Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session T13: Neutron stars: Theory and observation |
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Sponsoring Units: DAP Chair: Huei Sears, Northwestern University Room: Marquette IV - 2nd Floor |
Tuesday, April 18, 2023 10:45AM - 10:57AM |
T13.00001: An updated glitch rate-age law inferred from radio pulsars Margaret Millhouse Radio pulsar glitches probe far-from-equilibrium processes involving stress accumulation and relaxation in neutron star interiors. Previous studies of radio pulsar glitch rates have focused on individual pulsars with as many recorded glitches as possible. In this work we analyze glitch rates using all available glitch data, including objects that have glitched never or once. We assume the glitch rate follows a homogeneous Poisson process. Calculating relevant Bayes factors shows that a model in which the glitch rate λ scales as a power of the characteristic age τ is preferred over models which depend arbitrarily on powers of the spin frequency ν and/or its time derivative. For the preferred model λ=A(τ/τref)γ where τref=1 yr is a reference time, we produce Bayesian posterior distributions on A and γ using both the data set containing pulsars with one or more observed glitches, and a new data set where objects with zero recorded glitches are included. The updated estimates still support increased glitch activity for younger pulsars, while demonstrating that the large number of objects with zero glitches contain important statistical information about the rate, provided that they are part of the same population as opposed to a disjoint population which never glitches for some unknown physical reason. |
Tuesday, April 18, 2023 10:57AM - 11:09AM |
T13.00002: Galactic Accelerometry via Millisecond Pulsar Timing Reza Ebadi, Aakash Ravi, David F Phillips, Ronald L Walsworth Millisecond pulsars serve as precise astronomical clocks distributed throughout the Milky Way. The galactic acceleration experienced by pulsars manifests as chirps in their periodic signals. Using pulsar timing data, we can measure the local galactic acceleration, which can be used to reconstruct the galactic gravitational potential, similar to the techniques used to measure Earth's gravitational potential using terrestrial atomic clocks. We present the first measurement of the local Galactic acceleration using the orbital periods of an ensemble of 13 binary millisecond pulsar systems. Local acceleration is measured with 3σ precision and in good agreement with expectations. This work is a first step toward dynamically measuring acceleration gradients that will eventually inform us about the dark matter density distribution in the Milky Way galaxy. |
Tuesday, April 18, 2023 11:09AM - 11:21AM |
T13.00003: Exploring the Effects of Solar Wind on Pulsars using the Low Frequency Array (LOFAR) Telescope SAI CHAITANYA SUSARLA Pulsars are rapidly rotating neutron stars mainly visible as pulsating radio sources. Their rotation is so reliable that it can be used as a highly-precise clock-like signal. By studying this clock signal, via their emitted radio pulses, pulsars can be used to probe a number of effects, such as interstellar weather like the Solar Wind. The Solar Wind (SW) is a highly magnetized stream of plasma out of the Sun due to the pressure of the hot solar corona. The free electrons in the SW induce noise in the pulsar signals that can be measured to gain a deeper understanding of the heliospheric magnetic field and the Solar corona. The ecliptic pulsar whose line-of-sight (LoS) comes close to the sun are best used to track the variations in the electron content of the SW. This is quantified by a parameter known as the Dispersion Measure (DM). Variations in DMs have strong, inverse dependencies on the observing frequency which makes LOFAR, that covers frequencies below 240 MHz, one of the best-suited instruments to measure the effects of the SW. We have obtained data from 7 LOFAR stations which have been observed in the frequency range 110-190 MHz band at a weekly cadence for the past 10 years. |
Tuesday, April 18, 2023 11:21AM - 11:33AM |
