Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session E11: Solar-/Cosmo-Terrestrial Physics and New Instrumentation |
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Sponsoring Units: DAP Chair: Brenda Dingus, Los Alamos National Laboratory Room: Hyatt Regency Jacksonville Riverfront City Terrace 7 |
Saturday, April 14, 2007 3:30PM - 3:42PM |
E11.00001: \textit{Milagro} Measurements of Solar Energetic Particles during the 2005 January 20 Ground Level Event Trevor Morgan \textit{Milagro} is a ground-based TeV gamma-ray telescope employing the water \c{C}erenkov technique. As such, it is sensitive to muons produced by GeV solar protons entering the atmosphere. Located in the Jemez Mountains near Los Alamos New Mexico, it is near the Climax neutron monitor station operated by the University of New Hampshire. Using both instruments that have different instrument responses one can obtain a measure of the solar energetic proton spectrum above several GV rigidity. The 2005 January 20 event was the most intense in a half century. At several GV it exhibited a strong impulsive signal at both these stations suggesting that a narrow proton beam was well aligned with the asympototic direction associated with \textit{Milagro}. Using multi-PMT scalers and the signal from Climax we can estimate the spectrum above the geomagnetic cutoff and can constrain the degree of anisotropy during the intense leading edge of the event. Based on extensive computer simulations of the \textit{Milagro} response to isotropic and beam-like bursts of protons over a range of rigidity, we will report results of this exercise. [Preview Abstract] |
Saturday, April 14, 2007 3:42PM - 3:54PM |
E11.00002: Imaging 2-20 MeV solar neutrons in the inner heliosphere with the FNIT detector Ulisse Bravar, Paul Bruillard, Erwin Flueckiger, Alec MacKinnon, John Macri, Mark McConnell, Amaresh Motamarri, Michael Moser, James Ryan, Richard Woolf The Fast Neutron Imaging Telescope (FNIT), a neutron detector with imaging and energy measurement capabilities sensitive to neutrons in the 2-20 MeV energy range, is specifically conceived as a candidate instrument for the Solar Sentinels program. Different design concepts have been explored to optimize the detection capabilities for solar-flare neutrons in the inner heliosphere. The detection principle is based on multiple elastic neutron-proton scatterings in organic scintillators. By measuring the scattering coordinates and determining the energy of recoil protons and the momentum of scattered neutrons, the energy spectrum and incident direction of primary neutrons can be reconstructed. We present the results of recent Monte Carlo and laboratory efforts and describe the performance of the most advanced FNIT prototype design, structured around liquid scintillator detectors for neutron identification. [Preview Abstract] |
Saturday, April 14, 2007 3:54PM - 4:06PM |
E11.00003: Measurement of Spectra with Milagro Using an Event-by-Event Energy Estimation Algorithm Branden Allen An event-by-event energy estimation algorithm for the Milagro gamma ray observatory which depends upon the observed characteristics of an extensive air shower has been devised. This algorithm has been applied to the Crab nebula for the measurement of the high energy spectrum in the energy range from 1 to 100 TeV. Our results are similar to those of atmospheric Cherenkov telescopes. Preliminary results show a weak indication of a high enrgy cutoff above 10 TeV for the Crab spectrum. [Preview Abstract] |
Saturday, April 14, 2007 4:06PM - 4:18PM |
E11.00004: ABSTRACT WITHDRAWN |
Saturday, April 14, 2007 4:18PM - 4:30PM |
