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David J. Nice

Publications and source records attributed to David J. Nice.

At least 73 records · Page 4Linked to original sources
arXiv2021

The NANOGrav 11yr Data Set: Limits on Supermassive Black Hole Binaries in Galaxies within 500Mpc

Supermassive black hole binaries (SMBHBs) should form frequently in galactic nuclei as a result of galaxy mergers. At sub-parsec separations, binaries become strong sources of low-frequency gravitational waves (GWs), targeted by Pulsar Timing Arrays (PTAs). We used recent upper limits on continuous GWs from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11yr dataset to place constraints on putative SMBHBs in nearby massive galaxies. We compiled a comprehensive catalog of ~44,000 galaxies in the local universe (up to redshift ~0.05) and populated them with hypothetical binaries, assuming that the total mass of the binary is equal to the SMBH mass derived from global scaling relations. Assuming circular equal-mass binaries emitting at NANOGrav's most sensitive frequency of 8nHz, we found that 216 galaxies are within NANOGrav's sensitivity volume. We ranked the potential SMBHBs based on GW detectability by calculating the total signal-to-noise ratio (S/N) such binaries would induce within the NANOGrav array. We placed constraints on the chirp mass and mass ratio of the 216 hypothetical binaries. For 19 galaxies, only very unequal-mass binaries are allowed, with the mass of the secondary less than 10 percent that of the primary, roughly comparable to constraints on a SMBHB in the Milky Way. Additionally, we were able to exclude binaries delivered by major mergers (mass ratio of at least 1/4) for several of these galaxies. We also derived the first limit on the density of binaries delivered by major mergers purely based on GW data.

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arXiv2020

The NANOGrav 12.5 yr Data Set: Observations and Narrowband Timing of 47 Millisecond Pulsars

We present time-of-arrival (TOA) measurements and timing models of 47 millisecond pulsars (MSPs) observed from 2004 to 2017 at the Arecibo Observatory and the Green Bank Telescope by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). The observing cadence was three to four weeks for most pulsars over most of this time span, with weekly observations of six sources. These data were collected for use in low-frequency gravitational wave searches and for other astrophysical purposes. We detail our observational methods and present a set of TOA measurements, based on "narrowband" analysis, in which many TOAs are calculated within narrow radio-frequency bands for data collected simultaneously across a wide bandwidth. A separate set of "wideband" TOAs will be presented in a companion paper. We detail a number of methodological changes compared to our previous work which yield a cleaner and more uniformly processed data set. Our timing models include several new astrometric and binary pulsar measurements, including previously unpublished values for the parallaxes of PSRs J1832-0836 and J2322+2057, the secular derivatives of the projected semi-major orbital axes of PSRs J0613-0200 and J2229+2643, and the first detection of the Shapiro delay in PSR J2145-0750. We report detectable levels of red noise in the time series for 14 pulsars. As a check on timing model reliability, we investigate the stability of astrometric parameters across data sets of different lengths. We report flux density measurements for all pulsars observed. Searches for stochastic and continuous gravitational waves using these data will be subjects of forthcoming publications.

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arXiv2020

The NANOGrav 12.5-year Data Set: Wideband Timing of 47 Millisecond Pulsars

We present a new analysis of the profile data from the 47 millisecond pulsars comprising the 12.5-year data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), which is presented in a parallel paper (Alam et al. 2021a; NG12.5). Our reprocessing is performed using "wideband" timing methods, which use frequency-dependent template profiles, simultaneous time-of-arrival (TOA) and dispersion measure (DM) measurements from broadband observations, and novel analysis techniques. In particular, the wideband DM measurements are used to constrain the DM portion of the timing model. We compare the ensemble timing results to NG12.5 by examining the timing residuals, timing models, and noise model components. There is a remarkable level of agreement across all metrics considered. Our best-timed pulsars produce encouragingly similar results to those from NG12.5. In certain cases, such as high-DM pulsars with profile broadening, or sources that are weak and scintillating, wideband timing techniques prove to be beneficial, leading to more precise timing model parameters by 10-15%. The high-precision, multi-band measurements of several pulsars indicate frequency-dependent DMs. Compared to the narrowband analysis in NG12.5, the TOA volume is reduced by a factor of 33, which may ultimately facilitate computational speed-ups for complex pulsar timing array analyses. This first wideband pulsar timing data set is a stepping stone, and its consistent results with NG12.5 assure us that such data sets are appropriate for gravitational wave analyses.

