arXiv subjects

T. Abu-Zayyad

Publications and source records attributed to T. Abu-Zayyad.

At least 55 records · Page 3Linked to original sources

arXiv2013

Search for correlations of the arrival directions of ultra-high energy cosmic ray with extragalactic objects as observed by the telescope array experiment

We search for correlations between positions of extragalactic objects and arrival directions of Ultra-High Energy Cosmic Rays (UHECRs) with primary energy $E \ge 40$ EeV as observed by the surface detector array of the Telescope Array (TA) experiment during the first 40 months of operation. We examined several public astronomical object catalogs, including the Veron-Cetty and Veron catalog of active galactic nuclei. We counted the number of TA events correlated with objects in each catalog as a function of three parameters: the maximum angular separation between a TA event and an object, the minimum energy of the events, and the maximum redshift of the objects. We determine combinations of these parameters which maximize the correlations, and calculate the chance probabilities of having the same levels of correlations from an isotropic distribution of UHECR arrival directions. No statistically significant correlations are found when penalties for scanning over the above parameters and for searching in several catalogs are taken into account.

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arXiv2013

Energy Spectrum of Ultra-High Energy Cosmic Rays Observed with the Telescope Array Using a Hybrid Technique

We measure the spectrum of cosmic rays with energies greater than $10^{18.2}$ eV with the Fluorescence Detectors (FDs) and the Surface Detectors (SDs) of the Telescope Array Experiment using the data taken in our first 2.3-year observation from May 27 2008 to September 7 2010. A hybrid air shower reconstruction technique is employed to improve accuracies in determination of arrival directions and primary energies of cosmic rays using both FD and SD data. The energy spectrum presented here is in agreement with our previously published spectra and the HiRes results.

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arXiv2013

The Energy Spectrum of Ultra-High-Energy Cosmic Rays Measured by the Telescope Array FADC Fluorescence Detectors in Monocular Mode

We present a measurement of the energy spectrum of ultra-high-energy cosmic rays performed by the Telescope Array experiment using monocular observations from its two new FADC-based fluorescence detectors. After a short description of the experiment, we describe the data analysis and event reconstruction procedures. Since the aperture of the experiment must be calculated by Monte Carlo simulation, we describe this calculation and the comparisons of simulated and real data used to verify the validity of the aperture calculation. Finally, we present the energy spectrum calculated from the merged monocular data sets of the two FADC-based detectors, and also the combination of this merged spectrum with an independent, previously published monocular spectrum measurement performed by Telescope Array's third fluorescence detector (Abu-Zayyad {\it et al.}, {Astropart. Phys.} 39 (2012), 109). This combined spectrum corroborates the recently published Telescope Array surface detector spectrum (Abu-Zayyad {\it et al.}, {Astrophys. Journ.} 768 (2013), L1) with independent systematic uncertainties.

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arXiv2013

An Absence of Neutrinos Associated with Cosmic Ray Acceleration in Gamma-Ray Bursts

Gamma-Ray Bursts (GRBs) have been proposed as a leading candidate for acceleration of ultra high-energy cosmic rays, which would be accompanied by emission of TeV neutrinos produced in proton-photon interactions during acceleration in the GRB fireball. Two analyses using data from two years of the IceCube detector produced no evidence for this neutrino emission, placing strong constraints on models of neutrino and cosmic-ray production in these sources.

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arXiv2013

The Cosmic Ray Energy Spectrum Observed with the Surface Detector of the Telescope Array Experiment

The Telescope Array (TA) collaboration has measured the energy spectrum of ultra-high energy cosmic rays with primary energies above 1.6 x 10^(18) eV. This measurement is based upon four years of observation by the surface detector component of TA. The spectrum shows a dip at an energy of 4.6 x 10^(18) eV and a steepening at 5.4 x 10^(19) eV which is consistent with the expectation from the GZK cutoff. We present the results of a technique, new to the analysis of ultra-high energy cosmic ray surface detector data, that involves generating a complete simulation of ultra-high energy cosmic rays striking the TA surface detector. The procedure starts with shower simulations using the CORSIKA Monte Carlo program where we have solved the problems caused by use of the "thinning" approximation. This simulation method allows us to make an accurate calculation of the acceptance of the detector for the energies concerned.

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arXiv2012

A Search for UHE Tau Neutrinos with IceCube

The first dedicated search for ultra-high energy (UHE) tau neutrinos of astrophysical origin was performed using the IceCube detector in its 22-string configuration with an instrumented volume of roughly 0.25 km^3. The search also had sensitivity to UHE electron and muon neutrinos. After application of all selection criteria to approximately 200 live-days of data, we expect a background of 0.60 +/- 0.19 (stat.) $^{+0.56}_{-0.58}$ (syst.) events and observe three events, which after inspection emerge as being compatible with background but are kept in the final sample. Therefore, we set an upper limit on neutrinos of all-flavors from UHE astrophysical sources at 90% CL of $E^{2} Φ(ν_{x}) < 16.3 * 10^-8 GeV cm^-2 sr^-1 s^-1 over an estimated primary neutrino energy range of 340 TeV to 200 PeV.

