Observation of TeV-energy Cosmic-ray Anisotropy with the HAWC Observatory PDF Download

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Languages : en
Pages : 314

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Over the past two decades, ground-based measurements of the arrival directions of TeV cosmic rays have revealed an unexpected anisotropy. Multiple detectors have recorded fluxes above all-sky averages to high statistical significance for features at large (about 180°) and small (about 5°) angular sizes. Likely sources of high-energy cosmic rays are no closer than about 100 pc, about 100,000 Larmor radii for a TeV proton in typical interstellar magnetic fields of order several microGauss. This thesis outlines methods to search for signals in cosmic-ray arrival directions on data from the High-Altitude Water Cherenkov (HAWC) Observatory -- an extended air shower detector array in Puebla, Mexico, sensitive to gamma rays and cosmic rays at TeV energies. The detector is currently under construction, but data acquisition with the partially deployed detector started in 2013. An analysis of the cosmic-ray arrival direction distribution based on 86 billion events recorded between June 2013 and July 2014 shows anisotropy at the 10^(-4) level on angular scales of about 10°. The HAWC cosmic-ray sky map exhibits three regions of significantly enhanced cosmic-ray flux; two of these regions were first reported by the Milagro experiment. A third region coincides with an excess recently reported by the ARGO-YBJ experiment. An angular power spectrum analysis of the sky shows that all terms up to l=15 contribute significantly to the excesses. Large angular scales (>60°) are also considered, but the results are still preliminary as they are contaminated with non-sidereal signals which cancel for integer years of continuous data. An analysis of the cosmic-ray Moon shadow is shown to demonstrate the angular resolution and energy scale of the data set and to evaluate part of the analysis technique.

Author: Zigfried Hampel-Arias
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Languages : en
Pages : 346

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Over the past two decades, a more detailed understanding of TeV-scale cosmic rays has emerged which appears to deviate from the isotropic, single power law description of the cosmic ray flux. This may be the result of the distribution of sources within the Galaxy, changes in source spectra, effects from the propagation of cosmic rays from their sources to Earth, or a combination of the three. Supernova remnants are thought to be the most likely source of Galactic cosmic rays, providing a natural power law source spectrum with sufficient power to generate the observed cosmic ray energy density. Yet, recent results from balloon-borne experiments hint at a possible change in the spectral index between 20−50 TeV. These direct detection apparatuses provide the most precise measurements of the cosmic ray flux up to ~30 TeV, beyond which they are limited by the combined effects of their physical dimensions, runtime durations, and a rapidly decreasing flux. Above ~100 TeV, the spectrum has been measured by ground based air shower arrays, with typical systematic uncertainties of order 10%. Despite having the combined measurements from various experimental techniques, their different energy scales and systematics imply that identifying finer structure between 10−100 TeV requires a single experimental method to span the entire range. Furthermore, as the nearest potential source is hundreds of parsecs away and the Larmor radius of TeV scale charged cosmic rays in the Galaxy is of order 10−3 parsecs, the previously observed anisotropy in arrival directions of cosmic rays is unexpected. In order to attain the statistical power necessary to observe TeV cosmic ray anisotropy at the 10−3 level and below, the long data taking periods required are only attainable by air shower arrays. This thesis presents a measurement of the cosmic ray energy spectrum and the energy dependence of the anisotropy on small scales O(10°) using data from the High Altitude Water Cherenkov (HAWC) Observatory, an air-shower array located near Puebla, Mexico that is sensitive to gamma rays and cosmic rays at TeV energies. The analyses in this work comprise data taking periods of order 1 yr containing ~1010 events. An analysis of the cosmic ray Moon shadow is first presented as a verification of the angular resolution and energy scale of the detector. Next, a measurement of the all-particle cosmic ray energy spectrum from 10−500 TeV is shown, with an indication of structure deviating from a single power law. The final results presented in this work show an improved spectral measurement of a particular region of cosmic ray excess at the 10−4 level, previously observed both in HAWC and in other experiments.

Author: Chang Dong Rho
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Languages : en
Pages : 204

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"Astrophysical sources of very-high-energy (VHE) gamma-ray radiation provide unique information about astrophysical particle acceleration and cosmic-ray production. In particular, compact binary systems, composed of a compact object (a neutron star or black hole) in orbit with a massive stellar companion, provide an ideal environment for VHE gamma-ray production. They are not only powerful particle accelerators, but they also exhibit periodic emission that makes them excellent astrophysical laboratories. However, only a handful of binary systems have ever been observed in VHE gamma rays. Partly, this is because VHE gamma-ray binaries appear to be very rare, and part is due to observational bias. Most instruments operating at TeV are pointed and must allocate time to observing many kinds of objects. The High Altitude Water Cherenkov (HAWC) Observatory, on the other hand, has high uptime (duty cycle >95%) and a wide field of view (2 sr), making it well-suited for observing transient and time-varying sources such as binaries. HAWC is also currently the only detector that is sensitive to gamma-ray photons above 10 TeV. Collected HAWC data spanning33 months between November 2014 and January 2018 are used to analyze the known and candidate VHE gamma-ray binary systems in this work. "Microquasars" are a special subclass of X-ray binaries that are also candidate VHE gamma-ray sources. Unlike other types of binaries, compact objects in microquasars accrete matter from their companion star. This process forms an accretion disk around the compact object and relativistic jets of particles are released perpendicular to the accretion disk. This feature is very similar to active galactic nuclei (AGN), only smaller in size. Given the fact that direct observation of particle acceleration in distant AGN is very challenging, microquasars grant the valuable opportunity to model similar processes using nearby objects in our own Galaxy. SS 433 is a known microquasar that has two jets ("east" and "west") terminating in radio lobes of a surrounding supernova remnant, W 50. The recent observation of SS 433 with HAWC marked the first direct evidence of gamma-ray emission from the jets of a microquasar. Using HAWC data, we have measured a VHE flux of [formula not rendered] at the jet interaction region e1 in the east lobe and [formula not rendered] in the west lobe with a combined post-trial statistical significance of 5:4. The systematic studies used to confirm the VHE gamma-ray emission at 20 TeV from the SS 433 jet interaction regions is discussed in this work, along with a brief description of the theoretical interpretation associated with the observation. The HAWC data were also used to search for gamma rays from the known VHE binaries HESS J0632+057 and LS 5039. No emission was observed from HESS J0632+057, so we compute upper limits on its flux. Emission at low statistical significance is observed from LS 5039, which is located in a crowded region of the Galactic plane and is contaminated by gamma rays from nearby extended sources. A multiple-source analysis of the region surrounding LS 5039, as well as a time-series analysis of the light curve from LS 5039, are presented. At this time, data from HAWC are not significant enough to support multi-TeV emission from LS 5039"--Pages xi-xiii.

Author: Fegan David
Publisher: World Scientific
ISBN: 9813276878
Category : Science
Languages : en
Pages : 344

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This book documents how TeV gamma-ray astronomy painstakingly emerged from 20th century traditional cosmic-ray physics to become a keystone feature of contemporary high-energy astrophysics, fundamental to our understanding of high-energy cosmic processes and interactions. Contemporary TeV observations are based on the Imaging Atmospheric Cherenkov Technique and in excess of two hundred individual galactic and extra-galactic gamma-ray sources have now been discovered and studied in detail.The book tells the story from the perspective of the Whipple Observatory collaboration, pioneers of the imaging technique. At the same time, parallel developments by the broader community are constantly referenced, discussed and evaluated, mainly in the TeV energy regime but also where relevant at PeV energies. The narrative traces the contributions of many important participants active in the field since the mid-1950s and critically evaluates and provides commentary on the progress of research until the first sources were established beyond doubt, during the late 1980s and early 1990s. The final chapter presents a short summary of the contemporary status of TeV gamma-ray astronomy.Written predominantly from a historical perspective, the author guides readers through many decades of instrumental development and evolution, using only minimal mathematical background. This book will appeal to astrophysicists, particle physicists, traditional optical and radio astronomers, as well as others working across a variety of related cognate disciplines. It should be of interest and value to graduate students involved with contemporary fourth-generation TeV research programs such as CTA (Cherenkov Telescope Array).

