PSR B0329 Research Articles

Identifying Pulsar Candidates in Interferometric Radio Images Using Scintillation

Pulsars have been primarily detected by their narrow pulses or periodicity in time domain data. Interferometric surveys for pulsars are challenging due to the trade-off between beam sensitivity and beam size and the corresponding tradeoff between survey sensitivity (depth), sky coverage, and computational efforts. The detection sensitivity of time domain searches for pulsars is affected by dispersion smearing, scattering, and rapid orbital motion of pulsars in binaries. We have developed a new technique to select pulsar candidates in interferometric radio images by identifying scintillating sources and measuring their scintillation bandwidth and timescale. Identifying likely candidates allows sensitive, focused time-domain searches, saving computational effort. Pulsar scintillation is independent of its timing properties and hence offers a different selection of pulsars compared to time-domain searches. Candidates identified from this method could allow us to find hard-to-detect pulsars, such as submillisecond pulsars and pulsars in very compact, highly accelerated binary orbits. We use upgraded Giant Metrewave Radio Telescope (uGMRT) observations in the fields of PSR B1508+55, PSR J0437−4715, and PSR B0031−07 as test cases for our technique. We demonstrate that the technique correctly differentiates between the pulsar and other nonscintillating point sources and show that the extracted dynamic spectrum of the pulsar is equivalent to that extracted from the uGMRT phased array beam. We show the results from our analysis of known pulsar fields and discuss challenges in dealing with interference and instrumental effects.

Fine frequency structure of interstellar scintillation pattern in radio emission of the PSR B1133+16 at 111 MHz

The B1133+16 pulsar was observed at a frequency of 111 MHz with the LPA PRAO radio telescope from October 2022 to March 2023. Observations were made twice a week for two days in a row. In total 38 measurements of the scattering parameters were carried out with a high frequency resolution (up to 65 Hz). We used continuous recording of voltage in the frequency band 2.5 MHz with 8-bit digitization. The signal was reconstructed using the coherent dedispersion method. Dynamic spectra (DSP) were constructed for each observing session. Then, for each DSP, we calculated a two-dimensional autocorrelation function (2DACF) and analyzed its frequency and time sections. We have studied the fine frequency structure of pulsar scintillations by analyzing both the dynamic spectra, and the spectra of individual pulses. It has been found that the intrinsic shape of diffraction distortion on average can be represented by a sharp two-sided function with a characteristic frequency width of 1–2 kHz. The long-term variability of the following parameters has been carefully studied: characteristic scales in frequency and time (fdifandtdif), and rotation measureRM. Based on the analysis of long-term variations, it is suggested that the true frequency form of scintillations may be distorted by ionospheric effects. We also compared the scintillation parameters separately for the two mean profile components, and no differences between the parameters were found.

The FRB-searching Pipeline of the Tianlai Cylinder Pathfinder Array

This paper presents the design, calibration, and survey strategy of the Fast Radio Burst (FRB) digital backend and its real-time data processing pipeline employed in the Tianlai Cylinder Pathfinder Array. The array, consisting of three parallel cylindrical reflectors and equipped with 96 dual-polarization feeds, is a radio interferometer array designed for conducting drift scans of the northern celestial semi-sphere. The FRB digital backend enables the formation of 96 digital beams, effectively covering an area of approximately 40 square degrees with the 3 dB beam. Our pipeline demonstrates the capability to conduct an automatic search of FRBs, detecting at quasi-real-time and classifying FRB candidates automatically. The current FRB searching pipeline has an overall recall rate of 88%. During the commissioning phase, we successfully detected signals emitted by four well-known pulsars: PSR B0329+54, B2021+51, B0823+26, and B2020+28. We report the first discovery of an FRB by our array, designated as FRB 20220414A. We also investigate the optimal arrangement for the digitally formed beams to achieve maximum detection rate by numerical simulation.

