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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.
Gamma-ray binaries are systems that comprise a compact object orbiting a companion star and display the maximum of the non-thermal Spectral Energy Distribution (SED) in gamma rays. Currently we know five gamma-ray binaries. All of them host an early type star and a compact object of unknown nature, either a black hole or a neutron star, except for one of them where radio pulsations have been detected. The optical emission received from gamma-ray binaries is produced by the optical star and its environment. If the optical star is a Be star, then it presents a circumstellar decretion disk, being its size traced by the Equivalent Width of the Halpha line (EW). Numerical simulations of gamma-ray binaries hosting a Be star suggest that the circumstellar decretion disk is perturbed/disrupted during the periastron passage of the compact object by the tidal forces and/or the putative pulsar wind. The circumstellar disk contribution to the optical photometry is a significant fraction of the total optical emission. The observed optical photometric flux from it will be proportional to the projected area of the optically emitting disk. Therefore, any orbital variability in the optical light curves can be associated to changes in the circumstellar disk. We conducted long-term optical photometric and EW observations of the gamma-ray binary LS I +61 303, aimed to unveil the optical superorbital variability seen at other wavelengths. We obtained the following results from the observations: 1) The optical photometry and EW present a superorbital variability of the orbital phase of the maximum, as seen in radio and X-rays, providing an evidence of the coupling between the thermal and non-thermal emission processes in LS I +61 303. 2) The optical observations present a superorbital variability of the flux compatible with the 1667 d superorbital period. 3) This superorbital variability is attenuated or missing in some orbital phases. 4) Orbital variability in a multi-wavelength context presents lags that can be naturally interpreted considering different emitting regions. 5) The observations seem to be only compatible with an extended and (quasi)-coplanar circumstellar disk. 6) The observations are compatible with a density wave scenario, and with a very restrictive precessing-disk model. Gamma-ray binaries hosting a massive star and a young non-accreting pulsar present strong interaction between the relativistic pulsar wind, and the wind of the stellar companion, resulting in efficient particle acceleration and in the production of non-thermal radiation, from radio to gamma rays. The study of the dynamical interaction between the winds can be conducted through numerical simulations, allowing a qualitative analysis of the radiative output of the system. Furthermore, the two-wind interaction region might suffer the impact of an inhomogeneous stellar wind (hereafter clumps), making its dynamics and hence its radiative output more complex. We conducted RHD simulations of the interaction of relativistic winds from young pulsars with inhomogeneous stellar winds aimed to provide a plausible framework for the high-energy variability observed in gamma-ray binaries. We obtained the following results from the numerical simulations: 1) The two-wind interaction structure is very unstable and sensitive to the tiniest perturbations, which lead to quick Rayleigh-Taylor (RT) and in particular Kelvin-Helmholtz (KH) instability growth. 2) The arrival of clumps can have a very strong impact on the whole interaction structure, which is expected to strongly affect the non-thermal radiation as well. 3) The clumps trigger violent RT/KH instabilities leading to quick changes of the shocked pulsar-wind region. 4) Clumps generate quick and global variations in the shocked pulsar wind. This can lead to strong short time-scale flux variability in the non-thermal radiation of gamma-ray binaries.
In view of the current and forthcoming observational data on pulsar wind nebulae, this book offers an assessment of the theoretical state of the art of modelling them. The expert authors also review the observational status of the field and provide an outlook for future developments. During the last few years, significant progress on the study of pulsar wind nebulae (PWNe) has been attained both from a theoretical and an observational perspective, perhaps focusing on the closest, more energetic, and best studied nebula: the Crab, which appears in the cover. Now, the number of TeV detected PWNe is similar to the number of characterized nebulae observed at other frequencies over decades of observations. And in just a few years, the Cherenkov Telescope Array will increase this number to several hundreds, actually providing an essentially complete account of TeV emitting PWNe in the Galaxy. At the other end of the multi-frequency spectrum, the SKA and its pathfinder instruments, will reveal thousands of new pulsars, and map in exquisite detail the radiation surrounding them for several hundreds of nebulae. By carefully reviewing the state of the art in pulsar nebula research this book prepares scientists and PhD students for future work and progress in the field.