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arXiv2020

Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set

When galaxies merge, the supermassive black holes in their centers may form binaries and, during the process of merger, emit low-frequency gravitational radiation in the process. In this paper we consider the galaxy 3C66B, which was used as the target of the first multi-messenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C66B to less than $(1.65\pm0.02) \times 10^9~{M_\odot}$ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits, and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data to `blind' pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences.

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arXiv2019

Relativistic Shapiro delay measurements of an extremely massive millisecond pulsar

Despite its importance to our understanding of physics at supranuclear densities, the equation of state (EoS) of matter deep within neutron stars remains poorly understood. Millisecond pulsars (MSPs) are among the most useful astrophysical objects in the Universe for testing fundamental physics, and place some of the most stringent constraints on this high-density EoS. Pulsar timing - the process of accounting for every rotation of a pulsar over long time periods - can precisely measure a wide variety of physical phenomena, including those that allow the measurement of the masses of the components of a pulsar binary system (Lorimer & Kramer 2005). One of these, called relativistic Shapiro delay (Shapiro 1964), can yield precise masses for both an MSP and its companion; however, it is only easily observed in a small subset of high-precision, highly inclined (nearly edge-on) binary pulsar systems. By combining data from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set with recent orbital-phase-specific observations using the Green Bank Telescope, we have measured the mass of the MSP J0740+6620 to be $\mathbf{2.14^{+0.10}_{-0.09}}$ solar masses (68.3% credibility interval; 95.4% credibility interval is $\mathbf{2.14^{+0.20}_{-0.18}}$ solar masses). It is highly likely to be the most massive neutron star yet observed, and serves as a strong constraint on the neutron star interior EoS.

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arXiv2018

The NANOGrav 11-Year Data Set: Arecibo Observatory Polarimetry And Pulse Microcomponents

We present the polarization pulse profiles for 28 pulsars observed with the Arecibo Observatory by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) timing project at 2.1 GHz, 1.4 GHz, and 430 MHz. These profiles represent some of the most sensitive polarimetric millisecond pulsar profiles to date, revealing the existence of microcomponents (that is, pulse components with peak intensities much lower than the total pulse peak intensity). Although microcomponents have been detected in some pulsars previously, we present microcomponents for PSRs B1937+21, J1713+0747, and J2234+0944 for the first time. These microcomponents can have an impact on pulsar timing, geometry, and flux density determination. We present rotation measures for all 28 pulsars, determined independently at different observation frequencies and epochs, and find the Galactic magnetic fields derived from these rotation measures to be consistent with current models. These polarization profiles were made using measurement equation template matching, which allows us to generate the polarimetric response of the Arecibo Observatory on an epoch-by-epoch basis. We use this method to describe its time variability, and find that the polarimetric responses of the Arecibo Observatory's 1.4 and 2.1 GHz receivers vary significantly with time.

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arXiv2018

The NANOGrav 11-year Data Set: High-precision timing of 45 Millisecond Pulsars

We present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, aimed at detecting and characterizing low-frequency gravitational waves. The pulsars were observed with the Arecibo Observatory and/or the Green Bank Telescope at frequencies ranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximately monthly cadence, with six high--timing-precision pulsars observed weekly, and all were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. We describe our methods for data processing, time-of-arrival (TOA) calculation, and the implementation of a new, automated method for removing outlier TOAs. We fit a timing model for each pulsar that includes spin, astrometric, and, if necessary, binary parameters, in addition to time-variable dispersion delays and parameters that quantify pulse-profile evolution with frequency. The new timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of large orbital-period variations. We fit models that characterize sources of noise for each pulsar. We find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. Future papers will use these data to constrain or detect the signatures of gravitational-wave signals.

