Download or read book X ray and Optical Studies of Active Galactic Nuclei and Quasi stellar Objects written by Gerard Anthony Kriss and published by . This book was released on 1982 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Astrophysics Of Quasi Stellar Objects And Active Galactic Nuclei written by Joseph S. Miller and published by University Science Books. This book was released on 1985 with total page 532 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Based on the 1984 Santa Cruz Astrophysics Workshop"--Verso t.p.
Download or read book X ray Studies of the Central Engine in Active Galactic Nuclei with Suzaku written by Hirofumi Noda and published by Springer. This book was released on 2015-12-07 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this research was to use the X-ray satellite Suzaku to establish a picture of a central engine that effectively converts the gravitational energy of accreting matter onto the supermassive black hole to a huge amount of radiation in an active galactic nucleus. Although the engine is known to consist of a Comptonizing corona and an accretion disk, its image has remained unclear because primary emissions, coming directly from the engine, cannot be identified in X-ray spectra without models. The book describes a technique of time variability assisted spectral decomposition to model-independently examine X-ray signals, and how this was applied to the Suzaku archive data of active galactic nuclei. As a result, at least three distinct primary X-ray components have been discovered in an X-ray from an active galactic nucleus, presumably indicating a novel picture that the engine is composed of multiple coronae with different physical properties in an accretion flow. Furthermore, the determination of the spectral shapes of the primary X-rays has a significant impact on estimations of black hole spins, because it is essential to quantify reprocessed X-ray spectra. The successful model-independent decomposition of X-ray spectral components with flux variations of active galactic nuclei is likely to be effective in future data analyses from the soon-to-be-launched Japanese X-ray satellite ASTRO-H, which is capable of achieving unprecedented fine spectros copy and broad energy band coverage.
Download or read book X ray and Optical Studies of Extragalactic X ray Emitters written by Gail Anne Reichert and published by . This book was released on 1982 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book X ray and Multiwavelength Studies of Active Galactic Nuclei from Large Area Sky Surveys written by Jianfeng Wu and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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).
Download or read book Cosmological Evolution of X ray Emitting Active Galactic Nuclei written by John David Silverman and published by . This book was released on 2004 with total page 396 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Astrophysics of Active Galactic Nuclei Variability in Large Scale Spectroscopic Surveys written by John J. Ruan and published by . This book was released on 2017 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: More than 50 years after the initial discovery of the extragalactic nature of quasi-stellar objects (quasars) by Schmidt (1963), studies of luminous active galactic nuclei (AGN) have revolutionized our understanding of black hole growth across cosmic time, accretion and jet physics, as well as galaxy evolution and cosmology. In the coming decade, these studies will be further fueled by large (a few x10^6) samples of quasars from massive optical spectroscopic surveys (e.g., from eBOSS and DESI). These spectra will be accompanied by well-sampled photometric light curves from time-domain imaging surveys (e.g., from Pan-STARRS and LSST), enabling discovery of rare objects and new time-domain phenomena. Current spectroscopic and imaging surveys have well-established that nearly all Type 1 quasars are optically variable, although the origin of this variability is still unknown. The primary goal of this thesis is to investigate various AGN variability phenomena in the UV/optical, to understanding their origin. In particular, I investigate the origin of 10-20% flux variability ubiquitously observed in quasars, the apparent change in accretion states observed in ‘transition blazars’, as well as the rapid fading observed in the recently-discovered ‘changing-look quasars’ phenomenon. I also prepare for the science enabled by the large samples of AGN that will be discovered in future time-domain imaging surveys, by characterizing the unique properties of variability-selected AGN. The primary technique I use in this dissertation to probe AGN variability is repeat optical spectroscopy. AGN optical spectra contain a wealth of information about the central engine, encoded in the properties of the emission lines, absorption lines, and continuum emission. Repeat optical spectroscopy can further probe the time-variable nature of these emission components, but this has previously been little explored in comparison to single-epoch spectroscopy. One notable exception in repeat AGN spectroscopy is the well-established reverberation mapping technique of mapping the size of AGN broad line