Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session U4: Supernovae, GRBs and Other Transients |
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Sponsoring Units: DAP Chair: Elizabeth Ferrara, University of Maryland - College Park Room: Virginia A |
Monday, January 30, 2017 3:30PM - 3:42PM |
U4.00001: ABSTRACT WITHDRAWN |
Monday, January 30, 2017 3:42PM - 3:54PM |
U4.00002: Multidimensional neutrino-transport simulations of the core-collapse supernova central engine Evan O'Connor, Sean Couch Core-collapse supernovae (CCSNe) mark the explosive death of a massive star. The explosion itself is triggered by the collapse of the iron core that forms near the end of a massive star's life. The core collapses to nuclear densities where the stiff nuclear equation of state halts the collapse and leads to the formation of the supernova shock. In many cases, this shock will eventually propagate throughout the entire star and produces a bright optical display. However, the path from shock formation to explosion has proven difficult to recreate in simulations. Soon after the shock forms, its outward propagation is stagnated and must be revived in order for the CCSNe to be successful. The leading theory for the mechanism that reenergizes the shock is the deposition of energy by neutrinos. In 1D simulations this mechanism fails. However, there is growing evidence that in 2D and 3D, hydrodynamic instabilities can assist the neutrino heating in reviving the shock. In this talk, I will present new multi-D neutrino-radiation-hydrodynamic simulations of CCSNe performed with the FLASH hydrodynamics package. I will discuss the efficacy of neutrino heating in our simulations and show the impact of the multi-D hydrodynamic instabilities. [Preview Abstract] |
Monday, January 30, 2017 3:54PM - 4:06PM |
U4.00003: Monte Carlo Neutrino Transport in Core-Collapse Supernovae Sherwood Richers, Joshua Dolence, Christian Ott Neutrino interactions dominate the energetics of core-collapse supernovae (CCSNe) and determine the composition of the matter ejected from CCSNe and gamma-ray bursts (GRBs). Three dimensional (3D) CCSN and neutron star merger simulations are rapidly improving, but still suffer from approximate treatments of neutrino transport that cripple their reliability and realism. I use my relativistic time-independent Monte Carlo neutrino transport code SEDONU to evaluate the effectiveness of leakage, moment, and discrete ordinate schemes in the context of core-collapse supernovae. I also developed a relativistic extension to the Random Walk approximation that greatly accelerates convergence in diffusive regimes, making full-domain simulations possible. [Preview Abstract] |
Monday, January 30, 2017 4:06PM - 4:18PM |
U4.00004: Multi-D Full Boltzmann Neutrino Hydrodynamic Simulations in Core Collapse Supernovae and their detailed comparison with Monte Carlo method Hiroki Nagakura, Sherwood Richers, Christian Ott, Wakana Iwakami, Shun Furusawa, Kohsuke Sumiyoshi, Shoichi Yamada We have developed a multi-d radiation-hydrodynamic code which solves first-principles Boltzmann equation for neutrino transport. It is currently applicable specifically for core-collapse supernovae (CCSNe), but we will extend their applicability to further extreme phenomena such as black hole formation and coalescence of double neutron stars. In this meeting, I will discuss about two things; (1) detailed comparison with a Monte-Carlo neutrino transport (2) axisymmetric CCSNe simulations. The project (1) gives us confidence of our code. The Monte-Carlo code has been developed by Caltech group and it is specialized to obtain a steady state. Among CCSNe community, this is the first attempt to compare two different methods for multi-d neutrino transport. I will show the result of these comparison. For the project (2), I particularly focus on the property of neutrino distribution function in the semi-transparent region where only first-principle Boltzmann solver can appropriately handle the neutrino transport. In addition to these analyses, I will also discuss the "explodability" by neutrino heating mechanism. [Preview Abstract] |
Monday, January 30, 2017 4:18PM - 4:30PM |
U4.00005: r-Process nucleosynthesis in neutron star merger disk outflows Jonas Lippuner, Rodrigo Fernandez, Luke Roberts, Francois Foucart, Dan Kasen, Brian Metzger Neutron star mergers are the most promising site of heavy element synthesis via the rapid neutron-capture process (r-process). Just before the neutron stars merge, they tidally disrupt each other, which unbinds extremely neutron-rich material where nucleosynthesis can easily reach the third r-process peak. After the merger, an accretion disk forms around the central compact object, which is either a black hole or a hypermassive neutron star (HMNS). Neutrino emissions from the disk (and HMNS if there is one) and angular momentum transport processes within the disk drive a neutron-rich outflow off the disk's surface where r-process nucleosynthesis can take place. In this work we investigate r-process nucleosynthesis in the disk outflow and we pay special attention to how the nucleosynthesis depends on the lifetime of the HMNS. Increasing the lifetime of the HMNS not only results in a significantly larger ejecta mass, but also makes the ejecta less neutron-rich thus preventing the r-process from reaching the third peak. [Preview Abstract] |
