Ann Schmiedekamp
A5058254329- Pulsars and Gravitational Waves Research
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Geophysics and Gravity Measurements
- Radio Astronomy Observations and Technology
- Gamma-ray bursts and supernovae
- Advanced Chemical Physics Studies
- Cosmology and Gravitation Theories
- Magnetism in coordination complexes
- Molecular Spectroscopy and Structure
- Metal-Catalyzed Oxygenation Mechanisms
- Spectroscopy and Quantum Chemical Studies
- Atmospheric Ozone and Climate
- Metal complexes synthesis and properties
- Supramolecular Chemistry and Complexes
- Astrophysics and Cosmic Phenomena
- Astrophysical Phenomena and Observations
- Crystallography and molecular interactions
- Engineering Education and Pedagogy
- Advanced Frequency and Time Standards
- Black Holes and Theoretical Physics
- Chemical Reactions and Mechanisms
- Molecular Sensors and Ion Detection
- Statistical and numerical algorithms
- Luminescence and Fluorescent Materials
Pennsylvania State University
2009-2024
Abington Memorial Hospital
2003-2024
National Postdoctoral Association
2024
Albert Einstein College of Medicine
2024
Campbell Collaboration
2023
Bucknell University
2020
Johns Hopkins University
2020
UPMC Altoona
2020
Tufts University
2020
National Cancer Institute
1994
Abstract We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by North American Nanohertz Observatory Gravitational Waves. The correlations follow Hellings–Downs pattern expected gravitational-wave background. presence such background with power-law spectrum favored over model only independent noises Bayes factor in excess 10 14 , and this same an uncorrelated common factors 200–1000, depending on...
Abstract The 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) shows positive evidence presence of a low-frequency gravitational-wave (GW) background. In this paper, we investigate potential cosmological interpretations signal, specifically cosmic inflation, scalar-induced GWs, first-order phase transitions, strings, and domain walls. We find that, with exception stable strings field theory origin, all these models can...
The NANOGrav 15-year data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such gravitational waves, here we analyze signal as coming from population supermassive black hole (SMBH) binaries distributed throughout Universe. We show that astrophysically motivated models SMBH binary populations are able to reproduce both amplitude and shape observed spectrum. multiple model variations GWB spectrum at our current...
Abstract We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15 yr data set North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is a pulsar array (PTA) experiment that sensitive to low-frequency gravitational waves (GWs). This NANOGrav’s fifth public release, including both “narrowband” “wideband” time-of-arrival (TOA) measurements corresponding models. have added 21 MSPs extended our baselines by 3 yr, now spanning nearly...
Pulsar timing arrays (PTAs) are galactic-scale gravitational wave detectors. Each individual arm, composed of a millisecond pulsar, radio telescope, and kiloparsecs-long path, differs in its properties but, aggregate, can be used to extract low-frequency (GW) signals. We present noise sensitivity analysis accompany the NANOGrav 15-year data release associated papers, along with an in-depth introduction PTA models. As first step our analysis, we characterize each pulsar set three types white...
Abstract Evidence for a low-frequency stochastic gravitational-wave background has recently been reported based on analyses of pulsar timing array data. The most likely source such is population supermassive black hole binaries, the loudest which may be individually detected in these data sets. Here we present search individual binaries NANOGrav 15 yr set. We introduce several new techniques, enhance efficiency and modeling accuracy analysis. uncovered weak evidence two candidate signals,...
Abstract The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence the presence of an isotropic nanohertz gravitational-wave background (GWB) in its 15 yr data set. However, if GWB is produced by a population inspiraling supermassive black hole binary (SMBHB) systems, then predicted to be anisotropic, depending on distribution these systems local Universe and statistical properties SMBHB population. In this work, we search anisotropy using multiple...
Abstract The NANOGrav 15 yr data provide compelling evidence for a stochastic gravitational-wave (GW) background at nanohertz frequencies. simplest model-independent approach to characterizing the frequency spectrum of this signal consists simple power-law fit involving two parameters: an amplitude A and spectral index γ . In Letter, we consider next logical step beyond minimal model, allowing running (i.e., logarithmic dependence) index, <mml:math...
The NANOGrav 15-year data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such gravitational waves, here we analyze signal as coming from population supermassive black hole (SMBH) binaries distributed throughout Universe. We show that astrophysically motivated models SMBH binary populations are able to reproduce both amplitude and shape observed spectrum. multiple model variations GWB spectrum at our current...
Abstract Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more metric theories of gravity can have additional modes, produce different interpulsar correlations. In this work, search the NANOGrav set quadrupolar HD scalar-transverse (ST) We find that are best fit to no significant...
