the signals produced by the secondary particles emerging from the interaction of single, multiple, and even from the complete flux of primary cosmic rays with the atmosphere. These signals are simulated for any particle detector located at any place (latitude, longitude and altitude), including the real-time atmospheric, geomagnetic and detector conditions. Formulated through a sequence of codes written in C++, Fortran, Bash and Perl, it provides an easy-to-use integration of three different simulation environments: MagnetoCosmics, CORSIKA and Geant4. These tools evaluate the geomagnetic field effects on the primary flux and simulate atmospheric showers of cosmic rays and the detectors’ response to the secondary flux of particles. In this work, we exhibit the usage of the ARTI framework by calculating the total expected signal flux at eight selected sites of the Latin American Giant Observatory: a cosmic ray Observatory all over Lati...
For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved qu... more For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above ∼50 EeV are provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second...
The LAGO (Latin American Giant Observatory) observatory is an experiment that spans over Latin Am... more The LAGO (Latin American Giant Observatory) observatory is an experiment that spans over Latin America in a wide range of latitudes that gives different rigidity cut offs for the enter of cosmic rays in the atmosphere. The motivation of the Observatory is to study atmospheric radiation and space weather through the measurement of the secondary emission of low energy cosmic rays at ground level using Water Cherenkov Detectors (WCD). This work presents the contributions of the LAGO collaboration to the 2019 36th ICRC.
arXiv: Instrumentation and Methods for Astrophysics, 2020
The Latin American Giant Observatory (LAGO) is a distributed cosmic ray observatory that spans ov... more The Latin American Giant Observatory (LAGO) is a distributed cosmic ray observatory that spans over Latin America in a wide range of latitudes and altitudes. One of the main goals of LAGO is to study atmospheric radiation and space weather through the measurement of the secondary particles from cosmic ray flux at ground level using Water Cherenkov Detectors (WCD). Thus, due to differences in the local geomagnetic rigidity cut-off affecting the low energy cosmic rays impinging on the atmosphere and the well-known relation between altitude and the development of the extended atmospheric showers, different secondary particle fluxes are expected at each LAGO site. It is therefore crucial for our objectives to be able to determine the expected flux of secondary particles at any place in the World and for any geomagnetic or atmospheric conditions. To characterize the response of a particular LAGO site we developed ARTI, a complete framework intended to simulate the WCD signals produced by...
Contributions of the Pierre Auger Collaboration to the 33rd International Cosmic Ray Conference, ... more Contributions of the Pierre Auger Collaboration to the 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2013
The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of... more The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between $$2\times 10^{17}$$2×1017 and $$2\times 10^{18}$$2×1018 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at $$10^{{17.5}}\, {\mathrm{eV}} $$1017.5eV and $$10^{{18}}\, {\mathrm{eV}} $$1018eV. We find that, for the models to explain the data, an increase in the muon density of $$38\%$$38%$$\pm 4\% (12\%)$$±4%(12%)$$\pm {}^{...
An in-situ calibration of a logarithmic periodic dipole antenna with a frequency coverage of 30 M... more An in-situ calibration of a logarithmic periodic dipole antenna with a frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of a radio station system used for detection of cosmic ray induced air showers at the Engineering Radio Array of the Pierre Auger Observatory, the so-called Auger Engineering Radio Array (AERA). The directional and frequency characteristics of the broadband antenna are investigated using a remotely piloted aircraft carrying a small transmitting antenna. The antenna sensitivity is described by the vector effective length relating the measured voltage with the electric-field components perpendicular to the incoming signal direction. The horizontal and meridional components are determined with an overall uncertainty of 7.4 +0.9 −0.3 % and 10.3 +2.8 −1.7 % respectively. The measurement is used to correct a simulated response of the frequency and directional response of the antenna. In addition, the influence of the ground conductivity and permittivity on the antenna response is simulated. Both have a negligible influence given the ground conditions measured at the detector site. The overall uncertainties of the vector effective length components result in an uncertainty of 8.8 +2.1 −1.3 % in the square root of the energy fluence for incoming signal directions with zenith angles smaller than 60 • .
