On The Gamma Ray Emission From Reticulum Ii And Other Dwarf Galaxies PDF Download
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| Release | : 2015 |
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Download On The Gamma-Ray Emission From Reticulum II and Other Dwarf Galaxies Book in PDF, ePub and Kindle
The recent discovery of ten new dwarf galaxy candidates by the Dark Energy Survey (DES) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) could increase the Fermi Gamma-Ray Space Telescope's sensitivity to annihilating dark matter particles, potentially enabling a definitive test of the dark matter interpretation of the long-standing Galactic Center gamma-ray excess. In this paper, we compare the previous analyses of Fermi data from the directions of the new dwarf candidates (including the relatively nearby Reticulum II) and perform our own analysis, with the goal of establishing the statistical significance of any gamma-ray signal from these sources. We confirm the presence of an excess from Reticulum II, with a spectral shape that is compatible with the Galactic Center signal. The significance of this emission is greater than that observed from 99.84% of randomly chosen high-latitude blank-sky locations, corresponding to a local detection significance of 3.2[sigma]. We caution that any dark matter interpretation of this excess must be validated through observations of additional dwarf spheroidal galaxies, and improved calculations of the relative J-factor of dwarf spheroidal galaxies. We improve upon the standard blank-sky calibration approach through the use of multi-wavelength catalogs, which allow us to avoid regions that are likely to contain unresolved gamma-ray sources.
| Author | : Volker Schönfelder |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 418 |
| Release | : 2013-03-14 |
| Genre | : Science |
| ISBN | : 3662045931 |
Download The Universe in Gamma Rays Book in PDF, ePub and Kindle
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 | : Alberto Salvio |
| Publisher | : Frontiers Media SA |
| Total Pages | : 265 |
| Release | : 2019-12-06 |
| Genre | : |
| ISBN | : 2889632059 |
Download From the Fermi Scale to Cosmology Book in PDF, ePub and Kindle
| Author | : P. V. Ramana Murthy |
| Publisher | : Cambridge University Press |
| Total Pages | : 275 |
| Release | : 1993-04 |
| Genre | : Nature |
| ISBN | : 0521420814 |
Download Gamma-ray Astronomy Book in PDF, ePub and Kindle
The recent launch of NASA's Gamma-Ray Observatory will increase interest in gamma-ray astronomy. This is a fully up-dated new edition of the authors' earlier volume published in 1986 and covers both the background science and the current state-of-the-art in this field. The emphasis is on the astronomy and astrophysics of known sources of cosmic gamma-rays outside the solar system. The authors discuss the mechanisms for the production and absorption of gamma-rays. The gamma-ray line astronomy of the interstellar medium, galactic centre, and various discrete sources is then considered. Gamma-ray bursts are treated in considerable detail in chapter three, and the final two chapters describe medium energy and ultra-high energy gamma-rays. Relevant data from supernova SN1987A is also included in this edition. The book includes comprehensive references to the primary literature, together with many figures and tables. The concentration on phenomenology makes this book a fine introduction to gamma-ray astronomy.
| Author | : Joshua S. Bloom |
| Publisher | : Universal-Publishers |
| Total Pages | : 198 |
| Release | : 2002 |
| Genre | : Science |
| ISBN | : 1581121695 |
Download Toward an Understanding of the Progenitors of Gamma-Ray Bursts Book in PDF, ePub and Kindle
The various possibilities for the origin ("progenitors") of gamma-ray bursts (GRBs) manifest in differing observable properties. Through deep spectroscopic and high-resolution imaging observations of some GRB hosts, I demonstrate that well-localized long-duration GRBs are connected with otherwise normal star-forming galaxies at moderate redshifts of order unity. Using high-mass binary stellar population synthesis models, I quantify the expected spatial extent around galaxies of coalescing neutron stars, one of the leading contenders for GRB progenitors. I then test this scenario by examining the offset distribution of GRBs about their apparent hosts making extensive use of ground-based optical data from Keck and Palomar and space-based imaging from the Hubble Space Telescope. The offset distribution appears to be inconsistent with the coalescing neutron star binary hypothesis (and, similarly, black-hole--neutron star coalescences); instead, the distribution is statistically consistent with a population of progenitors that closely traces the ultra-violet light of galaxies. This is naturally explained by bursts which originate from the collapse of massive stars ``collapsars''). This claim is further supported by the unambiguous detections of intermediate-time (approximately three weeks after the bursts) emission ``bumps'' which appear substantially more red than the afterglows themselves. I claim that these bumps could originate from supernovae that occur at approximately the same time as the associated GRB; if true, GRB 980326 and GRB 011121 provide strong observational evidence connecting cosmological GRBs to high-redshift supernovae and implicate massive stars as the progenitors of at least some long-duration GRBs.
