Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session L8: Supernovae and Extragalactic Backgrounds |
Hide Abstracts |
Sponsoring Units: DAP Chair: Dany Page, Instituto de Astronomia, UNAM Room: Governor's Square 10 |
Sunday, April 14, 2013 3:30PM - 3:42PM |
L8.00001: Progenitor Dependence of the Early Neutrino Signal in Core-Collapse Supernova Evan O'Connor, Christian Ott Not all massive stars are destroyed equally. This is especially true when discussing the early neutrino signal from a core-collapse supernovae. In this talk, I will present the results of a study in which we simulated the preexplosion neutrino emission from 32 progenitor stars ranging in mass from 12 to 120 solar masses. The neutrino signal up to the time of explosion (during the accretion phase) carries definite information pertaining to the presupernova stellar structure. To quantify this information, we classify the presupernova models according to their ``compactness.'' In the 32 model we simulated, the magnitude of the neutrino luminosity during the accretion phase varies by over a factor of 4 between models and, as I will show, is directly proportional to the compactness parameter. With the current generation of neutrino detectors, the electron anti-neutrino signal from the next galactic core-collapse supernova will tell us direct and detailed information on the progenitor core structure, aiding in our modelling of the evolution of massive stars. [Preview Abstract] |
Sunday, April 14, 2013 3:42PM - 3:54PM |
L8.00002: Impact of Sterile Neutrinos on Core-Collapse Supernovae MacKenzie Warren, Matthew Meixner, Grant Mathews, J. Hidaka, T. Kajino Despite significant advancements in modeling core-collapse supernovae, there are still phenomena that we do not understand. The existence of a heavy right-handed sterile neutrino may provide a means of solving some of the issues related to the lepton fraction, neutrino spectrum and energy transport within the collapsing core. Recent anomalous reactor results and cosmological constraints provide some bounds on the sterile neutrino mass $m_{s}$ and mixing angle $\sin^{2} 2 \theta_{s}$. We have included the effects of a coherent active-sterile conversion for a $\sim$keV mass sterile neutrino, including matter effects through the MSW mechanism, into a self-consistent supernova model. Preliminary results show that a few milliseconds prior to the core bounce there is a coherent conversion of electron neutrinos to sterile neutrinos, which alters the neutrino spectrum and dynamics of the collapse. [Preview Abstract] |
Sunday, April 14, 2013 3:54PM - 4:06PM |
L8.00003: ABSTRACT WITHDRAWN |
Sunday, April 14, 2013 4:06PM - 4:18PM |
L8.00004: The Most Powerful Stellar Explosions Ke-Jung Chen, Alexander Heger, Stan Woosley, Ann Almgren, Weiqun Zhang We present the results from our 3D simulations of thermonuclear supernovae from the stars with initial masses above 80 solar masses by using CASTRO, a new, massively parallel, multidimensional Eulerian, adaptive mesh refinement (AMR), radiation-hydrodynamics code. We first use Kepler, a one-dimensional spherically-symmetric Lagrangian code to model the possible explosions beyond hypernovae. These extreme explosions include two types of electron/positron production instability supernovae and one type of general relativity instability supernovae. The resulting 1D presupernova profiles are mapped onto 3D grids of CASTRO as initial conditions. We simulate the explosion in 3D and resolve the emergent fluid instabilities. In this talk, we will discuss the energetics, nucleosynthesis, and possible observational signatures of these supernovae. [Preview Abstract] |
Sunday, April 14, 2013 4:18PM - 4:30PM |
L8.00005: Acceleration, beaming, and synchrotron radiation above the 160 MeV limit from relativistic pair reconnection Gregory Werner, Benoit Cerutti, Dmitri Uzdensky, Mitchell Begelman Magnetic reconnection converts magnetic field energy into particle kinetic energy, accelerating particles to sufficient energies to emit gamma-ray synchrotron radiation in astrophysical contexts, possibly including pulsar wind nebulae, Gamma-Ray Bursts, and blazar jets. A balance between acceleration (by the electric field E) and synchrotron braking (while orbiting a B-field line) limits particle energy so that synchrotron processes cannot emit photons above about 160 MeV, unless E $>$ B. However, short, intense gamma-ray flares of much higher energies have recently been observed in the Crab nebula. This work demonstrates, using 2D simulations, that reconnection in relativistic electron-positron pair plasmas can accelerate particles in Speiser orbits around the magnetic null (where E $>$ B) such that the particles can emit synchrotron photons above the 160 MeV limit. Furthermore, reconnection bunches particles and focuses them into beams; high-energy synchrotron radiation is also strongly beamed, and the sweeping of the beam across the observer's line of sight can explain the fast time variability of the flares. [Preview Abstract] |
