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Search Results: 1 - 10 of 189846 matches for " G. Sinnis "
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Current Status of VHE Astronomy
Gus Sinnis
Physics , 1999,
Abstract: Very-high-energy astronomy studies the Universe at energies between 30 GeV and 100 TeV. The past decade has seen enormous progress in this field. There are now at least seven known sources of VHE photons. By studying these objects in the VHE regime one can begin to understand the environments surrounding these objects, and how particle acceleration is realized in nature. In addition the photon beams from the extragalactic gamma-ray sources can be used to study the electromagnetic fields in the intervening space. This recent progress can be traced to the development of a new class of detector with the ability to differentiate between air showers produced by gamma rays and those produced by the much more numerous hadronic cosmic-ray background. Much more sensitive instruments are currently in the design phase and two new types of instruments are beginning to take data. In this paper we will discuss the physics of these sources and describe the existing and planned detectors.
Milagro Limits on the Rate-Density of Primordial Black Holes
T. U. Ukwatta,D. Stump,J. T. Linnemann,K. Tollefson,V. Vasileiou,G. Sinnis,J. H. MacGibbon
Physics , 2013,
Abstract: Primordial Black Holes (PBHs) created early in the universe are dark matter candidates. One method of detecting these PBHs is through their Hawking radiation. PBHs created with an initial mass of 5.0 x 10^14 g should be evaporating today with bursts of high-energy particles, including gamma radiation in the GeV - TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is ideally suited for the direct search of PBH bursts. Based on a search in Milagro data, we report PBH upper limits according to the standard model.
Gamma-Ray Summary Report
J. Buckley,T. Burnett,G. Sinnis,P. Coppi,P. Gondolo,J. Kapusta,J. McEnery,J. Norris,P. Ullio,D. A. Williams
Physics , 2002,
Abstract: This paper reviews the field of gamma-ray astronomy and describes future experiments and prospects for advances in fundamental physics and high-energy astrophysics through gamma-ray measurements. We concentrate on recent progress in the understanding of active galaxies, and the use of these sources as probes of intergalactic space. We also describe prospects for future experiments in a number of areas of fundamental physics, including: searches for an annihilation line from neutralino dark matter, understanding the energetics of supermassive black holes, using AGNs as cosmological probes of the primordial radiation fields, constraints on quantum gravity, detection of a new spectral component from GRBs, and the prospects for detecting primordial black holes.
Tests of Lorentz Invariance Violation with Gamma Rays to probe Quantum Gravity
N. Otte,M. Errando,S. Griffiths,P. Kaaret,H. Krawczynski,A. McCann,G. Sinnis,F. Stecker,I. Taboada,V. Vasileiou,B. Zitzer
Physics , 2013,
Abstract: We discuss the prospects of doing tests of Lorentz invariance with gamma-rays observed with present and future ground based gamma-ray observatories.
Plasmodium Protease ROM1 Is Important for Proper Formation of the Parasitophorous Vacuole
Iset Medina Vera,Wandy L. Beatty,Photini Sinnis,Kami Kim
PLOS Pathogens , 2011, DOI: 10.1371/journal.ppat.1002197
Abstract: Apicomplexans are obligate intracellular parasites that invade host cells by an active process leading to the formation of a non-fusogenic parasitophorous vacuole (PV) where the parasite replicates within the host cell. The rhomboid family of proteases cleaves substrates within their transmembrane domains and has been implicated in the invasion process. Although its exact function is unknown, Plasmodium ROM1 is hypothesized to play a role during invasion based on its microneme localization and its ability to cleave essential invasion adhesins. Using the rodent malaria model, Plasmodium yoelii, we carried out detailed quantitative analysis of pyrom1 deficient parasites during the Plasmodium lifecycle. Pyrom1(-) parasites are attenuated during erythrocytic and hepatic stages but progress normally through the mosquito vector with normal counts of oocyst and salivary gland sporozoites. Pyrom1 steady state mRNA levels are upregulated 20-fold in salivary gland sporozoites compared to blood stages. We show that pyrom1(-) sporozoites are capable of gliding motility and traversing host cells normally. Wildtype and pyrom1(-) sporozoites do not differ in the rate of entry into Hepa1–6 hepatocytes. Within the first twelve hours of hepatic development, however, only 50% pyrom1(-) parasites have developed into exoerythrocytic forms. Immunofluorescence microscopy using the PVM marker UIS4 and transmission electron microscopy reveal that the PV of a significant fraction of pyrom1(-) parasites are morphologically aberrant shortly after invasion. We propose a novel function for PyROM1 as a protease that promotes proper PV modification to allow parasite development and replication in a suitable environment within the mammalian host.
