A Search for the Extragalactic Magnetic Field Via Its Influence on the Gamma-ray Signals from Blazars PDF Download
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Author: Thomas Raymond Weisgarber
Publisher:
ISBN: 9781267438843
Category :
Languages : en
Pages : 152
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Book Description
In this work, I develop a new method for accurately quantifying the extended gamma-ray halo that arises due to the influence of the EGMF on the extragalactic cascades. This method is sensitive to EGMF strengths between 3 × 10 –17 and 10–14 Gauss. I compare the predictions from a Monte Carlo simulation to combined data from ground-based imaging atmospheric Cherenkov telescopes and the Fermi Gamma-Ray Space Telescope in an attempt to measure or constrain the properties of the EGMF. Depending on certain assumptions about the source lifetime, I interpret the absence of any detectable gamma-ray halo around the blazars RGB J0710+591 and 1ES 0229+200 as evidence for an EGMF with a strength greater than 3 × 10 –15 Gauss. This represents the strongest firm lower limit on the EGMF strength at the present time.
Author: Thomas Raymond Weisgarber
Publisher:
ISBN: 9781267438843
Category :
Languages : en
Pages : 152
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Book Description
In this work, I develop a new method for accurately quantifying the extended gamma-ray halo that arises due to the influence of the EGMF on the extragalactic cascades. This method is sensitive to EGMF strengths between 3 × 10 –17 and 10–14 Gauss. I compare the predictions from a Monte Carlo simulation to combined data from ground-based imaging atmospheric Cherenkov telescopes and the Fermi Gamma-Ray Space Telescope in an attempt to measure or constrain the properties of the EGMF. Depending on certain assumptions about the source lifetime, I interpret the absence of any detectable gamma-ray halo around the blazars RGB J0710+591 and 1ES 0229+200 as evidence for an EGMF with a strength greater than 3 × 10 –15 Gauss. This represents the strongest firm lower limit on the EGMF strength at the present time.
![Probing Intergalactic Magnetic Fields from [gamma]-ray Observations PDF](https://books.google.com/books/content/images/frontcover/Y1BinQAACAAJ?fife=w80-h100)
Author: Wenlei Chen
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 171
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Book Description
The large-scaled magnetic fields in intergalactic space may contain detailed information of the primordial magnetic fields produced in the early Universe. The generation of the cosmological matter-antimatter asymmetry may produce helical magnetic fields via CP (charge conjugation and parity) violating interactions during matter-genesis. Thus, the study of the intergalactic magnetic field (IGMF) could provide a new window on early-Universe cosmology. IGMFs deflect the electron-positron pairs produced by TeV gamma-rays from blazars, resulting in broadened beams of cascade GeV gamma-rays known as pair halos. In the presence of helical IGMFs, cascade GeV gamma-rays at different energies from a distant source fall into patterns in the observation plane in the GeV gamma-ray sky that have a similar chirality. These signatures of the IGMF on the gamma-ray emission from extragalactic sources, i.e. pair halos and helical patterns, can be observed using data from the Fermi Large Area Telescope (Fermi-LAT). In this dissertation, I describe methods for probing the IGMF using gamma-ray observations. I report on the results of a search for gamma-ray pair halos with a stacking analysis of low-redshift blazars using data from Fermi-LAT. For this analysis we used a number of a priori selection criteria, including the spatial and spectral properties of the Fermi sources. The angular distribution of ~1 GeV photons around 24 stacked isolated high-synchrotron-peaked BL Lacs with redshift z 0.5 shows an excess over that of point-like sources. A frequentist test yields a p-value of p ~0.01 for the extended emission against the point-source hypothesis. A Bayesian estimation provides the common logarithm of Bayes factors 2, consistent with expectations for pair halos produced in the IGMF with strength of ~10−17 to 10−15 Gauss. In addition, I present a search for parity violating signatures of helical IGMFs in the GeV gamma-ray sky. In this study, the IGMF helicity is examined by evaluating a parity-odd statistic using gamma-ray data obtained from Fermi-LAT observations at high galactic latitudes. The resulting negative values of the parity-odd statistic imply that there is an excess of left-handed spirals in the gamma-ray sky, indicating a left-handed helicity consistent with a helical magnetic field with strength of ~10−14 Gauss on ~10 Mpc scales.