Sunday, April 14, 2013 4:30PM - 4:42PM |
L8.00006: The Imprint of the Extragalactic Background Light in the Gamma-ray Spectra of Blazars Marco Ajello, Rolf Buehler, Anita Reimer The light emitted by stars throughout the history of the Universe is encoded in the intensity of the extragalactic background light (EBL). Knowledge of the EBL is important for understanding the nature of star formation and galaxy evolution. Direct measurements of the EBL are very difficult due to the intense zodiacal light and the Galactic foreground emission. High-energy gamma rays may interact with photons of the EBL and generate positron-electron pairs. This introduces an attenuation feature in the spectra of distant gamma-ray sources that has been used in the past to set upper limits on the opacity of the Universe and the energy density of the EBL. In this talk, we will report the first detection of an absorption feature seen in the combined spectra of a sample of gamma-ray blazars detected by the Fermi Large Area Telescope (LAT) out to a redshift of z\textgreater 1.6. This feature is caused by attenuation of gamma rays by the EBL at optical to UV frequencies, and points to a minimal level of EBL, consistent with the observed star formation rate and with low-opacity EBL models. We will present the Fermi observations and discuss the implications for the generation of a diffuse UV background at high redshifts. The prospects for a refined measurement of the EBL extending to redshifts higher than 1.6 will also be discussed. [Preview Abstract] |
Sunday, April 14, 2013 4:42PM - 4:54PM |
L8.00007: The Impact of Gamma-ray Halos on the Angular Anisotropy of the Extragalactic Gamma-ray Background Tonia Venters, Vasiliki Pavlidou The study of the development of electromagnetic cascades in intergalactic magnetic fields (IGMF) serves as a robust probe into the strength and structure of these magnetic fields. Charged particles in electromagnetic cascades are deflected by magnetic fields giving rise to gamma-ray halos around extragalactic sources of very-high energy gamma rays such as blazars. Such gamma-ray halos can have a profound impact on the intensity and angular properties of the contribution of VHE blazars to the extragalactic gamma-ray background (EGB) as measured by the Fermi-LAT at GeV energies. Previously, we demonstrated that the deflection of cascades by the IGMF could have a profound impact on the collective spectrum of blazar at and below GeV energies, and that the effect of the IGMF on cascades may leave an imprint on the angular anisotropy of the EGB as a function of energy. Thus, the measurement of the angular anisotropy of the EGB by the Fermi-LAT could be used as a probe of the IGMF. We provide an update of our work on the subject, including comparisons with Fermi anisotropy measurements. [Preview Abstract] |
Sunday, April 14, 2013 4:54PM - 5:06PM |
L8.00008: Predicting the Blazar Anisotropy Energy Spectrum of the Gamma-Ray Background Cassandra Lochhaas, Jennifer Siegal-Gaskins The gamma-ray background is created by many objects and processes that emit light at high energies, including blazars, star-forming galaxies, and possibly dark matter annihilation or decay. We predict the contribution of unresolved blazars to the anisotropy of the gamma-ray background using updated models of the blazar population. We create simulated catalogs of blazars for each model, which include an energy spectrum for each blazar varied to match the observed differences in blazar spectra, a luminosity and redshift for each blazar drawn from the luminosity function, and the observed flux accounting for the attenuation of high-energy photons due to interactions with the extragalactic background light. Sky maps of the blazar population at different energies are generated from the catalog. We calculate the angular power spectrum of each sky map and compare our simulated measure to recent gamma-ray background anisotropy measurements by the Fermi Large Area Telescope to determine the consistency of each model with the data. Identifying the blazar contribution to the gamma-ray background places constraints on the contributions of other known and proposed gamma-ray sources, including dark matter. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700