Person: Arqueros Martínez, Fernando
Universidad Complutense de Madrid
Faculty / Institute
Estructura de la Materia, Física Térmica y Electrónica
Física Atómica, Molecular y Nuclear
Now showing 1 - 10 of 78
PublicationThe relevance of fluorescence radiation in Cherenkov telescopes(IOP Publishing Ltd, 2019) Arqueros Martínez, Fernando; Rosado Vélez, Jaime; Morcuende Parrilla, Daniel; Contreras González, José LuisCherenkov telescopes are also sensitive to the atmospheric fluorescence produced by the extensive air showers. However this contribution is neglected by the reconstruction algorithms of imaging air Cherenkov telescopes IACTs and wide-angle Cherenkov detectors WACDs. In this paper we evaluate the fluorescence contamination in the Cherenkov signals from MC simulations in both kinds of Cherenkov telescopes and for some typical observational situations. Results for an observation level of 2200 m a.s.l. are shown. In addition, the feasibility and capabilities of IACTs working as fluorescence telescopes are discussed with the assistance of some geometrical calculations. PublicationSearch for patterns by combining cosmic-ray energy and arrival directions at the Pierre Auger Observatory(Springer, 2015-06-20) Aranda, V. M.; Arqueros Martínez, Fernando; García Pinto, Diego; Minaya Flores, Ignacio Andrés; Rosado Vélez, Jaime; Vázquez Peñas, José RamónEnergy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with E >= 6 x 10(19) eV by analyzing cosmic rays with energies above E >= 5 x 10(18) eV arriving within an angular separation of approximately 15 degrees. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis. The comparison of these measurements with astrophysical scenarios can therefore be used to obtain constraints on related model parameters such as strength of cosmic-ray deflection and density of point sources. PublicationModeling crosstalk and afterpulsing in silicon photomultipliers(Elsevier science BV, 2015-07-01) Rosado Vélez, Jaime; Aranda, V. M.; Blanco Ramos, Francisco; Arqueros Martínez, FernandoAn experimental method to characterize the crosstalk and afterpulsing in silicon photomultipliers has been developed and applied to two detectors fabricated by Hamamatsu. An analytical model of optical crosstalk that we presented in a previous publication has been compared with new measurements, confirming our results. Progresses on a statistical model to describe afterpulsing and delayed crosstalk are also shown and compared with preliminary experimental data. (C) 2014 Elsevier B.V. All rights reserved. PublicationUltrahigh Energy Neutrinos at the Pierre Auger Observatory(Hindawi Publishing Corporation, 2013) Arganda, E.; Arqueros Martínez, Fernando; Blanco Ramos, Francisco; García Pinto, Diego; Minaya Flores, Ignacio Andrés; Ortiz Ramis, Montserrat; Rosado Vélez, Jaime; Vázquez Peñas, José RamónThe observation of ultrahigh energy neutrinos (UHE nu s) has become a priority in experimental astroparticle physics. UHE nu s can be detected with a variety of techniques. In particular, neutrinos can interact in the atmosphere (downward-going nu) or in the Earth crust (Earth-skimming nu), producing air showers that can be observed with arrays of detectors at the ground. With the surface detector array of the Pierre Auger Observatory we can detect these types of cascades. The distinguishing signature for neutrino events is the presence of very inclined showers produced close to the ground (i.e., after having traversed a large amount of atmosphere). In this work we review the procedure and criteria established to search for UHE nu s in the data collected with the ground array of the Pierre Auger Observatory. This includes Earth-skimming as well as downward-going neutrinos. No neutrino candidates have been found, which allows us to place competitive limits to the diffuse flux of UHE nu s in the EeV range and above. PublicationA search for anisotropy in the arrival directions of ultra high energy cosmic rays recorded at the Pierre Auger Observatory(IOP Publishing, 2012-04) Arganda, E.; Arqueros Martínez, Fernando; Blanco Ramos, Francisco; García Pinto, Diego; Minaya Flores, Ignacio Andrés; Ortiz Ramis, Montserrat; Rosado Vélez, Jaime; Vázquez Peñas, José RamónObservations of cosmic rays 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 for both angular and energy resolutions. If the sources of UHECRs follow the same large scale structure as ordinary galaxies in the local Universe and if UHECRs are deflected no more than a few degrees, a study of mock maps suggests that these three method can efficiently respond to the resulting anisotropy with a P-value = 1.0% or smaller with data sets as few as 100 events. using data taken from January 1, 2004 to July 31, 2010 we examined the 20, 30, ... , 110 highest energy events with a corresponding minimum energy threshold of about 49.3 EeV. The minimum P-values found were 13.5% using the 2pt-L method, 1.0% using the 2pt+ method and 1.1% using the 3pt method for the highest 100 energy events. In view of the multiple (correlated) scans performed on the data set, these catalog-independent methods do not yield strong evidence of anisotropy in the highest energy cosmic rays. PublicationReconstruction of inclined air showers detected with the pierre Auger Observatory(IOP Publising LTD, 2014) Arqueros Martínez, Fernando; Blanco Ramos, Francisco; García Pinto, Diego; Minaya Flores, Ignacio