Bulletin of the American Physical Society
2011 Annual Meeting of the California-Nevada Section of the APS
Volume 56, Number 14
Friday–Saturday, November 11–12, 2011; Menlo Park, California
Session B2: Astrophysics |
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Chair: Virginia Trimble, University of California, Irvine Room: Bldg 48 - ROB Redwood C/D |
Friday, November 11, 2011 1:30PM - 1:42PM |
B2.00001: Fermi Large Area Telescope Second Source Catalog Seth Digel, Jean Ballet, Thompson Burnett, Gino Tosti We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi). The Second Fermi LAT catalog (2FGL) is the product of a comprehensive analysis of the first 2 years of LAT science data. The catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1170 as being reliably associated with counterparts of known or likely gamma-ray-producing source classes. In addition, 576 of the 2FGL sources have no plausible counterparts at other wavelengths. The 2FGL catalog and associated products are available from the Fermi Science Support Center. We look forward to extensive use of this catalog in high-energy astrophysics. [Preview Abstract] |
Friday, November 11, 2011 1:42PM - 1:54PM |
B2.00002: Measurement of the cosmic-ray positron spectrum with the Fermi LAT using the Earth's magnetic field Justin Vandenbroucke, Markus Ackermann, Stefan Funk, Warit Mitthumsiri, Carmelo Sgro In addition to its primary purpose as a gamma-ray telescope, the Fermi Large Area Telescope is an excellent cosmic-ray electron and positron detector and has measured their combined spectrum between 7 GeV and 1 TeV. Although the LAT itself cannot distinguish electrons and positrons, the Earth's magnetic field creates natural ``shadows'' from which particular charges are forbidden because their paths are blocked by the Earth. Using a precise model of the geomagnetic field produced by an international collaboration of geophysicists, we trace particle trajectories in order to separate electrons and positrons. We have used this geomagnetic technique for the first time to measure the electron-only spectrum, the positron-only spectrum, and the positron fraction, all between 20 GeV and 200 GeV. We also note the LAT's capability to identify secondary positrons produced by cosmic ray air showers. [Preview Abstract] |
Friday, November 11, 2011 1:54PM - 2:06PM |
B2.00003: Limits on Large Extra Dimensions Based on Observations of Neutron Stars with the Fermi-LAT Bijan Berenji, Elliott Bloom, Johann Cohen-Tanugi We present limits for the compactification scale in the theory of Large Extra Dimensions (LED) of Arkani-Hamed, Dimopoulos, and Dvali. We use 11-months of Fermi-LAT data to set $\gamma$-ray flux limits for 6 gamma-ray faint neutron stars (NS). To set limits on LED, we use the model of Hannestad and Raffelt (HR) that calculates the Kaluza-Klein graviton ($G_{KK}$) production in supernova cores and the large fraction subsequently gravitationally bound around the resulting NS. The decays $G_{KK}\to\gamma\gamma$ should contribute to the flux from NSs. For $n=2,3,...,7$ LED of the same size in the context of the HR model, we use MC techniques to calculate the expected differential flux of gamma-rays arising from these KK gravitons, including the effects of the age of the NS, graviton orbit, and absorption of gamma-rays in the magnetosphere of the NS. We compare our MC differential flux to the experimental differential flux using maximum likelihood techniques, and obtain limits on LED that are more restrictive than past EGRET-based optimistic limits that do not include these important corrections. Additionally, our limits are more stringent than collider limits for 3 or fewer LED. If the effective Planck scale is around a TeV, then with $n=2,3$, the LED topology is non-toroidal. [Preview Abstract] |
Friday, November 11, 2011 2:06PM - 2:18PM |
B2.00004: The VERITAS Extragalactic Sky: Contemporaneous Modeling of Very High Energy Blazars with Constraints from Swift Amy Furniss In the past decade, remarkable progress has been made in very high energy (VHE; E$>$100 GeV) gamma-ray astrophysics. The VHE source catalog currently contains 48 extragalactic objects. VERITAS has detected 23 of these, including 10 VHE blazar discoveries, and many of the detected blazars have exhibited significant VHE variability. TeV blazars have spectral energy distributions (SEDs) with a synchrotron peak in the X-ray/UV/optical bands and a second peak at GeV energies, often thought to be due to inverse Compton emission. Each VERITAS blazar discovery, as well as each observed VHE flaring episode, was promptly followed up with Swift target-of-opportunity observations. These data allow the investigation of flux and spectral variability patterns of the highest energy particles, strongly constrained by the Swift XRT and UVOT exposures. Broadband SED modeling of these data has provided insights into the the energetics and timescales of particle acceleration and cooling, which are critical to understanding the physics of jets in these VHE blazars. [Preview Abstract] |
Friday, November 11, 2011 2:18PM - 2:30PM |
B2.00005: VERITAS Investigation of Very High Energy Emission from B2 1215+303 Melinda Soares The Very Energetic Radiation Imaging Telescope Array System (VERITAS) consists of four 12m imaging atmospheric Cherenkov telescopes, stationed at the Fred Lawrence Whipple Observatory in southern Arizona. The investigation of gamma-ray emission from blazars is one of the VERITAS collaboration's key science projects. This presentation reports the detection and systematic investigation of very high energy emission from the low-frequency-peaked BL Lacertae object B2 1215+303 located at a redshift of z=0.013. B2 1215+303 was first reported as a VHE source by the MAGIC Telescope Collaboration in early 2011 January during a flare that lasted four nights. The Magic Collaboration reported a flux of 2.0{\%} of the Crab Nebula flux above 250 GeV. Based on VERITAS observations performed from 2008 December to 2011 June and augmented with target of opportunity observations from NASA's Swift satellite at X-ray energies in 2011, flux and spectral variability as well as the X-ray-TeV gamma-ray flux correlation are explored. [Preview Abstract] |