The Bright Single Pulse Emission from PSR B1133+16

We have conducted a comprehensive investigation into the bright single pulse emission from PSR B1133+16 using the Giant Metrewave Radio Telescope. High time resolution data (61 μs) were obtained at a center frequency of 322 MHz with a bandwidth of 32 MHz over a continuous observation period of 7.45 hr. A total of 1082 bright pulses were sporadically detected with peak flux densities ranging from 10 to 23 times stronger than the average pulse profile. However, no giant pulse-like emission with a relative pulse energy larger than 10 and extremely short duration was detected, indicating that these bright pulses cannot be categorized as giant pulse emission. The majority of these bright pulses are concentrated in pulse phases at both the leading and trailing windows of the average pulse profile, with an occurrence ratio of approximately 2.74. The pulse energy distribution for all individual pulses can be described by a combination of two Gaussian components and a cutoff power-law with an index of α = − 3.2. An updated nulling fraction of 15.35% ± 0.45% was determined from the energy distribution. The emission of individual pulses follows a log-normal distribution in peak flux density ratio. It is imperative that regular phase drifting in bright pulse sequence is identified in both the leading and trailing components for the first time. Possible physical mechanisms are discussed in detail to provide insights into these observations.

Dynamic estimation method for pulsar periods based on photon energy distribution folding and image template matching

The accuracy of the pulsar period estimation directly affects the restoration effect of the signal profile. A more accurate pulsar profile will help improve the accuracy of pulsar delay estimation and thereby improve the performance of X-ray pulsar navigation. This paper proposes a pulsar period estimation method based on photon energy distribution folding and image template matching (PETM). This method uses the probability distribution information of photon energy for weighted epoch folding. The one-dimensional (1D) profile information was converted into two-dimensional (2D) image information through reverse space-filling curve (SFC) encoding. Then, a feature matching was performed between the target structure and the template structure. At the same time, the criterion of Pearson correlation coefficient (PCC) was used to quantitatively evaluate the matching effect to estimate the optimal period. The simulation results show that the period estimation accuracy of the PETM method is significantly improved, as compared with the traditional \( method. This work also analyzes the folding effect based on the photon energy distribution model and conducts simulation experiments and comparisons on influencing factors, such as noise interference and data quality. At the same time, we also specifically demonstrated the effectiveness of the PETM method for the glitch phenomenon (i.e., a sudden change in period) of pulsar periods. Finally, we also used China's XPNAV-1 satellite to conduct experiments and analysis of the actual observation data of PSR B0531+21 pulsar within a fixed period of time. The results show that the period estimation accuracy of this method is 4.8190$ns$, which is 50.23<!PCT!> higher than the traditional \( method. The method proposed in this article has the advantages of high estimation accuracy, stable estimation performance, strong anti-interference ability, and excellent dynamic period estimation performance. Therefore, it can further improve the navigation performance of X-ray pulsars.

An energy-based pulsar period estimation method using Hilbert curve and double CNNs

In order to accurately estimate the period of X-ray pulsars to improve navigation performance, this paper proposes a pulsar period estimation method based on photon energy using reverse Hilbert coding and double Convolutional Neural Networks (CNNs) discrimination. This method uses photon energy information to perform epoch folding. It converts one-dimensional contour information into two-dimensional image signals through reverse Hilbert curve and recognizes contour image features through CNN models to determine the optimal period. According to the simulation results, the period estimation accuracy of this method is 0.5350 ns, which is 65.71% higher than the χ2 epoch folding method. The contour phase accuracy is 0.0004767, which is 41.93% higher than the χ2 epoch folding method. At the same time, the observation time and noise interference that may affect the accuracy of period estimation are also quantitatively analyzed. In addition, in order to simulate real navigation scenarios, this paper also conducts dynamic period estimation experiments on PSR B0531+21 pulsar in a specific period of time. The method proposed in this paper has the advantages of high precision, fast calculation speed, strong anti-interference ability and accurate dynamic period estimation, which can significantly improve the navigation performance of X-ray pulsars.

