Bulletin of the American Physical Society
2015 Annual Meeting of the APS Mid-Atlantic Section
Volume 60, Number 14
Friday–Sunday, October 23–25, 2015; Morgantown, West Virginia
Session C6: Astrophysics III |
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Chair: Zachariah Etienne, West Virginia University Room: Waterfront Hotel Salon G |
Sunday, October 25, 2015 9:00AM - 9:36AM |
C6.00001: Numerical Relativity's Contribution to Theoretical Astrophysics, and Its Path Forward Invited Speaker: Zachariah Etienne In the extreme violence of merger and mass accretion, compact objects like black holes, neutron stars, and white dwarfs launch the most luminous outbursts of electromagnetic, neutrino, and gravitational wave energy in the Universe. Modeling these systems realistically is extremely challenging, for two key reasons. First, the emission mechanisms often stem from magnetized flows and dynamical gravitational fields spanning many orders of magnitude in lengthscale and timescale, from the strong-field region near compact objects, to the often magnetically-dominated, weak-field regions far away. Second, the equations governing the dynamics are highly complex and nonlinear, including the full general relativistic (GR) field equations as coupled to the equations of GR radiation magnetohydrodynamics (RGRMHD).\\ I will review some of the current progress in using numerical relativity to advance theoretical astrophysics. In short, although numerical relativity simulations have begun to address key astrophysical questions, large gaps in our understanding remain. Bridging these gaps will require a continued focus on adding more physics to our simulations, as well as developing more computationally-efficient formulations of the equations and the algorithms for solving them. [Preview Abstract] |
Sunday, October 25, 2015 9:36AM - 9:48AM |
C6.00002: A New Hyperbolic Solver for Initial Data in Numerical Relativity Maria Babiuc, Jeffrey Winicour Numerical relativity is essential to the efforts of detecting gravitational waves from mergers of binary compact object. The first requirement for the success of numerical relativity simulations is a reliable and accurate method of constructing initial data (ID) by solving the Hamiltonian and momentum constraints. The common approach, of decomposing the constraints into elliptic equations, is plagued by junk radiation and ambiguities about which component is constrained. Recently, I. Racz introduced a new way of solving the constraints, obtaining one algebraic equation for the hamiltonian, and a system of three strongly hyperbolic equations for the momentum. ~Racz and Winicour applied this method to nonlinear perturbations of a Schwarzchild black hole, and established its well-posedness. Here we present our first steps towards the numerical implementation of this scheme. The code takes as input the 3D metric, the lapse and the shift, calculates the new variables and performs the radial inward integration. The angular derivatives are expressed in terms of spherical harmonics. Our long term goal is to generate a novel numerical initial data solver and explore whether it can produce astrophysical-relevant initial data. [Preview Abstract] |
Sunday, October 25, 2015 9:48AM - 10:00AM |
C6.00003: Supersymmetry of IIA Warped Flux AdS and Flat backgrounds Samuel Beck, George Papadopoulos, Jan Gutowski Although there have been a wide variety of AdS backgrounds in supergravity theories have been enumerated, there has not previously been an attempt to determine the exact supersymmetry fractions these backgrounds preserve. Additionally, when the supersymmetries of these backgrounds are discussed, it is typically under the assumption that the Killing spinors factor into a Killing spinor on the AdS space and a Killing spinor on the transverse space. We have identified the fractions of supersymmetry preserved by the most general warped flux AdS and flat backgrounds in both massive and standard IIA supergravities, and have determined that the Killing spinors do not, in general, factorize. We have found that $AdS_n\times_w M^{10-n}$ backgrounds preserve $2^{[{n\over2}]} k$ Killing spinors for $n \leq 4$ and $2^{[{n\over2}]+1} k$ for 4$<$$n \leq 7$ supersymmetries, $k \in \mathbf{N}_{+}$. Additionally, we have proven that, if the fields and the transverse space are restricted so as to satisfy the conditions of the Hopf maximum principle, then the Killing spinors of these backgrounds are exactly the zero-modes of Dirac-like operators on the transverse space, $M^{10-n}$. These results are similar to results that have been found for IIB and heterotic backgrounds. [Preview Abstract] |
Sunday, October 25, 2015 10:00AM - 10:12AM |