Accretion flows, winds and jets of compact astrophysical objects and stars are generally described within the framework of hydrodynamical and magnetohydrodynamical (MHD) flows. Analytical analysis of the problem provides profound physical insights, which are essential for interpreting and understanding the results of numerical simulations. Providing such a physical understanding of MHD Flows in Compact Astrophysical Objects is the main goal of this book, which is an updated translation of a successful Russian graduate textbook. The book provides the first detailed introduction into the method of the Grad-Shafranov equation, describing analytically the very broad class of hydrodynamical and MHD flows. It starts with the classical examples of hydrodynamical accretion onto relativistic and nonrelativistic objects. The force-free limit of the Grad-Shafranov equation allows us to analyze in detail the physics of the magnetospheres of radio pulsars and black holes, including the Blandford-Znajek process of energy extraction from a rotating black hole immersed in an external magnetic field. Finally, on the basis of the full MHD version of the Grad-Shafranov equation the author discusses the problems of jet collimation and particle acceleration in Active Galactic Nuclei, radio pulsars, and Young Stellar Objects. The comparison of the analytical results with numerical simulations demonstrates their good agreement. Assuming that the reader is familiar with the basic physical and mathematical concepts of General Relativity, the author uses the 3+1 split approach which allows the formulation of all results in terms of physically clear language of three dimensional vectors. The book contains detailed derivations of equations, numerous exercises, and an extensive bibliography. It therefore serves as both an introductory text for graduate students and a valuable reference work for researchers in the field.
This book presents the theory of the electrodynamic phenomena that occur in the magnetosphere of a pulsar. It also provides a clear picture of the formation and evolution of neutron stars. The authors address the basic physical processes of electron-positron plasma production, the generation of electric fields and currents, and the emission of radio waves and gamma rays. The book also reviews the current observational data, and devotes a complete chapter to a detailed comparison of this data with accepted theory and with some recent theoretical predictions. Tables containing the values of the physical parameters of all observed radio pulsars are also provided.
This volume extends the ISSI series on magnetic fields in the Universe into the domain of what are by far the strongest fields in the Universe, and stronger than any field that could be produced on Earth. The chapters describe the magnetic fields in non-degenerate strongly magnetized stars, in degenerate stars (such as white dwarfs and neutron stars), exotic members called magnetars, and in their environments, as well as magnetic fields in the environments of black holes. These strong fields have a profound effect on the behavior of matter, visible in particular in highly variable processes like radiation in all known wavelengths, including Gamma-Ray bursts. The generation and structure of such strong magnetic fields and effects on the environment are also described.
This book constitutes the proceedings of the XVIII International Symposium on Lepton-Photon Interactions. It contains 30 review papers on the latest developments by experts in the field. The subjects cover the structure of photons and hadrons, progress in QCD and diffraction, heavy quark (c, b, t) physics, electroweak precision measurements and tests, CP violation, neutrino physics, searches for new particles and phenomena, cosmology, progress in theory and physics at future colliders.
We present a deep observation with the X-Ray Multimirror Mission of PSR B1823-13, a young pulsar with similar properties to the Vela pulsar. We detect two components to the X-ray emission associated with PSR B1823-13: an elongated core of extent 30 min immediately surrounding the pulsar embedded in a fainter, diffuse component of emission 5 sec in extent, seen only on the southern side of the pulsar. The pulsar itself is not detected, either as a point source or through its pulsations. Both components of the X-ray emission are well fitted by a power-law spectrum, with photon index Gamma approx. 1.6 and X-ray luminosity (0.5-10 keV) L(sub X) approx. 9 x 10(exp 32) ergs/s for the core and Gamma approx. 2.3 and L(sub X) approx. 3 x 10(exp 33) ergs/s for the diffuse emission, for a distance of 4 kpc. We interpret both components of emission as corresponding to a pulsar wind nebula, which we designate G18.0-0.7. We argue that the core region represents the wind termination shock of this nebula, while the diffuse component indicates the shocked downstream wind. We propose that the asymmetric morphology of the diffuse emission with respect to the pulsar is the result of a reverse shock from an associated supernova remnant, which has compressed and distorted the pulsar-powered nebula. Such an interaction might be typical for pulsars at this stage in their evolution. The associated supernova remnant is not detected directly, most likely being too faint to be seen in existing X-ray and radio observations. Gaensler, Bryan and Mushotzky, Richard (Technical Monitor) Goddard Space Flight Center