• An extended rigidity cutoff is calculated under quiet (secular) & transient conditions for the ... more • An extended rigidity cutoff is calculated under quiet (secular) & transient conditions for the geomagnetic field. • Penumbra region is reinterpreted as a probability function of the arrival direction. • The effect of the geomagnetic field in the flux of Galactic Cosmic Rays can be estimated from changes on the flux of secondary particles at ground level.
We present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 ... more We present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 EeV measured using the Pierre Auger Observatory. For the energy bins [4, 8] EeV and E ≥ 8 EeV, the most 4 The Pierre Auger Collaboration significant signal is a dipolar modulation in right ascension at energies above 8 EeV, as previously reported. In this paper we further scrutinize the highest-energy bin by splitting it into three energy ranges. We find that the amplitude of the dipole increases with energy above 4 EeV. The growth can be fitted with a power law with index β = 0.79 ± 0.19. The directions of the dipoles are consistent with an extragalactic origin of these anisotropies at all the energies considered. Additionally we have estimated the quadrupolar components of the anisotropy: they are not statistically significant. We discuss the results in the context of the predictions from different models for the distribution of ultrahigh-energy sources and cosmic magnetic fields.
In this work we evaluate the physical acceptability of relativistic anisotropic spheres modeled b... more In this work we evaluate the physical acceptability of relativistic anisotropic spheres modeled by two polytropic equations of state-with the same newtonian limit-commonly used to describe compact objects in General Relativity. We integrate numerically the corresponding Lane-Emden equation in order to get density, mass and pressure profiles. An ansatz is used for the anisotropic pressure allowing us to have material configurations slightly deviated from isotropic condition. Numerical models are classified in a parameter space according to the number of physical acceptability conditions that they fulfil. We found that the polytropes considering total energy density are more stable than the second type of polytropic EoS.
This paper explored the physical acceptability conditions for anisotropic matter configurations i... more This paper explored the physical acceptability conditions for anisotropic matter configurations in General Relativity. The study considered a generalized polytropic equation of state P = κρ γ +αρ−β for a heuristic anisotropy. We integrated the corresponding Lane-Emden equation for several hundred models and found the parameter-space portion ensuring the physical acceptability of the configurations. Polytropes based on the total energy density are more viable than those with baryonic density, and small positive local anisotropies produce acceptable models. We also found that polytropic configurations where tangential pressures are greater than radial ones are also more acceptable. Finally, convective disturbances do not generate cracking instabilities. Several models emerging from our simulations could represent candidates of astrophysical compact objects.
We sketch an algorithm to generate exact anisotropic solutions starting from a barotropic EoS and... more We sketch an algorithm to generate exact anisotropic solutions starting from a barotropic EoS and setting an ansatz on the metric functions. To illustrate the method, we use a generalization of the polytropic equation of state consisting of a combination of a polytrope plus a linear term. Based on this generalization, we develop two models which are not deprived of physical meaning as well as fulfilling the stringent criteria of physical acceptability conditions. We also show that some relativistic anisotropic polytropic models may have singular tangential sound velocity for polytropic indexes greater than one. This happens in anisotropic matter configurations when the polytropic equation of state is implemented together with an ansatz on the metric functions. The generalized polytropic equation of state is free from this pathology in the tangential sound velocity.
ARTI is a complete framework designed to simulate the signals produced by the secondary particles... more ARTI is a complete framework designed to simulate the signals produced by the secondary particles emerging from the interaction of single, multiple, and even from the complete flux of primary cosmic rays with the atmosphere. These signals are simulated for any particle detector located at any place (latitude, longitude and altitude), including the real-time atmospheric, geomagnetic and detector conditions. Formulated through a sequence of codes written in C++, Fortran, Bash and Perl, it provides an easy-to-use integration of three different simulation environments: MagnetoCosmics, CORSIKA and Geant4. These tools evaluate the geomagnetic field effects on the primary flux and simulate atmospheric showers of cosmic rays and the detectors’ response to the secondary flux of particles. In this work, we exhibit the usage of the ARTI framework by calculating the total expected signal flux at eight selected sites of the Latin American Giant Observatory: a cosmic ray Observatory all over Lati...
For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved qu... more For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above ∼50 EeV are provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second...
