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Author: Robert Archibald
Publisher:
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Languages : en
Pages :
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"Pulsars are the rotating compact remnants of exploded massive stars. The region surrounding the neutron star, known as the magnetosphere, has properties which are determined by the magnetic ield of the star. In this thesis, I present several observational results involving rotation-powered radio pulsars and magnetars which indicate that pulsar magnetospheres have a more complex structure than a simple dipole, and that the magnetosphere can have a strong efect on all the observed properties of neutron stars. One way to probe the pulsar magnetosphere is through the measurement of braking indices. A braking index quantifies the dependence of the torque on the spin frequency. In Chapter 4 I present a long-term timing study of the rotation-powered pulsar PSR J1846−0258, where we show that the change in braking index reported in this source is long-lived. The most plausible explanation for this changed braking index appears to be due to a change in magnetospheric configuration. In Chapter 5, I present the measurement of a new braking index for the rotation-powered pulsar PSR J1640−4631 of n= 3.15 ± 0.03 - the first measured braking index higher than the canonical three of a magnetic dipole. This result demonstratesthat other physical mechanisms, such as mass or magnetic quadrupole moments most likely need to be taken into account to describe pulsar spin-down & energetics.Another way to probe the magnetospheres of pulsars is by studying the extreme variability seen in the magnetar class. In Chapter 6 I present two years of flux and spin evolution monitoring of the magnetar 1E 1048.1−5937 following an outburst. By comparing to previous outbursts from the source, we show that this pattern of behaviour repeats itself with a quasi-period of ∼1800 days. This behaviour, when compared to similar less extreme events seen in rotation-powered pulsars, appears to implicate processes in the stellar magnetosphere. In Chapter 7, I present the results of monitoring the magnetar 4U 0142+61 over two outbursts, including one with a net spin-down timing event, and compare this timing event to previous such events in other pulsars with high magnetic fields anddiscuss net spin-down glitches now seen in several young, high-B pulsars. The observations that these spin-down events occur in only high-B sources strongly implicates the influence of a large magnetic field in spin-down events and, coupled with the radiatively loud nature of the plurality of spin-down events, suggests an origin in the magnetosphere of the star. In Chapter 8 I present observations of a magnetar-like outburst from the high-magnetic-field pulsar PSR J1119−6127, providing an unambiguous connection between the radio pulsar and magnetar populations.Finally, in Chapter 9, I put these new results in context with recent advances in neutron-star astrophysics, and speculate on avenues for future advancement in the field." --
Author: Robert Archibald
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"Pulsars are the rotating compact remnants of exploded massive stars. The region surrounding the neutron star, known as the magnetosphere, has properties which are determined by the magnetic ield of the star. In this thesis, I present several observational results involving rotation-powered radio pulsars and magnetars which indicate that pulsar magnetospheres have a more complex structure than a simple dipole, and that the magnetosphere can have a strong efect on all the observed properties of neutron stars. One way to probe the pulsar magnetosphere is through the measurement of braking indices. A braking index quantifies the dependence of the torque on the spin frequency. In Chapter 4 I present a long-term timing study of the rotation-powered pulsar PSR J1846−0258, where we show that the change in braking index reported in this source is long-lived. The most plausible explanation for this changed braking index appears to be due to a change in magnetospheric configuration. In Chapter 5, I present the measurement of a new braking index for the rotation-powered pulsar PSR J1640−4631 of n= 3.15 ± 0.03 - the first measured braking index higher than the canonical three of a magnetic dipole. This result demonstratesthat other physical mechanisms, such as mass or magnetic quadrupole moments most likely need to be taken into account to describe pulsar spin-down & energetics.Another way to probe the magnetospheres of pulsars is by studying the extreme variability seen in the magnetar class. In Chapter 6 I present two years of flux and spin evolution monitoring of the magnetar 1E 1048.1−5937 following an outburst. By comparing to previous outbursts from the source, we show that this pattern of behaviour repeats itself with a quasi-period of ∼1800 days. This behaviour, when compared to similar less extreme events seen in rotation-powered pulsars, appears to implicate processes in the stellar magnetosphere. In Chapter 7, I present the results of monitoring the magnetar 4U 0142+61 over two outbursts, including one with a net spin-down timing event, and compare this timing event to previous such events in other pulsars with high magnetic fields anddiscuss net spin-down glitches now seen in several young, high-B pulsars. The observations that these spin-down events occur in only high-B sources strongly implicates the influence of a large magnetic field in spin-down events and, coupled with the radiatively loud nature of the plurality of spin-down events, suggests an origin in the magnetosphere of the star. In Chapter 8 I present observations of a magnetar-like outburst from the high-magnetic-field pulsar PSR J1119−6127, providing an unambiguous connection between the radio pulsar and magnetar populations.Finally, in Chapter 9, I put these new results in context with recent advances in neutron-star astrophysics, and speculate on avenues for future advancement in the field." --