Erratum to: The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329+54

Erratum to: The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329+54

The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329#

The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329#

Cover Picture: Astron. Nachr. 2/2024

It has been proposed that the building blocks of pulsar matter could be ‘an’, strangeons analogy of atomic nucleons but with negative strangeness. A bare strangeon star should not have a smooth surface, but be covered with small hills (‘zits’), as indicated by red spots in this schematic illustration. These zits on the pulsar surface might be responsible for the magnetospheric activity and the mysterious coherent radio emission, as discussed in the contribution by Xu and Wang, this issue, p. e230153. Zits may also be responsible for the significantly non‐symmetrical sparking discovered in the 110‐min polarization observation of pulsar PSR B0950+08 targeted with China's Five‐hundred‐meter Aperture Spherical radio Telescope, FAST. Details can be found in the contribution by Wang et al., this issue, e240010. image

Fine Frequency Structure of Interstellar Scintillation Pattern in Radio Emission of the PSR B1133+16 at 111 MHz

Fine Frequency Structure of Interstellar Scintillation Pattern in Radio Emission of the PSR B1133+16 at 111 MHz

On the cusp of cusps: a universal model for extreme scattering events in the ISM

ABSTRACT The scattering structures in the interstellar medium responsible for so-called extreme scattering events (ESEs), observed in quasars and pulsars, remain enigmatic. Current models struggle to explain the high-frequency light curves of ESEs, and a recent analysis of a double lensing event in PSR B0834+06 reveals features of ESEs that may also be challenging to accommodate via existing models. We propose that these features arise naturally when the lens has a cusp-like profile, described by the elementary A3 cusp catastrophe. This is an extension of previous work describing pulsar scintillation as arising from A2 fold catastrophes in thin, corrugated plasma sheets along the line of sight. We call this framework of describing the lens potentials via elementary catastrophes ‘doubly catastrophic lensing’, as catastrophes (e.g. folds and cusps) have long been used to describe universal features in the light curves of lensing events that generically manifest, regardless of the precise details of the lens. Here, we argue that the lenses themselves may be described by these same elementary structures. If correct, the doubly catastrophic lensing framework would provide a unified description of scintillation and ESEs, where the lenses responsible for these scattering phenomena are universal and can be fully described by a small number of unfolding parameters. This could enable their application as giant cosmic lenses for precision measurements of coherent sources, including fast radio bursts and pulsars.

Single pulse emission from PSR B0809+74 at 150 MHz using Polish LOFAR station

ABSTRACT We report the observations of single pulse emission from the pulsar B0809+74 at 150 MHz using the Polish LOFAR station, PL-611. The three major phenomena of subpulse drifting, nulling, and mode changing associated with single pulse variations are prominently seen in these observations. The pulsar has a single-component conal profile and the single pulses are primarily in the ‘normal’ drift mode with periodicity (P3) 11.1 ± 0.5 P for 96 per cent of the observing duration, while the shorter duration ‘slow-drift’ mode has P3 = 15.7 ± 1.2 P. We were able to measure the phase behaviour associated with drifting from the fluctuation spectral analysis that showed identical linear phase variations across the pulse window for both modes despite their different periodic behaviour. Earlier studies reported that the transitions from the normal state to the slow-drift mode were preceded by the presence of nulling with typical durations of 5 to 10 periods. Our observations however seem to suggest that the transition to nulling follows shortly after the pulsar switches to the slow-drift mode and not at the boundary between the modes, with one instance of complete absence of nulling between mode switching. In addition, we also detected a second type of short-duration nulls not associated with the mode changing that showed quasi-periodic behaviour with periodicity PN ∼ 44 ± 7. The variety of features revealed in the single pulse sequence makes PSR B0809+74 an ideal candidate to understand the physical processes in the Partially Screened Gap dominated by non-dipolar magnetic fields.