Author: Tonia M. Venters
Publisher:
ISBN: 9781109314168
Category :
Languages : en
Pages : 54
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Book Description
As very-high--energy photons propagate through the extragalactic background light (EBL), they interact with the soft photons and initiate electromagnetic cascades of lower energy photons and electrons. The collective intensity of a cosmological population emitting at very-high energies (VHE) will be attenuated at the highest energies through interactions with the EBL and enhanced at lower energies by the resulting cascade. We calculate the cascade radiation created by VHE photons produced by blazars and investigate the effects of cascades on the collective intensity of blazars and the resulting effects on the extragalactic gamma-ray background. We find that cascade radiation greatly enhances the collective intensity from blazars at high energies before turning over due to attenuation. The prominence of the resulting features depends on the blazar gamma-ray luminosity function, spectral index distribution, and the model of the EBL. We additionally calculate the cascade radiation from the distinct spectral sub-populations of blazars, BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs), finding that the collective intensity of BL Lacs is considerably more enhanced by cascade radiation than that of the FSRQs. Finally, we discuss the implications that this analysis and upcoming Fermi observations could have for the nature of the EBL, the evolution of blazars, blazar spectra, and other sources of gamma-ray emission.
Author: Josep M. Paredes
Publisher: Springer Science & Business Media
ISBN: 140206117X
Category : Science
Languages : en
Pages : 496
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Book Description
This book provides a theoretical and observational overview of the state of the art of gamma-ray astrophysics, and their impact and connection with the physics of cosmic rays and neutrinos. With the aim of shedding new and fresh light on the problem of the nature of the gamma-ray sources, particularly those yet unidentified, this book summarizes contributions to a workshop that continues today.
Author: Timothy Christian Arlen
Publisher:
ISBN:
Category :
Languages : en
Pages : 210
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Book Description
Gamma ray photons, with energies>TeV propagating cosmological distances will be attenuated by pair production with diffuse extragalactic background photon fields-both the cosmic microwave background (CMB) radiation and the UV - far-IR extragalactic background light (EBL). The produced electron/positron pairs will subsequently inverse Compton scatter background photons up to GeV - TeV energies, and some of these upscattered photons may also initiate pair production in the formation of an electromagnetic cascade. If an intergalactic magnetic field (IGMF) exists on cosmological length scales of relevance to the cascade, it will deflect the electrons and positrons and will leave an imprint on the resulting spectral, angular, and temporal properties of the cascade radiation. The primary goal of this study was to constrain the properties of the IGMF using data from known sources of TeV gamma-rays. This thesis describes the construction of a high precision, 3-dimensional, particle-tracking Monte Carlo simulation code to model the intergalactic electromagnetic cascade, and uses it to systematically explore the effects of the IGMF on the cascades in multiple observational domains. We then compare the simulations with gamma-ray data from current generation ground-based gamma-ray instruments such as VERITAS, HESS, and MAGIC, sensitive to TeV-scale energies, as well as the Fermi satellite, sensitive to the GeV-scale. This novel technique of constraining the IGMF has rapidly emerged over the last decade as gamma-ray instruments have become more sensitive and as theoretical understanding of the cascade process has progressed. This emerging field has proven to be richly complex and we find that the data from current generation gamma-ray instruments do not allow for an unambiguous upper or lower limit to be placed on the IGMF at present. We do find it likely that the next generation ground based gamma-ray observatory, the Cherenkov Telescope Array (CTA) will be able to detect unambiguous signatures of gamma-ray cascading if the IGMF magnitude is within a certain range, and thus provide a robust constraint on IGMF properties.
