Scintillation Arcs Research Articles

Measuring interstellar delays of PSR J0613−0200 over 7 yr, using the Large European Array for Pulsars

ABSTRACT Using data from the Large European Array for Pulsars, and the Effelsberg telescope, we study the scintillation parameters of the millisecond pulsar PSR J0613−0200 over a 7 yr timespan. The ‘secondary spectrum’ – the 2D power spectrum of scintillation – presents the scattered power as a function of time delay, and contains the relative velocities of the pulsar, observer, and scattering material. We detect a persistent parabolic scintillation arc, suggesting scattering is dominated by a thin, anisotropic region. The scattering is poorly described by a simple exponential tail, with excess power at high delays; we measure significant, detectable scattered power at times out to ${\sim}5 \, \mu {\rm s}$, and measure the bulk scattering delay to be between 50 to 200 ns with particularly strong scattering throughout 2013. These delays are too small to detect a change of the pulse profile shape, yet they would change the times of arrival as measured through pulsar timing. The arc curvature varies annually, and is well fitted by a one-dimensional scattering screen ${\sim}40{{\ \rm per\ cent}}$ of the way towards the pulsar, with a changing orientation during the increased scattering in 2013. Effects of uncorrected scattering will introduce time delays correlated over time in individual pulsars, and may need to be considered in gravitational wave analyses. Pulsar timing programmes would benefit from simultaneously recording in a way that scintillation can be resolved, in order to monitor the variable time delays caused by multipath propagation.

FAST interstellar scintillation observation of PSR B1929+10 and PSR B1842+14

In this paper, we present the Five-hundred-meter Aperture Spherical radio Telescope (FAST) observations of PSRs B1929+10 and B1842+14. Through analysis of the pulsars’ scintillation pattern, we detected the known scintillation arc from PSR B1929+10 and two previously undetected scintillation arcs from B1842+14. We find that the B1929+10 arc’s curvature scales with observing frequency as η− ∝ ν−2.1±0.1 and η+ ∝ ν−1.8±0.2, consistent with Arecibo results and the theoretical expectations of η ∝ ν−2. From the arc curvature, we infer the scattering screen to be located at 0.20±0.02 kpc from the Earth, close to what was measured by RadioAstron at 324 MHz. From B1842+14, we find two scintillation arcs for the first time. The arcs’ curvatures imply that they are caused by two scattering screens located at a distance of 0.3±0.2 kpc and 1.6±0.6 kpc from the Earth, respectively. The screen distance uncertainties mainly come from the uncertainty in pulsar’s dispersion measure (DM)-derived distance. We present these FAST scintillation observations and discuss the future prospect of FAST pulsar scintillation study.

Scintillation Arc Brightness and Electron Density for an Analytical Noodle Model

Abstract We show that narrow filaments or sheets of over- or under-dense plasma, or “noodles,” with fluctuations of scattering phase of less than a radian, can form the scintillation arcs seen for many pulsars. The required local fluctuations of electron density are indefinitely small. We assume a cosine profile for the electron column and find the scattered field by analytic Kirchhoff integration. For a large electron column, corresponding to large amplitude of phase variation, the stationary-phase approximation is accurate; we call this regime “ray optics”. For smaller-amplitude phase variation, the stationary-phase approximation is inaccurate or inapplicable; we call this regime “wave optics”. We show that scattering is most efficient when the width of the strip equals that of one pair of Fresnel zones, and in the wave-optics regime. We show that the resolution of present observations is about 100 Fresnel zones on the scattering screen. Incoherent superposition of strips within a resolution element tends to increase the scattered field. We find that observations match a single noodle per resolution element with phase of up to 12 radians; or many noodles per resolution element with arbitrarily small phase variation each, for net phase of less than a radian. Observations suggest a minimum radius for noodles of about 650 km, comparable to the ion inertial scale or the ion cyclotron radius in the scattering plasma.

