Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session R8: Observation, Acceleration and Propagation of Cosmic Rays |
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Sponsoring Units: DAP Chair: Dietrich Muller, University of Chicago Room: Governor's Square 17 |
Monday, May 4, 2009 1:30PM - 1:42PM |
R8.00001: Composition Studies of Ultra-High Energy Cosmic Rays using $X_{max}$ by the High-Resolution Fly's Eye Observatory John Belz Both the mean value of airshower maximum $X_{max}$ and the width of the $X_{max}$ distribution are known to be sensitive to the chemical composition of cosmic rays initiating a set of extensive airshowers. Thus, studies of $X_{max}$ are an important part of efforts to understand the nature and origin of Ultra-High Energy Cosmic Rays, the most energetic elementary particles known in the universe. With the Northern Hemisphere's largest exposure to date to cosmic rays above $10^{18}$~eV, the two fluorescence detectors of the High-Resolution Fly's Eye (HiRes) Observatory are uniquely positioned to study this phenomenon. Here, we report the results of recent studies of the depth of airshower maximum $X_{max}$ in cosmic-ray induced extensive airshowers observed in stereo by HiRes. [Preview Abstract] |
Monday, May 4, 2009 1:42PM - 1:54PM |
R8.00002: An Alternate view of the Formation of Most Cosmic Rays Stirling Colgate, Hui Li, Ken Fowler The likely total energy of extra galactic cosmic rays, per galaxy spacing volume, is a few{\%} of the Super Massive Black Hole, (SMBH), energy of each galaxy. This assumes that all cosmic rays are accelerated in a universal power-law spectrum, dE/E = -$\Gamma $(dN/N), $\Gamma \sim $ -2.6. The energy of these extra galactic CRs is then 10$^{5}$ greater than the CR energy within the galaxy. We believe that magnetized jets, radio lobes, and extra galactic CRs are a natural result of the formation of SMBHs. A major fraction of the free energy of accretion is explained as magnetized AGN (jets, radio lobes) as force free magnetic twisted helical fields. The magnetic energy of these force-free fields is transformed efficiently to particle energy by E(parallel to B) acceleration of J(parallel) current carriers. These current carriers run-away in the E(parallel to B) fields and are ``starved'' in number and are marginally sufficient to carry the current at c. They are lost at the SMBH event horizon and also preferentially along tangled fields. LAUR-0805268. [Preview Abstract] |
Monday, May 4, 2009 1:54PM - 2:06PM |
R8.00003: Inductive acceleration of UHECRs in sheared relativistic jets Maxim Lyutikov Relativistic outflows carrying large scale magnetic fields have large inductive potential and may accelerate protons to ultra high energies. We discuss a novel scheme of Ultra-High Energy Cosmic Ray acceleration due to drifts in magnetized, cylindrically collimated, sheared jets of powerful active galaxies. The key features of the mechanism are (i) the highest rigidity particles are accelerated most efficiently implying the dominance of light nuclei for extragalactic CRs; (ii) acceleration rate increases with energy and does reach the theoretical maximum of inverse relativistic gyro-frequency. [Preview Abstract] |
Monday, May 4, 2009 2:06PM - 2:18PM |
R8.00004: Composition and Propagation of Galactic Cosmic-Ray Nuclei at High Energies A. Obermeier, M. Ave, P. Boyle, J. Marshall, D. M\"uller Information on the sources of cosmic rays must be deduced from observations of composition and energy spectra of the arriving particles, except for the very highest energies, where anisotropies in arrival directions may identify specific sources. TRACER, currently the largest balloon-borne detector, has been designed for direct composition measurements up to the energy regime where air shower experiments begin to provide indirect information. A long duration flight of TRACER from Antarctica (2003) has determined the energy spectra of primary nuclei (O to Fe) up to several $10^{14}$ eV per particle, and has led to a self-consistent model for the generation and propagation of these particles in the Galaxy. For a second flight launched in Sweden (2006), the instrument was upgraded to allow the lighter elements B,C and N to be included in the measurement. The analysis of this data set is ongoing, and preliminary results with emphasis on secondary and primary abundances will be presented. To further improve the knowledge of cosmic rays in the multi-TeV energy range, additional exposure time is needed. Improvements in charge resolution, e.g. by inclusion of an aerogel Cerenkov counter in TRACER, would allow detailed measurements of all secondary nuclei, including a determination of the sub-iron to iron abundance ratio. We will discuss the scientific prospects of such measurements. [Preview Abstract] |
Monday, May 4, 2009 2:18PM - 2:30PM |
