Bulletin of the American Physical Society
77th Annual Meeting of the Southeastern Section of the APS
Volume 55, Number 10
Wednesday–Saturday, October 20–23, 2010; Baton Rouge, Louisiana
Session HC: Astrophysics: Gamma Rays, Supernovae, and Black Holes |
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Chair: Jorge Piekarewicz, Florida State University Room: Nicholson Hall 118 |
Friday, October 22, 2010 1:30PM - 1:42PM |
HC.00001: All-Sky Imaging With Fermi's GBM in the Hard X-ray Regime J. Rodi, G.L. Case, M.L. Cherry, C.A. Wilson-Hodge The 12 sodium iodide (NaI) detectors that provide the hard x-ray (8-1000 keV) coverage for the Fermi satellite mission's Gamma-Ray Burst Monitor (GBM) can utilize the Earth Occultation Technique to measure the flux of x-ray and gamma-ray sources. When a source moves behind (or out from behind) the Earth, a step-like feature occurs in the detector count rate. The $ \sim 53$ day orbital precession period allows for complete sky coverage, though the coverage is not uniform. The standard analysis relies on a catalog of known sources for obtaining occultation times and flux measurements. To search for unknown sources, imaging techniques must be used such as the Differential Filter Technique being developed at LSU. A grid with $0.25^{\circ}$ spacing is overlaid on the sky, and the data near a given grid point's occultation times are folded over multiple days. The folded data are then passed through the filter, amplifying an occultation step while damping background and providing an estimate of the intensity from that grid point. Results using GBM will be presented. [Preview Abstract] |
Friday, October 22, 2010 1:42PM - 1:54PM |
HC.00002: All-Sky Imaging of the Gamma-Ray Sky with BATSE Y. Zhang, G.L. Case, M.L. Cherry Earth occultation provides a means of monitoring gamma-ray sources over the entire sky. The technique has been demonstrated with the Burst And Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO), and is now being used with the Gamma-ray Burst Monitor (GBM) instrument on the Fermi mission. Although the approach provides a powerful wide-field monitoring capability, the BATSE and GBM implementations of the technique have so far limited the analysis to a catalog of previously identified sources. We present an indirect imaging method that permits searching for unknown sources by applying the Differential Filter Technique (DFT) to archival BATSE data. Occultation steps are transformed into gaussian-like features corresponding to the intensities measured from each pixel in the sky. Coupling this to the $ \sim 51$-day precession cycle of the CGRO orbit (with $28.5^{\circ}$ inclination) makes it possible to perform an all-sky survey. By applying standard imaging deconvolution techniques, it becomes possible to locate known and unknown sources with spatial resolution to $\sim 0.5^{\circ}$ accuracy. Initial results from the application of the approach to BATSE will be presented. [Preview Abstract] |
Friday, October 22, 2010 1:54PM - 2:06PM |
HC.00003: Monitoring the $>100$ keV Gamma-Ray Sky Using GBM: The First Two Years G.L. Case, A. Camero-Arranz, V. Chaplin, M.L. Cherry, M.H. Finger, P. Jenke, J. Rodi, C.A. Wilson-Hodge The Gamma-Ray Burst Monitor (GBM) onboard Fermi is being used to monitor hard x-ray/soft gamma-ray sources in the energy range of 8-1000 keV using the Earth occultation technique. Through the first two years of this monitoring program, eight sources have been detected at energies above 100 keV, including six persistent sources (Crab, Cyg X-1, Cen A, 1E 1740-29, SWIFT J1753.5-0127, and GRS 1915+105) and two transients (XTE J1752-223 and GX 339-4). Light curves of all eight sources using the GBM 8-channel CTIME data are presented along with discussion of the high energy behavior. [Preview Abstract] |
Friday, October 22, 2010 2:06PM - 2:18PM |
HC.00004: Ground-Based Observations of Terrestrial Gamma-Ray Flashes R.A. Ringuette, N. Cannady, G.L. Case, M.L. Cherry, D. Granger, J. Isbert, M. Stewart First seen from space by the BATSE gamma ray telescope in the 1990s, Terrestrial Gamma ray Flashes (TGFs) consist of extremely fast bursts of high energy (up to 40 MeV) gamma rays correlated with intense lightning from thunderstorms. Spacecraft experiments are sensitive to very large events, but ground-based detectors closer to the thunderstorms may provide data on the intensity spectrum of smaller events. Four detectors consisting of NaI scintillators viewed by photomultipliers have been placed on rooftops at LSU's Baton Rouge campus to monitor TGFs. The setup and design of the ground-based experiment will be discussed. [Preview Abstract] |
Friday, October 22, 2010 2:18PM - 2:30PM |
HC.00005: Accretion-Induced Collapse of White Dwarfs Ernazar Abdikamalov, Christian Ott, Luciano Rezzolla, Luc Dessart, Harald Dimmelmeier, Andreas Marek, Hans-Thomas Janka The accretion-induced collapse (AIC) of a white dwarf may lead to the formation of a protoneutron star and a supernova explosion. This process represents a path alternative to thermonuclear disruption of accreting white dwarfs in Type Ia supernovae. In the AIC scenario, the supernova explosion energy is expected to be small and the resulting transient short-lived, making it hard to detect by electromagnetic and neutrino means alone. Gravitational-wave observations may provide crucial information necessary to reveal a potential AIC. In this talk, I present results from recent numerical simulations of AIC. I will discuss the prospects for observing electromagnetic and gravitational wave signal from AIC. [Preview Abstract] |