E11.00005: R\&D towards a Liquid Xenon Advanced Compton Telescope (LXeACT) Uwe Oberlack, Christopher Olsen, Petr Shagin, Elena Aprile, Karl Ludwig Giboni, Roberto Santorelli The scientific potential of gamma-ray astronomy in the energy regime of nuclear transitions has long been recognized. Yet, only the tip of the iceberg has been probed by gamma-ray telescopes to-date, due to a lack of sensitivity. A future ``Advanced Compton Telescope'' (ACT) could boost this field by improving sensitivity 100-fold over current instruments. We are working on advancing the liquid xenon time projection chamber (LXeTPC) technology to combine the uniq advantages of this detector type (large homogeneous sensitive volumes with a minimum of electronics channels and hence power, high efficiency, radiation hardness, low background, etc.) with the spectroscopic requirements of the ACT. Rapid advances in UV photosensor technologies have opened new opportunities for the successful development of a LXeACT. These are: (a) Improvement of energy resolution by combination of ionization and scintillation signals. (b) Application of time-of-flight in a compact telescope configuration. We report on the status of our current R\&D program, which includes characterization of novel photosensors, such as APDs and Geiger-mode APD pixel arrays (SiPMs), inside LXe. [Preview Abstract] |
Saturday, April 14, 2007 4:30PM - 4:42PM |
E11.00006: Terrestrial Effects of Astrophysical Ionizing Photon Events: Spectrum and Variability Adrian Melott, Larissa Ejzak, Brian Thomas, Mikhail Medvedev A variety of astrophysical ionizing photon sources such as gamma-ray bursts, supernovae, magnetars, and solar flares represent a hazard to the Earth's biosphere, primarily through breaking the strong triple bond in the N$_{2}$ molecule in the atmosphere. This produces oxides of nitrogen which catalyze depletion of the O$_{3}$ shield. As a result, greatly increased levels of solar UVB reach the surface. UVB is absorbed by and damages the DNA molecule, and is known to be lethal for organisms such as phytoplankton which lie at the base of the food chain. Such astrophysical sources vary greatly in their time dependence and spectrum of photon energies. We have computationally explored the parameter space of such variation, and describe the consequences for the biosphere. [Preview Abstract] |
Saturday, April 14, 2007 4:42PM - 4:54PM |
E11.00007: Spectral Analysis of Biodiversity Cycles and Galactic Dynamics Bruce Lieberman, Adrian Melott We have analyzed the power spectral and phase relationships of fluctuations in biodiversity, species origination, extinction rate, and motion of the solar system normal to the galactic plane over the last $\sim $500 My. The period of the dominant spectral component is the same 62 My for all these except extinction. It is also the same as the rate of gene duplication events (as determined by Ding et al.), suggesting some sort of causal relationship. The spectra suggest that the biodiversity cycle is more closely related to origination rates than extinction rates. Biodiversity and solar motion are offset by $\pi $, with gene duplication and origination lagging and leading biodiversity by $\sim $2 radians. A picture emerges consistent with a rising rate of mutation and stress on the biosphere as the solar system moves to galactic north, possibly exposed to higher cosmic rays from a galactic bow shock, as proposed elsewhere, and increasing species origination as it returns to the magnetic shielding of the galactic disk. [Preview Abstract] |
Saturday, April 14, 2007 4:54PM - 5:06PM |
E11.00008: Distribution of Cosmic Rays in the Galaxy -- a Link to Biodiversity Cycles Mikhail Medvedev The spectral analysis of fluctuations of biodiversity (Rohde \& Muller, 2005) and the subsequent re-analysis of the diversity record, species origination and extinction rates, gene duplication, etc (Melott \& Liebermann, 2007) indicate the presence of a 62$\pm$3My cyclicity, for the last 500My. Medvedev \& Melott (2006) proposed that the cyclicity may be related to the periodicity of the Solar motion with respect to the Galactic plane, which exhibits a 63My oscillation, and the inhomogeneous distribution of Cosmic Rays (CR) throughout the Milky Way, which may affect the biosphere by changing mutation rate, climate, food chain, etc. Here we present a model of CR propagation in the Galactic magnetic fields, in the presence of both the mean field gradient and the strong MHD turbulence in the interstellar medium. We explore the ``magnetic shielding effect'' as a function of CR energy and composition and estimate the resultant flux of mutagenic secondary muons at the Earth surface. [Preview Abstract] |
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