R8.00005: Preliminary Results from the second Balloon Flight of BESS-Polar Experiment Thomas Hams The BESS (Balloon-borne Experiment with a Superconducting Spectrometer) program uses elementary particle measurements on a balloon-borne instrument to search for antimatter in the cosmic radiation. The search for cosmic-ray antimatter allows studying the early Universe. The BESS instrument measures the energy spectra of cosmic-ray antiprotons to investigate signatures of possible exotic sources, and searches for heavier antinuclei. Previous BESS flights have confirmed that the majority of cosmic-ray antiprotons are secondary products of the interactions of primary cosmic-ray nuclei. However, flights near the Solar minimum in 1995 and 1997 showed a slightly higher low-energy antiproton flux in excess of the expected secondary production, suggesting a possible primary antiproton component. To improve the measurement at low-energies, the BESS-Polar instrument was optimized for a long-duration balloon flight in Antarctica. In this paper we report preliminary results from the second and main science flight conducted 2007-2008 from Antarctica at solar minimum yielding an observation time of 24.5 days. [Preview Abstract] |
Monday, May 4, 2009 2:30PM - 2:42PM |
R8.00006: Short term transient variation of the proton and helium fluxes during BESS-Polar I Neeharika Thakur In addition to the long term solar modulation of the galactic diffuse cosmic ray flux due to the solar activity cycle, there may be short term transient variations caused by sudden solar magnetic activity. The causes of these transients are not yet completely understood. The BESS-Polar (Balloon-borne Experiment with a Superconducting Spectrometer) completed its first successful flight from Williams Field near McMurdo Station, Antarctica from December 13 -- 21, 2004. One of its many goals is to study the day scale time variations in the galactic cosmic ray flux. Some variation in the cosmic ray flux was observed during this flight. An initial study shows that there is a correlation between the BESS-Polar I cosmic ray flux and neutron monitor data as well as the solar wind data. The proton and helium fluxes calculated from the BESS-Polar I data will be presented and compared to the magnetic field and solar wind data to better understand this phenomenon. Details of such studies will be presented. [Preview Abstract] |
Monday, May 4, 2009 2:42PM - 2:54PM |
R8.00007: Abundance measurements of Zn, Ga, and Ge from the Cosmic Ray Isotope Spectrometer (CRIS) experiment on the Advanced Composition Explorer (ACE) satellite W.R. Binns, A.C. Cummings, G.A. DeNolfo, M.H. Israel, R.A. Leske, R.A. Mewaldt, T.T. von Rosenvinge, E.C. Stone, M.E. Wiedenbeck The cosmic ray elemental abundances of Zn, Ga, and Ge provide important tests of the emerging model of the OB-association origin of galactic cosmic rays. These ultra-heavy (Z$>$29) nuclei are very rare and require an instrument with a large geometrical factor exposed over a long period of time. We have measured these abundances using the CRIS instrument, which has a large geometrical factor of about 250 cm2sr, on the NASA-ACE spacecraft. Over the 11+ years since launch in 1997 we have collected $\sim $400 nuclei with Z$>$29 at energies of $\sim $150 to 600 MeV/nucleon. These measured abundances relative to Nickel will be presented and compared with those expected if OB associations are the source of most galactic cosmic rays. Additionally, our measurements will be compared with results from the TIGER and HEAO-3 experiments. [Preview Abstract] |
Monday, May 4, 2009 2:54PM - 3:06PM |
R8.00008: Physics from the Milagro observation of Cosmic-Ray Shadows of the Moon and Sun Grant Christopher Preliminary results will be presented on studies of the the Solar and Lunar cosmic-ray shadows observed with Milagro. Milagro is a water-cerenkov detector for astrophysical TeV gamma and cosmic rays situated near Los Alamos NM. In the geomagnetic field, TeV cosmic rays are deflected on the order of a few degrees. The Moon acts a sink for cosmic rays so it is possible to observe a shadow of the Moon in the otherwise nearly isotropic arrival of cosmic rays. Such a shadow has been previously seen by several observatories. However, Milagro's unique capabilities allow measurement of the dependence of shadow's characteristics on cosmic-ray particle energy. This can provide the first energy calibration for an extensive air shower detector which is essentially independent of monte carlo simulations. The Sun is also a sink in the sky for cosmic rays and a Solar shadow has also been observed by several experiments. However, the Sun has it's own time varying magnetic field which is not completely known. Direct measurements have been made of this field on the Solar surface from the Zeeman effect and in areas of the far-field region through which satellites have passed. Milagro observation of the Solar shadow can be compared with simulations using theoretical models of the solar magnetic field to put constraints on the field in the near-Sun region. [Preview Abstract] |
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