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Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory
Marko Zavrtanik, Danilo Zavrtanik, Lili Yang, Serguei Vorobiov, Darko Veberič, Marta Trini, Samo Stanič, Ahmed Saleh, Gašper Kukec Mezek, Andrej Filipčič, A. Aab, 2016, original scientific article

Abstract: The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects related to the angles of incidence of the particles into the detectors. The magnitude of the effect depends upon the zenith angle and state of development of the shower and thus provides a novel observable, (secθ)max, sensitive to the mass composition of cosmic rays above 3×1018  eV. By comparing measurements with predictions from shower simulations, we find for both of our adopted models of hadronic physics (QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass increases slowly with energy, as has been inferred from other studies. However, the mass estimates are dependent on the shower model and on the range of distance from the shower core selected. Thus the method has uncovered further deficiencies in our understanding of shower modeling that must be resolved before the mass composition can be inferred from (secθ)max.
Found in: osebi
Keywords: ultra-high energy cosmic rays (UHECR), UHECR mass composition, Pierre Auger Observatory, extensive air showers, Auger Surface Detector signals risetime, azimuthal symmetry
Published: 15.04.2016; Views: 1923; Downloads: 0
.pdf Fulltext (698,19 KB)

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High Energy Astrophysics
Lili Yang, unpublished conference contribution

Abstract: I was invited as a lecturer at the Sumer School on Astrophysics and Astroparticles in Petnica Serbia. I gave talks on "High Energy Astrophysics", where I mainly focused on the production, propagation and detection of high energy astroparticles. Especially, I introduced the current experiments and technique and facilities.
Found in: osebi
Keywords: High-energy astroparticles, experiments, detection, production
Published: 06.12.2016; Views: 1392; Downloads: 0
.pdf Fulltext (16,77 MB)
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High Energy Emission from Gamma Ray Bursts
Lili Yang, invited lecture at foreign university

Abstract: Gamma Ray Bursts (GRBs) are the most energetic explosions in the universe, and they have been proposed as the most promising candidate sources of ultra-high energy cosmic rays (UHECRs). As a result of interactions of UHECR within the host environment and during their propagation towards Earth, high energy neutrinos and photons are also expected from both prompt and afterglow emission. In this talk, I will review the standard theory of particle acceleration and production in a GRB fireball, and multi-wavelength and multi-messeger observations of GRB emission. I will present the prediction of PeV — EeV neutrino production and evidence of GeV gamma ray radiation, and the expected detection in IceCube, Pierre Auger Observatory and CTA (the next generation of Imaging Atmospheric Cherenkov Telescopes). The investigation of high-energy particles will provide insight into the nature and complicated mechanisms of GRBs.
Found in: osebi
Keywords: Gamma-Ray Bursts, high-energy emission, blastwave afterglow
Published: 06.12.2016; Views: 1348; Downloads: 0
.pdf Fulltext (20,49 MB)

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High-energy Astroparticle Detection
Lili Yang, invited lecture at foreign university

Abstract: Astroparticle Physics has evolved as a new interdisciplinary field at the intersection of particle physics, astronomy and cosmology, addressing some of the most fundamental questions of contemporary physics. As the cosmic messengers, neutrinos, cosmic rays, gamma rays and also gravitational waves, take the information from the universe to tell us more about the story. Physicists have been developing experiments to detect and study these messengers. I would like to talk about the basic ideas and searching results from the dedicate cosmic ray detector Pierre Auger Observatory and also the future performance of Cherenkov Telescope Array (CTA), the next-generation ground based telescope array. CTA will play an very important role in detecting GeV-TeV gamma rays and represents the era of precision gamma ray astronomy. The multi-messenger and multi-wavelength study with various messengers are the main field in astrophysics.
Found in: osebi
Keywords: High-energy astroparticles, CTA, Pierre Auger Observatory
Published: 06.12.2016; Views: 1250; Downloads: 0
.pdf Fulltext (32,92 MB)
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Multi-messenger study of the Fermi Bubbles
Lili Yang, invited lecture at foreign university

Abstract: The Fermi Bubbles have been imaged in sub-TeV gamma rays at Fermi-LAT, and, if their origin is hadronic, they might have been seen with low statistics in ∼0.1−1 PeV neutrinos at IceCube. I discuss the detectability of these objects at the new High Altitude Water Cherenkov (HAWC). HAWC will view the North Bubble for ∼2−3 hours a day, and will map its spectrum at 0.1-100 TeV. For the hard primary proton spectrum required to explain five events at IceCube, a high significance detection at HAWC will be achieved in less than 30 days. I will discuss how the combination of results at HAWC and IceCube will substantiate the hadronic model, or constrain its spectral parameters and how sensitive Cherenkov Telescope Array(CTA) is to the bubbles.
Found in: osebi
Keywords: Fermi Bubbles, neutrinos, HAWC
Published: 06.12.2016; Views: 1366; Downloads: 0
.pdf Fulltext (5,54 MB)
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Search for UHE neutrinos – in coincidence with LIGO GW150914 event – with the Pierre Auger Observatory
Lili Yang, 2016, published scientific conference contribution abstract

Abstract: The first gravitational wave transient GW150914 was observed by Advanced LIGO on September 14th, 2015 at 09:50:45 Universal Time. In addition to follow-up electromagnetic observations, the detection of neutrinos will probe deeply and more on the nature of astrophysical sources, especially in the ultra-high energy regime. Neutrinos in the EeV energy range were searched in data collected at the surface detector of the Pierre Auger Observatory within ± 500 s and 1 day after the GW150914 event. No neutrino candidates were found. Based on this non-observation, we derive the first and only one neutrino fluence upper limit at EeV energies for this event at 90% CL, and report constraints on existence of accretion disk around mergers.
Found in: osebi
Keywords: gravitational waves, neutrinos, black hole physics
Published: 06.12.2016; Views: 1563; Downloads: 0
.pdf Fulltext (627,39 KB)

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