What Are Gamma-Ray Bursts -- The Unique Role of Very High Energy Gamma-Ray Observations
D. A. Williams,A. D. Falcone,M. G. Baring,J. Buckley,V. Connaughton,P. Coppi,C. Dermer,S. Digel,B. Dingus,C. Fryer,N. Gehrels,J. Granot,D. Horan,J. I. Katz,P. Meszaros,J. Norris,P. Saz Parkinson,A. Pe'er,S. Razzaque,G. Sinnis,X. Y. Wang,T. C. Weekes,B. Zhang
Physics , 2009,
Abstract: Gamma-ray bursts (GRBs) have been an enigma since their discovery forty years ago. However, considerable progress unraveling their mysteries has been made in recent years. Developments in observations, theory, and instrumentation have prepared the way so that the next decade can be the one in which we finally answer the question, "What are gamma-ray bursts?" This question encompasses not only what the progenitors are that produce the GRBs, but also how the enormous luminosity of the GRBs, concentrated in gamma rays, is achieved. Observations across the electromagnetic spectrum, from both the ground and space, will be required to fully tackle this important question. This white paper, mostly distilled from a recent study commissioned by the Division of Astrophysics of the American Physical Society, focuses on what very high energy (~100 GeV and above) gamma-ray observations can contribute. Very high energy gamma rays probe the most extreme high energy particle populations in the burst environment, testing models of lepton and proton acceleration in GRBs and constraining the bulk Lorentz factor and opacity of the outflow. Sensitivity improvements of more than an order of magnitude in the very high energy gamma-ray band can be achieved early in the next decade, in order to contribute to this science.
Planning the Future of U.S. Particle Physics (Snowmass 2013): Chapter 4: Cosmic Frontier
J. L. Feng,S. Ritz,J. J. Beatty,J. Buckley,D. F. Cowen,P. Cushman,S. Dodelson,C. Galbiati,K. Honscheid,D. Hooper,M. Kaplinghat,A. Kusenko,K. Matchev,D. McKinsey,A. E. Nelson,A. Olinto,S. Profumo,H. Robertson,L. Rosenberg,G. Sinnis,T. M. P. Tait
Physics , 2014,
Abstract: These reports present the results of the 2013 Community Summer Study of the APS Division of Particles and Fields ("Snowmass 2013") on the future program of particle physics in the U.S. Chapter 4, on the Cosmic Frontier, discusses the program of research relevant to cosmology and the early universe. This area includes the study of dark matter and the search for its particle nature, the study of dark energy and inflation, and cosmic probes of fundamental symmetries.
Spectrum and Morphology of the Two Brightest Milagro Sources in the Cygnus Region: MGRO J2019+37 and MGRO J2031+41
A. A. Abdo,B. T. Allen,T. Aune,D. Berley,E. Bonamente,G. E. Christopher,T. DeYoung,B. L. Dingus,R. W. Ellsworth,J. G. Galbraith-Frew,M. M. Gonzalez,J. A. Goodman,C. M. Hoffman,P. H. Huentemeyer,B. E. Kolterman,J. T. Linnemann,J. E. McEnery,A. I. Mincer,T. Morgan,P. Nemethy,J. Pretz,J. M. Ryan,P. M. Saz Parkinson,G. Sinnis,A. J. Smith,V. Vasileiou,G. P. Walker,D. A. Williams,G. B. Yodh
Physics , 2012, DOI: 10.1088/0004-637X/753/2/159
Abstract: The Cygnus region is a very bright and complex portion of the TeV sky, host to unidentified sources and a diffuse excess with respect to conventional cosmic-ray propagation models. Two of the brightest TeV sources, MGRO J2019+37 and MGRO J2031+41, are analyzed using Milagro data with a new technique, and their emission is tested under two different spectral assumptions: a power law and a power law with an exponential cutoff. The new analysis technique is based on an energy estimator that uses the fraction of photomultiplier tubes in the observatory that detect the extensive air shower. The photon spectrum is measured in the range 1 to 200 TeV using the last 3 years of Milagro data (2005-2008), with the detector in its final configuration. MGRO J2019+37 is detected with a significance of 12.3 standard deviations ($\sigma$), and is better fit by a power law with an exponential cutoff than by a simple power law, with a probability $>98$% (F-test). The best-fitting parameters for the power law with exponential cutoff model are a normalization at 10 TeV of $7^{+5}_{-2}\times10^{-10}$ $\mathrm{s^{-1}\: m^{-2}\: TeV^{-1}}$, a spectral index of $2.0^{+0.5}_{-1.0}$ and a cutoff energy of $29^{+50}_{-16}$ TeV. MGRO J2031+41 is detected with a significance of 7.3$\sigma$, with no evidence of a cutoff. The best-fitting parameters for a power law are a normalization of $2.4^{+0.6}_{-0.5}\times10^{-10}$ $\mathrm{s^{-1}\: m^{-2}\: TeV^{-1}}$ and a spectral index of $3.08^{+0.19}_{-0.17}$. The overall flux is subject to an $\sim$30% systematic uncertainty. The systematic uncertainty on the power law indices is $\sim$0.1. A comparison with previous results from TeV J2032+4130, MGRO J2031+41 and MGRO J2019+37 is also presented.
