Probing The Geometry And Physics Of The Emission Region In Active Galactic Nuclei Using Hard X Ray Gamma Ray Observations

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Probing The Geometry And Physics Of The Emission Region In Active Galactic Nuclei Using Hard X Ray Gamma Ray Observations

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Author :
language : en
Publisher:
Release Date : 2010

Probing The Geometry And Physics Of The Emission Region In Active Galactic Nuclei Using Hard X Ray Gamma Ray Observations written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.

The X-ray spectra of (almost equal to)200 AGN collected from Swift-BAT were analyzed to test the Unified Model for AGN. Specifically, the photon indices, high energy cutoffs, and reflection components of Sy1 and Sy2 were compared. Under the Unified Model, the photon indices and reflection components for Sy1 should be larger than Sy2 and the high energy cutoffs should be the same. Fitting a simple power law model to the sample spectra proved to be insufficient. The PEXRAV model fit the spectra of the Sy1 and Sy2 significantly better, indicating that a reflection component and/or high energy cutoff exists as the Unified Model expects. Using both the simple power law and PEXRAV models it was concluded that in the population studied, Sy1 had a larger photon index than Sy2, as expected by the Unified Model. For Sy1 and Sy2, the reflection components were found to be compatible, but given the large errors, this finding cannot be said to be evidence against the Unified Model. However, it was concluded that Sy1 and Sy2 have different high energy cutoffs, which is unexpected under the Unified Model.

X Ray And Multiwavelength Studies Of Active Galactic Nuclei From Large Area Sky Surveys

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Author : Jianfeng Wu
language : en
Publisher:
Release Date : 2012

X Ray And Multiwavelength Studies Of Active Galactic Nuclei From Large Area Sky Surveys written by Jianfeng Wu and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.

Active galactic nuclei (AGNs) are ideal laboratories for fundamental physics and cosmology. Our knowledge of AGNs has been greatly advanced during the past decades thanks to the unprecedentedly powerful X-ray missions (e.g., Chandra, XMM-Newton, and Swift) and modern large area surveys in the optical/UV band (e.g., the Sloan Digital Sky Survey; SDSS). Studies on the relation between multiwavelength properties of AGNs can reveal the physics of AGN accretion process. In this dissertation, I mainly study the relation between the AGN X-ray properties and their optical/UV spectral properties on emission lines, absorption lines and continuum. I also investigate the X-ray properties of AGNs with extreme radio properties in the early Universe. (1) We studied the X-ray properties of a class of radio-quiet SDSS quasars with weak broad emission lines (weak-line quasars; WLQs). Although the WLQ population shows diverse X-ray properties, they have an excess of X-ray weak sources. Besides having weak emission lines, the X-ray weak WLQs generally show other unusual UV emission-line properties similar to those of the remarkable X-ray weak quasar PHL 1811 (e.g., highly blueshifted C IV lines, weak semi-forbidden lines, and strong UV Fe emission). They are classified as "PHL 1811 analogs". The X-ray weak WLQs also show a harder X-ray spectrum, while the WLQ with normal X-ray brightness have similar X-ray spectral properties to those of typical quasars. We proposed an AGN geometry which can potentially unify the X-ray weak and X-ray normal WLQ populations via orientation effect. The infrared-to-UV spectral energy distributions (SEDs) of X-ray weak and X-ray normal WLQs have consistent SEDs with those for typical quasars, which disfavors the BL Lac-like scenario for the nature of these quasars (Chapters 2 and 3). (2) We have led the best X-ray study to date on quasars with intermediate-width absorption lines (mini-BALs). We found the X-ray brightness of mini-BAL quasars are more close to those of typical quasars than to BAL quasars (which are generally X-ray weak), showing they do not have substantial X-ray absorption. Strong correlations were found between the X-ray brightness and UV absorption parameters, e.g., the absorption strength and maximum outflow velocity. We further proposed new UV absorption parameters which better correlate with the X-ray properties than existing parameters do (Chapter 4). (3) We studied the relation between the optical/UV luminosity and X-ray luminosity (quantified by the alpha_ox parameter) for the most-luminous quasars over a wide range of redshifts. Our correlation analyses provide better constraints on the alpha_ox-UV luminosity correlation. We have also verified that the alpha_ox parameter does not significantly evolve with redshift. We provide the individual and composite mid-infrared-to-UV SEDs for the most-luminous quasars. (Chapter 5). (4) We presented the X-ray and multiwavelength properties of the highly radio-loud quasars (HRLQs) at z > 4. Our HRLQs show a significant enhancement of X-ray emission over those HRLQs at lower redshift with similar optical/UV and radio luminosities, suggesting that the jet-linked X-ray emission mechanism in the early universe may differ from that in the more evolved universe. The optical/UV emission-line strength of RLQs are correlated with radio loudness, but not with relative X-ray brightness. Our HRLQs generally follow the anti-correlation between radio loudness and X-ray power-law photon index. We also studied the broad-band SEDs of HRLQs. Some HRLQs have an excess of mid-infrared emission which may originate from the jet synchrotron emission. None of our z > 4 HRLQs is detected by the Fermi LAT two-year survey (Chapter 6).