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arXiv2012

Search for Anisotropy of Ultra-High Energy Cosmic Rays with the Telescope Array Experiment

We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events collected by the Telescope Array (TA) detector in the first 40 months of operation. Following earlier studies, we examine event sets with energy thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the events in right ascension and declination are compatible with an isotropic distribution in all three sets. We then compare with previously reported clustering of the UHECR events at small angular scales. No significant clustering is found in the TA data. We then check the events with E>57 EeV for correlations with nearby active galactic nuclei. No significant correlation is found. Finally, we examine all three sets for correlations with the large-scale structure of the Universe. We find that the two higher-energy sets are compatible with both an isotropic distribution and the hypothesis that UHECR sources follow the matter distribution of the Universe (the LSS hypothesis), while the event set with E>10 EeV is compatible with isotropy and is not compatible with the LSS hypothesis at 95% CL unless large deflection angles are also assumed. We show that accounting for UHECR deflections in a realistic model of the Galactic magnetic field can make this set compatible with the LSS hypothesis.

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arXiv2012

The surface detector array of the Telescope Array experiment

The Telescope Array (TA) experiment, located in the western desert of Utah,USA, is designed for observation of extensive air showers from extremely high energy cosmic rays. The experiment has a surface detector array surrounded by three fluorescence detectors to enable simultaneous detection of shower particles at ground level and fluorescence photons along the shower track. The TA surface detectors and fluorescence detectors started full hybrid observation in March, 2008. In this article we describe the design and technical features of the TA surface detector.

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arXiv2012

Searches for periodic neutrino emission from binary systems with 22 and 40 strings of IceCube

In this paper we present the results of searches for periodic neutrino emission from a catalog of binary systems. Such modulation, observed in the photon flux, would be caused by the geometry of these systems. In the analysis, the period is fixed by these photon observations, while the phase and duration of the neutrino emission are treated as free parameters to be fit with the data. If the emission occurs during ~20% or less of the total period, this analysis achieves better sensitivity than a time-integrated analysis. We use the IceCube data taken from May 31, 2007 to April 5, 2008 with its 22-string configuration, and from April 5, 2008 to May 20, 2009 with its 40-string configuration. No evidence for neutrino emission is found, with the strongest excess occurring for Cygnus X-3 at 2.1 sigma significance after accounting for trials. Neutrino flux upper limits for both periodic and time-integrated emission are provided.

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arXiv2012

The Energy Spectrum of Telescope Array's Middle Drum Detector and the Direct Comparison to the High Resolution Fly's Eye Experiment

The Telescope Array's Middle Drum fluorescence detector was instrumented with telescopes refurbished from the High Resolution Fly's Eye's HiRes-1 site. The data observed by Middle Drum in monocular mode was analyzed via the HiRes-1 profile-constrained geometry reconstruction technique and utilized the same calibration techniques enabling a direct comparison of the energy spectra and energy scales between the two experiments. The spectrum measured using the Middle Drum telescopes is based on a three-year exposure collected between December 16, 2007 and December 16, 2010. The calculated difference between the spectrum of the Middle Drum observations and the published spectrum obtained by the data collected by the HiRes-1 site allows the HiRes-1 energy scale to be transferred to Middle Drum. The HiRes energy scale is applied to the entire Telescope Array by making a comparison between Middle Drum monocular events and hybrid events that triggered both Middle Drum and the Telescope Array's scintillator Ground Array.

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arXiv2012

All-particle cosmic ray energy spectrum measured with 26 IceTop stations

We report on a measurement of the cosmic ray energy spectrum with the IceTop air shower array, the surface component of the IceCube Neutrino Observatory at the South Pole. The data used in this analysis were taken between June and October, 2007, with 26 surface stations operational at that time, corresponding to about one third of the final array. The fiducial area used in this analysis was 0.122 km^2. The analysis investigated the energy spectrum from 1 to 100 PeV measured for three different zenith angle ranges between 0° and 46°. Because of the isotropy of cosmic rays in this energy range the spectra from all zenith angle intervals have to agree. The cosmic-ray energy spectrum was determined under different assumptions on the primary mass composition. Good agreement of spectra in the three zenith angle ranges was found for the assumption of pure proton and a simple two-component model. For zenith angles θ < 30°, where the mass dependence is smallest, the knee in the cosmic ray energy spectrum was observed between 3.5 and 4.32 PeV, depending on composition assumption. Spectral indices above the knee range from -3.08 to -3.11 depending on primary mass composition assumption. Moreover, an indication of a flattening of the spectrum above 22 PeV were observed.