Author: Margaret Anne Livingstone
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: James J. Condon
Publisher: Princeton University Press
ISBN: 069113779X
Category : Science
Languages : en
Pages : 376
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Book Description
The ideal text for a one-semester course in radio astronomy Essential Radio Astronomy is the only textbook on the subject specifically designed for a one-semester introductory course for advanced undergraduates or graduate students in astronomy and astrophysics. It starts from first principles in order to fill gaps in students' backgrounds, make teaching easier for professors who are not expert radio astronomers, and provide a useful reference to the essential equations used by practitioners. This unique textbook reflects the fact that students of multiwavelength astronomy typically can afford to spend only one semester studying the observational techniques particular to each wavelength band. Essential Radio Astronomy presents only the most crucial concepts—succinctly and accessibly. It covers the general principles behind radio telescopes, receivers, and digital backends without getting bogged down in engineering details. Emphasizing the physical processes in radio sources, the book's approach is shaped by the view that radio astrophysics owes more to thermodynamics than electromagnetism. Proven in the classroom and generously illustrated throughout, Essential Radio Astronomy is an invaluable resource for students and researchers alike. The only textbook specifically designed for a one-semester course in radio astronomy Starts from first principles Makes teaching easier for astronomy professors who are not expert radio astronomers Emphasizes the physical processes in radio sources Covers the principles behind radio telescopes and receivers Provides the essential equations and fundamental constants used by practitioners Supplementary website includes lecture notes, problem sets, exams, and links to interactive demonstrations An online illustration package is available to professors
Author: Prakash Arumugasamy
Publisher:
ISBN:
Category :
Languages : en
Pages :
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The dissertation focuses on the study of rotation-powered pulsars, the primary observational manifestation of neutron stars. These objects are powerful sources of electromagnetic radiation and relativistic particles whose emission is provided by the loss of pulsar rotational energy. Understanding the evolution of pulsars, which happens over billion year timescales, requires detection and study of pulsars at different stages of evolution. I present detailed X-ray analyses of pulsars at four distinct stages of evolution and compare their emission behavior with that of other pulsars expected to be in similar evolutionary stages. I also show key characteristics of the pulsars that make them unique in their group. I start with a young and energetic pulsar, PSR J2022+3842 (characteristic age approximately 9 kyr, spin-down power = 3E37 erg/s), with powerful non-thermal emission. X-ray timing of the pulsar revealed double-peaked X-ray profile with a period twice the previously established value. Our analysis allowed us to update the pulsar's spin-down power and X-ray efficiency using the correct timing results, which brought the pulsar more in-line with other young X-ray pulsars. I also provide the phase-dependent behavior of the pulsar's non-thermal emission. Pulsars with true ages, often substituted by characteristic age, below ~ 100 kyr are considered young and ones with ages > 1 Myr are considered old, with the 'middle-aged' pulsars in the middle. My next pulsar is a 1.8 Myr old J1836+5925 (spin-down power = 1E34 erg/s), which is perhaps the brightest X-ray source among the oldest pulsars still observable in the gamma-rays. Detailed timing and spectral analyses show strong evidence of an absorption feature (perhaps an electron cyclotron line) in the pulsar's spectrum. Characterizing its thermal emission might have important implications for the neutron star cooling models. Moving another two orders of magnitude up in characteristic age, we have one of the oldest known non-recycled X-ray pulsars, PSR J0108-3430, with characteristic age = 166 Myr and spin-down power = 5.8E30 erg/s. The pulsar's spectrum likely consists of a thermal component, emitted from a hot polar cap, and a non-thermal component, emitted from its magnetosphere. The X-ray pulse profile shows a single, asymmetric peak which could be explained by an axially-asymmetric temperature distribution at the pole or by the non-thermal emission from the outer gap. The three pulsars represent important stages in the evolutionary path that a hypothetical single young pulsar like J2022+3842 might take, as it passes through stages close to gamma-ray emission turn-off (like J1836+5925) and X-ray turn-off (similar to J0108-3430).Pulsars in binaries can follow an alternative path. By accreting matter from their companions they can be 'recycled' to short millisecond periods and emit X-rays and gamma-rays for billions of years. I also present a special class of such recycled pulsars which are believed to be in the process of fatally ablating their companions. I present the X-ray analysis of PSR J1446-4701, a pulsar with spin-down power = 3.6E34 erg/s in a 6.7 hr binary orbit, and PSR J1311-3430, a pulsar with spin-down power = 4.9E34 erg/s, in an extreme 1.6 hr binary orbit. PSR J1446-4701 turned out to be a non-eclipser with possibly low (face-on) orbital inclination, with emission from both the pulsar and the intra-binary shock observable throughout the binary orbit. PSR J1311-3430 is a known eclipser, in which we find hints of spectral variability between pulsar superior and inferior conjunction phases. I also present a comprehensive comparison of the sample of such extremely low-mass binary pulsars. We reveal the true nature of pulsars, slowly and steadily, usually one target at a time, but eventually we expect useful patterns to emerge that improves our understanding of the population of rotation powered pulsars.
