Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session J16: Low-Frequency Gravitational Wave Detectors: PTAs and LISA |
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Sponsoring Units: DGRAV Chair: Thomas Kupfer, KITP, Santa Barbara Room: Sheraton Grand Ballroom I |
Sunday, April 14, 2019 1:30PM - 1:42PM |
J16.00001: Optimizing Pulsar Timing Array Observational Cadences for Sensitivity to Low-Frequency Gravitational Wave Sources Michael T Lam We can improve the sensitivity of a pulsar timing array (PTA) to different gravitational-wave sources by observing pulsars with low timing noise over years to decades and distributed across the sky. We discuss observing strategies for a PTA focused on a stochastic gravitational-wave background or single continuous-wave sources. We describe the method to calculate a PTA's sensitivity to different gravitational-wave-source classes. We then apply our method to the 45 pulsars presented in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set. For expected amplitudes of the stochastic background, we find that all pulsars contribute significantly over the timescale of decades; the exception is for very pessimistic values of the background amplitude. For individual single sources, we find that a number of pulsars contribute to the sensitivity of a given source but that which pulsars contribute are different depending on the source, or versus an all-sky metric. Our results show that it is also imperative to locate and time as many high-precision pulsars as possible, as quickly as possible, to maximize the sensitivity of next-generation PTA detectors. |
Sunday, April 14, 2019 1:42PM - 1:54PM |
J16.00002: Implications on the Design of Next Generation Gravity Missions (NGGMs) from Gravitational Reference Sensor Tests on the ESA-NASA Pathfinder Mission for the LISA Gravitational Wave Mission Peter L Bender, Kaixuan Kang The main objective of the recently launched GRACE Follow-On Mission (GFO) is to continue the roughly monthly determinations of variations in the global gravity field that were started by the GRACE mission (2002 - 2017). However, with much improved accuracy for measuring changes in the separation of the 2 satellites by laser ranging interferometry (LRI) having been demonstrated on GFO, major reductions in the relative acceleration noise level in possible designs for NGGMs appear to be worth considering. Such reductions would be of particular value in regions where local models of the geopotential time variations are being developed. And the necessary high accuracy for isolating reference test masses from both internal and external disturbances has been demonstrated on the LISA Pathfinder mission. For the limited objective of determining variations in the geopotential along the mean orbit, it appears that strongly reducing the relative acceleration noise by drag-free operation of the satellites or a high degree of AC drag-compensation would deserve a high priority in the design. We have investigated the accuracy achievable at GFO altitude with what we call Along Track Analysis in a limited study where only acceleration noise and the distance measurement noise are considered. |
Sunday, April 14, 2019 1:54PM - 2:06PM |
J16.00003: Measurements of test mass charging in the LISA Pathfinder mission Peter Wass, Daniel Hollington, Tim Sumner, Henrique Araujo LISA Pathfinder, a precursor to the space-based gravitational wave observatory, LISA, operated at the L1 Lagrange point between the Sun and the Earth between January 2016 and July 2017. The ESA-led mission successfully demonstrated the technology required to achieve the ambitious goals of LISA, most notably the pure free-fall of test masses undisturbed by relative accelerations above a few fm/s2 in the milli-Hz band. Electrical charging of the test masses by cosmic rays and solar particles gives rise to electrostatic forces that, uncorrected, can compromise this performance. We present measurements of the test mass charging rates made in orbit and compare with predictions from high-fidelity, high-energy particle simulations using the GEANT4 software toolkit. Combining charge measurements with the results of in situ measurements with a dedicated particle detector allows us to probe fluctuations in the charging rate driven by cosmic ray variations. We also identify a charging dependence on the electric field around the test mass caused by low-energy secondary electrons emitted from its gold-coated surfaces and surroundings. |
Sunday, April 14, 2019 2:06PM - 2:18PM |
J16.00004: Charge Management System for the LISA Gravitational Reference Sensor using UV LED-Based Charge Control via the Photoelectric Effect Samantha Parry, Ben Letson, Taiwo J Olatunde, Simon Barke, Myles Clark, Guido Mueller, Peter J Wass, Timothy Sumner, John Conklin The LISA observatory, a gravitational wave detector in space, consists of three drag-free spacecraft flying in equilateral triangle formation governed by their inertial reference sensors: a test mass (TM) in free fall surrounded by an electrode housing. Critical to operation is maintaining a force noise level below a fN/Hz1/2 within the mHz gravitational wave frequency band. Cosmic rays and solar energetic particles accrue charge on the TM, producing disturbance forces that must be mitigated. TM electrical charge can be controlled in a non-contact manner using UV light via the photoelectric effect. NASA’s contribution to the ESA mission includes the technology development for a Charge Management System (CMS), tasked to maintain the potential of the TM relative to its housing to below the required level via fiber-coupled UV LEDs. A charge management device (CMD) is being developed to control UV LEDs in both a continuous and pulsing manner via user-specified inputs designed for integration with the LISA science instrument. Also, over 100 UV LEDs are being tested for space performance and lifetime integrity for the projected 10-year long mission. Discussion will include the status of the CMD development and the preliminary results from UV LED testing. |
