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Abstract: The observation of primary photons with energies around 10[sup]16 eV would be particularly interesting after the discovery of Galactic gamma-ray sources with spectra extending into the PeV range. Since photons are connected to the acceleration of charged particles, searches for photons enhance the multi-messenger understanding of cosmic-ray sources as well as of transient astrophysical phenomena, while offering wealthy connections to neutrino astronomy and dark matter. Additionally, diffuse photon fluxes are expected from cosmic-ray interactions with Galactic matter and background radiation fields. Previously, the energy domain between 1 PeV and 200 PeV was only explored from the Northern Hemisphere. The Pierre Auger Observatory is the largest astroparticle experiment in operation and, thanks to its location, has a sizable exposure to the Southern sky, including the Galactic center region. In this contribution, we present the first search for photons from the Southern hemisphere between 50 and 200 PeV exploiting the Auger data acquired during ∼4 yr of operation. We describe the method to discriminate photons against the dominating hadronic background; it is based on the measurements of air showers taken with the low-energy extension of the Pierre Auger Observatory composed by 19 water-Cherenkov detectors spanning ∼ 2km[sup]2 and an Underground Muon Detector. The search for a diffuse flux of photons is presented and its results are interpreted according to theoretical model predictions. This study extends the range of Auger photon searches to almost four decades in energy.
Keywords: Pierre auger observatory, cosmic rays, photons, Water-Cherenkov detectors, Underground Muon detector
Published in RUNG: 26.09.2023; Views: 29; Downloads: 0
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Abstract: The Pierre Auger Observatory uses fluorescence telescopes in conjunction with ground level particle detectors to measure high-energy cosmic rays and reconstruct, with greater precision, their arrival direction, their energy and the depth of shower maximum. The depth of shower maximum is important to infer cosmic ray mass composition. The fluorescence detector is capable of directly measuring the longitudinal shower development, which is used to reconstruct the cosmic ray energy and the atmospheric depth of shower maximum. However, given the limited field of view of the fluorescence detector, the shower profile is not always fully contained within the detector observation volume. Therefore, considerations need to be taken in order to reconstruct some events. In this contribution we will describe the method that the Pierre Auger Collaboration uses to reconstruct the longitudinal profiles of showers and present the details of its performance, namely its resolution and systematic uncertainties.
Keywords: ultra-high-energy cosmic rays (UHECRs), Pierre Auger Observatory, extensive air showers, longitudinal shower profiles, shower maximum, fluorescence detectors
Published in RUNG: 20.09.2023; Views: 69; Downloads: 0
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Abstract: We use the surface detector of the Pierre Auger Observatory to search for air showers initiated by photons with an energy above 10[sup]19 eV. Photons in the zenith angle range from 30 deg. to 60 deg. can be identified in the overwhelming background of showers initiated by charged cosmic rays through the broader time structure of the signals induced in the water-Cherenkov detectors of the array and the steeper lateral distribution of shower particles reaching ground. Applying the search method to data collected between January 2004 and June 2020, upper limits at 95% CL are set to an E[sup]-2 diffuse flux of ultra-high energy photons above 10[sup]19 eV, 2 × 10[sup]19 eV and 4 × 10[sup]19 eV amounting to 2.11 × 10[sup]-3, 3.12 × 10[sup]-4 and 1.72 × 10[sup]-4 km-2 sr-1 yr-1, respectively. While the sensitivity of the present search around 2 × 10[sup]19 eV approaches expectations of cosmogenic photon fluxes in the case of a pure-proton composition, it is one order of magnitude above those from more realistic mixed-composition models. The inferred limits have also implications for the search of super-heavy dark matter that are discussed and illustrated.
Keywords: ultra-high-energy (UHE) cosmic rays, UHE photons, Pierre Auger Observatory, extensive air showers, water Cherenkov detectors
Published in RUNG: 18.08.2023; Views: 174; Downloads: 3
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Keywords: ultra-high energy (UHE) cosmic rays, Pierre Auger Observatory, UHE photon flux upper limits, super-heavy dark matter models
Published in RUNG: 09.02.2023; Views: 561; Downloads: 0
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Abstract: The Pierre Auger Observatory, being the largest air-shower experiment in the world, offers an unprecedented exposure to neutral particles at the highest energies. Since the start of data taking more than 18 years ago, various searches for ultra-high-energy (UHE, E > 10[sup]17 eV) photons have been performed: either for a diffuse flux of UHE photons, for point sources of UHE photons or for UHE photons associated with transient events like gravitational wave events. In the present paper, we summarize these searches and review the current results obtained using the wealth of data collected by the Pierre Auger Observatory.
Keywords: photons, ultra-high energies, air showers, Pierre Auger Observatory, upper limits, transients
Published in RUNG: 03.01.2023; Views: 695; Downloads: 0
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