Author: Norman I. Palma Cruz
Publisher:
ISBN:
Category : BL Lacertae objects
Languages : en
Pages :

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Author: Stephen Kerby
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
The most recent catalogue of Fermi-LAT gamma-ray point sources includes over 4000 associated sources, most of which are pulsars or blazars. However, over 2000 sources are "unassociated", defying confident classification or identification based on gamma-ray data alone. Our understanding of the high-energy sky is systematically incomplete while these unassociated sources remain unexamined. An ongoing search for low-energy counterparts using the Neil Gehrels Swift Observatory has identified over three hundred X-ray/UV/optical counterparts to Fermi unassociated sources and placed limits on the maximum X-ray flux for almost a thousand more; these discoveries facilitate spatial localization and broadband SED analysis of the unassociated sources. Analyzing Swift-XRT and -UVOT data for these counterparts, we conduct machine learning classification to identify likely blazars and pulsars from this sample. Between random forest, neural network, and support vector machine classifiers, we find that the unassociated sources with low-energy counterparts are mostly dimmer blazars while also discovering several unusual sources and new gamma-ray pulsars. Using Fermi, Swift, and archival IR and radio data, we create a sample of 106 new blazars; via another machine learning program, we show that these dimmer blazars tend to have higher synchrotron peak frequencies like BL Lac objects. These findings align with the predictions of the blazar sequence, extending and confirming that observational framework with a totally new sample. While the dim blazars in our new sample confirm the predictions of the blazar sequence, many of the unassociated targets without Swift-XRT detections may be even dimmer blazars, especially those at high galactic latitude. Furthermore, several sources are not well-explained by either pulsar or blazar models, or are coincident with stars or known galactic binaries. In-depth examination of these unique objects shows that - like the associated sources - the unassociated sources contain rare minority classes ranging from low-mass X-ray binaries and cataclysmic variables to extreme Seyfert galaxies and star-forming regions.

Author: Margaret Angela Osterman
Publisher:
ISBN:
Category : Active galaxies
Languages : en
Pages :

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Book Description
The extreme AGN known as blazars can be classified based on their spectral properties into X-ray and radio selected objects, known as XBLs and RBLs, respectively. In this work, the results of new multiwavelength campaigns are presented for two XBLs and two RBLs. Each campaign contains simultaneous observations in the radio, optical, and X-ray regimes. A campaign on a third RBL was completed using near-simultaneous archival radio, optical/IR, and gamma-ray data. The simultaneous multiwavelength behavior exhibited in each campaign was analyzed by examining the multiwavelength variability and using spectral analysis. Observations of prominent optical microvariability were quantitatively analyzed. Previously published results for other blazars were compared to the new and archival results. Many interesting results emerged from these investigations. PG 1553+11, a radio-weak blazar, was found to be an extreme XBL. During three campaigns performed for the XBL PKS 2155-304, different variability behavior was observed each time. In a high flux state, the X-ray behavior was strongly correlated with the optical behavior. In a weak state, the X-ray and optical behaviors were not correlated. In an intermediate state, the X-ray behavior was somewhat correlated with the optical behavior. CTA 102, an RBL, exhibited some of the most extreme optical microvariability ever observed, including a brightening of about 0.07 magnitudes in less than 15 minutes. Surprisingly, the optical spectra of RBLs CTA 102, PKS 1622-297, and 3C 345 were found to become redder when in a brighter flux state. The RBLs all exhibited large amplitude optical microvariability. The campaigns on PG 1553+11, CTA 102, and PKS 1622-297 were the first simultaneous multiwavelength campaigns performed for these objects. For objects in which the results of at least two campaigns were available, including PKS 2155-304, correlations that appeared to be present at one epoch seemed to vanish at other times. The SSC model represented many of the observations well. Color studies of the selected BL Lac objects found them to be bluer when brighter, while the selected FSRQs were found to be redder when brighter. These results provide strong motivation for future multiwavelength campaigns that provide broader wavelength and more extensive temporal coverage.

Author: Stephen Edward Healey
Publisher:
ISBN:
Category :
Languages : en
Pages : 92

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Author:
Publisher:
ISBN:
Category :
Languages : de
Pages : 16

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Book Description

Author: Johannes Andersen
Publisher: Springer Science & Business Media
ISBN: 9780792355564
Category : Science
Languages : en
Pages : 612

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Book Description
Since 1967, the main scientific events of the General Assemblies of the International Astronomical Union have been published in the separate series, Highlights of Astronomy. The present Volume 11 presents the major scientific presentations made at the XXIIIrd General Assembly, August 18-30, 1997, in Kyoto, Japan. The two volumes (11A+B) contain the texts of the three Invited Discourses as well as the proceedings or extended summaries of the 21 Joint Discussions and two Special Sessions held during the General Assembly.

Author: Volker Schönfelder
Publisher: Springer Science & Business Media
ISBN: 3662045931
Category : Science
Languages : en
Pages : 418

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Book Description
After describing cosmic gamma-ray production and absorption, the instrumentation used in gamma-ray astronomy is explained. The main part of the book deals with astronomical results, including the somewhat surprising result that the gamma-ray sky is continuously changing.

Author: International Astronomical Union
Publisher:
ISBN:
Category : Astronomy
Languages : en
Pages : 616

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Book Description
Vol. 1- contain papers, etc., from 13th- General Assembly.

Author: William C Keel
Publisher: Springer
ISBN: 9789400756083
Category : Science
Languages : en
Pages : 0

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Book Description
This is volume 6 of Planets, Stars and Stellar Systems, a six-volume compendium of modern astronomical research, covering subjects of key interest to the main fields of contemporary astronomy. This volume on “Extragalactic Astronomy and Cosmology” edited by William C. Keel presents accessible review chapters on Galaxy Morphology, Elliptical and Disk Galaxy Structure and Modern Scaling Laws, Star Formation in Galaxies, The Cool ISM in Galaxies, The Influence of Environment on Galaxy Evolution, Clusters of Galaxies, Active Galactic Nuclei, Large Scale Structure of the Universe, Distance Scale of the Universe, Galaxies in the Cosmological Context, Evolution of Active Galactic Nuclei, The Intergalactic Medium, and Cosmic Microwave Background. All chapters of the handbook were written by practicing professionals. They include sufficient background material and references to the current literature to allow readers to learn enough about a specialty within astronomy, astrophysics and cosmology to get started on their own practical research projects. In the spirit of the series Stars and Stellar Systems published by Chicago University Press in the 1960s and 1970s, each chapter of Planets, Stars and Stellar Systems can stand on its own as a fundamental review of its respective sub-discipline, and each volume can be used as a textbook or recommended reference work for advanced undergraduate or postgraduate courses. Advanced students and professional astronomers in their roles as both lecturers and researchers will welcome Planets, Stars and Stellar Systems as a comprehensive and pedagogical reference work on astronomy, astrophysics and cosmology.

Author: Markus Boettcher
Publisher: John Wiley and Sons
ISBN: 3527410376
Category : Science
Languages : en
Pages : 425

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Book Description
Written by a carefully selected consortium of researchers working in the field, this book fills the gap for an up-to-date summary of the observational and theoretical status. As such, this monograph includes all used wavelengths, from radio to gamma, the FERMI telescope, a history and theory refresher, and jets from gamma ray bursts. For astronomers, nuclear physicists, and plasmaphysicists.