Noodle model for scintillation arcs

I show that narrow, parallel strips of phase-changing material, or "noodles," generically produce parabolic structures in the delay-rate domain. Such structures are observed as "scintillation arcs" for many pulsars. The model assumes the strips have widths of a few Fresnel zones or less, and are much longer than they are wide. I use the Kirchhoff integral to find the scattered field. Along the strips, integration leads to a stationary-phase point where the strip is closest to the line of sight. Across the strip, the integral leads to a 1D Fourier transform. In the limit of narrow bandwidth and short integration time, the integral reproduces the observed scintillation arcs and secondary arclets. The set of scattered paths follows the pulsar as it moves. Cohorts of noodles parallel to different axes produce multiple arcs, as often observed. A single strip canted with respect to the rest produces features off the main arc. I present calculations for unrestricted frequency ranges and integration times; behavior of the arcs matches that observed, and can blur the arcs. Physically, the noodles may correspond to filaments or sheets of over- or under-dense plasma, with a normal perpendicular to the line of sight. The noodles may lie along parallel magnetic field lines that carry density fluctuations, perhaps in reconnection sheets. If so, observations of scintillation arcs would allow visualization of magnetic fields in reconnection regions.

The Frequency Dependence of Scintillation Arc Thickness in Pulsar B1133+16

Abstract Scintillation arcs have become a powerful tool for exploring scattering in the ionized interstellar medium. There is accumulating evidence that the scattering from many pulsars is extremely anisotropic resulting in highly elongated, linear brightness functions. We present a three-frequency (327, 432, 1450 MHz) Arecibo study of scintillation arcs from one nearby, bright, high-velocity pulsar, PSR B1133+16. We show that a one-dimensional (1D), linear brightness function is in good agreement with the data at all three observing frequencies. We use two methods to explore the broadening of the 1D brightness function B(θ) as a function of frequency: (1) cross-cuts of the forward arc at constant delay and (2) a 1D modeling of B(θ) using a comparison between model and observed secondary spectrum as a goodness-of-fit metric. Both methods show that the half-power width of B(θ) deviates from the expected dependence , where ν is the observing frequency. Our estimates of a have moderately large uncertainties but imply , and so are inconsistent with the expected a = 2.0 for plasma refraction or a = 2.2 for Kolmogorov turbulence. In addition the shape of B(θ) cuts off more steeply than predicted for Kolmogorov turbulence. Ultimately, we conclude that the underlying physics of the broadening mechanism remains unexplained. Our results place the scattering screen at a distance that is broadly consistent with an origin at the boundary of the Local Bubble.

Testing of MAES analyzers with BLPP-2000 and BLPP-4000 photodetector linear arrays in a “GRAND-POTOK” spectral system

For the development of “Grand-Potok” spectral systems and rapid high-sensitivity scintillation atomic emission spectrometry, the “VMK-Optoelektronika” company created a new BLPP-2000 photodetector linear array. Testing of the array as part of “Grand-Potok” spectral system had shown its advantages over a BLPP-369М1 array in recording scintillations of the gold Au 267.595 nm analytical spectral line. Further studies of the BLPP-2000 detector revealed the need to increase the spectral resolution of the system. For this, a new BLPP-4000 photodetector linear array has been developed. It was expected that its use would improve the resolution of the Grand spectrometer over the entire wavelength range, but a reduction in the sensitivity of the spectrometer could be possible. The objectives of this study were to experimentally compare the resolution and signal-to-noise ratio of the “Grand-Potok” spectral system using BLPP-2000, BLPP-4000, and BLPP-369М1 photodetector linear arrays and contrast the obtained results with the characteristics of the higher-resolution Grand-1500 spectrometer with BLPP-2000, which had shown good performance in determination of noble metals in geological samples with complex matrix. The data on the intensities and widths of the spectral lines were obtained from the spectra of the standard samples of various compositions and used to compare the signal-to-noise ratio and spectral resolution of the systems. The study showed that the use of the new MAES analyzers based on BLPP-4000 linear photodetector arrays in the Grand spectrometer increased the resolution of the instrument by a factor of two, while the signal-to-noise ratio of the instrument decreased by a factor of 4-6, leading to the deterioration of the detection limits in the scintillation arc atomic-emission spectrometry. Nevertheless, Grand spectrometers based on BLPP-4000 could be used instead of higher-resolution Grand-1500 spectrometers without deterioration of the detection limits as its aperture is 5–20 times higher. In addition, the signal-to-noise ratio and the resolution in Grand spectrometers with BLPP-369M1 detector arrays used in analytical laboratories could be increased by replacing the detectors with BLPP-4000 arrays. Keywords: Grand-Potok spectral system, MAES high-speed analyzer, spectral resolution, geological samples, scintillation atomic emission spectrometry (Russian) DOI: http://dx.doi.org/10.15826/analitika.2019.23.1.005 A.A. Dzyuba 1,2 , V.A. Labusov 1,2,3 , and S.A. Babin 1,2 1 Institute of Automation and Electrometry, Siberian Branch, Russian Academy of Sciences, pr. Akademika Koptyuga, 1, Novosibirsk, 630090, Russian Federation 2 VMK-Optoelektronika, pr. Akademika Koptyuga, 1, Novosibirsk, 630090, Russian Federation 3 Novosibirsk State Technical University, pr. K. Marksa, 20, Novosibirsk, 630073, Russian Federation