Astronomical Polarisation From The Infrared To Gamma Rays

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Author : Roberto Mignani
language : en
Publisher: Springer Nature
Release Date : 2019-09-14

Astronomical Polarisation From The Infrared To Gamma Rays written by Roberto Mignani and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019-09-14 with Science categories.

This book serves as both a primer to astronomical polarimetry and an authoritative overview of its application to various types of astronomical objects from AGN, compact stars, binary systems, stars across the HR diagram, transients, the interstellar medium and solar system bodies. It starts with an historical perspective, a discussion of polarimetric theory, instrumentation and techniques in wave bands from the near infrared to gamma rays. The book presents the state of the art in astronomical polarimetry. It is motivated by the new X-ray polarimeters due to be launched in the next four years and improved optical polarimeters on large telescopes requiring a new analysis of polarimetric theory, methodology and results.This book will be suitable as advanced undergraduate companion text, a primer for graduate students and all researchers with an interest in astronomical polarimetry.

Probing The Physics Of Active Galactic Nuclei By Multiwavelength Monitoring

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Author : Bradley M. Peterson
language : en
Publisher:
Release Date : 2001

Probing The Physics Of Active Galactic Nuclei By Multiwavelength Monitoring written by Bradley M. Peterson and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with Science categories.

Annotation Papers from a June 2000 meeting discuss multiwavelength monitoring methods for studying active galactic nuclei, the potential of dedicated facilities for multiwavelength monitoring, and future multiwavelength programs. Some topics discussed are multiwavelength observations of blazars, time delays of blazar flares observed at different wavebands, low radiative-efficiency accretion flows, spectrochronography, and variability of the intrinsic UV absorption lines in Seyfert galaxies. Other topics are the variable diffuse continuum emission of broad-line clouds, the MIDEX concept, and the mission. Peterson teaches astronomy at The Ohio State University. This volume lacks a subject index. Annotation c. Book News, Inc., Portland, OR (booknews.com)

Probing The Physics Of Agn Feedback With High Resolution X Ray Spectroscopy

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Author : Anna Maria Ogorzalek
language : en
Publisher:
Release Date : 2019

Probing The Physics Of Agn Feedback With High Resolution X Ray Spectroscopy written by Anna Maria Ogorzalek and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with categories.