Milagro Observations of Multi-TeV Emission from Galactic Sources in the Fermi Bright Source List
A. A. Abdo,B. T. Allen,T. Aune,D. Berley,C. Chen,G. E. Christopher,T. DeYoung,B. L. Dingus,R. W. Ellsworth,M. M. Gonzalez,J. A. Goodman,E. Hays,C. M. Hoffman,P. H. Huentemeyer,B. E. Kolterman,J. T. Linnemann,J. E. McEnery,T. Morgan,A. I. Mincer,P. Nemethy,J. Pretz,J. M. Ryan,P. M. Saz Parkinson,A. Shoup,G. Sinnis,A. J. Smith,V. Vasileiou,G. P. Walker,D. A. Williams,G. B. Yodh
Physics , 2009, DOI: 10.1088/0004-637X/703/2/L185
Abstract: We present the result of a search of the Milagro sky map for spatial correlations with sources from a subset of the recent Fermi Bright Source List (BSL). The BSL consists of the 205 most significant sources detected above 100 MeV by the Fermi Large Area Telescope. We select sources based on their categorization in the BSL, taking all confirmed or possible Galactic sources in the field of view of Milagro. Of the 34 Fermi sources selected, 14 are observed by Milagro at a significance of 3 standard deviations or more. We conduct this search with a new analysis which employs newly-optimized gamma-hadron separation and utilizes the full 8-year Milagro dataset. Milagro is sensitive to gamma rays with energy from 1 to 100 TeV with a peak sensitivity from 10-50 TeV depending on the source spectrum and declination. These results extend the observation of these sources far above the Fermi energy band. With the new analysis and additional data, multi-TeV emission is definitively observed associated with the Fermi pulsar, J2229.0+6114, in the Boomerang Pulsar Wind Nebula (PWN). Furthermore, an extended region of multi-TeV emission is associated with the Fermi pulsar, J0634.0+1745, the Geminga pulsar.
Instrumented Water Tanks can Improve Air Shower Detector Sensitivity
R. Atkins,W. Benbow,D. Berley,M. -L. Chen,D. G. Coyne,R. S. Delay,B. L. Dingus,D. E. Dorfan,R. W. Ellsworth,D. Evans,A. Falcone,L. Fleysher,R. Fleysher,G. Gisler,J. A. Goodman,T. J. Haines,C. M. Hoffman,S. Hugenberger,L. A. Kelley,I. Leonor,J. Macri,M. McConnell,J. F. McCullough,J. E. McEnery,R. S. Miller,A. I. Mincer,M. F. Morales,P. Nemethy,J. M. Ryan,M. Schneider,B. Shen,A. Shoup,G. Sinnis,A. J. Smith,G. W. Sullivan,T. N. Thompson,O. T. Tumer,K. Wang,M. O. Wascko,S. Westerhoff,D. A. Williams,T. Yang,G. B. Yodh
Physics , 1999,
Abstract: Previous works have shown that water Cherenkov detectors have superior sensitivity to those of scintillation counters as applied to detecting extensive air showers (EAS). This is in large part due to their much higher sensitivity to EAS photons which are more than five times more numerous than EAS electrons. Large area water Cherenkov detectors can be constructed relatively cheaply and operated reliably. A sparse detector array has been designed which uses these types of detectors to substantially increase the area over which the Milagro Gamma Ray Observatory collects EAS information. Improvements to the Milagro detector's performance characteristics and sensitivity derived from this array and preliminary results from a prototype array currently installed near the Milagro detector will be presented.
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