Noble metals in black shales of the Sukhoi Log gold deposit (East Siberia): evidence from scintillation arc atomic-emission spectrometry

Scintillation arc atomic-emission spectrometry (SAES) is used to study noble metals (NM), including Au, Ag, Pt, Pd, Ir, Os, Rh, and Ru, in black shales of the Sukhoi Log gold deposit (Irkutsk Region, Russia), with a focus on NM total contents in samples and on the compositions and sizes of NM-bearing particles. The estimated sizes of gold particles and their distribution are confirmed by results of scanning electron microscopy combined with energy dispersive X-ray microanalysis (SEM-EDX). The SAES results are in satisfactory agreement with earlier SEM-EDX data on NM species but reveal a much greater number and diversity of element associations.

Interstellar scintillation observations for PSR B0355+54

In this paper, we report our investigation of pulsar scintillation phenomena by monitoring PSR B0355$+$54 at 2.25 GHz for three successive months using \emph{Kunming 40-m radio telescope}. We have measured the dynamic spectrum, the two-dimensional correlation function, and the secondary spectrum. In those observations with high signal-to-noise ratio ($S/N\ge100$), we have detected the scintillation arcs, which are rarely observable using such a small telescope. The sub-microsecond scale width of the scintillation arc indicates that the transverse scale of structures on scattering screen is as compact as AU size. Our monitoring has also shown that both the scintillation bandwidth, timescale, and arc curvature of PSR B0355$+$54 were varying temporally. The plausible explanation would need to invoke multiple-scattering-screen or multiple-scattering-structure scenario that different screens or ray paths dominate the scintillation process at different epochs.

Extreme scattering events towards two young pulsars

We have measured the scintillation properties of 151 young, energetic pulsars with the Parkes radio telescope and have identified two extreme scattering events (ESEs). Towards PSR J1057-5226 we discovered a three-year span of strengthened scattering during which the variability in flux density and the scintillation bandwidth decreased markedly. The transverse size of the scattering region is ~23 au, and strong flux density enhancement before and after the ESE may arise from refractive focusing. Long observations reveal scintillation arcs characteristic of interference between rays scattered at large angles, and the clearest arcs appear during the ESE. The arcs suggest scattering by a screen 100-200 pc from the earth, perhaps ionized filamentary structure associated with the boundary of the local bubble(s). Towards PSR J1740-3015 we observed a "double dip" in the measured flux density similar to ESEs observed towards compact extragalactic radio sources. The observed shape is consistent with that produced by a many-au scale diverging plasma lens with electron density ~500cm$^{-3}$ . The continuing ESE is at least 1500 d long, making it the longest detected event to date. These detections, with materially different observational signatures, indicate that well-calibrated pulsar monitoring is a keen tool for ESE detection and ISM diagnostics. They illustrate the strong r\^ole au-scale non-Kolmogorov density fluctuations and the local ISM structure play in such events and are key to understanding both their intrinsic physics and their impact on other phenomena, particularly fast radio bursts.

