Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session Q8: Cosmic Ray Electrons |
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Sponsoring Units: DAP Chair: Jonathan Ormes, University of Denver Room: Governor's Square 17 |
Monday, May 4, 2009 10:45AM - 10:57AM |
Q8.00001: Observations of High Energy Cosmic Ray Electrons by the ATIC Balloon Experiment T. Gregory Guzik Recently the Advanced Thin Ionization Calorimeter (ATIC) balloon experiment reported observations of high energy cosmic ray electrons over the energy range 300 to 800 GeV, indicating a feature or ``bump'' in the otherwise smoothly decreasing energy spectrum. The severe energy losses that occur as these high energy particles traverse the galaxy render the cosmic ray electron spectrum sensitive to local (a few kiloparsecs) sources and, hence, very interesting. The ATIC results are the first time that such a cosmic ray spectrum anomaly has been observed at high energy. Potential sources of this electron excess include pulsars, micro-quasars, supernovae remnants as well as the annihilation of exotic dark matter candidate particles. ATIC has had three successful high altitude flights over the continent of Antarctica 2000-2001, 2002-2003 and 2007-2008. Only results from the first two flights have been reported so far. During this talk we will discuss the ATIC experiment, the electron observations (including preliminary results from the most recent ATIC flight), examine the merits of the various source models and compare the ATIC observations with other recent measurements. [Preview Abstract] |
Monday, May 4, 2009 10:57AM - 11:09AM |
Q8.00002: Event analysis for high energy cosmic ray electron spectrum with the Fermi Large Area Telescope Luca Latronico The Fermi Large Area Telescope (LAT) has been collecting data continuously in nominal operations since August 2008, providing exciting results that are contributing to changing our understanding of the extreme Universe. Designed as a high sensitivity and resolution gamma-ray observatory, the LAT is also a powerful electron detector with an unrivaled acceptance of about $2 m^{2} \times sr$ at 100GeV. Combining information from its silicon-strip tracker, its hodoscopic CsI calorimeter and the external anticoincidence detector, it is possible to detect electrons with very high efficiency and to reduce the overwhelming hadron background to low enough rates to effectively measure the steep primary electron spectrum up to around $\sim$1 TeV. We present here the LAT electron events analysis, addressing details of the instrument energy response and its background rejection capability. Validations of this performance from simulated, beam test and fligth data will be discussed, as well as studies of the associated systematic errors. [Preview Abstract] |
Monday, May 4, 2009 11:09AM - 11:21AM |
Q8.00003: First results on the high energy cosmic ray electron spectrum from Fermi-LAT Alexander Moiseev The Large Area Telescope was launched in June 2008 onboard the Fermi mission and since August 2008 has been collecting routine science data. Fermi science topics cover practically all aspects of high-energy astrophysics, and among them is the measurement and interpretation of the high energy cosmic ray electron spectrum. Due to their low mass and rapid energy losses by the synchrotron radiation and inverse Compton effect, cosmic ray electrons provide unique information about the origin and propagation of cosmic rays in nearby Galactic space. An accurate measurement of their spectrum will also contribute to the understanding of astrophysical dark matter, because certain dark matter models predict features in the electron spectrum. It has been demonstrated that the LAT, being a high energy gamma-ray telescope, is also capable of detecting cosmic ray electrons with the effective geometric factor of $\sim $ 2 m$^{2}$sr at 100 GeV. It has sufficient particle identification capability to reject hadrons to an adequate level, and collects unprecedented statistics of more than 10$^{7}$ electrons per year with energy above 20 GeV with good energy resolution of $<$20{\%}. In this work we present our first results on the measurement of the spectrum of high energy cosmic ray electrons from 20 GeV to around 1 TeV and discuss their interpretation. [Preview Abstract] |
Monday, May 4, 2009 11:21AM - 11:33AM |
Q8.00004: On the Sources of the High Energy Electrons and Positrons detected by Fermi Stefano Profumo The FERMI Large Area Telescope is providing us with unprecedented accuracy and detail in the measurement of the spectrum of high energy (20 GeV to 1 TeV) cosmic ray electrons and positrons. Candidate sources for the observed cosmic ray electrons and positrons include the standard primary and secondary diffuse galactic contribution, as well as nearby point-sources, the latter expected to contribute more and more significantly the higher the energy. The most natural and obvious class of such sources is that of galactic pulsars. A more exotic, but widely discussed possibility is that weakly interacting particle dark matter annihilation also contributes to the high energy electron-positron flux. In this talk we discuss the FERMI results in relation with (1) other recent experimental data on energetic electrons and positrons (specifically those reported by PAMELA, ATIC and PPB-BETS), (2) possible contributions from astrophysical galactic objects and from dark matter, and (3) the role of Fermi gamma-ray data in providing us with a coherent and well-rounded picture of the origin of high energy cosmic ray electrons and positrons, in connection to both pulsars and dark matter. [Preview Abstract] |
Monday, May 4, 2009 11:33AM - 11:45AM |
Q8.00005: Cosmic-ray electron signatures of dark matter Martin Pohl There is evidence for an excess in cosmic-ray electrons at about 500~GeV energy, that may be related to dark-matter annihilation. I have calculated the expected electron contributions from a pulsar and from Kaluza-Klein dark matter, based on a realistic treatment of the electron propagation in the Galaxy. Both pulsars and dark-matter clumps are quasi-pointlike and few, and therefore their electron contributions at Earth generally have spectra that deviate from the average spectrum one would calculate for a smooth source distribution. I find that pulsars younger than about $10^5$~years naturally cause a narrow peak at a few hundred GeV in the locally observed electron spectrum, similar to that observed. On the other hand, for a density $n_c = 10\ {\rm kpc^{-3}}$ of dark-matter clumps the sharp cut-off in the contribution from Kaluza-Klein particles is sometimes more pronounced, but often smoothed out and indistinguishable from a pulsar source, and therefore the spectral shape of the electron excess is insufficient to discriminate a dark-matter origin from more conventional astrophysical explanations. The amplitude of variations in the spectral feature caused by dark matter predominantly depends on the density of dark-matter clumps, which is not well known. [Preview Abstract] |
Monday, May 4, 2009 11:45AM - 11:57AM |
Q8.00006: Crest: A Balloon-borne Instrument to Measure Cosmic-ray Electrons above TeV Energies S. Nutter, T. Anderson, S. Coutu, M. Geske, C. Bower, J. Musser, D. Muller, N. Park, S. Wakely, M. Schubnell, G. Tarle, A. Yagi The flux of high-energy ($>$1 TeV)~electrons provides information about the spatial distribution and abundance of nearby cosmic ray sources. CREST, a balloon-borne array of 1024 BaF2 crystals viewed by PMTs, will measure the spectrum of multi-TeV electrons through detection of the x-ray synchrotron photons generated as the electrons traverse the Earth's magnetic field. This method naturally discriminates against the proton and gamma ray backgrounds, and achieves very large detector apertures, since the instrument need only intersect a portion of the kilometers-long line of photons and not the electron itself. Thus CREST's acceptance is several times its geometric area up to energies of 50 TeV, $\sim $10 times higher in energy than ground based techniques can reach. This measurement will overlap the recent HESS results and extend to higher energies. CREST is scheduled to fly in a long duration circumpolar orbit over Antarctica in 2010. An overview of the detector design and status will be presented. [Preview Abstract] |
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