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Register a new userSearch for photons with energies above 10$^{18}$ eV using the hybrid detector of the Pierre Auger Observatory
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A search for ultra-high energy photons with energies above 1 EeV is performed using nine years of data collected by the Pierre Auger Observatory in hybrid operation mode. An unprecedented separation power between photon and hadron primaries is achieved by combining measurements of the longitudinal air-shower development with the particle content at ground measured by the fluorescence and surface detectors, respectively. Only three photon candidates at energies 1 - 2 EeV are found, which is compatible with the expected hadron-induced background. Upper limits on the integral flux of ultra-high energy photons of 0.038, 0.010, 0.009, 0.008 and 0.007 km$^{-2}$ sr$^{-1}$ yr$^{-1}$ are derived at 95% C.L. for energy thresholds of 1, 2, 3, 5 and 10 EeV. These limits bound the fractions of photons in the all-particle integral flux below 0.14%, 0.17%, 0.42%, 0.86% and 2.9%. For the first time the photon fraction at EeV energies is constrained at the sub-percent level. The improved limits are below the flux of diffuse photons predicted by some astrophysical scenarios for cosmogenic photon production. The new results rule-out the early top-down models $-$ in which ultra-high energy cosmic rays are produced by, e.g., the decay of super-massive particles $-$ and challenge the most recent super-heavy dark matter models.
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A measurement of the cosmic-ray spectrum for energies exceeding $4{times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{times}10^{18}$ eV, the ankle, the flux can be described by a power law $E^{-gamma}$ with index $gamma=2.70 pm 0.02 ,text{(stat)} pm 0.1,text{(sys)}$ followed by a smooth suppression region. For the energy ($E_text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_text{s}=(5.12pm0.25,text{(stat)}^{+1.0}_{-1.2},text{(sys)}){times}10^{19}$ eV.
We report a measurement of the energy spectrum of cosmic rays for energies above $2.5 {times} 10^{18}~$eV based on 215,030 events recorded with zenith angles below $60^circ$. A key feature of the work is that the estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. The measurement is the most precise made hitherto with the accumulated exposure being so large that the measurements of the flux are dominated by systematic uncertainties except at energies above $5 {times} 10^{19}~$eV. The principal conclusions are: (1) The flattening of the spectrum near $5 {times} 10^{18}~$eV, the so-called ankle, is confirmed. (2) The steepening of the spectrum at around $5 {times} 10^{19}~$eV is confirmed. (3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index $gamma$ of the particle flux ($propto E^{-gamma}$) changes from $2.51 pm 0.03~{rm (stat.)} pm 0.05~{rm (sys.)}$ to $3.05 pm 0.05~{rm (stat.)} pm 0.10~{rm (sys.)}$ before changing sharply to $5.1 pm 0.3~{rm (stat.)} pm 0.1~{rm (sys.)}$ above $5 {times} 10^{19}~$eV. (4) No evidence for any dependence of the spectrum on declination has been found other than a mild excess from the Southern Hemisphere that is consistent with the anisotropy observed above $8 {times} 10^{18}~$eV.
We report a measurement of the energy spectrum of cosmic rays above $2.5{times} 10^{18}$ eV based on $215,030$ events. New results are presented: at about $1.3{times} 10^{19}$ eV, the spectral index changes from $2.51 pm 0.03 textrm{ (stat.)} pm 0.05 textrm{ (sys.)}$ to $3.05 pm 0.05 textrm{ (stat.)}pm 0.10textrm{ (sys.)}$, evolving to $5.1pm0.3textrm{ (stat.)} pm 0.1textrm{ (sys.)}$ beyond $5{times} 10^{19}$ eV, while no significant dependence of spectral features on the declination is seen in the accessible range. These features of the spectrum can be reproduced in models with energy-dependent mass composition. The energy density in cosmic rays above $5{times} 10^{18}$ eV is $(5.66 pm 0.03 textrm{ (stat.)} pm 1.40 textrm{ (sys.)} ) {times} 10^{53}~$erg Mpc$^{-3}$.
We search for ultra-high energy photons by analyzing geometrical properties of shower fronts of events registered by the Telescope Array surface detector. By making use of an event-by-event statistical method, we derive upper limits on the absolute flux of primary photons with energies above 10^19, 10^19.5 and 10^20 eV based on the first three years of data taken.
We present the results of the search for ultra-high-energy photons with nine years of data from the Telescope Array surface detector. A multivariate classifier is built upon 16 reconstructed parameters of the extensive air shower. These parameters are related to the curvature and the width of the shower front, the steepness of the lateral distribution function, and the timing parameters of the waveforms sensitive to the shower muon content. A total number of two photon candidates found in the search is fully compatible with the expected background. The $95%,$CL limits on the diffuse flux of the photons with energies greater than $10^{18.0}$, $10^{18.5}$, $10^{19.0}$, $10^{19.5}$ and $10^{20.0}$ eV are set at the level of $0.067$, $0.012$, $0.0036$, $0.0013$, $0.0013~mbox{km}^{-2}mbox{yr}^{-1}mbox{sr}^{-1}$ correspondingly.
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