Scintillation Arcs Shed Light on Scattering from Planar Plasma Sheets

AbstractScintillation arcs provide an unprecedented degree of detail into the scattering of radio waves from pulsars. We review evidence that has emerged over the last fifteen years that: a) the scattering of many nearby pulsars is dominated by one or several relatively thin “screens” of material, b) the resulting image on the sky is highly linear, with axial ratios at least as high as 10:1, and c) this arrangement is persistent for at least one source (B1133+16) for at least 25 years. We expand on the idea of Pen and Levin (2014) and previous authors that such scattering may be caused by linear sheets of plasma seen nearly edge-on. Further analysis of such scintillation arcs, including new work on multi-frequency, multi-epoch observations, should help elucidate the astrophysical nature of these ubiquitous scattering entities, which are currently not convincingly linked with any known structures.

Evolution of the low-frequency pulse profile of PSR B2217+47

AbstractAn evolution of the low-frequency pulse profile of PSR B2217+47 is observed during a six-year observing campaign with the LOFAR telescope at 150 MHz. The evolution is manifested as a new component in the profile trailing the main peak. The leading part of the profile, including a newly-observed weak component, is steady during the campaign. The transient component is not visible in simultaneous observations at 1500 MHz using the Lovell telescope, implying a chromatic effect. A variation in the dispersion measure of the source is detected in the same timespan. Precession of the pulsar and changes in the magnetosphere are investigated to explain the profile evolution. However, the listed properties favour a model based on turbulence in the interstellar medium (ISM). This interpretation is confirmed by a strong correlation between the intensity of the transient component and main peak in single pulses. Since PSR B2217+47 is the fourth brightest pulsar visible to LOFAR, we speculate that ISM-induced pulse profile evolution might be relatively common but subtle and that SKA-Low will detect many similar examples. In this scenario, similar studies of pulse profile evolution could be used in parallel with scintillation arcs to characterize the properties of the ISM.

EFFECTS OF INTERMITTENT EMISSION: NOISE INVENTORY FOR THE SCINTILLATING PULSAR B0834+06

We compare signal and noise for observations of the scintillating pulsar B0834+06, using very-long baseline interferometry and a single-dish spectrometer. Comparisons between instruments and with models suggest that amplitude variations of the pulsar strongly affect the amount and distribution of self-noise. We show that noise follows a quadratic polynomial with flux density, in spectral observations. Constant coefficients, indicative of background noise, agree well with expectation; whereas second-order coefficients, indicative of self-noise, are about 3 times values expected for a pulsar with constant on-pulse flux density. We show that variations in flux density during the 10-sec integration account for the discrepancy. In the secondary spectrum, about 97% of spectral power lies within the pulsar's typical scintillation bandwidth and timescale; an extended scintillation arc contains about 3%. For a pulsar with constant on-pulse flux density, noise in the dynamic spectrum will appear as a uniformly-distributed background in the secondary spectrum. We find that this uniform noise background contains 95% of noise in the dynamic spectrum for interferometric observations; but only 35% of noise in the dynamic spectrum for single-dish observations. Receiver and sky dominate noise for our interferometric observations, whereas self-noise dominates for single-dish. We suggest that intermittent emission by the pulsar, on timescales < 300 microseconds, concentrates self-noise near the origin in the secondary spectrum, by correlating noise over the dynamic spectrum. We suggest that intermittency sets fundamental limits on pulsar astrometry or timing. Accounting of noise may provide means for detection of intermittent sources, when effects of propagation are unknown or impractical to invert.

Using pulsar scintillation to probe AU-size structure in the interstellar medium

It is well known that pulsar dynamic spectra occasionally show pronounced fringing or criss-cross patterns. It was a surprise, however, that a two-dimensional Fourier analysis of these spectra showed faint, parabolic features, which are now called scintillation arcs. I will show evidence that the scintillation arc phenomenon is widespread and that it underpins many other scintillation phenomena. If an estimate of the distance to the pulsar and a measurement of its proper motion exist, then the location of the scattering material along the line of sight can be determined. There is often pronounced substructure in the arcs, and it translates along the main arc in a manner that is determined by the proper motion of the pulsar. This substructure may be produced by lens-like features in the ionized interstellar medium that are far out of pressure balance with the warm ionized medium and that may be related to deterministic structures that cause extreme scattering events. Observations with this technique, which...