Pulsar timing arrays (PTAs) use an array of millisecond pulsars to search for gravitational waves in the nanohertz regime pulse time arrival data. This paper presents rigorous tests PTA methods, examining their consistency across relevant parameter space. We discuss updates 15-year isotropic gravitational-wave background analyses and corresponding code representations. Descriptions internal structure flagship algorithms enterprise ptmcmcsampler are given facilitate understanding likelihood...
Abstract Pulsar timing arrays (PTAs) are designed to detect low-frequency gravitational waves (GWs). GWs induce achromatic signals in PTA data, meaning that the delays do not depend on radio frequency. However, pulse arrival times also affected by radio-frequency-dependent “chromatic” noise from sources such as dispersion measure (DM) and scattering delay variations. Furthermore, characterization of GW may be influenced choice chromatic model for each pulsar. To better understand this...
Abstract The cosmic merger history of supermassive black hole binaries (SMBHBs) is expected to produce a low-frequency gravitational wave background (GWB). Here we investigate how signs the discrete nature this GWB can manifest in pulsar timing arrays (PTAs) through excursions from, and breaks in, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mi>GW</mml:mi> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> <mml:mo...
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInvestigation of the basis valence shell electron pair repulsion model by ab initio calculation geometry variations in a series tetrahedral and related moleculesAnn Schmiedekamp, D. W. J. Cruickshank, Steen Skaarup, Peter Pulay, Istvan Hargittai, James E. BoggsCite this: Am. Chem. Soc. 1979, 101, 8, 2002–2010Publication Date (Print):April 1, 1979Publication History Published online1 May 2002Published inissue 1 April...
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence the presence of an isotropic nanohertz gravitational wave background (GWB) in its 15 yr dataset. However, if GWB is produced by a population inspiraling supermassive black hole binary (SMBHB) systems, then predicted to be anisotropic, depending on distribution these systems local Universe and statistical properties SMBHB population. In this work, we search anisotropy using multiple methods bases...
Abstract The Green Bank North Celestial Cap (GBNCC) pulsar survey will cover the entire northern sky ( δ > −40°) at 350 MHz, and is one of most uniform sensitive all-sky surveys to date. We have created a pipeline reanalyze GBNCC data take MHz census all pulsars detected by survey, regardless their discovery survey. Of 1413 in region, we were able recover 670. For these present measured signal-to-noise ratios (S/N), flux densities, pulse widths, profiles, where appropriate, refined...
This paper presents rigorous tests of pulsar timing array methods and software, examining their consistency across a wide range injected parameters signal strength. We discuss updates to the 15-year isotropic gravitational-wave background analyses corresponding code representations. Descriptions internal structure flagship algorithms \texttt{Enterprise} \texttt{PTMCMCSampler} are given facilitate understanding PTA likelihood structure, how models built, what currently used in sampling...
Abstract Evidence has emerged for a stochastic signal correlated among 67 pulsars within the 15 yr pulsar-timing data set compiled by NANOGrav collaboration. Similar signals have been found in from European, Indian, Parkes, and Chinese pulsar timing arrays. This interpreted as indicative of presence nanohertz gravitational-wave background (GWB). To explore internal consistency this result, we investigate how recovered strength changes remove one set. We calculate using (noise-marginalized)...
Abstract Based on the rate of change its orbital period, PSR J2043+1711 has a substantial peculiar acceleration 3.5 ± 0.8 mm s –1 yr , which deviates from predicted by equilibrium Milky Way (MW) models at 4 σ level. The magnitude is too large to be explained disequilibrium effects MW interacting with orbiting dwarf galaxies (∼1 ), and small caused period variations due pulsar being redback. We identify examine two plausible causes for anomalous acceleration: stellar flyby, long-period...
Abstract We report the first discovery of a fast radio burst (FRB), FRB 20200125A, by Green Bank Northern Celestial Cap (GBNCC) Pulsar Survey conducted with Telescope at 350 MHz. 20200125A was detected Galactic latitude 58.°43 dispersion measure 179 pc cm 3 , while electron density models predict maximum contribution 25 along this line sight. Moreover, no apparent foreground sources ionized gas that could account for excess DM are visible in multiwavelength surveys region. This argues source...
A b initio SCF molecular orbital calculations with complete geometry optimization have been performed using consistent basis sets for each member of the series NH3, NH2F, NHF2, NF3 and PH3, PH2F, PHF2, PF3. The were repeated same molecules constrained to planar configuration which is transition state inversion, all other geometrical parameters being energy optimized. In configuration, shorter N–F, N–H, P–H bonds resulted as well a change from nearly equal pyramidal bond angles highly...
Abstract Analyses of pulsar timing data have provided evidence for a stochastic gravitational wave background in the nanohertz frequency band. The most plausible source this is superposition signals from millions supermassive black hole binaries. standard statistical techniques used to search and assess its significance make several simplifying assumptions, namely (i) Gaussianity, (ii) isotropy, often, (iii) power-law spectrum. However, finite collection binaries does not exactly satisfy any...