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| Total Pages | : 8 |
| Release | : 2015 |
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Download Search for Gamma-Ray Emission from DES Dwarf Spheroidal Galaxy Candidates with Fermi-LAT Data Book in PDF, ePub and Kindle
Due to their proximity, high dark-matter (DM) content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of DM. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. We found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If the estimated DM content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with masses $\lesssim 20\, \mathrm{GeV}$ annihilating via the $b\bar{b}$ or [tau](+)[tau]( - ) channels.
| Author | : Carl E. Fichtel |
| Publisher | : |
| Total Pages | : 442 |
| Release | : 1981 |
| Genre | : Gamma ray astronomy |
| ISBN | : |
Download Gamma Ray Astrophysics Book in PDF, ePub and Kindle
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| Release | : 2015 |
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Download Improving the Sensitivity of Gamma-ray Telescopes to Dark Matter Annihilation in Dwarf Spheroidal Galaxies Book in PDF, ePub and Kindle
The Fermi-LAT Collaboration has studied the gamma-ray emission from a stacked population of dwarf spheroidal galaxies and used this information to set constraints on the dark matter annihilation cross section. Interestingly, their analysis uncovered an excess with a test statistic (TS) of 8.7. If interpreted naively, this constitutes a 2.95[sigma] local excess (p-value=0.003), relative to the expectations of their background model. In order to further test this interpretation, the Fermi-LAT team studied a large number of blank sky locations and found TS>8.7 excesses to be more common than predicted by their background model, decreasing the significance of their dwarf excess to 2.2[sigma](p-value=0.027). We argue that these TS>8.7 blank sky locations are largely the result of unresolved blazars, radio galaxies, and star-forming galaxies, and show that multiwavelength information can be used to reduce the degree to which such sources contaminate the otherwise blank sky. In particular, we show that masking regions of the sky that lie within 1° of sources contained in the BZCAT or CRATES catalogs reduce the fraction of blank sky locations with TS>8.7 by more than a factor of 2. Taking such multiwavelength information into account can enable experiments such as Fermi to better characterize their backgrounds and increase their sensitivity to dark matter in dwarf galaxies, the most important of which remain largely uncontaminated by unresolved point sources. We also note that for the range of dark matter masses and annihilation cross sections currently being tested by studies of dwarf spheroidal galaxies, simulations predict that Fermi should be able to detect a significant number of dark matter subhalos. These subhalos constitute a population of subthreshold gamma-ray point sources and represent an irreducible background for searches for dark matter annihilation in dwarf galaxies.
| Author | : Miguel A. Sánchez-Conde |
| Publisher | : MDPI |
| Total Pages | : 220 |
| Release | : 2020-05-28 |
| Genre | : Mathematics |
| ISBN | : 3039360442 |
Download The Role of Halo Substructure in Gamma-Ray Dark Matter Searches Book in PDF, ePub and Kindle
An important, open research topic today is to understand the relevance that dark matter halo substructure may have for dark matter searches. In the standard cosmological model, halo substructure or subhalos are predicted to be largely abundant inside larger halos, for example, galaxies such as ours, and are thought to form first and later merge to form larger structures. Dwarf satellite galaxies—the most massive exponents of halo substructure in our own galaxy—are already known to be excellent targets for dark matter searches, and indeed, they are constantly scrutinized by current gamma-ray experiments in the search for dark matter signals. Lighter subhalos not massive enough to have a visible counterpart of stars and gas may be good targets as well, given their typical abundances and distances. In addition, the clumpy distribution of subhalos residing in larger halos may boost the dark matter signals considerably. In an era in which gamma-ray experiments possess, for the first time, the exciting potential to put to test the preferred dark matter particle theories, a profound knowledge of dark matter astrophysical targets and scenarios is mandatory should we aim for accurate predictions of dark matter-induced fluxes for investing significant telescope observing time on selected targets and for deriving robust conclusions from our dark matter search efforts. In this regard, a precise characterization of the statistical and structural properties of subhalos becomes critical. In this Special Issue, we aim to summarize where we stand today on our knowledge of the different aspects of the dark matter halo substructure; to identify what are the remaining big questions, and how we could address these; and, by doing so, to find new avenues for research.
| Author | : Joshua S. Bloom |
| Publisher | : Princeton University Press |
| Total Pages | : 271 |
| Release | : 2011-01-10 |
| Genre | : Science |
| ISBN | : 1400837006 |
Download What Are Gamma-Ray Bursts? Book in PDF, ePub and Kindle
A brief, cutting-edge introduction to the brightest cosmic phenomena known to science Gamma-ray bursts are the brightest—and, until recently, among the least understood—cosmic events in the universe. Discovered by chance during the cold war, these evanescent high-energy explosions confounded astronomers for decades. But a rapid series of startling breakthroughs beginning in 1997 revealed that the majority of gamma-ray bursts are caused by the explosions of young and massive stars in the vast star-forming cauldrons of distant galaxies. New findings also point to very different origins for some events, serving to complicate but enrich our understanding of the exotic and violent universe. What Are Gamma-Ray Bursts? is a succinct introduction to this fast-growing subject, written by an astrophysicist who is at the forefront of today's research into these incredible cosmic phenomena. Joshua Bloom gives readers a concise and accessible overview of gamma-ray bursts and the theoretical framework that physicists have developed to make sense of complex observations across the electromagnetic spectrum. He traces the history of remarkable discoveries that led to our current understanding of gamma-ray bursts, and reveals the decisive role these phenomena could play in the grand pursuits of twenty-first century astrophysics, from studying gravity waves and unveiling the growth of stars and galaxies after the big bang to surmising the ultimate fate of the universe itself. What Are Gamma-Ray Bursts? is an essential primer to this exciting frontier of scientific inquiry, and a must-read for anyone seeking to keep pace with cutting-edge developments in physics today.