Active galactic nuclei (AGN) significantly impact the evolution of their host galaxies, as they can prevent star formation by either expelling large fractions of gas with wide-angle outflows, or by heating up the halo gas with jets. However, how the AGN energy is transferred to the galaxy in either of these feedback modes is still not known. My dissertation research involves novel applications of modern inference techniques to high resolution X-ray spectra in order to gain new insights into the physical processes behind AGN feedback. First, our improved Bayesian framework for the self-consistent modelling of deep spectra from nearby AGN with X-ray detected outflows is introduced. For the first time we are able to perform robust model selection, while keeping all of the parameter space open. We applied our approach to a new, deep Chandra High Energy Transmission Grating observation of the Seyfert-1 galaxy NGC 4051, where we successfully mapped multiple absorbing components moving at a few 1000 km/s. We obtained one of the tightest outflow density constraints to date, thereby measuring the wind's impact on the galaxy. Second, our unprecedented measurements of the gas turbulent velocities in the cores of 13 nearby giant elliptical galaxies are presented. These new constraints were obtained by statistically combining resonant scattering and direct line broadening, studied with deep XMM-Newton Reflection Grating Spectrometer observations. This allowed us to explore the precise nature of the hot gas motions in massive galaxies and constrain models of AGN feedback in these objects. Then, a successful application of our resonant scattering analysis to the first X-ray microcalorimeter observation, the Hitomi Perseus Cluster spectrum, is discussed. This analysis allowed us to place constraints on the hot gas turbulence in a galaxy cluster that are independent of direct line width measurements. This technique can also provide unique clues to the three dimensional structure of the gas velocity field when statistical uncertainties are minimized. Both of the presented analyses will naturally extend to new data sets from the upcoming high spectral resolution X-ray missions, such as XRISM, ATHENA, Arcus, and Lynx.

The Structure Of Active Galactic Nuclei

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Author : National Aeronautics and Space Administration (NASA)
language : en
Publisher: Createspace Independent Publishing Platform
Release Date : 2018-07-13

The Structure Of Active Galactic Nuclei written by National Aeronautics and Space Administration (NASA) and has been published by Createspace Independent Publishing Platform this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-07-13 with categories.

We are continuing our systematic investigation of the nuclear structure of nearby active galactic nuclei (AGN). Upon completion, our study will characterize hypothetical constructs such as narrow-line clouds, obscuring tori, nuclear gas disks. and central black holes with physical measurements for a complete sample of nearby AGN. The major scientific goals of our program are: (1) the morphology of the NLR; (2) the physical conditions and dynamics of individual clouds in the NLR; (3) the structure and physical conditions of the warm reflecting gas; (4) the structure of the obscuring torus; (5) the population and morphology of nuclear disks/tori in AGN; (6) the physical conditions in nuclear disks; and (7) the masses of central black holes in AGN. We will use the Hubble Space Telescope (HST) to obtain high-resolution images and spatially resolved spectra. Far-UV spectroscopy of emission and absorption in the nuclear regions using HST/FOS and the Hopkins Ultraviolet Telescope (HUT) will help establish physical conditions in the absorbing and emitting gas. By correlating the dynamics and physical conditions of the gas with the morphology revealed through our imaging program, we will be able to examine mechanisms for fueling the central engine and transporting angular momentum. The kinematics of the nuclear gas disks may enable us to measure the mass of the central black hole. Contemporaneous X-ray observations using ASCA will further constrain the ionization structure of any absorbing material. Monitoring of variability in the UV and X-ray absorption will be used to determine the location of the absorbing gas, possibly in the outflowing warm reflecting gas, or the broad-line region, or the atmosphere of the obscuring torus. Supporting ground-based observations in the optical, near-IR, imaging polarimetry, and the radio will complete our picture of the nuclear structures. With a comprehensive survey of these characteristics in a complete sample of nearby AGN, our conclus...

Scientific And Technical Aerospace Reports

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Author :
language : en
Publisher:
Release Date : 1980

Scientific And Technical Aerospace Reports written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1980 with Aeronautics categories.

Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.

Exploring Active Galactic Nuclei At Extreme Energies

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Author : Anton Dmytriiev
language : en
Publisher:
Release Date : 2020

Exploring Active Galactic Nuclei At Extreme Energies written by Anton Dmytriiev and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.