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arXiv2016

The NANOGrav Nine-year Data Set: Mass and Geometric Measurements of Binary Millisecond Pulsars

We analyze 24 binary radio pulsars in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) nine-year data set. We make fourteen significant measurements of Shapiro delay, including new detections in four pulsar-binary systems (PSRs J0613$-$0200, J2017+0603, J2302+4442, and J2317+1439), and derive estimates of the binary-component masses and orbital inclination for these MSP-binary systems. We find a wide range of binary pulsar masses, with values as low as $m_{\rm p} = 1.18^{+0.10}_{-0.09}\text{M}_{\odot}$ for PSR J1918$-$0642 and as high as $m_{\rm p} = 1.928^{+0.017}_{-0.017}\text{M}_{\odot}$ for PSR J1614$-$2230 (both 68.3\% credibility). We make an improved measurement of the Shapiro timing delay in the PSR J1918$-$0642 and J2043+1711 systems, measuring the pulsar mass in the latter system to be $m_{\rm p} = 1.41^{+0.21}_{-0.18}\text{M}_{\odot}$ (68.3\% credibility) for the first time. We measure secular variations of one or more orbital elements in many systems, and use these measurements to further constrain our estimates of the pulsar and companion masses whenever possible. In particular, we used the observed Shapiro delay and periastron advance due to relativistic gravity in the PSR J1903+0327 system to derive a pulsar mass of $m_{\rm p} = 1.65^{+0.02}_{-0.02}\text{M}_{\odot}$ (68.3\% credibility). We discuss the implications that our mass measurements have on the overall neutron-star mass distribution, and on the "mass/orbital-period" correlation due to extended mass transfer.

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arXiv2016

The NANOGrav Nine-year Data Set: Monitoring Interstellar Scattering Delays

We report on an effort to extract and monitor interstellar scintillation parameters in regular timing observations collected for the NANOGrav pulsar timing array. Scattering delays are measured by creating dynamic spectra for each pulsar and observing epoch of wide-band observations centered near 1500 MHz and carried out at the Green Bank Telescope and the Arecibo Observatory. The ~800-MHz wide frequency bands imply dramatic changes in scintillation bandwidth across the bandpass, and a stretching routine has been included to account for this scaling. For most of the 10 pulsars for which the scaling has been measured, the bandwidths scale with frequency less steeply than expected for a Kolmogorov medium. We find estimated scattering delay values that vary with time by up to an order of magnitude. The mean measured scattering delays are similar to previously published values and slightly higher than predicted by interstellar medium models. We investigate the possibility of increasing the timing precision by mitigating timing errors introduced by the scattering delays. For most of the pulsars, the uncertainty in the time of arrival of a single timing point is much larger than the maximum variation of the scattering delay, suggesting that diffractive scintillation remains only a negligible part of their noise budget.

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arXiv2016

The NANOGrav Nine-year Data Set: Astrometric Measurements of 37 Millisecond Pulsars

Using the nine-year radio-pulsar timing data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), collected at Arecibo Observatory and the Green Bank Telescope, we have measured the positions, proper motions, and parallaxes for 37 millisecond pulsars. We report twelve significant parallax measurements and distance measurements, and eighteen lower limits on distance. We compare these measurements to distances predicted by the NE2001 interstellar electron density model and find them to be in general agreement. We use measured orbital-decay rates and spin-down rates to confirm two of the parallax distances and to place distance upper limits on other sources; these distance limits agree with the parallax distances with one exception, PSR J1024-0719, which we discuss at length. Using the proper motions of the 37 NANOGrav pulsars in combination with other published measurements, we calculate the velocity dispersion of the millisecond pulsar population in Galactocentric coordinates. We find the radial, azimuthal, and perpendicular dispersions to be 46, 40, and 24 km s-1, respectively, in a model that allows for high-velocity outliers; or 81, 58, and 62 km s-1 for the full population. These velocity dispersions are far smaller than those of the canonical pulsar population, and are similar to older Galactic disk populations. This suggests that millisecond pulsar velocities are largely attributable to their being an old population rather than being artifacts of their birth and evolution as neutron star binary systems. The components of these velocity dispersions follow similar proportions to other Galactic populations, suggesting that our results are not biased by selection effects.