T13.00004: Systematic errors due to quasi-universal relations in binary neutron stars and their correction for unbiased model selection Rahul Kashyap, Arnab Dhani, Bangalore S Sathyaprakash Inference of the equation-of-state (EOS) of dense nuclear matter in neutron-star cores is a principal science goal of X-ray and gravitational-wave observations of neutron stars. In particular, gravitational-wave observations provide an independent probe of the properties of bulk matter in neutron star cores that can then be used to compare with theoretically derived equations of state. In this talk, we quantify the systematic errors arising from the application of EOS-independent quasi-universal relations in the estimation of neutron star tidal deformabilities and radii from gravitational-wave measurements and introduce a strategy to correct for the systematic biases in the inferred radii. We apply this method to a simulated population of events expected to be observed by future upgrades of current detectors and the next-generation of ground-based observatories. We show that our approach can accurately correct for the systematic biases arising from approximate universal relations in the mass-radius curves of neutron stars. Using the posterior distributions of the mass and radius for the simulated population we infer the underlying EOS with a good degree of precision. Our method revives the possibility of using the universal relations for rapid Bayesian model selection of the dense matter EOS in gravitational-wave observations. |
Tuesday, April 18, 2023 11:33AM - 11:45AM |
T13.00005: I-Love-Q and quasinormal modes for proto-neutron stars Victor Santos Guedes, Kent Yagi, Cecilia Chirenti, Shu Yan Lau We investigate the time evolution of some universal relations that are well established for cold neutron stars but not for proto-neutron stars. We use an effective time-dependent equation of state extracted from three-dimensional core-collapse supernova simulations for different progenitors. We then obtain the structure of spherically symmetric proto-neutron stars and study their radial stability as the post-bounce time increases. Next, we solve the equations of non-radial oscillations for proto-neutron stars and calculate their quasinormal modes, more specifically, the oscillation frequency and the damping time of the polar f-mode and the fundamental axial w-mode. Finally, we solve the perturbation equations for slowly-rotating and tidally-deformed proto-neutron stars and obtain their moment of inertia (I), quadrupole moment (Q), and tidal deformability (related to the Love number). There are well-known universal relations between the aforementioned parameters for cold neutron stars, such as I-Love-Q or f-Love and w-Love. We verify that these relations, for different progenitors, approach those for cold neutron stars to within a post-bounce time of about 1 s, and we discuss the reliability of these relations in the context of future observations of, e.g., gravitational waves from core-collapse supernovae. |
Tuesday, April 18, 2023 11:45AM - 11:57AM |
T13.00006: On low-frequency waves and instabilities in QED-plasmas of magnetars Mikhail V Medvedev Magnetars are neutron stars with magnetic fields of ~1e15 Gauss or stronger. The quantum electrodynamic (QED) "corrections" on their magnetospheric plasma can produce and order unity effect. This plasmas with super-strong magnetic field exceeding the Schwinger (or QED) field are of great scientific interest. For this purpose, we have developed the theoretical 'QED plasma framework', which allows one to explore such strongly magnetized plasmas systematically. We show that the general structure of low-frequency plasma eigen-modes (shear and compressible Alfven, X and O electromagnetic waves, whistler waves) remains qualitatively the same as in ordinary magnetized plasmas. QED introduces quantitative effects, which can be used to study conditions in magnetar magnetospheres. |
Tuesday, April 18, 2023 11:57AM - 12:09PM |
T13.00007: Modeling neutron stars using first-order viscous relativistic hydrodynamics Alex Pandya, Elias R Most, Frans Pretorius Recent evidence suggests that weak interactions may noticeably impact the dynamics of binary neutron star mergers, potentially acting as an effective bulk viscosity in the process. Motivated by these results, we present progress toward the incorporation of dissipative fluid effects into neutron star models. To do so we make use of the so-called BDNK formalism, the only relativistic dissipative fluid theory to date rigorously proven to be causal, hyperbolic, and stable about thermodynamic equilibrium. In this talk, we briefly overview the construction of BDNK theory and contrast it with ideal (perfect fluid) hydrodynamics, summarize recent progress regarding numerical methods and the choice of model coefficients, and then discuss applications to neutron stars in spherical symmetry. |
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