Sunday, April 14, 2019 2:18PM - 2:30PM |
J16.00005: Upgraded University of Florida Torsion Pendulum for Testing Key LISA Technology Stephen M Apple, Andrew Chilton, Taiwo Olatunde, Samantha Parry, Henri Inchauspe, Anthony Davila, Peter J Wass, Guido Mueller, John Conklin This presentation describes the design and performance of the UF torsion pendulum facility. This facility tests inertial sensors and associated technology for the LISA (laser interferometer space antenna) space-based gravitational wave observatory mission. The torsion pendulum consists of a suspended cross-bar with LISA test mass (TM) mockups at each of its ends. Position of the TMs is measured using capacitive and laser interferometer readout with a broadband sensitivity of 30 nm/√Hz and 0.5 nm/√Hz respectively. The noise performance of the facility is 3 × 10-13 ms-2/√Hz at 2 mHz. This facility has been used to test and validate various UV LED-based charge management techniques including pulsed light (AC) charge control, as well as characterize gravitational reference sensor (GRS) noise using simplified GRSs. Data from initial charge management experiments have been compared to a newly developed analytical charge model. The facility has undergone many upgrades including the integration of a LISA-like GRS and a new cross-bar with precision polished TMs. These upgrades will facilitate more realistic charge management experiments and characterization of GRS noise performance with a LISA-like sensor. |
Sunday, April 14, 2019 2:30PM - 2:42PM |
J16.00006: Far field simulation for LISA Alexander J Weaver, Paul Fulda, Guido Mueller The Laser Interferometer Space Antenna (LISA) pushes the limit of interferometric precision for gravitational wave detection. Three spacecrafts exchange laser beams between them to measure subatomic length changes between free falling test masses separated by 2.5 gigameters. Our group uses high order Hermite-Gauss (HG) mode expansion, with analytically obtained mode coefficients, to provide quick and accurate renderings of the exchanged fields. We have used this to calculate tilt-to-length couplings from spacecraft pointing jitter, and can easily adjust the results to account for any potential mirror or phase distortions represented as Zernike polynomials. With this we intend to develop a means for fast and reliable representation of beams at any point along the optical chain of LISA. |
Sunday, April 14, 2019 2:42PM - 2:54PM |
J16.00007: The potential of multiband gravitational wave astronomy Kaze Wong, Ely Kovetz, Curt J Cutler, Emanuele Berti We discuss the prospects of multiband gravitational wave science and some recent developments in multiband data analysis. A ground-based detector network has detected several stellar-mass black hole merger events, and many more detections are expected in the near future. A space-based detector such as LISA could observe the early inspiral of these systems. Multiband observations can improve our ability to determine source parameters by removing degeneracies, and possibly allow us to measure parameters (such as the orbital eccentricity) that may not be measurable on the ground. Space-based inspiral detections could allow us to forecast merger events observable from the ground; vice versa, by post-processing LISA data and exploiting coincidence with mergers observed on the ground we could be able to detect LISA inspirals that would otherwise be sub-threshold. We will quantify these possibilities and discuss some of their astrophysical implications. |
Sunday, April 14, 2019 2:54PM - 3:06PM |
J16.00008: Physical objects approaching the Cauchy horizon of a fast spinning Kerr black hole Caroline Mallary, Gaurav Khanna, Lior M Burko We solve the 2+1-dimensional Teukolsky equation numerically for the Weyl scalars ψ0 and ψ4 along a time-like geodesic intersecting with the Cauchy horizon of a rapidly rotating perturbed Kerr black hole. We find that both the amplitude and frequency of the Weyl scalars agree with the results of linear perturbation analysis. We then model a physical object by a simple damped harmonic oscillator, which is driven by an external force that mimics the tidal force experienced by the infalling object. We use this model to find the total deformation of the object at the Cauchy horizon, and the resonant effect when the driving force’s frequency matches the internal frequency of the oscillator that models the object. |
Sunday, April 14, 2019 3:06PM - 3:18PM |
J16.00009: Extreme Mass Ratio Inspiral (EMRI) Search Techniques for the LISA Mission Joey Shapiro Key Extreme Mass Ratio Inspirals (EMRIs) describe the long-lasting inspiral and plunge of stellar origin black holes into massive black holes in the centers of galaxies. The small black hole spends 103 to 105 orbits in close vicinity of the massive black hole, and the orbit displays extreme forms of periastron and orbital plan precession. The large number of orbital cycles allows ultra precise measurements of the parameters of the binary system as the gravitational wave signal encodes information about the spacetime of the central massive object. EMRI waveforms are complex and the signals need to be coherently tracked for hundreds to thousands of cycles to produce a detection, making EMRI signals one of the most challenging data analysis problems in all of gravitational wave astronomy. To address these challenges we consider the collection of harmonics for the system, filtering short segments of data against a comb of harmonics. The number of important harmonics depends on the source properties such as the eccentricity and black hole spin and these properties can be exploited to identify EMRI signals in simulated data for the Laser Interferometer Space Antenna (LISA) mission. |
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