Monday, January 30, 2017 4:30PM - 4:42PM |
U4.00006: The Second Fermi Large Area Telescope GRB Catalog Daniel Kocevski The high-energy emission from gamma-ray bursts (GRBs) is a formidable probe of extreme physics, requiring rapid variability from highly relativistic sources. Despite the advancements in our understanding of GRBs through observations by NASA's Swift and Fermi spacecraft, many fundemental questions regarding the particle acceleration and radiative processes associated with these events remain unanswered. Here we present the most extensive search for emission from GRBs above 40 MeV performed by the Fermi Large Area Telescope (LAT). The resulting catalog includes more than 130 detections and represents an improvement in the detection efficency of GRBs at high-energies of over 50\% compared to the first LAT GRB catalog. We utilize this improved sensativity to characterize the high-energy emission from GRBs and review how these observations further our understanding of the nature of these events. [Preview Abstract] |
Monday, January 30, 2017 4:42PM - 4:54PM |
U4.00007: More Gamma-ray Bursts from the Fermi Gamma-ray Burst Monitor Michael Briggs The Fermi Gamma-ray Burst Monitor (GBM) Team has developed an offline search for weak gamma-ray bursts which were not already detected in-orbit as "triggers". This search is "untargeted", searching all of the GBM data without guidance from other observations. The initial version of the search has been operational from January 2016, finding several likely short GRBs per month that are posted to a webpage. The GBM individual photon data are binned to various timescales, a background model is created and the binned data are searched for significant signals above the background that are coincident in two or more detectors. The current search has a latency of several days because several steps require manual intervention. An improved version will be fully automatic so that the latency in detecting candidates will be dominated by the few hours delay in receiving the data. The new version of the search will also include additional detection algorithms to increase the GRB detection rate and will also detect some long GRBs. We will report the candidates via the Gamma-ray Coordinates Network (GCN). These prompt GRB detections and localization should aid multi-messenger observations, in some cases refining localizations on timescales useful for followup observations. [Preview Abstract] |
Monday, January 30, 2017 4:54PM - 5:06PM |
U4.00008: Searching For Fast Radio Burst Counterparts with Swift's Burst Alert Telescope James DeLaunay, Derek Fox Fast Radio Bursts (FRBs) are millisecond-long bursts of GHz-frequency emission [1-2] with Dispersion Measures large enough to be of a cosmological origin. There has yet to be a non-radio counterpart or high-confidence host galaxy detected for any FRB, leaving their true nature to be very mysterious. Using sub-threshold archival data from Swift's Burst Alert Telescope (BAT; [3]) we searched for evidence of a gamma-ray counterpart to any of the FRBs. In this talk I will present the details and results of our search. If real-time FRB alerts are integrated into the Astrophysical Multimessenger Observatory Network (AMON; [4]), sub-threshold FRBs can be detected through real-time spatial and temporal coincidences with other messengers. I will also talk about the real-time AMON analysis that's currently running. \newline [1] Lorimer, D. R. et al. 2007, Science, 318, 777 \newline [2] Thornton, D. et al. 2013, Science, 341, 53 \newline [3] Barthelmy, S. D. et al. 2005, Space Sci. Rev., 120, 143 \newline [4] Smith et al. 2013, Particle Astrophysics 45, 56–70 [Preview Abstract] |
Monday, January 30, 2017 5:06PM - 5:18PM |
U4.00009: Beaming Properties of Energetic Electrons and Photons Inside Thunderstorms Eric Cramer, Michael Briggs It has been well established that thunderstorm environments allow relativistic runaway electron avalanches (RREAs) to develop under the influence of strong electric fields. This process can be seeded by external sources, such as cosmic-ray secondary electrons. The resulting $\textit{bremsstrahlung}$ x-rays and gamma rays that are emitted, propagate through the atmosphere and into space where they are detected by orbiting spacecraft, e.g. NASA Fermi. These high energy radiation blasts are known as Terrestrial Gamma-ray Flashes (TGFs). Using a Monte Carlo particle simulation, we show beaming characteristics of these electrons and photons such as the angular distribution, energy spectra, and the radial distribution from the thunderstorm source to the observation point of orbiting spacecraft. These features are related to the thunderstorm electric field, Earth’s geomagnetic field, and the potential inside the thundercloud region. Observations of TGFs made by the Gamma-ray Burst Monitor (GBM) will also be discussed, as well as a future multipoint CubeSat mission targeted to measure the beaming geometry of the gamma rays. [Preview Abstract] |
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