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 Physics , 2014, DOI: 10.1088/0004-637X/805/2/95 Abstract: Star-forming galaxies, due to their high star-formation rates and hence large number of supernova remnants therein, are huge reservoirs of cosmic rays (CRs). These CRs collide with gases in the galaxies and produce high-energy neutrinos through $pp$ collisions. In this paper, we calculate the neutrino production efficiency in star-forming galaxies by considering realistic galaxy properties, such as the gas density and galactic wind in star-forming galaxies. To calculate the accumulated neutrino flux, we use the infrared luminosity function of star-forming galaxies obtained by {\em Herschel} PEP/HerMES survey recently. The intensity of CRs producing PeV neutrinos in star-forming galaxies is normalized with the observed CR flux at EeV ({1\,EeV=$10^{18}\,$eV}), assuming that supernova remnants or hypernova remnants in star-forming galaxies can accelerate protons to EeV energies. Our calculations show that the accumulated neutrino emission produced by CRs in star-forming galaxies can account for the flux and spectrum of the sub-PeV/PeV neutrinos under reasonable assumptions on the CR confinement time in these galaxies.
 Physics , 2015, DOI: 10.1016/j.physletb.2015.04.032 Abstract: IceCube has measured a diffuse astrophysical flux of TeV-PeV neutrinos. The most plausible sources are unique high energy cosmic ray accelerators like hypernova remnants (HNRs) and remnants from gamma ray bursts in star-burst galaxies, which can produce primary cosmic rays with the required energies and abundance. In this case, however, ordinary supernova remnants (SNRs), which are far more abundant than HNRs, produce a comparable or larger neutrino flux in the ranges up to 100-150 TeV energies, implying a spectral break in the IceCube signal around these energies. The SNRs contribution in the diffuse flux up to these hundred TeV energies provides a natural baseline and then constrains the expected PeV flux.
 Physics , 2014, DOI: 10.1093/ptep/ptu090 Abstract: We show that the PeV neutrinos detected by IceCube put unique constraints on "secret" interactions of neutrinos with the cosmic neutrino background (C$\nu$B). The coupling must be $g <0.03$ for the mediating boson mass $m_{X} \lesssim 2$ MeV, $g/m_{X} < 5$ GeV$^{-1}$ for $m_{X} \gtrsim 20$ MeV, and $g/m_{X} < 0.07$ GeV$^{-1}$ in between. We also investigate the possibility that neutrino cascades degrade high-energy neutrinos to PeV energies by upgrading C$\nu$B where the energy flux of PeV neutrinos can coincide with the Waxman-Bahcall bound or the cosmogenic neutrino flux for protons, thanks to energy conservation. However a large coupling is required, which is disfavored by laboratory decay constraints. The suppression of PeV-EeV neutrinos is a testable prediction for the Askaryan Radio Array.
 Physics , 2013, DOI: 10.1088/0004-637X/774/1/74 Abstract: The IceCube collaboration discovery of 28 high-energy neutrinos over the energy range 30 TeV <~ E_nu <~ 1 PeV, a 4.3-sigma excess over expected backgrounds, represents the first high-confidence detection of cosmic neutrinos at these energies. In light of this discovery, we explore the possibility that some of the Sub-PeV cosmic neutrinos might originate in our Galaxy's TeV unidentified (TeV UnID) sources. While typically resolved at TeV energies, these sources lack prominent radio or X-ray counterparts, and so have been considered promising sites for hadron acceleration within our Galaxy. Modeling the TeV UnID sources as Galactic hypernova remnants, we predict Sub-PeV neutrino fluxes and spectra consistent with their contributing a minority of n_nu <~ 2 of the observed events. This is consistent with our analysis of the spatial distribution of the Sub-PeV neutrinos and TeV UnID sources, which finds that a best-fit of one, and maximum of 3.8 (at 90%-confidence), of the ~16 non-atmospheric Sub-PeV neutrinos may originate in TeV UnID sources, with the remaining 75% to 95% of events being drawn from an isotropic background. If our scenario is correct, we expect excess Sub-PeV neutrinos to accumulate along the Galactic plane, within |l| <~ 30 deg of the Galactic center and in the Cygnus region, as observations by IceCube and other high-energy neutrino facilities go forward. Our scenario also has implications for radio, X-ray, and TeV observations of the TeV UnID sources.
 Physics , 2014, DOI: 10.1103/PhysRevD.91.043003 Abstract: Ultrahigh-energy cosmic rays (UHECRs), if accelerated in the gamma-ray burst (GRB) blastwave, are expected to produce PeV-EeV neutrinos by interacting with long-lived GRB afterglow photons. Detailed spectral and temporal properties of the flux of these neutrinos depend on the GRB blastwave evolution scenario, but can last for days to years time scale in contrast to the seconds to minutes time scale for "burst" neutrino flux contemporaneous with the prompt gamma-ray emission and which has been constrained by IceCube in the $\sim$ 50 TeV-2 PeV range. We compute expected neutrino events in IceCube in the PeV-EeV range from the blastwave of long-duration GRBs, both for the diffuse flux and for individual GRBs in the nearby universe. We show that IceCube will be able to detect the diffuse GRB blastwave neutrino flux after 5 years of operation, and will be able to distinguish it from the cosmogenic neutrino flux arising from GZK process in case the UHECRs are heavy nuclei. We also show that EeV neutrinos from the blastwave of an individual GRB can be detected with long-term monitoring by a future high-energy extension of IceCube for redshift up to $z\sim 0.5$.