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arXiv2011

Multi-year search for dark matter annihilations in the Sun with the AMANDA-II and IceCube detectors

A search for an excess of muon-neutrinos from dark matter annihilations in the Sun has been performed with the AMANDA-II neutrino telescope using data collected in 812 days of livetime between 2001 and 2006 and 149 days of livetime collected with the AMANDA-II and the 40-string configuration of IceCube during 2008 and early 2009. No excess over the expected atmospheric neutrino background has been observed. We combine these results with the previously published IceCube limits obtained with data taken during 2007 to obtain a total livetime of 1065 days. We provide an upper limit at 90% confidence level on the annihilation rate of captured neutralinos in the Sun, as well as the corresponding muon flux limit at the Earth, both as functions of the neutralino mass in the range 50 GeV-5000 GeV. We also derive a limit on the neutralino-proton spin-dependent and spin-independent cross section. The limits presented here improve the previous results obtained by the collaboration between a factor of two and five, as well as extending the neutralino masses probed down to 50 GeV. The spin-dependent cross section limits are the most stringent so far for neutralino masses above 200 GeV, and well below direct search results in the mass range from 50 GeV to 5 TeV.

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arXiv2011

Searching for soft relativistic jets in Core-collapse Supernovae with the IceCube Optical Follow-up Program

Context. Transient neutrino sources such as Gamma-Ray Bursts (GRBs) and Supernovae (SNe) are hypothesized to emit bursts of high-energy neutrinos on a time-scale of \lesssim 100 s. While GRB neutrinos would be produced in high relativistic jets, core-collapse SNe might host soft-relativistic jets, which become stalled in the outer layers of the progenitor star leading to an efficient production of high-energy neutrinos. Aims. To increase the sensitivity to these neutrinos and identify their sources, a low-threshold optical follow-up program for neutrino multiplets detected with the IceCube observatory has been implemented. Methods. If a neutrino multiplet, i.e. two or more neutrinos from the same direction within 100 s, is found by IceCube a trigger is sent to the Robotic Optical Transient Search Experiment, ROTSE. The 4 ROTSE telescopes immediately start an observation program of the corresponding region of the sky in order to detect an optical counterpart to the neutrino events. Results. No statistically significant excess in the rate of neutrino multiplets has been observed and furthermore no coincidence with an optical counterpart was found. Conclusion. The search allows, for the first time, to set stringent limits on current models predicting a high-energy neutrino flux from soft relativistic hadronic jets in core-collapse SNe. We conclude that a sub-population of SNe with typical Lorentz boost factor and jet energy of 10 and 3\times10^{51} erg, respectively, does not exceed 4.2% at 90% confidence.

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arXiv2011

Constraints on the Extremely-high Energy Cosmic Neutrino Flux with the IceCube 2008-2009 Data

We report on a search for extremely-high energy neutrinos with energies greater than $10^6$ GeV using the data taken with the IceCube detector at the South Pole. The data was collected between April 2008 and May 2009 with the half completed IceCube array. The absence of signal candidate events in the sample of 333.5 days of livetime significantly improves model independent limit from previous searches and allows to place a limit on the diffuse flux of cosmic neutrinos with an $E^{-2}$ spectrum in the energy range $2.0 \times 10^{6}$ $-$ $6.3 \times 10^{9}$ GeV to a level of $E^2 ϕ\leq 3.6 \times 10^{-8}$ ${\rm GeV cm^{-2} sec^{-1}sr^{-1}}$.

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arXiv2011

Background studies for acoustic neutrino detection at the South Pole

The detection of acoustic signals from ultra-high energy neutrino interactions is a promising method to measure the tiny flux of cosmogenic neutrinos expected on Earth. The energy threshold for this process depends strongly on the absolute noise level in the target material. The South Pole Acoustic Test Setup (SPATS), deployed in the upper part of four boreholes of the IceCube Neutrino Observatory, has monitored the noise in Antarctic ice at the geographic South Pole for more than two years down to 500 m depth. The noise is very stable and Gaussian distributed. Lacking an in-situ calibration up to now, laboratory measurements have been used to estimate the absolute noise level in the 10 to 50 kHz frequency range to be smaller than 20 mPa. Using a threshold trigger, sensors of the South Pole Acoustic Test Setup registered acoustic pulse-like events in the IceCube detector volume and its vicinity. Acoustic signals from refreezing IceCube holes and from anthropogenic sources have been used to localize acoustic events. Monte Carlo simulations of sound propagating from the established sources to the SPATS sensors have allowed to check corresponding model expectations. An upper limit on the neutrino flux at energies $E_ν> 10^{11}$ GeV is derived from acoustic data taken over eight months.