Friday, October 22, 2010 2:30PM - 2:42PM |
HC.00006: Dust Formation in Core Collapse Supernovae Jennifer Andrews, Geoffrey Clayton Recent detections of large amounts of dust in high redshift galaxies suggest that core collapse supernovae (CCSNe) may play an important role in the dust budget of the universe. At an age of only 1Gyr, there has not been enough time for low-mass stars to form and evolve to the asymptotic giant branch, but there has been sufficient time for CCSNe, which quickly evolve and return their material to the surrounding interstellar medium. For the past three years, we have been following numerous, nearby CCSNe with Gemini, HST, and Spitzer to look for indications of dust formation, which appear within the first few years of explosion. With our dataset containing large temporal and wavelength coverage, we have discovered unusual and interesting results. I will discuss these results and their implications for SNe as major dust contributors in the universe. [Preview Abstract] |
Friday, October 22, 2010 2:42PM - 2:54PM |
HC.00007: General initial data for simulations of compact binary systems Frank L\"offler, Roland Haas, Tanja Bode, Bruno Mundim Some of the most energetic events in astrophysics are believed to be connected to the interaction and merger of compact binaries, consisting of neutron stars and/or black holes. Yet, there are still a lot of uncertainties, especially on binaries involving at least one neutron star. General relativistic effects have to be taken into account when studying these compact objects, which make analytic studies very hard. Computer simulations of binaries of neutron stars and/or black holes typically solve Einstein's equations of General Relativity and a system of hydrodynamics equations in order to obtain a time sequence. However, the initial data needed to start this sequence also has to satisfy a set of elliptic constraint equations. Solving these equations is difficult for general initial configurations, which is why most solvers are restricted to a very narrow set of parameters. In this talk, we describe one method of generating intial data for compact binary systems, leaving most of the parameters, such as momenta and spins, free to choose. [Preview Abstract] |
Friday, October 22, 2010 2:54PM - 3:06PM |
HC.00008: Non-axisymmetric Instabilities in Thick Self-Gravitating Tori Around Black Holes in Dynamical General Relativistic Framework Oleg Korobkin, Erik Schnetter, Nikolaos Stergioulas, Burkhard Zink, Ernazar Abdikamalov Thick self-gravitating accretion disks around black holes play a major role in several astrophysical scenarios of gamma-ray bursts. These objects can form as a result of massive star core collapse, merger of two neutron stars or a neutron star and a black hole, they have very high densities and relativistic rotation speeds. In this study, we address stability of thick constant angular momentum accretion tori using a fully dynamical general relativistic framework. We have performed evolutions of several accretion tori models and identified two distinct types of non-axisymmetric instabilities. The first type corresponds to the Papaloizou-Pringle instability, enhanced by a motion of the central black hole. The second type corresponds to the I-mode, previously found in Newtonian studies. We discuss the types, growth rates and pattern speeds of the unstable modes, as well as the detectability of the gravitational waves from such objects. [Preview Abstract] |
Friday, October 22, 2010 3:06PM - 3:18PM |
HC.00009: Magnetized Equilibrium Accretion Tori around Kerr Black Holes in General Relativistic Magneto-hydrodynamic Simulations Tyler Landis, Peter Diener, Erik Schnetter, Burkhard Zink Accretion onto black holes is one of the most likely candidates for generating many of the high energy events observed in our universe, which include gamma ray bursts, active galactic nuclei, and X-ray binaries. Key to this process is the formation and dynamics of magnetized accretion disks. We have developed a general relativistic magnetohydrodynamics code for studying such black hole accretion systems in global three dimensional simulations. This gives us the ability to study the non-axisymmetric instabilities of these systems that arise from the nonlinearity of the governing equations. Here, I will present recent results from simulations of a magnetized torus in equilibrium around a black hole on fixed spacetime backgrounds and give preliminary results studying the non-axisymmetric instabilities of the system. [Preview Abstract] |
Friday, October 22, 2010 3:18PM - 3:30PM |
HC.00010: Measuring the Distance to Low-Mass Star Forming Cores Chadwick Young, Leah Garber, Tyler Bourke The study of low-mass star formation has made great advances in the past decade with the advent of space and ground-based telescopes. However, the understanding of these regions is often hindered by a lack of knowledge of the star-forming cores' distance. We present a simple plan and preliminary results to determine the distance to areas of low-mass star formation. [Preview Abstract] |
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