 Physics , 2011, DOI: 10.1088/2041-8205/736/1/L12 Abstract: We report the first observational search for tau neutrinos from gamma ray bursts (GRBs) using one of the Ashra light collectors. The earth-skimming tau-neutrino technique of imaging Cherenkov tau showers was applied as a detection method. We set stringent upper limits on the tau-neutrino fluence in PeV-EeV region for 3780 s (between 2.83 and 1.78 hours before) and another 3780 s (between 21.2 and 22.2 hours after) surrounding GRB081203A triggered by the Swift satellite. This first search for PeV-EeV tau neutrino complements other experiments in energy range and methodology, and suggests the prologue of "multi-particle astronomy" with a precise determination of time and location.
 Physics , 2014, Abstract: This Letter of Intent (LoI) describes the outline and plan for the Neutrino Telescope Array (NTA) project. High-energy neutrinos provide unique and indisputable evidence for hadronic acceleration. Recently, IceCube has reported astronomical neutrino candidates in excess of expectation from atmospheric secondaries, but is limited by the water Cherenkov detection method. A next generation high-energy neutrino telescope should be capable of establishing indisputable evidence for cosmic high-energy neutrinos. It should not only have orders-of-magnitude larger sensitivity, but also enough pointing accuracy to probe known or unknown astronomical objects, without suffering from atmospheric secondaries. The proposed installation is a large array of compound eye stations of imaging atmospheric Cherenkov and fluorescence detectors, with wide field of view and refined observational ability of air showers from cosmic tau neutrinos in the PeV-EeV energy range. This advanced optical complex system is based substantially on the development of All-sky Survey High Resolution Air-shower detector (Ashra) and applies the tau shower Earth-skimming method to survey PeV-EeV tau neutrinos. It allows wide (30 deg x 360 deg) and deep (~400 Mpc) survey observation for PeV-EeV tau neutrinos assuming the standard GRB neutrino fluence.In addition, it enjoys the pointing accuracy of better than 0.2 deg in essentially background-free conditions. With the advanced imaging of Earth-skimming tau showers in the wide field of view, we aim for clear discovery and identification of astronomical tau neutrino sources, providing inescapable evidence of the astrophysical hadronic model for acceleration and/or propagation of extremely high energy protons in the precisely determined direction.
 Soebur Razzaque Physics , 2013, DOI: 10.1103/PhysRevD.88.103003 Abstract: Long duration gamma-ray bursts are powerful sources that can accelerate particles to ultra-high energies. Acceleration of protons in the forward shock of the highly relativistic GRB blastwave allows PeV--EeV neutrino production by photopion interactions of ultra-high energy protons with X-ray to optical photons of the GRB afterglow emission. Four different blastwave evolution scenarios are considered: adiabatic and fully radiative blastwaves in a constant density circumburst medium and in a wind environment with the particle density in the wind decreasing inversley proportional to the square of the radius from the center of the burst. The duration of the neutrino flux depends on the evolution of the blastwave, and can last up to a day in the case of an adibatic blastwave in a constant density medium. Neutrino fluxes from the three other blastwave evolution scenarios are also calculated. Diffuse neutrino fluxes calculated using the observed rate of long-duration GRBs are consistent with the recent IceCube upper limit on the prompt GRB neutrino flux below PeV. The diffuse neutrino flux needed to explain the two neutrino events at PeV energies recently detected by IceCube can partially come from the presented GRB blastwave diffuse fluxes. Future observations by IceCube and upcoming huge radio Askaryan experiments will be able to probe the flux models presented here or constrain the GRB blastwave properties.
 Physics , 2012, DOI: 10.1016/j.astropartphys.2012.10.001 Abstract: We describe a method of observation for PeV--EeV tau neutrinos using Cherenkov light from the air showers of decayed taus produced by tau neutrino interactions in the Earth. Aiming for the realization of neutrino astronomy utilizing the Earth-skimming tau neutrino detection technique, highly precise determination of arrival direction is key due to the following issues: (1) Clear identification of neutrinos by identifying those vertices originating within the Earth's surface; (2) Identification of very high energy neutrino sources. The Ashra detector uses newly developed light collectors which realize both a 42 degree-diameter field-of-view and arcminute resolution. Therefore, it has superior angular resolution for imaging Cherenkov air showers. In this paper, we estimate the sensitivity of and cosmic-ray background resulting from application of the Ashra-1 Cherenkov tau shower observation method. Both data from a commissioning run and a long-term observation (with fully equipped trigger system and one light collector) are presented. Our estimates are based on a detailed Monte Carlo simulation which describes all relevant shower processes from neutrino interaction to Cherenkov photon detection produced by tau air showers. In addition, the potential to determine the arrival direction of Cherenkov showers is evaluated by using the maximum likelihood method. We conclude that the Ashra-1 detector is a unique probe into detection of very high energy neutrinos and their accelerators.
 Physics , 2009, DOI: 10.1088/0004-637X/709/2/1337 Abstract: We investigate hypernova (hyper-energetic supernova) and gamma-ray burst (GRB) remnants in our Galaxy as TeV gamma-ray sources, particularly in the role of potential TeV unidentified sources, which have no clear counterpart at other wavelengths. We show that the observed bright sources in the TeV sky could be dominated by GRB/hypernova remnants, even though they are fewer than supernova remnants (SNRs). If this is the case, TeV SNRs are more extended (and more numerous) than deduced from current observations. In keeping with their role as cosmic ray accelerators, we discuss hadronic gamma-ray emission from pi^0 decay, from beta decay followed by inverse Compton emission, and propose a third, novel process of TeV gamma-ray emission arising from the decay of accelerated radioactive isotopes such as 56Co entrained by relativistic or semi-relativistic jets in GRBs/hypernovae. We discuss the relevant observational signatures which could discriminate between these three mechanisms.
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