regions; this has lead to the development of black hole mass estimates based on broad Balmer emission line widths in single-epoch spectroscopy. However, these and other studies based on repeat AGN spectroscopy are only available for small samples of a few dozen AGN at low redshifts, due to the expensive nature of repeat spectroscopy for large samples of faint quasars at higher redshifts. The development of multi-object spectrographs now have the ability to do repeat spectroscopy for large numbers of quasars, opening new windows into AGN astrophysics in the time-domain. Surveys dedicated to repeat quasar spectroscopy, including currently in SDSS-IV and in the future in SDSS-V, will fuel the early science results from this dissertation. In this dissertation, I first use SDSS repeat spectroscopy of quasars to quantify the bluer-when-brighter trend of wavelength-dependent quasar spectral variability, and use it to con- strain simple models of quasar variability. In particular, I test whether the observed spectral variability is consistent with recent toy models of inhomogeneous accretion disks with large temperature fluctuations. These models provide a natural explanation for quasar UV/optical variability, and the first to be consistent with measurements of quasar accretion disk sizes and characteristic timescales of variability. I show that the observed spectral variability can be reproduced by strongly inhomogeneous disks with large temperature fluctuations. I then use SDSS repeat spectroscopy to investigate the origin of the ‘transition blazars’ phenomenon, which is observed in a handful of AGN with relativistic jets aligned with the line of sight. In transition blazars, the blazars appear to switch between BL Lac objects and Flat-Spectrum Radio Quasars (FSRQs) classifications, which correspond to low- and high- accretion rate states, respectively. I show that transition blazars are FSRQs with especially strong beaming, such that the strongly-beamed continuum swamps the broad emission lines. This occasionally causes the broad emission lines to disappear and reappear, producing the transitional behavior. Furthermore, I mine SDSS repeat spectroscopy to uncover the origin of the recently-discovered ‘changing-look quasars’ phenomenon. Repeat optical spectroscopy of this new class of objects show dramatic transitions from luminous broad line quasars into quiescent galaxies or low-luminosity AGN. Surprisingly, these changes occur over timescales of just a few years, a factor of >10^4 faster than both theoretical expectations and scaling spectral state transition timescales in X-ray binaries to 10^8 M_sun supermassive black holes (SMBHs). To understand this phenomenon, I perform the first large systematic search for CL quasars and I show that the fading of the continuum and broad emission lines in CL quasars is consistent with rapidly decreasing accretion rates, while disfavoring alternative interpretations including changes in intrinsic dust extinction and transient tidal disruption events or supernovae. Finally, future time-domain imaging surveys such as the ZTF and LSST will discover a few x10^7 variable objects, and AGN will constitute the majority of variable objects discovered. To understand the science enabled by these massive variability-selected samples of AGN, I utilized spectra from the Time-Domain Spectroscopic Survey (TDSS) to understand the unique properties of variability-selected quasars. TDSS is the first systematic spectroscopic survey of variable objects, and I show that variability-selected quasars complement color-based selection by selecting additional redder quasars, resulting in a smooth redshift distribution. Furthermore, I show that variability selection yields higher fractions of peculiar AGN such as broad absorption line quasars and blazars.
Download or read book Search for Quasisoft X Ray Sources in the Galactic Center written by To Li and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Search for Quasisoft X-ray Sources in the Galactic Center" by To, Li, 李韜, 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: Abstract of thesis entitled SEARCH FOR QUASISOFT X-RAY SOURCES IN THE GALACTIC CENTER Submitted by Li To for the degree of Master of Philosophy at The University of Hong Kong in November 2007 Quasisoft X-ray sources (QSSs) are X-ray emitting objects which emit a sig- 36 1 nicant amount of photons below 2keV. QSSs are luminous (L >10 erg s ) and their characteristic temperatures are in range 100350 eV. Their spectra are harder than supersoft X-ray sources (SSSs), which are characterized by tens of eV; while QSSs are still softer than canonical X-ray sources. The physical na- ture of QSSs remains unknown. One promising possibility is that QSSs may be intermediate mass black holes (IMBHs) whose masses are a few hundred times solar. Other possibilities include stellar mass black holes, neutron stars, white dwarfs, or supernova remnants (SNRs). QSSs had been identiedin external galaxies, but not yet in our own Galaxy. SearchforQSSsinourGalaxyisimportantforunderstandingthenatureofQSSs. We had examined X-ray images of the Galactic center taken by the Chandra X- 0 0 rayObservatory. Atotalof2146detectedX-raypointsourcesinthe1717 eldaround Sgr