The LAGO (Latin American Giant Observatory) observatory is an experiment that spans over Latin Am... more The LAGO (Latin American Giant Observatory) observatory is an experiment that spans over Latin America in a wide range of latitudes that gives different rigidity cut offs for the enter of cosmic rays in the atmosphere. The motivation of the Observatory is to study atmospheric radiation and space weather through the measurement of the secondary emission of low energy cosmic rays at ground level using Water Cherenkov Detectors (WCD). This work presents the contributions of the LAGO collaboration to the 2019 36th ICRC.
arXiv: Instrumentation and Methods for Astrophysics, 2020
The Latin American Giant Observatory (LAGO) is a distributed cosmic ray observatory that spans ov... more The Latin American Giant Observatory (LAGO) is a distributed cosmic ray observatory that spans over Latin America in a wide range of latitudes and altitudes. One of the main goals of LAGO is to study atmospheric radiation and space weather through the measurement of the secondary particles from cosmic ray flux at ground level using Water Cherenkov Detectors (WCD). Thus, due to differences in the local geomagnetic rigidity cut-off affecting the low energy cosmic rays impinging on the atmosphere and the well-known relation between altitude and the development of the extended atmospheric showers, different secondary particle fluxes are expected at each LAGO site. It is therefore crucial for our objectives to be able to determine the expected flux of secondary particles at any place in the World and for any geomagnetic or atmospheric conditions. To characterize the response of a particular LAGO site we developed ARTI, a complete framework intended to simulate the WCD signals produced by...
Contributions of the Pierre Auger Collaboration to the 33rd International Cosmic Ray Conference, ... more Contributions of the Pierre Auger Collaboration to the 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2013
The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of... more The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between $$2\times 10^{17}$$2×1017 and $$2\times 10^{18}$$2×1018 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at $$10^{{17.5}}\, {\mathrm{eV}} $$1017.5eV and $$10^{{18}}\, {\mathrm{eV}} $$1018eV. We find that, for the models to explain the data, an increase in the muon density of $$38\%$$38%$$\pm 4\% (12\%)$$±4%(12%)$$\pm {}^{...
An in-situ calibration of a logarithmic periodic dipole antenna with a frequency coverage of 30 M... more An in-situ calibration of a logarithmic periodic dipole antenna with a frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of a radio station system used for detection of cosmic ray induced air showers at the Engineering Radio Array of the Pierre Auger Observatory, the so-called Auger Engineering Radio Array (AERA). The directional and frequency characteristics of the broadband antenna are investigated using a remotely piloted aircraft carrying a small transmitting antenna. The antenna sensitivity is described by the vector effective length relating the measured voltage with the electric-field components perpendicular to the incoming signal direction. The horizontal and meridional components are determined with an overall uncertainty of 7.4 +0.9 −0.3 % and 10.3 +2.8 −1.7 % respectively. The measurement is used to correct a simulated response of the frequency and directional response of the antenna. In addition, the influence of the ground conductivity and permittivity on the antenna response is simulated. Both have a negligible influence given the ground conditions measured at the detector site. The overall uncertainties of the vector effective length components result in an uncertainty of 8.8 +2.1 −1.3 % in the square root of the energy fluence for incoming signal directions with zenith angles smaller than 60 • .
• An extended rigidity cutoff is calculated under quiet (secular) & transient conditions for the ... more • An extended rigidity cutoff is calculated under quiet (secular) & transient conditions for the geomagnetic field. • Penumbra region is reinterpreted as a probability function of the arrival direction. • The effect of the geomagnetic field in the flux of Galactic Cosmic Rays can be estimated from changes on the flux of secondary particles at ground level.
We present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 ... more We present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 EeV measured using the Pierre Auger Observatory. For the energy bins [4, 8] EeV and E ≥ 8 EeV, the most 4 The Pierre Auger Collaboration significant signal is a dipolar modulation in right ascension at energies above 8 EeV, as previously reported. In this paper we further scrutinize the highest-energy bin by splitting it into three energy ranges. We find that the amplitude of the dipole increases with energy above 4 EeV. The growth can be fitted with a power law with index β = 0.79 ± 0.19. The directions of the dipoles are consistent with an extragalactic origin of these anisotropies at all the energies considered. Additionally we have estimated the quadrupolar components of the anisotropy: they are not statistically significant. We discuss the results in the context of the predictions from different models for the distribution of ultrahigh-energy sources and cosmic magnetic fields.
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Papers by Luis A. Nunez