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Author: Stephen Kerby Publisher: ISBN: Category : Languages : en Pages : 0
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: Stephen Kerby Publisher: ISBN: Category : Languages : en Pages : 0
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: Brice Michael Williams Publisher: ISBN: Category : Astrophysics Languages : en Pages : 0
Book Description
The latest data release from the Fermi Gamma-Ray Space Telescope (the Fourth Fermi LAT Catalog) has more than 50% of the detected galactic sources yet to be identified. In an attempt to uncover the nature of some of these unknown sources, we observed thirteen sources within the galactic plane using the Chandra X-Ray Observatory (CXO). Analysis was performed using Chandra Interactive Analysis of Observations (CIAO) software in order to determine if any of these Fermi sources also emitted in the X-ray spectrum. We performed spectral analysis of seven X-ray sources, which had higher quality data. We also found fainter X-ray sources that lied within the Fermi radii and performed X-ray analysis on them. We also analyzed the available multi-wavelength data to shed light on the nature of these high energy sources.
Author: E. VALTAOJA (Ed) Publisher: Cambridge University Press ISBN: 9780521413510 Category : Science Languages : en Pages : 484
Book Description
Blazars (also known as BL Lac objects), first discovered in 1978, are unusually energetic objects in the extragalactic universe. About 200 are known or suspected. They are radio sources with highly variable optical and radio emission, as well as high polarisation, and their optical spectra normally have no distinguishable features. It is generally accepted that they belong to that class of galaxies with active galactic nuclei, which are presumed to be driven by infall of matter to a supermassive black hole. In this book researchers give a complete summary of the observations of blazars and the theoretical interpretation. A comprehensive listing of confirmed and candidate objects is included. Mechanisms in which the variability can arise from shocks and relativistic jets are discussed. There are at least four different answers given to the question: what is a blazar? This book is a complete overview of the violent activity observed in these extreme active galactic nuclei.
Author: Michael J. Way Publisher: CRC Press ISBN: 1439841748 Category : Computers Languages : en Pages : 744
Book Description
Advances in Machine Learning and Data Mining for Astronomy documents numerous successful collaborations among computer scientists, statisticians, and astronomers who illustrate the application of state-of-the-art machine learning and data mining techniques in astronomy. Due to the massive amount and complexity of data in most scientific disciplines
Author: Eric Wallace Publisher: ISBN: Category : Gamma ray astronomy Languages : en Pages : 78
Book Description
The Large Area Telescope (LAT) aboard the Fermi Gamma-Ray Space Telescope has revolutionized gamma-ray astronomy, allowing the detection of thousands of point sources of gamma rays. Variability studies are of significant interest as a potential source of information about the emission mechanisms, and as a means to identify gamma-ray sources with known sources in other wavelengths and to improve detection sensitivity in searches for new sources. The inclusion of temporal resolution, however, adds to the already considerable complexity of the required analysis, and as a result, variability studies have generally been limited either in scope or in detail, or both, compared to time-integrated spectral analyses. Pointlike is a software package designed for fast maximum likelihood analysis of LAT data, allowing for interactive and large-scale analyses. Here, we present an application of pointlike to the characterization of the variability of the full sample of known gamma-ray point sources. We describe the construction of light curves in one-month time bins, spanning the first 42 months of the Fermi mission, for a sample of 2652 sources. We discuss the use of the detection significance in individual months to improve the significance of detection of marginal sources, and show that including that measure of significance increases the set of significantly detected sources by nearly 20% compared to using only the average significance. We describe a statistical measure of the significance of variability in a light curve, and examine the variability of the sample as whole, and of subsets associated with particular source types, especially pulsars. We discuss the use of pulsars, which are generally non-variable on long timescales, to calibrate variability statistics, and to assess the importance of systematic errors in estimates of variability. Finally, we discuss the potential to extend the method to produce light curves of longer duration and finer time binning, and to search for transient sources.