A* weredetermined. Multi-energy X-raycountsof the X-raysources were determined. Using the X-ray photometry, we had identied 81 QSSs. The spatial distribution of QSSs was found to be quite homogeneous. In contrast with QSSs, the majority of X-ray sources tended to concentrate around center and spread radially. Most QSSs found were weak and soft. We also matched all the X-ray point sources with optical and infrared objects in the USNO B1.0 and 2MASS Point Source catalogs, and found that while only about 9% and 25% of canonical X-ray sources had optical and infrared counterparts respectively, nearly 60% and 70% of QSSs had optical and infrared counterparts respectively. This implies the QSSs or the companions of QSSs in our Galactic center tend to be able to emit at optical and infrared wavelengths. Spectra of the brightest QSSs were extracted. When modeled as blackbody, the range of temperature was about 100200 eV. X-ray to optical ux ratios of all QSSs were between 2 and 1. Number of background objects such as active galactic nuclei (AGNs) wereestimatedby Chandra deepeld. WhileX-raytoopticaluxratiosofmost foreground stars were less than1, those of X-ray binaries were mostly positive. We suggest that few QSSs are backgrounds objects (34%), but the nature of majority is still not known. At least 10% of all QSSs are likely to be foreground stars. X-ray binaries, including those with IMBHs, are still possible candidates for some QSSs, especially those QSSs with positive X-ray to optical ux ratios. DOI: 10.5353/th_b3955746 Subjects: X-ray sources, Galactic X-ray spectroscopy Galactic center
Download or read book X ray and Optical Properties of X ray Luminous Active Galactic Nuclei written by Mirko Krumpe and published by . This book was released on 2007 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Optical and X ray Properties of X ray Selected Active Galactic Nuclei written by Gerard Anthony Kriss and published by . This book was released on 1982 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Active Galactic Nuclei written by John Edward Dyson and published by Manchester University Press. This book was released on 1985 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book X ray and Optical Studies of Active Galactic Nuclei written by Jonathan Patrick Duncan Mittaz and published by . This book was released on 1991 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Optical Spectroscopy of X ray selected Active Galactic Nuclei written by Sally Anne Stephens and published by . This book was released on 1987 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Active Galactic Nuclei written by D.E. Osterbrock and published by Springer. This book was released on 1989-06-30 with total page 592 pages. Available in PDF, EPUB and Kindle. Book excerpt: IAU Symposium No. 134 on Active Galactic Nuclei was hosted by the Lick Observatory, as part of the celebration of its centennial, for the Observatory went into operation as part of the University of California on June 1, 1888. Twenty years later, in 1908, Lick Observatory graduate student Edward A. Fath recognized the unusual emission-line character of the spectrum of the nucleus of the spiral "nebula" NGC 1068, an object now well-known as one of the nearest and brightest Seyfert galaxies and active galactic nuclei. Ten years after that, and seventy years before this Symposium, Lick Observatory faculty member Heber D. Curtis published his description of the "curious straight ray" in M 87, "apparently connected with the nucleus by a thin line of matter," which we now recognize as an example of one of the jets which are the subject of so much current AGN research. The symposium was held at Kresge College on the campus of the University of California, Santa Cruz, only a short walk through the redwood groves to the Lick Observatory offices. A total of 232 astronomers and astrophysicists from 24 countries attended and took part in the Symposium. About 200 more had applied to come, but could not be accepted in order to keep the meeting at a reasonable size. Most of the participants lived in the Kresge College apartments immediately adjacent to the Kresge Town Hall in which the oral sessions took place.
Download or read book Are There Intrinsically X Ray Quiet Quasars written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-05-29 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent ROSAT studies have identified a significant population of Active Galactic Nuclei (AGN) that are notably faint in soft X-rays relative to their optical fluxes. Are these AGN intrinsically X-ray weak or are they just highly absorbed? Brandt, Laor & Wills have systematically examined the optical and UV spectral properties of a well-defined sample of these soft X-ray weak (SXW) AGN drawn from the Boroson & Green sample of all the Palomar Green AGN 00 with z
Download or read book A Study of the Optical and X ray Properties of Quasars written by Steven Ever Bradley and published by . This book was released on 1985 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Study Week on Nuclei of Galaxies April 13 18 1970 written by D. J. K. O'Connell and published by . This book was released on 1971 with total page 836 pages. Available in PDF, EPUB and Kindle. Book excerpt:
