skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: THE NANOGRAV NINE-YEAR DATA SET: OBSERVATIONS, ARRIVAL TIME MEASUREMENTS, AND ANALYSIS OF 37 MILLISECOND PULSARS

Abstract

We present high-precision timing observations spanning up to nine years for 37 millisecond pulsars monitored with the Green Bank and Arecibo radio telescopes as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project. We describe the observational and instrumental setups used to collect the data, and methodology applied for calculating pulse times of arrival; these include novel methods for measuring instrumental offsets and characterizing low signal-to-noise ratio timing results. The time of arrival data are fit to a physical timing model for each source, including terms that characterize time-variable dispersion measure and frequency-dependent pulse shape evolution. In conjunction with the timing model fit, we have performed a Bayesian analysis of a parameterized timing noise model for each source, and detect evidence for excess low-frequency, or “red,” timing noise in 10 of the pulsars. For 5 of these cases this is likely due to interstellar medium propagation effects rather than intrisic spin variations. Subsequent papers in this series will present further analysis of this data set aimed at detecting or limiting the presence of nanohertz-frequency gravitational wave signals.

Authors:
 [1]; ; ; ;  [2]; ;  [3];  [4];  [5];  [6]; ; ;  [7];  [8]; ;  [9]; ;  [10];  [11];  [12] more »; ; « less
  1. Center for Research and Exploration in Space Science and Technology and X-Ray Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States)
  2. Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States)
  3. National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States)
  4. Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201 (United States)
  5. Department of Physics and Astronomy, Franklin and Marshall College, P.O. Box 3003, Lancaster, PA 17604 (United States)
  6. Department of Physics, Montana State University, Bozeman, MT 59717 (United States)
  7. Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada)
  8. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr. Pasadena CA 91109 (United States)
  9. Department of Physics, McGill University, 3600 rue Universite, Montreal, QC H3A 2T8 (Canada)
  10. Department of Physics, West Virginia University, P.O. Box 6315, Morgantown, WV 26505 (United States)
  11. Center for Gravitational Wave Astronomy, University of Texas at Brownsville, Brownsville, TX 78520 (United States)
  12. Department of Physics, Columbia University, 550 W. 120th St. New York, NY 10027 (United States)
Publication Date:
OSTI Identifier:
22518719
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 813; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCURACY; DATA ANALYSIS; FREQUENCY DEPENDENCE; GRAVITATIONAL WAVES; NOISE; PULSARS; RADIO TELESCOPES; SIGNAL-TO-NOISE RATIO; SPIN; TIME MEASUREMENT; VARIATIONS