Author: Heinrich J. Völk
Publisher: Springer Science & Business Media
ISBN: 9400901712
Category : Science
Languages : en
Pages : 447

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The `International Heidelberg Workshop on TeV Gamma-Ray Astrophysics' brought together astrophysicists from the various fields which play a role in the formation of high energy gamma-ray emission. In particular, theoretical and observational aspects of the physics and astrophysics of pulsars and quasars, the acceleration of particles at Supernova Remnants and other strong astrophysical shock fronts, and cascade processes in universal background photon fields were comprehensively discussed in more than thirty reviews by leading experts. In their entirety these reviews describe the birth of a new field of astronomy. This field concerns cosmic gamma-rays of very high energy which are observed with ground-based optical telescopes due to the Cherenkov emission of the secondary particles created by the interaction of these gamma-rays with atoms in the Earth's atmosphere. Beyond that, the workshop encompassed the latest developments and trends in theory and observation of cosmic gamma-ray sources of all energies, from nuclear gamma-ray lines in the MeV-region, through the Bremsstrahlung, Inverse Compton, and pion decay continuum emission, to gamma-rays due the decay of exotic relics from the early Universe. Audience: Specialists as well as students in physics and astrophysics and young research workers.

Author: Nicole Firestone
Publisher:
ISBN:
Category :
Languages : en
Pages :

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As neutrally-charged astrophysical messengers, gamma rays serve as powerful tools for determining the origins of incredibly high-energy particles from across our universe [1]. Gamma rays are considered to have the highest energy of all electromagnetic radiation, with energies spanning from 0.5 MeV to about 100 TeV [2]. Although lower-energy gamma rays can originate from within our solar system, gamma rays in the GeV and TeV ranges tend to originate from sources beyond our solar system [1]. By investigating these sources, we can understand more about the astrophysical phenomena that characterize the most extreme conditions in our universe, such as supernova remnants, gamma-ray bursts, and pulsars [3]. The High Altitude Water Cherenkov Gamma-Ray Observatory (HAWC) is one of the most sensitive gamma-ray detectors in the very high energy (VHE) regime, with the capability to observe gamma rays from 100 GeV and 100 TeV [4]. In 2017, HAWC conducted a blind search encompassing two thirds of the sky and 508 days of observations [4]. In this search, there were 16 VHE gamma-ray excesses that were unassociated with any previously discovered gamma-ray sources [4]. Now with data from 1523 days of observations, we begin to study these 16 unassociated candidate TeV sources in more detail. In this work, we update the locations of maximum significance for these candidate TeV sources and analyze the temporal progression of their significance and flux. This allows us to determine if they have faded into the diffuse gamma radiation or if they can still be considered unassociated candidate TeV sources. We then reevaluate the morphologies and spectral energy distributions of the remaining sources and discuss any recent observations from other gamma-ray observatories. We find that 10 of these 16 unassociated candidate TeV sources can still be considered candidate sources. In the future, we plan to use data from other observatories to continue to put better constrains on the morphology and spectral energy distributions for these sources and better understand their acceleration mechanisms. In addition, we plan to conduct a similar investigation with new HAWC excesses discovered with recent data from 1523 days of observations [5]. By investigating these excesses in the high-energy gamma-ray sky, we can discover and characterize new extreme astrophysical phenomena and ultimately uncover valuable information about the physical mechanisms that accelerate particles to very high energies.

Author: Zachary Dean Griffith
Publisher:
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Languages : en
Pages : 0

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Over the last several decades, a wealth of observations of gamma-ray emission at TeV energies has increased our understanding of the extreme physical processes happening in our Galaxy. However, fundamental questions remain unanswered. To how high an energy are cosmic rays able to be accelerated in our galaxy, and how does that connect with the features observed in the cosmic-ray energy spectrum such as the "knee'', the "second knee'', and the "ankle''? Answers to these questions can be searched for by extending gamma-ray observations to higher energies. As the only experiment sensitive to PeV gamma rays in the Southern Hemisphere, the IceCube observatory can address these issues from a unique perspective. In this work, gamma-ray candidate events are selected from data observed by the surface and in-ice arrays of the IceCube observatory. This is accomplished by leveraging characteristic properties of gamma-ray induced air showers such as low muonic content and a deep shower maximum. Using five years of data, several searches for gamma-ray emission using unbinned likelihood methods are presented. The results of all searches are consistent with background, resulting in 90% flux upper limits that are the most stringent ever placed on PeV emission. The limits set on PeV gamma-ray point sources constrain, for the first time, the energy extension of a power-law flux for sources observed by HESS to have no break in their energy spectrum at TeV energies. Additionally, the resulting limit set by a search for an angular-integrated diffuse flux from the Galactic plane provides an upper bound useful for constructing Galactic cosmic-ray transport models