Author: Timothy Robishaw
Publisher: Universal-Publishers
ISBN: 1599426846
Category : Science
Languages : en
Pages : 173
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Book Description
According to astrophysical theory, magnetic fields should play an important role in the structure and dynamics of the interstellar medium. While astronomical observations confirm this directly, the observational record is sparse. This is because magnetic fields can only be measured via polarimetric methods, and most of these methods can only provide an indirect inference of the magnetic field strength. The Zeeman effect, however, is the only method by which in situ measurements of astrophysical magnetic fields can be made. The spectral signature of Zeeman splitting is imprinted in the circular polarization spectrum of radiation received from an astronomical source. In order to make a reliable detection at radio frequencies, one must employ careful calibrations and account for instrumental effects. We begin this dissertation by covering the fundamentals of radio spectropolarimetry. We then offer historical details regarding the Zeeman effect and its use in single-dish radio observations. We present an outline of how one accurately measures the Zeeman effect using large single-dish radio telescopes. We follow this with results from an assessment of the polarization properties of the 100 m Green Bank Telescope (GBT). We then present magnetic field detections made via the Zeeman effect from the Galactic scale to cosmological distances. We begin with GBT observations of 21 cm emission toward the Taurus Molecular Cloud (TMC) complex. Recent observations have suggested that fields stronger than 20 microgauss are located at the distance of the TMC. Our Zeeman observations rule out fields of this strength, but do show a clear +5 microgauss detection from HI emission at the velocity of the TMC. More surprisingly, we have discovered multiple detections of a line-of-sight magnetic field of strength roughly +40 microgauss in a filament near -50 km/s. We then present a windfall of detections of milligauss-strength magnetic fields in starburst galaxies. Detected by means of Zeeman splitting of 1667 MHz hydroxyl megamaser emission, these Arecibo and GBT results represent the first extragalactic Zeeman measurements to probe the field inside an external galaxy. Finally, we climb the cosmological distance ladder, and present a dramatic GBT detection of a magnetic field in a damped Lyman-alpha absorber at a redshift of 0.692. We discuss possible scenarios for the creation of an 84 microgauss field at a look-back time of 6.4 Gyr.
Author: T.C. Weekes
Publisher: CRC Press
ISBN: 1420033190
Category : Science
Languages : en
Pages : 234
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Book Description
High energy gamma-ray photons are the prime probes of the relativistic or high-energy universe, populated by black holes, neutron stars, supernovae, quasars, and matter-antimatter annihilations. Through studying the gamma-ray sky, astrophysicists are able to better understand the formation and behavior of these exotic and energetic bodies. V
Author: A.A. Ruzmaikin
Publisher: Springer Science & Business Media
ISBN: 9400928351
Category : Science
Languages : en
Pages : 322
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Book Description
Magnetism, when extended beyond normal frameworks into cosmic space is characterized by an enormous spatial scale. Because of their large sizes the nature of magnets such as the Earth and the Sun is entirely different from the nature of a horseshoe magnet. The source of cosmic magnetism is associated with the hydrodynamic motions of a highly conductive medium. In this aspect, cosmic magnets resemble a dynamo. However, currents in the dynamo flow along properly ordered wires, while chaotic, turbulent motions are dominant inside stars and liquid planetary cores. This makes more intriguing and surprising the fact that these motions maintain a regular magnetic field. Maintenance of magnetic fields is even more impressive in huge magnets, i.e. galaxies. In fact, we are living inside a giant dynamo machine, the Milky Way galaxy. Although the idea of the global magnetic field of our Galaxy was clearly proposed almost 40 years ago, firm observational evidence and definite theoretical concepts of galactic magnetism have been developed only in the last decade. This book is the first attempt at a full and consistent presentation of this problem. We discuss both theoretical views on the origin of galactic magnetism and the methods of observational study. Previous discussions were on the level of review articles or separate chapters in monographs devoted to cosmic magnetic fields (see, e.g., H. K. Moffatt, 1978, E. N. Parker, 1979 and Zeldovich et aI., 1983).
Author: Richard Wielebinski
Publisher: Springer Science & Business Media
ISBN: 9783540241751
Category : Science
Languages : en
Pages : 306
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Book Description
While magnetic fields permeate the universe on all scales, the present book is dedicated to their investigation on the largest scales and affords a balanced account of both theoretical and observational aspects. Written as a set of advanced lectures and tutorial reviews that lead up to the forefront of research, this book offers both a modern source of reference for the experienced researchers as well as a high-level introductory text for postgraduate students and nonspecialist researchers working in related areas.
![A Study of the Intergalactic Magnetic Field Using Extra-galactic Ultra High Energy [gamma]-ray Sources PDF](https://books.google.com/books/content/images/frontcover/VK2GuAAACAAJ?fife=w80-h100)
Author: M. Honda
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Book Description