Author: Chun-Kwan Leung Publisher: Open Dissertation Press ISBN: 9781361348550 Category : Languages : en Pages :
Book Description
This dissertation, "Gamma-ray Emissions From Pulsar Binaries" by Chun-kwan, Leung, 梁晉堃, 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: The launch of the Fermi Gamma-ray Space Telescope marked a new era in observing gamma-rays from astrophysical sources. Fermi's high sensitivity in the 0.1-300GeV energy range opens an important window in the observation of the gamma-ray emissions from pulsar binaries, which emit most of their radiation energy in the gamma-ray range. We can now observe the gamma-ray emissions from pulsar binaries at an unprecedented accuracy, and investigate their origin in detail. In this thesis, we present the studies on two systems of pulsar binary of two distinct classes. The gamma-ray emissions from the high-mass gamma-ray binary LS 5039 were studied using the latest data from Fermi. The emission is modulated according to the 3.9 hr orbital period of the system. The results can be explained by the contribution of three components: the pulsar magnetospheric emission, the pulsar wind emission and the emissions from the shock formed from the interaction between the pulsar wind and companion's stellar wind. The results were compared with observed data from Fermi and also in X-ray and TeV. In addition, the emissions from the millisecond pulsar PSR J1023+0038 and its low mass binary companion were also studied. This system recently went through a transition from the rotation-powered state to the accretion state, after going the opposite way in 2007. This state transition, discovered through the disappearance of radio pulsation, was accompanied by the brightening in GeV, X-ray and UV fluxes. A detailed Fermi observation was performed, supplemented by multi-wavelength observations. It was found that the emission from this system can also be described by the emissions from the pulsar magnetosphere, the pulsar wind and its shock. These two systems, although of distinct classes of pulsar binaries, provide complementary cases for the study of high-energy radiation processes in pulsar binaries. DOI: 10.5353/th_b5317064 Subjects: Gamma ray astronomy Pulsars
Author: The Cta Consortium Publisher: World Scientific ISBN: 9813270101 Category : Science Languages : en Pages : 365
Book Description
This book summarizes the science to be carried out by the upcoming Cherenkov Telescope Array, a major ground-based gamma-ray observatory that will be constructed over the next six to eight years. The major scientific themes, as well as core program of key science projects, have been developed by the CTA Consortium, a collaboration of scientists from many institutions worldwide.CTA will be the major facility in high-energy and very high-energy photon astronomy over the next decade and beyond. CTA will have capabilities well beyond past and present observatories. Thus, CTA's science program is expected to be rich and broad and will complement other major multiwavelength and multimessenger facilities. This book is intended to be the primary resource for the science case for CTA and it thus will be of great interest to the broader physics and astronomy communities. The electronic version (e-book) is available in open access.
Author: Matthew Pryal Publisher: ISBN: Category : Languages : en Pages :
Book Description
The Large Area Telescope on board the Fermi Gamma-Ray Space Telescope has revolutionized the detection and identification of gamma-ray emitting astrophysical objects since the launch of Fermi in 2008. Gamma-rays are the highest energy photons observed in the universe and our understanding of objects that emit gamma-rays is essential to our understanding of physics at its greatest limits. The 1FGL, 2FGL, and 3FGL Fermi catalogs outline the identification of over 2000 gamma-ray emitting objects such as blazars and pulsars, but there still remains many unassociated objects in the Fermi catalogs. In this thesis we attempt to statistically show associations of these Fermi unassociated objects in the 1FGL and 2FGL catalogs by utilizing data mining and machine learning techniques to find distinct separations in the properties of known blazars and pulsars. Our analysis is unique in that we will be utilizing known X-ray fluxes for the unassociated objects observed by the Swift X-ray Telescope in addition to the gamma-ray properties available in the Fermi catalogs. Our analysis shows distinct separations in the gamma-ray properties of known blazars and pulsars when compared to X-ray flux and we were able to suggest possible associations to 136 previously unassociated Fermi objects.
Author: Stephen Kerby
Author: Stephen Kerby
Author: Brice Michael Williams
Author: Dieter H. B. Hartmann
Author: E. VALTAOJA (Ed)
Author: Michael J. Way
Author: Eric Wallace
Author: Chun-Kwan Leung
Author: Norman I. Palma Cruz
Author: The Cta Consortium
Author: Matthew Pryal