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arXiv2011

Time-Dependent Searches for Point Sources of Neutrinos with the 40-String and 22-String Configurations of IceCube

This paper presents searches for flaring sources of neutrinos using the IceCube neutrino telescope. For the first time, a search is performed over the entire parameter space of energy, direction and time looking for neutrino flares of 20 microseconds to a year duration from astrophysical sources among the atmospheric neutrino and muon backgrounds. Searches which integrate over time are less sensitive to flares because they are affected by a larger background of atmospheric neutrinos and muons that can be reduced by the time constraint. Flaring sources considered here, such as active galactic nuclei, soft gamma-ray repeaters and gamma-ray bursts, are promising candidate neutrino emitters. We used mainly data taken between April 5, 2008 and May 20, 2009 by a partially completed configuration of IceCube with 40 strings. For the presented searches an unbinned maximum likelihood method is used with a time-dependent prior to test several different source hypotheses. An "untriggered" search covers any possible time-dependent emission from sources not correlated to any other observation using other astrophysical messengers such as photons. Moreover, a similar time scan is performed for a predefined catalogue of sources that exhibit intense photon flares. Searches triggered by multi-wavelength information on flares from blazars and soft gamma-ray repeaters are performed using the 40 string data and also the data taken by the previous configuration of 22 strings in operation between May 31, 2007 and April 5, 2008. Flares for which extensive and continuous monitoring is available from Fermi-LAT and SWIFT and flares detected by imaging Cherenkov telescopes with shorter time-scale monitoring are considered. The results from all searches are compatible with a fluctuation of the background.

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arXiv2011

A Search for a Diffuse Flux of Astrophysical Muon Neutrinos with the IceCube 40-String Detector

The IceCube Neutrino Observatory is a 1 km$^{3}$ detector currently taking data at the South Pole. One of the main strategies used to look for astrophysical neutrinos with IceCube is the search for a diffuse flux of high-energy neutrinos from unresolved sources. A hard energy spectrum of neutrinos from isotropically distributed astrophysical sources could manifest itself as a detectable signal that may be differentiated from the atmospheric neutrino background by spectral measurement. This analysis uses data from the IceCube detector collected in its half completed configuration which operated between April 2008 and May 2009 to search for a diffuse flux of astrophysical muon neutrinos. A total of 12,877 upward going candidate neutrino events have been selected for this analysis. No evidence for a diffuse flux of astrophysical muon neutrinos was found in the data set leading to a 90 percent C.L. upper limit on the normalization of an $E^{-2}$ astrophysical $ν_μ$ flux of $8.9 \times 10^{-9} \ \mathrm{GeV \ cm^{-2} \ s^{-1} \ sr^{-1}}$. The analysis is sensitive in the energy range between $35 \ \mathrm{TeV} - 7 \ \mathrm{PeV}$. The 12,877 candidate neutrino events are consistent with atmospheric muon neutrinos measured from 332 GeV to 84 TeV and no evidence for a prompt component to the atmospheric neutrino spectrum is found.

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arXiv2011

IceCube Sensitivity for Low-Energy Neutrinos from Nearby Supernovae

This paper describes the response of the IceCube neutrino telescope located at the geographic South Pole to outbursts of MeV neutrinos from the core collapse of nearby massive stars. IceCube was completed in December 2010 forming a lattice of 5160 photomultiplier tubes that monitor a volume of ~ 1 cubic kilometer in the deep Antarctic ice for particle induced photons. The telescope was designed to detect neutrinos with energies greater than 100 GeV. Owing to subfreezing ice temperatures, the photomultiplier dark noise rates are particularly low. Hence IceCube can also detect large numbers of MeV neutrinos by observing a collective rise in all photomultiplier rates on top of the dark noise. With 2 ms timing resolution, IceCube can detect subtle features in the temporal development of the supernova neutrino burst. For a supernova at the galactic center, its sensitivity matches that of a background-free megaton-scale supernova search experiment. The sensitivity decreases to 20 standard deviations at the galactic edge (30 kpc) and 6 standard deviations at the Large Magellanic Cloud (50 kpc). IceCube is sending triggers from potential supernovae to the Supernova Early Warning System. The sensitivity to neutrino properties such as the neutrino hierarchy is discussed, as well as the possibility to detect the neutronization burst, a short outbreak of electron neutrinos released by electron capture on protons soon after collapse. Tantalizing signatures, such as the formation of a quark star or a black hole as well as the characteristics of shock waves, are investigated to illustrate IceCube's capability for supernova detection.

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