First detection of frequency-dependent, time-variable dispersion measures

Abstract

Context. High-precision pulsar-timing experiments are affected by temporal variations of the Dispersion Measure (DM), which are related to spatial variations in the interstellar electron content. Correcting for DM variations relies on the cold-plasma dispersion law which states that the dispersive delay varies with the squared inverse of the observing frequency. This may however give incorrect measurements if the probed electron content (and therefore the DM) varies with observing frequency, as is predicted theoretically. Aims. We study small-scale density variations in the ionised interstellar medium. These structures may lead to frequency-dependent DMs in pulsar signals and could inhibit the use of lower-frequency pulsar observations to correct time-variable interstellar dispersion in higher-frequency pulsar-timing data. Methods. We used high-cadence, low-frequency observations with three stations from the German LOng-Wavelength (GLOW) consortium, which are part of the LOw Frequency ARray (LOFAR). Specifically, 3.5 years of weekly observations of PSR J2219+4754 are presented. Results. We present the first detection of frequency-dependent DMs towards any interstellar object and a precise multi-year time-series of the time- and frequency-dependence of the measured DMs. The observed DM variability is significant and may be caused by extreme scattering events. Potential causes for frequency-dependent DMs are quantified and evaluated. Conclusions. We conclude that frequency-dependence of DMs has been reliably detected and is caused by small-scale (up to 10s of AUs) but steep density variations in the interstellar electron content. We find that long-term trends in DM variability equally affect DMs measured at both ends of our frequency band and hence the negative impact on long-term high-precision timing projects is expected to be limited.

to be published in A&A (accepted 2019-02-06), 11 pages, 7 figures, update: A&A language editing, typos

References in corpus (40)

• The Confrontation between General Relativity and Experiment
• LOFAR: The LOw-Frequency ARray
• TEMPO2, a new pulsar timing package. I: Overview
• A New Electron Density Model for Estimation of Pulsar and FRB Distances
• PSRCHIVE and PSRFITS An Open Approach to Radio Pulsar Data Storage and Analysis
• The Equation of State of Hot, Dense Matter and Neutron Stars
• DSPSR: Digital Signal Processing Software for Pulsar Astronomy
• The International Pulsar Timing Array: First Data Release
• Detecting the stochastic gravitational wave background using pulsar timing
• Measurement and correction of variations in interstellar dispersion in high-precision pulsar timing
• Observing pulsars and fast transients with LOFAR
• On Pulsar Distance Measurements and their Uncertainties
• Faint Scattering Around Pulsars: Probing the Interstellar Medium on Solar System Size Scales
• Development of a pulsar-based timescale
• 100 Microarcsecond Resolution VLBI Imaging of Anisotropic Interstellar Scattering towards Pulsar B0834+06
• Dispersion Measure Variations and their Effect on Precision Pulsar Timing
• Prospects for High-Precision Pulsar Timing with the New Effelsberg PSRIX Backend
• A LOFAR census of non-recycled pulsars: average profiles, dispersion measures, flux densities, and spectra
• Extreme scattering events and Galactic dark matter
• From Spin Noise to Systematics: Stochastic Processes in the First International Pulsar Timing Array Data Release
• The NANOGrav Nine-Year Data Set: Measurement and Interpretation of Variations in Dispersion Measures
• Frequency-Dependent Dispersion Measures and Implications for Pulsar Timing
• Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations
• Pulsar Observations of Extreme Scattering Events
• Elementary Wideband Timing of Radio Pulsars
• Pulsar polarisation below 200 MHz: Average profiles and propagation effects
• Pulsar scintillations from corrugated reconnection sheets in the ISM
• Refractive Convergent Plasma Lenses explain ESE and pulsar scintillation
• The NANOGrav Nine-Year Data Set: Noise Budget for Pulsar Arrival Times on Intraday Timescales
• The High Time Resolution Universe Pulsar Survey X: Discovery of four millisecond pulsars and updated timing solutions of a further 12
• Model-based asymptotically optimal dispersion measure correction for pulsar timing
• Extreme Scattering Events Towards Two Young Pulsars
• Plasma Diagnostics of the Interstellar Medium with Radio Astronomy
• Pulsar lensing geometry
• Pulsars probe the low-frequency gravitational sky: Pulsar Timing Arrays basics and recent results
• The Extreme Scattering Event Toward PKS 1741-038: VLBI Images
• Tracking pulsar dispersion measures using the GMRT
• The distance and luminosity probability distributions derived from parallax and flux with their measurement errors with application to the millisecond pulsar PSR J0218+4232
• Low-frequency pulse profile variation in PSR B2217+47: evidence for echoes from the interstellar medium
• Interpretation of Extreme Scattering Events