Friday, November 11, 2011 2:30PM - 2:42PM |
B2.00006: Coalescing Compact Binaries with Quark Star Component Sam Koshy, Prashanth Jaikumar, Michele Vallisneri Binary stars in close orbit around each other emit gravitational radiation, which causes their orbit to decay. Here we study the tidal interactions between such inspiraling compact binaries, with neutron star-quark star and black hole-quark star components. While the gravitational radiation waveforms from coalescing binaries can be calculated fairly accurately, tidal torques cause phase errors to accumulate in their gravitational wave signal, which become significant in the event the two stars tidally lock (i.e. their orbital and spin frequencies are synchronized). Given the large viscosity that a quark star can have, tidal synchronization for both types of binaries is shown to be possible; thereby hampering signal extraction if the resulting phase difference is not incorporated into the theoretical waveform templates. In addition, the signal strengths of a gravitational wave signal from such systems are shown. And finally, we consider the possibility of stable mass transfer from the quark star to the neutron star. [Preview Abstract] |
Friday, November 11, 2011 2:42PM - 2:54PM |
B2.00007: Current and Upcoming Sensitivities to Dark Matter in Gamma-Ray Observatories J. Patrick Harding, Kevork Abazajian Dark matter particle candidates naturally emerge at the weak scale in extensions to the Standard Model of particle physics. Our analysis finds that current constraints from the all-sky exposure of the Fermi Telescope exclude the canonical expected cross section for weakly-interacting massive particle dark matter, in agreement with complementary results from other groups. At higher photon energies, corresponding to higher dark matter particle masses, I show that the High Energy Spectroscopic System (HESS) observatory and High-Altitude Water Cerenkov (HAWC) observatory provide unprecedented sensitivities to extended models of dark matter at the TeV and higher mass scales. [Preview Abstract] |
Friday, November 11, 2011 2:54PM - 3:06PM |
B2.00008: A Globular effect to the CPT breaking on a Spherical Model of the Universe Richard Kriske If one accepts the idea that three dimensions can exist in a 4 dimensional Space-Time with Time being perpendicular at each point, then when one looks at the Horizon along the Minkowski Time Line, Space-Time separates into Space and Time at the Horizon. When this happens the symmetry between Space and Time is lost, but Space takes on a Globular (in the simplest model) a Spherical Shape. If one allows a duality between Geometry and Gravitation, one could say that the Geometry of the Sphere causes the Gravitation to come into being or one could say the Gravity causes the Universe to be a Sphere (in the Space dimension with the time dimension being perpendicular). One could claim that through symmetry, any time one could cause the Time Dimension to separate from Space-Time, whether by General Relativity as in this case, or by Special Relativity in a Particle Accelerator, that Mass is created. Another interesting aspect to this in that the Photon seems to have an internal mechanism that keeps track of the the Time Normal. If it where created near the Horizon, when the photon is detected here it is Red Shifted. What does one see for a Photon created on the other side of the Horizon? One could claim that this Time Arrow points in the wrong direction, and this ``Wrong Time State'' would show up as mass in the same symmetrical way as noted above, giving one another way of generating mass from energy (go beyond the Red-Shift,then tunnel). [Preview Abstract] |
Friday, November 11, 2011 3:06PM - 3:18PM |
B2.00009: Conformal theory of galactic halos Robert K. Nesbet In current cosmology, an observed galaxy is considered to be surrounded by a large spherical halo attributed to dark matter. Galaxy formation by condensation of mass-energy necessarily depletes the original uniform cosmic background. This must leave a scar, in the form of a gravitational field halo, as observed in anomalous galactic rotation and in gravitational lensing. Without invoking dark matter, conformal theory accounts for the otherwise counterintuitive centripetal effect. [Preview Abstract] |
Friday, November 11, 2011 3:18PM - 3:30PM |
B2.00010: The Problem of Big Bang Matter vs. Antimatter Symmetry Roger Ellman The equal matter and antimatter of a spherically symmetrical Big Bang should have mutually annihilated. A skew of the symmetry in favor of matter, all of the antimatter annihilating with part of the matter, is deemed to have made an all matter universe. Research seeks a violation of matter / antimatter symmetry to justify that skew. From analysis of the mechanism of mutual annihilation a total annihilation of original Big Bang matter and antimatter could not have occurred. Our present universe must contain equal amounts of both forms between some particles of which mutual annihilations can occasionally occur, current indication of which is Gamma Ray Bursts [GRB's]. It has been found that the GRB's rate increases with red shift over the range z = 0 -- 4 as about (1 + z)$^{1.5}$, which means the rate increases significantly with time into the past. That is inconsistent with the currently favored massive supernovae core collapse hypothesis for GRB's and supports GRB's being cosmic matter / antimatter mutual annihilations. [Preview Abstract] |
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