Author:
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Languages : en
Pages :

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This article provides a theory of using Liouville's theorem to map the anisotropy of TeV cosmic rays seen at Earth using the particle distribution function in the local interstellar medium (LISM). The ultimate source of cosmic ray anisotropy is the energy, pitch angle, and spatial dependence of the cosmic ray distribution function in the LISM. Because young nearby cosmic ray sources can make a special contribution to the cosmic ray anisotropy, the anisotropy depends on the source age, distance and magnetic connection, and particle diffusion of these cosmic rays, all of which make the anisotropy sensitive to the particle energy. When mapped through the magnetic and electric field of a magnetohydrodynamic model heliosphere, the large-scale dipolar and bidirectional interstellar anisotropy patterns become distorted if they are seen from Earth, resulting in many small structures in the observations. Best fits to cosmic ray anisotropy measurements have allowed us to estimate the particle density gradient and pitch angle anisotropies in the LISM. It is found that the heliotail, hydrogen deflection plane, and the plane perpendicular to the LISM magnetic field play a special role in distorting cosmic ray anisotropy. These features can lead to an accurate determination of the LISM magnetic field direction and polarity. The effects of solar cycle variation, the Sun's coronal magnetic field, and turbulence in the LISM and heliospheric magnetic fields are minor but clearly visible at a level roughly equal to a fraction of the overall anisotropy amplitude. Lastly, the heliospheric influence becomes stronger at lower energies. Below 1 TeV, the anisotropy is dominated by small-scale patterns produced by disturbances in the heliosphere.

Author: Ulisses Barres de Almeida
Publisher: Mdpi AG
ISBN: 9783036557274
Category :
Languages : en
Pages : 0

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This volume celebrates the 30th anniversary of the first very-high energy (VHE) gamma-ray Source detection: the Crab Nebula, observed by the pioneering ground-based Cherenkov telescope Whipple, at teraelectronvolts (TeV) energies, in 1989. As we entered a new era in TeV astronomy, with the imminent start of operations of the Cherenkov Telescope Array (CTA) and new facilities such as LHAASO and the proposed Southern Wide-Field Gamma-ray Observatory (SWGO), we conceived of this volume as a broad reflection on how far we have evolved in the astrophysics topics that dominated the field of TeV astronomy for much of recent history. In the past two decades, H.E.S.S., MAGIC and VERITAS pushed the field of TeV astronomy, consolidating the field of TeV astrophysics, from few to hundreds of TeV emitters. Today, this is a mature field, covering almost every topic of modern astrophysics. TeV astrophysics is also at the center of the multi-messenger astrophysics revolution, as the extreme photon energies involved provide an effective probe in cosmic-ray acceleration, propagation and interaction, in dark matter and exotic physics searches. The improvement that CTA will carry forward and the fact that CTA will operate as the first open observatory in the field, mean that gamma-ray astronomy is about to enter a new precision and productive era. This book aims to serve as an introduction to the field and its state of the art, presenting a series of authoritative reviews on a broad range of topics in which TeV astronomy provided essential contributions, and where some of the most relevant questions for future research lie.

Author:
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Languages : en
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The MINOS Near and Far Detectors are two large, functionally-identical, steel-scintillating sampling calorimeters located at depths of 220 mwe and 2100 mwe respectively. The detectors observe the muon component of hadronic showers produced from cosmic ray interactions with nuclei in the earth's atmosphere. From the arrival direction of these muons, the anisotropy in arrival direction of the cosmic ray primaries can be determined. The MINOS Near and Far Detector have observed anisotropy on the order of 0.1% at 1 and 11 TeV respectively. The amplitude and phase of the first harmonic at 1 TeV are 8.2 ± 1.7(stat.) x 10−4 and (8.9 ± 12.1(stat.)){sup o}, and at 11 TeV are 3.8 ± 0.5(stat.) x 10−4 and (27.2 ± 7.2(stat.)){sup o}.