Cited by in corpus (37)

• PINT: A Modern Software Package for Pulsar Timing
• The NANOGrav 12.5-year Data Set: Wideband Timing of 47 Millisecond Pulsars
• The CHIME Pulsar Project: System Overview
• The impact of Solar wind variability on pulsar timing
• A Gamma-ray Pulsar Timing Array Constrains the Nanohertz Gravitational Wave Background
• On the usefulness of existing Solar-wind models for pulsar timing corrections
• Dispersion measure variability for 36 millisecond pulsars at 150MHz with LOFAR
• A Scintillation Arc Survey of 22 Pulsars with Low to Moderate Dispersion Measures
• A census of the pulsar population observed with the international LOFAR station FR606 at low frequencies (25-80~MHz)
• Limits on the Weak Equivalence Principle and Photon Mass with FRB 121102 Sub-pulses
• Mass measurements for two binary pulsars discovered in the PALFA survey
• A polarization census of bright pulsars using the Ultra-Wideband Receiver on the Parkes radio telescope
• Pulsar scintillation studies with LOFAR. I. The census
• The effects of plasma lensing on the inferred dispersion measures of Fast Radio Bursts
• Pulsars with NenuFAR: backend and pipelines
• Discovery and modelling of broad-scale plasma lensing in black-widow pulsar J2051$-$0827
• High Precision Measurements of Interstellar Dispersion Measure with the upgraded GMRT
• Status Report on Global Pulsar-Timing-Array Efforts to Detect Gravitational Waves
• A precise mass measurement of PSR J2045+3633
• Variable Scintillation Arcs of Millisecond Pulsars observed with the Large European Array for Pulsars
• Pulsar Timing Array Experiments
• A comparative analysis of pulse time-of-arrival creation methods
• First Results from the REAL-time Transient Acquisition backend (REALTA) at the Irish LOFAR station
• On Frequency-Dependent Dispersion Measures and Extreme Scattering Events
• Follow-up of 27 radio-quiet gamma-ray pulsars at 110-190 MHz using the international LOFAR station FR606
• A high time resolution study of the millisecond pulsar J2241-5236 at frequencies below 300 MHz
• Decade Long Timing Study of the Black Widow Millisecond Pulsar J1544+4937
• Testing the Ampère-Maxwell law on the photon mass and Lorentz-Poincaré symmetry violation with MMS multi-spacecraft data
• Detection of frequency-dependent dispersion measure toward the millisecond pulsar PSR J2241-5236 from contemporaneous wide-band observations
• Pulsar Scintillation Studies with LOFAR: II. Dual-frequency scattering study of PSR J0826+2637 with LOFAR and NenuFAR
• Validation of heliospheric modeling algorithms through pulsar observations II: simulations with EUHFORIA
• Perturbative and numerical approach to plasma strong lensing
• A Multifrequency Census of 100 Pulsars below 100 MHz with LWA: A Systematic Study of Flux Density, Spectra, Timing, Dispersion, Polarization, and Its Variation from a Decade of Observations
• Long-term Timing Results of Ecliptic Pulsars Observed with I-LOFAR
• An updated constraint for the Gravitational Wave Background from the Gamma-ray Pulsar Timing Array
• Plasma lens with frequency-dependent dispersion measure effects on fast radio bursts
• 50-250 MHz Pulsar Census with an SKA-Low prototype station: Spectra and Polarization