Many questions related to the physics of jets of Active Galactic Nuclei remain open. A particular subclass of AGN, blazars, have a jet pointing towards the Earth. Such suitable orientation of the jet allows us to probe a rich variety of poorly understood physical phenomena related to relativistic outflows. Blazars show non-thermal emission, originating from the jet, which is highly variable across the entire electromagnetic spectrum, from radio frequencies to TeV gamma-rays. The energy flux can enhance by an order of magnitude on time-scales as short as minutes, a phenomenon referred to as a “flare”, and as long as months or even years. Despite the growing amount of available multi-wavelength (MWL) data, the origin and the physical mechanisms behind the frequently observed flaring events in blazars are still not well understood. Many attempts have been made to describe the flares with different emission models, but detailed properties of flux variation patterns (light curves) in different wavebands remain difficult to reproduce. In order to identify physical processes that are involved during blazar outbursts, I have developed a versatile radiative code, based on a time-dependent treatment of particle acceleration, escape and radiative cooling. The code computes time evolution of the distribution function of electrons in the blazar emitting zone and the spectrum of the Synchrotron Self-Compton (SSC) emission by these electrons. I applied the code to a giant MWL flare of the blazar Mrk 421, a representative of the BL Lacertae class, which is the brightest VHE flare ever detected from this source. In our approach, we consider the flare as a moderate perturbation of the quiescent state and search for interpretations with a minimum number of free parameters. As a result, I developed a novel physical scenario of the flaring activity that describes the data set, comprising spectra in the high state of the source in different energy ranges, and MWL light curves from the optical domain to the VHE gamma-ray band. In this scenario, the process initiating the outburst is the second-order Fermi acceleration of particles due to turbulence arising in the vicinity of the blazar stationary emission region. In this thesis, I also performed analysis of High Energy Stereoscopic System (H.E.S.S.) data of two giant flares of the blazar 3C 279, a representative of the Flat Spectrum Radio Quasars (FSRQ) class. Finally, I contributed to preparation of Cherenkov Telescope Array (CTA), which is a new-generation ground-based gamma-ray observatory, expected to start operations in 2022. The instrument, which is presently under development, will have greatly improved performance compared to currently operating Imaging Atmospheric Cherenkov Telescopes (IACTs), including unprecedented spectral coverage from a few tens of GeV to ~300 TeV. In the context of CTA, I performed simulations of the optical performance of the Gamma-Ray Cherenkov Telescope (GCT), one of the three proposed designs of Small-Size Telescopes (SST) for CTA. Also, using the observations of bright stars done by the telescope prototype installed on the site of Paris Observatory in Meudon, I studied the effect of micro-roughness of the telescope mirrors on the point spread function (PSF) and calculated the level of the mirror polishing quality required to optimize the performances.

The Physics Of Accretion Onto Black Holes

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Author : Maurizio Falanga
language : en
Publisher: Springer
Release Date : 2014-10-28

The Physics Of Accretion Onto Black Holes written by Maurizio Falanga and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014-10-28 with Science categories.

Provides a comprehensive summary on the physical models and current theory of black hole accretion, growth and mergers, in both the supermassive and stellar-mass cases. This title reviews in-depth research on accretion on all scales, from galactic binaries to intermediate mass and supermassive black holes. Possible future directions of accretion are also discussed. The following main themes are covered: a historical perspective; physical models of accretion onto black holes of all masses; black hole fundamental parameters; and accretion, jets and outflows. An overview and outlook on the topic is also presented. This volume summarizes the status of the study of astrophysical black hole research and is aimed at astrophysicists and graduate students working in this field. Originally published in Space Science Reviews, Vol 183/1-4, 2014.

Physics Briefs

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Author :
language : en
Publisher:
Release Date : 1994

Physics Briefs written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1994 with Physics categories.