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arXiv2010

Timing Measurements of the Relativistic Binary Pulsar PSR B1913+16

We present results of more than three decades of timing measurements of the first known binary pulsar, PSR B1913+16. Like most other pulsars, its rotational behavior over such long time scales is significantly affected by small-scale irregularities not explicitly accounted for in a deterministic model. Nevertheless, the physically important astrometric, spin, and orbital parameters are well determined and well decoupled from the timing noise. We have determined a significant result for proper motion, $μ_α = -1.43\pm0.13$, $μ_δ=-0.70\pm0.13$ mas yr$^{-1}$. The pulsar exhibited a small timing glitch in May 2003, with ${Δf}/f=3.7\times10^{-11}$, and a smaller timing peculiarity in mid-1992. A relativistic solution for orbital parameters yields improved mass estimates for the pulsar and its companion, $m_1=1.4398\pm0.0002 \ M_{\sun}$ and $m_2=1.3886\pm0.0002 \ M_{\sun}$. The system's orbital period has been decreasing at a rate $0.997\pm0.002$ times that predicted as a result of gravitational radiation damping in general relativity. As we have shown before, this result provides conclusive evidence for the existence of gravitational radiation as predicted by Einstein's theory.

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arXiv2010

A precise mass measurement of the intermediate-mass binary pulsar PSR J1802-2124

PSR J1802-2124 is a 12.6-ms pulsar in a 16.8-hour binary orbit with a relatively massive white dwarf (WD) companion. These properties make it a member of the intermediate-mass class of binary pulsar (IMBP) systems. We have been timing this pulsar since its discovery in 2002. Concentrated observations at the Green Bank Telescope, augmented with data from the Parkes and Nancay observatories, have allowed us to determine the general relativistic Shapiro delay. This has yielded pulsar and white dwarf mass measurements of 1.24(11) and 0.78(4) solar masses (68% confidence), respectively. The low mass of the pulsar, the high mass of the WD companion, the short orbital period, and the pulsar spin period may be explained by the system having gone through a common-envelope phase in its evolution. We argue that selection effects may contribute to the relatively small number of known IMBPs.

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arXiv2006

The Parallax and Proper Motion of PSR J0030+0451

We report the parallax and proper motion of millisecond pulsar J0030+0451, one of thirteen known isolated millisecond pulsars in the disk of the Galaxy. We obtained more than 6 years of monthly data from the 305 m Arecibo telescope at 430 MHz and 1410 MHz. We measure the parallax of PSR J0030+0451 to be 3.3 +/- 0.9 mas, corresponding to a distance of 300 +/- 90 pc. The Cordes and Lazio (2002) model of galactic electron distribution yields a dispersion measure derived distance of 317 pc which agrees with our measurement. We place the pulsar's transverse space velocity in the range of 8 to 17 km/s, making this pulsar one of the slowest known. We perform a brief census of velocities of isolated versus binary millisecond pulsars. We find the velocities of the two populations are indistinguishable. However, the scale height of the binary population is twice that of the isolated population and the luminosity functions of the two populations are different. We suggest that the scale height difference may be an artifact of the luminosity difference.