Daily observations of interstellar scintillation in PSR B0329+54

Quasi-continuous observations of PSR B03239+54 over 20 d using the Nanshan 25-m telescope at 1540 MHz have been used to study the effects of refractive scintillation on the pulsar flux density and diffractive scintillation properties. Dynamic spectra were obtained from data sets of 90 min duration and diffractive parameters derived from a two-dimensional auto-correlation analysis. Secondary spectra were also computed but these showed no significant evidence for arc structure. Cross-correlations between variations in the derived parameters were much lower than predicted by thin-screen models and in one case was of opposite sign to the prediction. Observed modulation indices were larger than predicted by thin-screen models with a Kolmogorov fluctuation spectrum. Structure functions were computed for the flux density, diffractive time-scale and decorrelation bandwidth. These indicated a refractive time-scale of 8 +/- 2 h, much shorter than predicted by the thin-screen model. The measured structure function slope of 0.4 +/- 0.2 is also inconsistent with scattering by a single thin screen for which a slope of 2.0 is expected. All observations are consistent with scattering by an extended medium having a Kolmogorov fluctuation spectrum which is concentrated towards the pulsar. This interpretation is also consistent with recent observations of multiple diffuse scintillation arcs for this pulsar.

Multiple Scintillation Arcs in Six Pulsars

Low-intensity scattering in discrete screens gives rise to parabolic scintillation arcs in pulsar secondary spectra. The curvature of the arc boundary is uniquely determined by the location of the screen along the line of sight, the distance to the pulsar, and the relative velocity of pulsar and Earth (assuming the transverse screen velocity to be small). This information is usually available for the strong pulsars needed to exhibit clear scintillation arcs. Early studies reported single arcs along most lines of sight. This seemed puzzling given the variety of distances and sight lines being probed. We report new, higher sensitivity observations that show up to four scintillation arcs for a particular sight line.

Scintillation Arcs: Probing Turbulence and Structure in the ISM

Multi-path scattering through inhomogeneities in the interstellar medium causes many related effects. In this review, I concentrate on the phenomenon of scintillation arcs, which are parabolic patterns in the secondary spectrum caused by interference between different angular components of the scatter-broadened image of a pulsar. Scintillation arcs are now fairly well understood. The measured curvature of the arc, together with proper motion and distance information about the pulsar, can be used to determine the location of thin scattering screens along the line of sight to the object. Some recent work of this type is presented. The puzzle of substructure in the power distribution of scintillation arcs is poorly understood, however, and is commented on as an open puzzle. In particular, some inferred physical structures in the ISM are small scale (~ 1 AU) and over-dense with respect to the background medium. Finally, an application of scintillation arc studies to the correction of high-precision pulsar timing is presented.

Pulsar Scintillation Arcs. I. Frequency Dependence

Dynamic spectra of pulsars often show low-level crisscross patterns as well as isolated interference maxima called scintles. Previously, we have shown that a power spectrum analysis of the dynamic spectrum usually exhibits a parabolic arc with a well-determined curvature. A simple analysis predicts that this curvature should scale with observing frequency as ν-2. We report on multifrequency observations of three pulsars at the Arecibo Observatory that are designed to test this prediction and explore the frequency behavior of the power distribution. We find that the arc curvature scales as expected over more than a factor of 5 in observing frequency (0.43-2.2 GHz). This allows us to compare arc curvature at different frequencies obtained over a long time span. Furthermore, we find that scintillation arcs are a broadband phenomenon: they are present contemporaneously, and with the same general appearance, over a wide frequency range. At higher frequencies (1 GHz) the arcs are more sharply defined, substructure is more prominent, and inverted subarcs often appear with vertices along the main parabola.