18693900
TeV Gamma-Ray Observations of the Perseus and Abell 2029 Galaxy Clusters
Galaxy clusters might be sources of TeV gamma rays emitted by high-energy protons and electrons accelerated by large-scale structure formation shocks, galactic winds, or active galactic nuclei. Furthermore, gamma rays may be produced in dark matter particle annihilation processes at the cluster cores. We report on observations of the galaxy clusters Perseus and A2029 using the 10 m Whipple Cerenkov telescope during the 2003-2004 and 2004-2005 observing seasons. We apply a two-dimensional analysis technique to scrutinize the clusters for TeV emission. In this paper we first determine flux upper limits on TeV gamma-ray emission from point sources within the clusters. Second, we derive upper limits on the extended cluster emission. We subsequently compare the flux upper limits with EGRET upper limits at 100 MeV and theoretical models. Assuming that the gamma-ray surface brightness profile mimics that of the thermal X-ray emission and that the spectrum of cluster cosmic rays extends all the way from thermal energies to multi-TeV energies with a differential spectral index of -2.1, our results imply that the cosmic-ray proton energy density is less than 7.9% of the thermal energy density for the Perseus Cluster.
56147520
Investigating Broadband Variability of the TeV Blazar 1ES 1959+ 650
We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift Ultraviolet and Optical Telescope, X-ray observations by the Swift X-ray Telescope, high-energy gamma-ray observations with the Fermi Large Area Telescope, and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 2012 April 17 and 2012 June 1 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected emission model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV.
118558915
TeV Gamma-Ray Observations of the Perseus Galaxy Cluster
We report on observations of the Perseus cluster of galaxies using the 10 m Whipple $\gamma$-ray telescope during the 2004-2005 observing season. We apply a two dimensional analysis technique to allow us to scrutinize the cluster for TeV emission. In this contribution we will first calculate flux upper limits on TeV gamma-ray sources within the cluster. Second, we derive an upper limit on the extended cluster emission. We then compare the flux upper limits with the EGRET upper limit at 100 MeV and theoretical models.
53709598
Multiwavelength Observations of the TeV Binary LS I +61° 303 with VERITAS, Fermi-LAT, and Swift/XRT during a TeV Outburst
We present the results of a multiwavelength observational campaign on the TeV binary system LS I +61° 303 with the VERITAS telescope array (>200 GeV), Fermi-LAT (0.3-300 GeV), and Swift/XRT (2-10 keV). The data were taken from 2011 December through 2012 January and show a strong detection in all three wavebands. During this period VERITAS obtained 24.9 hr of quality selected livetime data in which LS I +61° 303 was detected at a statistical significance of 11.9σ. These TeV observations show evidence for nightly variability in the TeV regime at a post-trial significance of 3.6σ. The combination of the simultaneously obtained TeV and X-ray fluxes do not demonstrate any evidence for a correlation between emission in the two bands. For the first time since the launch of the Fermi satellite in 2008, this TeV detection allows the construction of a detailed MeV-TeV spectral energy distribution from LS I +61° 303. This spectrum shows a distinct cutoff in emission near 4 GeV, with emission seen by the VERITAS observations following a simple power-law above 200 GeV. This feature in the spectrum of LS I +61° 303, obtained from overlapping observations with Fermi-LAT and VERITAS, may indicate that there are two distinct populations of accelerated particles producing the GeV and TeV emission.
207979209
Fermi-LAT DETECTION OF GRAVITATIONAL LENS DELAYED GAMMA-RAY FLARES FROM BLAZAR B0218+357
Using data from the Fermi Large Area Telescope (LAT), we report the first clear γ-ray measurement of a delay between flares from the gravitationally lensed images of a blazar. The delay was detected in B0218+357, a known double-image lensed system, during a period of enhanced γ-ray activity with peak fluxes consistently observed to reach > 20− 50× its previous average flux. An auto-correlation function analysis identified a delay in the γ-ray data of 11.46± 0.16 days (1σ) that is ∼ 1 day greater than previous radio measurements. Considering that it is beyond the capabilities of the LAT to spatially resolve the two images, we nevertheless decomposed individual sequences of superposing γ-ray flares/delayed emissions. In three such ∼ 8− 10 day-long sequences within a ∼ 4-month span, considering confusion due to overlapping flaring emission and flux measurement uncertainties, we found flux ratios consistent with ∼ 1, thus systematically smaller than those from radio observations. During the first, best-defined flare, the delayed emission was detailed with a Fermi pointing, and we observed flux doubling timescales of ∼ 3 − 6 hrs implying as well extremely compact γ-ray emitting regions. Subject headings: Galaxies: active — gravitational lensing: strong — gamma rays: galaxies — quasars: individual (B0218+357) 1 Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352, USA 2 email: Teddy.Cheung@nrl.navy.mil 3 Department of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden 4 The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden 5 Department of Astronomy, Stockholm University, SE-106 91 Stockholm, Sweden 6 Supported by the Royal Swedish Academy Crafoord Foundation 7 email: stefan@astro.su.se 8 Space Sciences Division, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA 9 email: Jeffrey.D.Scargle@nasa.gov 10 Kavli Institute for Cosmology and Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 11 W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA 12 Department of Physics, Stanford University, Stanford, CA 94305, USA 13 Agenzia Spaziale Italiana (ASI) Science Data Center, I00133 Roma, Italy 14 Istituto Nazionale di Astrofisica Osservatorio Astronomico di Roma, I-00040 Monte Porzio Catone (Roma), Italy 15 Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 16 University of Maryland Baltimore County, Baltimore, MD 21250, USA 17 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA 18 Department of Physics (Astrophyics), Oxford University, Oxford OX1 3RH, UK 19 Praxis Inc., Alexandria, VA 22303, resident at Naval Research Laboratory, Washington, DC 20375, USA 20 Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USA 21 Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I35131 Padova, Italy 22 Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, I-35131 Padova, Italy 23 Center for Earth Observing and Space Research, College of Science, George Mason University, Fairfax, VA 22030, resident at Naval Research Laboratory, Washington, DC 20375, USA 24 INAF Istituto di Radioastronomia, 40129 Bologna, Italy 25 Centre d’Études Nucléaires de Bordeaux Gradignan, IN2P3/CNRS, Université Bordeaux 1, BP120, F-33175 Gradignan Cedex, France 26 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 27 Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I56127 Pisa, Italy 28 Funded by contract FIRB-2012-RBFR12PM1F from the Italian Ministry of Education, University and Research (MIUR) 29 Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA https://ntrs.nasa.gov/search.jsp?R=20150008355 2019-11-11T04:04:43+00:00Z
16581023
Blazar Discoveries with VERITAS
Blazars are among the most energetic and violent objects in the universe. By observing blazars at very high energies (VHE, E > 100 GeV) we can better understand blazar emission mechanisms, jet structure, black hole accretion and the extragalactic background light (EBL). VERITAS, an array of four 12-meter diameter imaging atmospheric-Cherenkov telescopes, performs VHE studies of blazars through intense monitoring and discovery campaigns. Most blazars known to emit VHE gamma rays are high-frequency-peaked BL Lacertae (HBL) objects, and VERITAS has discovered VHE emission from two of these: 1ES 0806+524 and RGB J0710+591. VERITAS has also discovered VHE gamma rays from two intermediate-frequency-peaked BL Lacertae (IBL) objects: W Com and 3C 66A. The expansion of the VHE catalog to include IBL objects enables a better understanding of the AGN population as a whole. This contribution presents recent results from the VERITAS blazar discovery program.
118390823
Rapidity gaps in hard processes at D0
Latest results on jet production with rapidity gaps at the Fermilab Tevatron Collider are presented. Jet production via color-singlet exchange at high momenta transfer is observed as a class of events with low particle multiplicity (or rapidity gaps) between the two highest transverse energy jets. The particle multiplicity in various regions, and the dependencies on jet pseudorapidity separation and jet transverse energy are studied for these events. Results from two classes of dijet events with one or two forward rapidity gaps are also presented. The topology of these events is consistent with expectations for hard single diffraction and hard double pomeron exchange processes, respectively.
12334845
Stringent phenomenological investigation into heterotic string optical unification
For the weakly coupled heterotic string (WCHS) there is a well-known factor of 20 conflict between the minimum string coupling unification scale, {lambda}{sub H}{approx}5x10{sup 17} GeV, and the projected minimal supersymmetric standard model (MSSM) gauge coupling unification scale, {lambda}{sub U}{approx}2.5x10{sup 16} GeV, assuming an intermediate scale desert (ISD). From a bottom-up approach, renormalization effects of intermediate scale MSSM-charged exotics (ISME), which are endemic to quasirealistic string models, can resolve this issue by pushing the MSSM scale up to the string scale. However, for a generic string model, this implies that the projected {lambda}{sub U} unification under the ISD assumption is accidental. If the true unification scale is {lambda}{sub H} > or approx. 5.0x10{sup 17} GeV, is it possible that an illusionary unification at {lambda}{sub U}=2.5x10{sup 17} GeV in the ISD scenario is not accidental? (This is an issue recently raised again by Binetruy et al..) Optical unification suggests that {lambda}{sub U} might not be accidental. Through its ISME constraints, optical unification offers a mechanism whereby a generic MSSM scale {lambda}{sub U}<{lambda}{sub H} is guaranteed. A WCHS model was recently constructed that could yield optical unification, depending on the availability of anomaly-cancelling D- and F-flat directions that meet optical unification ISME more » requirements. We report the results of a systematic investigation of the optical unification properties of a subset of flat directions of this model that are stringently flat. Stringent flat directions do not require significant fine-tuning and can be easily guaranteed to be F-flat to all finite order (or to at least a given finite order consistent with electroweak scale supersymmetry breaking). They are the likely roots of more complicated (and arguably, more finely tuned) flat directions. To realize optical unification, a flat direction must keep all exotic triplets and doublets massless down to an intermediate mass scale, except for three extra pairs of Higgs which must acquire MSSM (or higher) scale mass. Additionally, six out of seven pairs of exotic hypercharged non-Abelian singlets must acquire MSSM (or higher) scale mass, while the remaining pair remains massless down to the intermediate scale. Our investigation revealed that the best stringent directions could induce MSSM scale or higher mass to at most three of the six pairs of exotic singlets, and to only two out of three pairs of exotic Higgs. Each of these stringent flat directions keeps all of the exotic triplets and remaining exotic doublets massless down to an intermediate scale. Thus, some fine-tuning away from stringent flat directions is necessary, if it is possible for an additional three pairs of exotic hypercharged singlets and one more pair of extra Higgs to become MSSM scale massive. Future research may indicate if such flat directions exist. This paper is a product of the 2003-2004 NSF REU program at Baylor University. « less