Technical Constraints on Interstellar Interferometry and Spatially Resolving the Pulsar Magnetosphere

Scintillation of pulsar radio signals caused by the interstellar medium can in principle be used for interstellar interferometry. Changes in the dynamic spectra as a function of pulsar longitude were in the past interpreted as having spatially resolved the pulsar magnetosphere. Guided by this prospect we used very long baseline interferometry observations of PSR B1237+25 with the Arecibo and Green Bank radio telescopes at 324 MHz and analyzed such scintillation at separate longitudes of the pulse profile. We found that the fringe phase characteristics of the visibility function changed quasi-sinusoidally as a function of longitude. Also, the dynamic spectra from each of the telescopes shifted in frequency as a function of longitude. Similar effects were found for PSR B1133+16. However, we show that these effects are not signatures of having resolved the pulsar magnetosphere. Instead, the changes can be related to the effect of low-level digitizing of the pulsar signal. After correcting for these effects the frequency shifts largely disappeared. Residual effects may be partly due to feed polarization impurities. Upper limits for the pulse emission altitudes of PSR B1237+25 would likely be well below the pulsar light cylinder radius. In view of our analysis, we think that observations with the intent of spatially resolving the pulsar magnetosphere need to be critically evaluated in terms of these constraints on interstellar interferometry.

High-resolution VLBI astrometry of pulsar scintillation screens with the θ - θ transform

ABSTRACT The recent development of $\theta - \theta$ techniques in pulsar scintillometry has opened the door for new high-resolution imaging techniques of the scattering medium. By solving the phase retrieval problem and recovering the wavefield from a pulsar dynamic spectrum, the Doppler shift, time delay, and phase offset of individual images can be determined. However, the results of phase retrieval from a single dish are only known up to a constant phase rotation, which introduces extra parameters when doing astrometry using very long baseline interferometry. We present an extension to previous $\theta - \theta$ methods using the interferometric visibilities between multiple stations to calibrate the wavefields. When applied to existing data for PSR B0834+06, we measure the effective screen distance and lens orientation with five times greater precision than was possible in previous work.

Pulsar Double Lensing Sheds Light on the Origin of Extreme Scattering Events

In extreme scattering events, the brightness of a compact radio source drops significantly, as light is refracted out of the line of sight by foreground plasma lenses. Despite recent efforts, the nature of these lenses has remained a puzzle, because any roughly round lens would be so highly overpressurized relative to the interstellar medium that it could only exist for about a year. This, combined with a lack of constraints on distances and velocities, has led to a plethora of theoretical models. We present observations of a dramatic double-lensing event in pulsar PSR B0834+06 and use a novel phase-retrieval technique to show that the data can be reproduced remarkably well with a two-screen model: one screen with many small lenses and another with a single, strong one. We further show that the latter lens is so strong that it would inevitably cause extreme scattering events. Our observations show that the lens moves slowly and is highly elongated on the sky. If similarly elongated along the line of sight, as would arise naturally from a sheet of plasma viewed nearly edge-on, no large overpressure is required and hence the lens could be long-lived.

Jiamusi pulsar observations – IV. The core-weak pattern of PSR B0329+54

ABSTRACT The bright pulsar PSR B0329+54 has been known for many years to have two emission modes. Sensitive observations of individual pulses revealed that the central component of the pulse profile, which is called the core component, is occasionally weakened considerably for a few periods and then recovered. This is the newly identified core-weak mode. Based on our long observations of PSR B0329+54 with the Jiamusi 66-m telescope at 2250 MHz, we report here that the profile components of individual pulses, including those for the core and the leading and trailing peaks, relatedly vary over some periods even before and after the core-weak mode, forming a regular pattern in the phase–time plot for a train of period-folded pulses. The pattern has a similar structure to the core-weak mode with a time-scale of 3 to 14 periods. It starts with an intensity brightening at the trailing phase of the core component, and then the core intensity decreases to a very low level, as if the core component is drifting out from the normal radiation window within 1 or 2 periods. Next the intensity in the trailing components is enhanced, and then the leading component appears at an advanced phase. Such a core-weak mode lasts for several periods. Finally, the core-weak mode ends up with an enhanced intensity at the leading phase for the core component, as if the core gradually comes back and finally stays at the phase of the profile centre, as it used to.