Author: Silvia Zane
Publisher: Springer Science & Business Media
ISBN: 1402059981
Category : Science
Languages : en
Pages : 654
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Book Description
This book is a collation of the contributions presented at a major conference on isolated neutron stars held in London in April 2006. Forty years after the discovery of radio pulsars it presents an up-to-date description of the new vision of isolated neutron stars that has emerged in recent years. The great variety of isolated neutron stars, from pulsars to magnetars, is well covered by descriptions of recent observational results and presentations of the latest theoretical interpretation of these data.
Author: Emre Tepedelenlioǧlu
Publisher:
ISBN:
Category :
Languages : en
Pages : 126
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Author: Andrew Lyne
Publisher: Cambridge University Press
ISBN: 1107010144
Category : Science
Languages : en
Pages : 375
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Book Description
Now in its fourth edition, Pulsar Astronomy provides a thoroughly revised and updated introduction to the field of pulsar astronomy.
Author: Yu Wang
Publisher: Open Dissertation Press
ISBN: 9781361334539
Category :
Languages : en
Pages :
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This dissertation, "Non-thermal X-ray and Soft Gamma-ray Radiation From the Young Pulsars" by Yu, Wang, 王禹, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: This thesis focuses on the radiation mechanisms of non-thermal X-rays and soft gamma-rays of two types of thousands year old spin-down powered pulsars. The thousands year old pulsars have distinct radiation behaviors from the middle-aged gamma-ray pulsars. In the magnetosphere of the pulsar, the particles are accelerated by the electric field resulting from the rotation of the neutron star. These accelerated particles move along the magnetic field lines and emit GeV gamma-ray curvature photons. For the middle-aged pulsars, most of the curvature photons, whose observed spectra are described well by power law with exponential cut-off, can escape out of the light cylinder. In X-ray band, the middle-aged pulsars usually have black body radiation with a weak non-thermal component described by power law. On the other hand, for the thousands-year-old pulsars, the curvature spectra in GeV band, which obey power law with exponential cut-off, are smeared out by the pair creation or missed by the line of sight. The secondary pairs generated by pair creation processes spiral around the magnetic field lines and emit synchrotron photons, and the young pulsars have stronger non-thermal X-ray and soft gamma-ray radiation than the middle-aged ones. Seven young pulsars have been studied here, they are the Crab pulsar, PSRs B0540-69, B1509-58, J1846-0258, J1811-1925, J1617-5055 and J1930+1852. These seven fall into two categories: the Crab-like pulsars and soft gamma-ray pulsars. The Crab-like pulsars include the Crab pulsar and the Giant Crab PSR B0540-69, and the soft gamma-ray pulsars include the other five. The main difference between the two types of young pulsars is that the Crab-like pulsars' spectra peak at E DOI: 10.5353/th_b5177322 Subjects: Gamma ray astronomy X-ray astronomy Pulsars
Author: Hua Zhang
Publisher: Springer Nature
ISBN: 9819945267
Category : Science
Languages : en
Pages : 251
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Book Description
This book highlights key technologies of signal processing in pulsar-based navigation. It discusses the modeling, simulation, acquisition, and correction of relativistic effects of signals from X-ray pulsars. It demonstrates the methods of contour reconstruction and denoising, and introduces the concept and methods of the average contour. The performance of the phase measurement methods using signal contour is analyzed. The role of wavelets and bispectral methods in the denoising of pulsar signals is discussed. The measurements of pulsar signals’ arriving time are looked into from the perspective of time series. The book is intended for researchers and engineers interested in pulsar-based navigation. It is also a good reference source for senior undergraduates and postgraduate students majoring in navigation and signal processing.
Author: Rudy Wijnands
Publisher: American Institute of Physics
ISBN: 9780735405998
Category : Science
Languages : en
Pages : 274
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Book Description
In X-ray binaries, neutron stars (the very dense stellar remnants of heavy stars) accrete matter from a close-by companion star. This matter eventually falls on the neutron star, significantly affecting it. I.e., the star is spun up to very high spin rates. In the end, it might rotate 1000 times a second which causes very fast oscillations in its X-ray brightness. This workshop was to celebrate the 10th anniversary of the discovery of the first system in which this signal was found and discuss the most recent observational and theoretical insight in the nature of these systems.