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arXiv2005

A 2.1 Solar Mass Pulsar Measured by Relativistic Orbital Decay

PSR J0751+1807 is a millisecond pulsar in a circular 6 hr binary system with a helium white dwarf secondary. Through high precision pulse timing measurements with the Arecibo and Effelsberg radio telescopes, we have detected the decay of its orbit due to emission of gravitational radiation. This is the first detection of the relativistic orbital decay of a low-mass, circular binary pulsar system. The measured rate of change in orbital period, corrected for acceleration biases, is dP_b/dt=(-6.4+-0.9)x10^-14. Interpreted in the context of general relativity, and combined with measurement of Shapiro delay, it implies a pulsar mass of 2.1+-0.2 solar masses, the most massive pulsar measured. This adds to the emerging trend toward relatively high neutron star masses in neutron star--white dwarf binaries. Additionally, there is some evidence for an inverse correlation between pulsar mass and orbital period in these systems. We consider alternatives to the general relativistic analysis of the data, and we use the pulsar timing data to place limits on violations of the strong equivalence principle.

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arXiv2005

The Millisecond Pulsars in NGC 6760

We present the results of recent Arecibo and Green Bank observations of the globular cluster NGC 6760. Using Arecibo, a phase-coherent timing solution has been obtained for the previously known binary pulsar in this cluster, PSR J1911+0102A. We have also discovered a new millisecond pulsar in NGC 6760, PSR J1911+0101B, an isolated object with a rotational period of 5.38 ms and a dispersion measure DM = 196.7 cm-3 pc. Both pulsars are located within 1.3 core radii of the cluster center and have negative period derivatives. The resulting lower limits for the accelerations of the pulsars are within the range expected given a simple model of the cluster. A search for eclipses in the PSR J1911+0102A binary system using both telescopes yielded negative results. The corresponding limits on the extra gas column density at superior conjunction are consistent with the hypothesis that the observational properties of ultra-low-mass binary pulsars like PSR J1911+0102A are strongly affected by the inclination of the orbital plane of the system. Among globular cluster pulsar populations, that of NGC 6760 exhibits one of the largest known spreads in DM. This quantity seems to be roughly proportional to a cluster's central DM; this suggests that the observed spread is caused by a turbulent interstellar medium at spatial scales of 1 pc.

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arXiv2004

GBT Observations of Very Low Mass Binary Millisecond Pulsars: A Search for Eclipses

We searched for eclipses of two millisecond pulsars, PSR J1807-2459 and PSR B1908+00. These pulsars are in very low mass binary systems with orbital parameters similar to those of eclipsing binaries. Observations were made with the GBT at frequencies as low as 575 MHz. No eclipses were detected in either system. Observations of well-established eclipsing binary J2051-0827 found eclipses to be substantially weaker than previously seen, with the pulsar detected throughout the eclipse region at 575 MHz and with an electron column density an order of magnitude smaller than previously measured.

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arXiv2004

Masses, Parallax, and Relativistic Timing of the PSR J1713+0747 Binary System

We report on 12 years of observations of PSR J1713+0747, a pulsar in a 68-day orbit with a white dwarf. Pulse times of arrival were measured with uncertainties as small as 200 ns. The timing data yielded measurements of the relativistic Shapiro delay, perturbations of pulsar orbital elements due to secular and annual motion of the Earth, and the pulsar's parallax, as well as pulse spin-down, astrometric, and Keplerian measurements. The observations constrain the masses of the pulsar and secondary star to be m1=1.3+-0.2 solar masses and m2=0.28+-0.03 solar masses, respectively (68% confidence). Combining the theoretical orbital period-core mass relation with the observational constraints yields a somewhat higher pulsar mass, m1=1.53-0.06+0.08 solar masses. The parallax is 0.89+-0.08 mas, corresponding to a distance of 1.1+-0.1 kpc; the precision of the parallax measurement is limited by uncertainties in the electron content of the solar wind. The transverse velocity is unusually small, 33+-3 km/s. We find significant timing noise on time scales of several years, but no more than expected by extrapolating timing noise statistics from the slow pulsar population. With the orientation of the binary orbit fully measured, we are able to improve on previous tests of equivalence principle violations.

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