Andrés; Ortiz Ramis, Montserrat; Rosado Vélez, Jaime; Vázquez Peñas, José RamónWe describe the method devised to reconstruct inclined cosmic-ray air showers with zenith angles greater than 60 degrees detected with the surface array of the Pierre Auger Observatory. The measured signals at the ground level are fitted to muon density distributions predicted with atmospheric cascade models to obtain the relative shower size as an overall normalization parameter. The method is evaluated using simulated showers to test its performance. The energy of the cosmic rays is calibrated using a sub-sample of events reconstructed with both the fluorescence and surface array techniques. The reconstruction method described here provides the basis of complementary analyses including an independent measurement of the energy spectrum of ultra-high energy cosmic rays using very inclined events collected by the Pierre Auger Observatory. PublicationA targeted search for point sources of eev neutrons(IOP Publishing, 2014-06-02) Arqueros Martínez, Fernando; Blanco Ramos, Francisco; García Pinto, Diego; Minaya Flores, Ignacio Andrés; Ortiz Ramis, Montserrat; Rosado Vélez, Jaime; Vázquez Peñas, José RamónA flux of neutrons from an astrophysical source in the Galaxy can be detected in the Pierre Auger Observatory as an excess of cosmic-ray air showers arriving from the direction of the source. To avoid the statistical penalty for making many trials, classes of objects are tested in combinations as nine "target sets," in addition to the search for a neutron flux from the Galactic center or from the Galactic plane. Within a target set, each candidate source is weighted in proportion to its electromagnetic flux, its exposure to the Auger Observatory, and its flux attenuation factor due to neutron decay. These searches do not find evidence for a neutron flux from any class of candidate sources. Tabulated results give the combined p-value for each class, with and without the weights, and also the flux upper limit for the most significant candidate source within each class. These limits on fluxes of neutrons significantly constrain models of EeV proton emission from non-transient discrete sources in the Galaxy. PublicationMeasurement of the proton-air cross section at root s=57 TeV with the Pierre Auger Observatory(American Physical Society, 2012-08-10) Arganda, E.; Arqueros Martínez, Fernando; Blanco Ramos, Francisco; García Pinto, Diego; Ortiz Ramis, Montserrat; Rosado Vélez, Jaime; Vázquez Peñas, José RamónWe report a measurement of the proton-air cross section for particle production at the center-of-mass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analyzing the tail of the distribution of the shower maxima, a proton-air cross section of [505 +/- 22(stat)(-36)(+28)(syst)] mb is found. PublicationProbing the radio emission from air showers with polarization measurements(Amer Physical Soc, 2014-03-14) Arqueros Martínez, Fernando; Blanco Ramos, Francisco; García Pinto, Diego; Minaya Flores, Ignacio Andrés; Ortiz Ramis, Montserrat; Rosado Vélez, Jaime; Vázquez Peñas, José RamónThe emission of radio waves from air showers has been attributed to the so-called geomagnetic emission process. At frequencies around 50 MHz this process leads to coherent radiation which can be observed with rather simple setups. The direction of the electric field induced by this emission process depends only on the local magnetic field vector and on the incoming direction of the air shower. We report on measurements of the electric field vector where, in addition to this geomagnetic component, another component has been observed that cannot be described by the geomagnetic emission process. The data provide strong evidence that the other electric field component is polarized radially with respect to the shower axis, in agreement with predictions made by Askaryan who described radio emission from particle showers due to a negative charge excess in the front of the shower. Our results are compared to calculations which include the radiation mechanism induced by this charge-excess process. PublicationRelevance of the fluorescence radiation in VHE gamma-ray observations with the Cherenkov technique(Elsevier Science BV, 2019-01) Morcuende, D.; Rosado, J.; Contreras González, José Luis; Arqueros Martínez, FernandoAtmospheric fluorescence is usually neglected in the reconstruction of the signals registered by Cherenkov telescopes, both IACTs and wide-angle detector arrays. In this paper we quantify the fluorescence contribution to the total light recorded in typical observational configurations. To this end we have implemented the production and tracking of fluorescence light in the CORSIKA code. Both the Cherenkov and fluorescence light distributions on ground (2200 m a.s.I.) have been simulated for gamma-ray showers in a wide energy range (10(-1) - 10(3) TeV). The relative fluorescence contribution has been evaluated as a function of the shower energy and zenith angle. Our results indicate that at distances from the impact point smaller than 200 m the fluorescence contamination is negligible in both types of telescopes. However, at about 1000 m, the contamination in IACTs is around 5%. At these core distances, the signals recorded by wide-angle detectors contain around 45% of atmospheric fluorescence in the PeV region. (C) 2018 Elsevier B.V. All rights reserved.