Single Pulse Studies of PSR B0950+08 with FAST

We report detailed polarization and single-pulse studies of PSR B0950+08 with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) at 1250 MHz. Significant bridge emission was observed between the inter-pulse and the main pulse and the height of the bridge decreased with increase in frequency. Our results support the interpretation that both the inter-pulse and the main pulse of this pulsar are from the same magnetic pole. From the relative peak flux density and the relative energy distribution, we conclude that no giant pulse was detected in PSR B0950+08. Our results provide opportunities to study the origin of the emission from PSR B0950+08 and offer new insights into the origins of pulsar emission and bridge emission.

On the peculiar rotational evolution of PSR B0950+08

ABSTRACT The long-term rotational evolution of the old, isolated pulsar, PSR B0950+08, is intriguing in that its spin-down rate displays sinusoidal-like oscillations due to alternating variations, both in magnitude and sign, of the second time derivative of the pulse frequency. We show that the large internal temperature to pinning energy ratio towards the base of the crust implied by the recent high surface temperature measurement of PSR B0950+08 leads to linear creep interaction between vortex lines and pinning sites to operate in this pulsar. Vortex lines assume a parabolic shape due to pinning to nuclear clusters and finite tension of vortices acts as a restoring force that tends to bring a vortex back to its straight shape. The resulting low-frequency oscillations of vortex lines combined with the time variable coupling between the internal superfluid components and the external pulsar braking torque give rise to an oscillatory spin-down rate. We apply this model to PSR B0950+08 observations for several external torque models. Our model has potential to constrain the radial extension of the closed magnetic field region in the outer core of neutron stars from the oscillation period of the spin-down rate.

A Fast Radio Burst Backend for the Tianlai Dish Pathfinder Array

The Tianlai Dish Pathfinder Array is a radio interferometer array consisting of 16 six-meter dish antennas. The original digital backend integration time is at the seconds level, designed for H i intensity mapping experiment. A new digital backend with millisecond response is added to enable it to search for fast radio burst during its observations. The design and calibration of this backend, and the real time search pipeline for it are described in this paper. It is capable of forming 16 digital beams for each linear polarization, covering an area of 19.6 square degrees. The search pipeline is capable of searching for, recording and classifying FRBs automatically in real time. In commissioning, we succeeded in capturing the signal pulses from the pulsars PSR B0329+54 and B2021+51.

The radio signal of PSR B0950 + 08 is detected over the whole pulse phase

ABSTRACT Pulsars are known as the ‘lighthouses’ of the Universe. Periodic pulses with a duty cycle of $\sim 10{{\ \rm per\ cent}}$ are detected when the radio beam of a rotating pulsar sweeps across the telescope. In this report, 160-min data of a nearby pulsar, PSR B0950 + 08, observed with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) are analysed. Thanks to the extremely high sensitivity of FAST, it is found that the radiation of PSR B0950 + 08 can be detected over the entire pulse period. To investigate the radiative characteristics of the pulsar’s ‘bridge emission’, a function, Θ(n), is defined to reveal the weak radiation there. It is suggested that the narrow peaks of both the main pulses and interpulses could be radiated at low altitude, while other weak emission (e.g. the ‘bridges’) comes from the upper magnetosphere, though its radiative mechanism is still a matter of debate. The measured mean pulse behaviours are consistent with previous results in the phase of strong emission of this pulsar, and both the frequency-independent separation between the interpulse and main pulse and the narrow pulse width may support a double-pole model. In order to understand the magnetospheric geometry of this pulsar, further polarization-calibrated observation with FAST and a proper determination of the baseline emission, especially during the weak emission phase, are surely required.