C6.00004: The Double Pulsar: A Laboratory for Relativistic Gravity and Pulsar Emission Physics Maura Mclaughlin The double pulsar system consists of two radio pulsars in a highly relativistic 2.5-hr orbit. It remains the only pulsar binary system in which both pulsars have been detectable. In this talk, we will present the results from 12 years of timing this unique system, including the best proof ever for the existence of gravitational waves. We will also discuss the interactions between the two pulsars in the system and show how they can be used to probe the size and shape of pulsar magnetospheres and emission heights. [Preview Abstract] |
Sunday, October 25, 2015 10:12AM - 10:24AM |
C6.00005: A 350-MHz Green Bank Telescope Survey of Unassociated Fermi LAT Sources Peter Gentile, Maura McLaughlin, Priyadarshini Bangale, Bhaswati Bhattacharyya, Fernando Camilo, Ismael Cognard, Megan DeCeasar, Elizabeth Ferrara, Jason Hessels, Tyrel Johnson, Matthew Kerr, Michael Wolff, Scott Ransom, Paul Ray, Mallory Roberts, Jayanta Roy, Siraprapa Sanpa-Arsa We have searched for radio pulsations in 49 \fermi\ Large Area Telescope $\gamma$-ray source error ellipses using the Green Bank Telescope at a radio frequency of 350 MHz. We detected 14 millisecond pulsars (MSPs) in blind searches of the data. Four of these had already been discovered in other surveys. An additional four MSPs discovered in a subsequent radio survey at 820 MHz were detected by folding our survey data at the known periods and dispersion measures. This survey, along with other similar surveys, suggests that the majority of Galactic $\gamma$-ray sources at high Galactic latitudes are either MSPs or relatively nearby non-recycled pulsars. It also confirms that in the past there had been a strong observational bias against finding short orbital period MSP systems and a bias in favor of finding isolated MSPs. [Preview Abstract] |
Sunday, October 25, 2015 10:24AM - 10:36AM |
C6.00006: A search for rotating radio transients and fast radio bursts in the Parkes high-latitude pulsar survey Akshaya Rane, Dr. Duncan Lorimer, Dr. Sam Bates, Natasha McMann, Dr. Maura McLaughlin, Kaustubh Rajwade In 2007, WVU researchers found a 5-ms long isolated burst at radio wavelengths that appeared to be of cosmological origin. Since then there have been a growing number of detections (11, so far) of such transient radio bursts (known as Fast Radio Bursts, FRBs), which have generated strong interest in identifying the origin of these bright, non-repeating, highly dispersed pulses. In this talk, I will present results of a search for dispersed radio bursts from the archival Parkes pulsar survey data. We re-detected 20 of the 42 pulsars and one rotating radio transient previously reported. We did not find any FRBs and after comparing with results from various surveys carried out with the Parkes telescope, we found that the lack of FRB detections, and detection rates in other surveys, is consistent with an all-sky FRB event rate of ${\cal R} = 4.4^{+5.2}_{-3.1} \times 10^3$ FRBs day$^{-1}$ sky$^{-1}$, where the uncertainties represent a $99\%$ confidence interval. However, we still require a larger sample of FRBs to further constrain this rate. [Preview Abstract] |
Sunday, October 25, 2015 10:36AM - 10:48AM |
C6.00007: New Timing Solutions for Rotating Radio Transients Bingyi Cui, Jason Boyles, Maura McLaughlin, Rossina Miller, Nipuni Palliyaguru Rotating radio transients (RRATs) are sporadic pulsars which have a wide range of emission properties. They can be loosely defined as objects that were discovered only through their single pulses. For most of these RRATs, the timing of these individual pulses is the most reliable method to measure their periods and determine timing solutions, while some of them that are less sporadic can be timed by using folding techniques as we do for normal pulsars. Here, based on Parkes and Green Bank Telescope (GBT) observations, we introduce our results on eight RRATs including their precise rotation parameters, positions, and dispersion measures (DMs), along with a series of studies on RRAT properties. By analyzing data for all RRATs with timing solutions, we find that the period derivatives of RRATsn are likely to be larger than that of normal pulsars. We also carry out Lomb-Scargle tests for the eight RRATs to search for periodicities in their pulse arrival times on long timescales, and significant periodicities are detected for all of them. Analyzing the single pulse amplitudes, the log-normal distributions provide the best fits, which imply that RRAT pulses represent the tail of an intensity distribution for normal pulsars. [Preview Abstract] |
Sunday, October 25, 2015 10:48AM - 11:00AM |
C6.00008: A Fast Radio Burst with measured Faraday Rotation Jeffrey Peterson A Fast Radio Burst detected using the Green Bank Telescope at 800 MHz shows substantial linear polarization and faraday rotation. Scintillation and scattering are also detected. The high rotation measure detected exceeds that expected for this line of site through the Milky Way, indicating substantial magnetization local to the source. [Preview Abstract] |
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