Citation Formats

Arzoumanian, Zaven, Brazier, Adam, Chatterjee, Shami, Cordes, James M., Dolch, Timothy, Burke-Spolaor, Sarah, Demorest, Paul B., Chamberlin, Sydney, Christy, Brian, Cornish, Neil, Crowter, Kathryn, Fonseca, Emmanuel, Gonzalez, Marjorie E., Ellis, Justin A., Ferdman, Robert D., Kaspi, Victoria M., Garver-Daniels, Nathan, Jones, Megan L., Jenet, Fredrick A., Jones, Glenn, E-mail: pdemores@nrao.edu, Collaboration: NANOGrav Collaboration, and and others. THE NANOGRAV NINE-YEAR DATA SET: OBSERVATIONS, ARRIVAL TIME MEASUREMENTS, AND ANALYSIS OF 37 MILLISECOND PULSARS. United States: N. p., 2015. Web. doi:10.1088/0004-637X/813/1/65.
Arzoumanian, Zaven, Brazier, Adam, Chatterjee, Shami, Cordes, James M., Dolch, Timothy, Burke-Spolaor, Sarah, Demorest, Paul B., Chamberlin, Sydney, Christy, Brian, Cornish, Neil, Crowter, Kathryn, Fonseca, Emmanuel, Gonzalez, Marjorie E., Ellis, Justin A., Ferdman, Robert D., Kaspi, Victoria M., Garver-Daniels, Nathan, Jones, Megan L., Jenet, Fredrick A., Jones, Glenn, E-mail: pdemores@nrao.edu, Collaboration: NANOGrav Collaboration, & and others. THE NANOGRAV NINE-YEAR DATA SET: OBSERVATIONS, ARRIVAL TIME MEASUREMENTS, AND ANALYSIS OF 37 MILLISECOND PULSARS. United States. doi:10.1088/0004-637X/813/1/65.
Arzoumanian, Zaven, Brazier, Adam, Chatterjee, Shami, Cordes, James M., Dolch, Timothy, Burke-Spolaor, Sarah, Demorest, Paul B., Chamberlin, Sydney, Christy, Brian, Cornish, Neil, Crowter, Kathryn, Fonseca, Emmanuel, Gonzalez, Marjorie E., Ellis, Justin A., Ferdman, Robert D., Kaspi, Victoria M., Garver-Daniels, Nathan, Jones, Megan L., Jenet, Fredrick A., Jones, Glenn, E-mail: pdemores@nrao.edu, Collaboration: NANOGrav Collaboration, and and others. 2015. "THE NANOGRAV NINE-YEAR DATA SET: OBSERVATIONS, ARRIVAL TIME MEASUREMENTS, AND ANALYSIS OF 37 MILLISECOND PULSARS". United States. doi:10.1088/0004-637X/813/1/65.
@article{osti_22518719,
title = {THE NANOGRAV NINE-YEAR DATA SET: OBSERVATIONS, ARRIVAL TIME MEASUREMENTS, AND ANALYSIS OF 37 MILLISECOND PULSARS},
author = {Arzoumanian, Zaven and Brazier, Adam and Chatterjee, Shami and Cordes, James M. and Dolch, Timothy and Burke-Spolaor, Sarah and Demorest, Paul B. and Chamberlin, Sydney and Christy, Brian and Cornish, Neil and Crowter, Kathryn and Fonseca, Emmanuel and Gonzalez, Marjorie E. and Ellis, Justin A. and Ferdman, Robert D. and Kaspi, Victoria M. and Garver-Daniels, Nathan and Jones, Megan L. and Jenet, Fredrick A. and Jones, Glenn, E-mail: pdemores@nrao.edu and Collaboration: NANOGrav Collaboration and and others},
abstractNote = {We present high-precision timing observations spanning up to nine years for 37 millisecond pulsars monitored with the Green Bank and Arecibo radio telescopes as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project. We describe the observational and instrumental setups used to collect the data, and methodology applied for calculating pulse times of arrival; these include novel methods for measuring instrumental offsets and characterizing low signal-to-noise ratio timing results. The time of arrival data are fit to a physical timing model for each source, including terms that characterize time-variable dispersion measure and frequency-dependent pulse shape evolution. In conjunction with the timing model fit, we have performed a Bayesian analysis of a parameterized timing noise model for each source, and detect evidence for excess low-frequency, or “red,” timing noise in 10 of the pulsars. For 5 of these cases this is likely due to interstellar medium propagation effects rather than intrisic spin variations. Subsequent papers in this series will present further analysis of this data set aimed at detecting or limiting the presence of nanohertz-frequency gravitational wave signals.},
doi = {10.1088/0004-637X/813/1/65},
journal = {Astrophysical Journal},
number = 1,
volume = 813,
place = {United States},
year = 2015,
month =
}
  • Gravitational wave (GW) astronomy using a pulsar timing array requires high-quality millisecond pulsars (MSPs), correctable interstellar propagation delays, and high-precision measurements of pulse times of arrival. Here we identify noise in timing residuals that exceeds that predicted for arrival time estimation for MSPs observed by the North American Nanohertz Observatory for Gravitational Waves. We characterize the excess noise using variance and structure function analyses. We find that 26 out of 37 pulsars show inconsistencies with a white-noise-only model based on the short timescale analysis of each pulsar, and we demonstrate that the excess noise has a red power spectrum formore » 15 pulsars. We also decompose the excess noise into chromatic (radio-frequency-dependent) and achromatic components. Associating the achromatic red-noise component with spin noise and including additional power-spectrum-based estimates from the literature, we estimate a scaling law in terms of spin parameters (frequency and frequency derivative) and data-span length and compare it to the scaling law of Shannon and Cordes. We briefly discuss our results in terms of detection of GWs at nanohertz frequencies.« less
  • We analyze dispersion measure (DM) variations of 37 millisecond pulsars in the nine-year North American Nanohertz Observatory for Gravitational Waves (NANOGrav) data release and constrain the sources of these variations. DM variations can result from a changing distance between Earth and the pulsar, inhomogeneities in the interstellar medium, and solar effects. Variations are significant for nearly all pulsars, with characteristic timescales comparable to or even shorter than the average spacing between observations. Five pulsars have periodic annual variations, 14 pulsars have monotonically increasing or decreasing trends, and 14 pulsars show both effects. Of the four pulsars with linear trends thatmore » have line-of-sight velocity measurements, three are consistent with a changing distance and require an overdensity of free electrons local to the pulsar. Several pulsars show correlations between DM excesses and lines of sight that pass close to the Sun. Mapping of the DM variations as a function of the pulsar trajectory can identify localized interstellar medium features and, in one case, an upper limit to the size of the dispersing region of 4 au. Four pulsars show roughly Kolmogorov structure functions (SFs), and another four show SFs less steep than Kolmogorov. One pulsar has too large an uncertainty to allow comparisons. We discuss explanations for apparent departures from a Kolmogorov-like spectrum, and we show that the presence of other trends and localized features or gradients in the interstellar medium is the most likely cause.« less
  • We report on an effort to extract and monitor interstellar scintillation parameters in regular timing observations collected for the North American Nanohertz Observatory for Gravitational Waves 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 hasmore » 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 are 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 as only a negligible part of their noise budget.« less
  • We present a Chandra X-ray Observatory investigation of the millisecond pulsars in the globular cluster M28 (NGC 6626). In what is one of the deepest X-ray observations of a globular cluster, we firmly detect seven and possibly detect two of the 12 known M28 pulsars. With the exception of PSRs B1821-24 and J1824-2452H, the detected pulsars have relatively soft spectra, with X-ray luminosities 10{sup 30}-10{sup 31} erg s{sup -1} (0.3-8 keV), similar to most 'recycled' pulsars in 47 Tucanae and the field of the Galaxy, implying thermal emission from the pulsar magnetic polar caps. We present the most detailed X-raymore » spectrum to date of the energetic PSR B1821-24. It is well described by a purely non-thermal spectrum with spectral photon index {Gamma} = 1.23 and luminosity 1.4 x 10{sup 33}{Theta}(D/5.5 kpc){sup 2} erg s{sup -1} (0.3-8 keV), where {Theta} is the fraction of the sky covered by the X-ray emission beam(s). We find no evidence for the previously reported line emission feature around 3.3 keV, most likely as a consequence of improvements in instrument calibration. The X-ray spectrum and pulse profile of PSR B1821-24 suggest that the bulk of unpulsed emission from this pulsar is not of thermal origin, and is likely due to low-level non-thermal magnetospheric radiation, an unresolved pulsar wind nebula, and/or small-angle scattering of the pulsed X-rays by interstellar dust grains. The peculiar binary PSR J1824-2452H shows a relatively hard X-ray spectrum and possible variability at the binary period, indicative of an intrabinary shock formed by interaction between the relativistic pulsar wind and matter from its non-degenerate companion star.« less