Null Phenomenon Research Articles

Single-pulse Emissions of PSRs J1611–0114 and J1617+1123

In this paper, the emissions from two pulsars, PSRs J1611−0114 and J1617+1123, were investigated using the Five-hundred-meter Aperture Spherical radio Telescope operating at a central frequency of 1250 MHz. The average pulse profile of PSR J1611−0114 shows two components, the first of which is relatively weak in intensity. The two-dimensional pulse stack exhibits an obvious nulling phenomenon, with an estimated nulling fraction of 40.1% ± 5.4%. The durations of the nulls and bursts are consistent with power-law distributions, and no periodic nulling phenomenon is found. The results from PSR J1617+1123 demonstrate that the average pulse profile is composed of four components. The peak intensity of the fourth component varies significantly, causing an unstable integrated profile. In addition, the modulation characteristics of J1611−0114 and J1617+1123 were studied by analyzing the modulation index, longitude resolved fluctuation spectrum and two-dimensional fluctuation spectrum using the software PSRSALSA. It was found that the two pulsars exhibit intensity modulation. In particular, J1611−0114 displays even–odd modulation, with the modulation period of approximately two pulses. The modulation period of J1617+1123 is relatively broad. There is an obvious subpulse drift phenomenon, and the value of P 2 is ∼0.125c/P 0, corresponding to 12 pulse longitude bins, and the drift rate (P 2/P 3) is about 0.29.

Single-pulse Emission Variation of Two Pulsars Discovered by FAST

We investigate the single-pulse emission variations of two pulsars, PSRs J0211+4235 and J0553+4111, observed with the Five-hundred-meter Aperture Spherical radio Telescope at the 1.25 GHz central frequency. The observation sessions span from 2020 December to 2021 July, with 21 and 22 observations for them respectively. The integrated pulse profile of PSR J0211+4235 shows that there is a weak pulse component following the main component, and PSR J0553+4111 displays a bimodal profile with a bridge component in the middle. PSR J0211+4235 presents significant nulling phenomenon with nulling duration lasting from 2 to 115 pulses and burst duration lasting from 2 to 113 pulses. The NF of each observation is determined to be 45%–55%. No emission greater than three σ is found in the mean integrated profile of all nulling pulses. In most cases, the pulse energy changes abruptly during the transition from null to burst, while in the transition from burst to null there are two trends: abrupt and gradual. We find that the nulling phenomenon of PSR J0211+4235 is periodic by the Fourier transform of the null and burst state. In addition, the single-pulse modulation characteristics of these two pulsars are investigated, and the distributions of modulation index, LRFS and 2DFS are analyzed with PSRSALSA. The left peak of PSR J0553+4111 has intensity modulation. Finally, the polarization properties of these two pulsars are obtained through polarization calibration, and their characteristics are analyzed. The possible physical mechanisms of these phenomena are discussed.

Multi-Task Learning with High-Dimensional Noisy Images

Recent medical imaging studies have given rise to distinct but inter-related datasets corresponding to multiple experimental tasks or longitudinal visits. Standard scalar-on-image regression models that fit each dataset separately are not equipped to leverage information across inter-related images, and existing multi-task learning approaches are compromised by the inability to account for the noise that is often observed in images. We propose a novel joint scalar-on-image regression framework involving wavelet-based image representations with grouped penalties that are designed to pool information across inter-related images for joint learning, and which explicitly accounts for noise in high-dimensional images via a projection-based approach. In the presence of nonconvexity arising due to noisy images, we derive nonasymptotic error bounds under nonconvex as well as convex grouped penalties, even when the number of voxels increases exponentially with sample size. A projected gradient descent algorithm is used for computation, which is shown to approximate the optimal solution via well-defined nonasymptotic optimization error bounds under noisy images. Extensive simulations and application to a motivating longitudinal Alzheimer’s disease study illustrate significantly improved predictive ability and greater power to detect true signals, that are simply missed by existing methods without noise correction due to the attenuation to null phenomenon. Supplementary materials for this article are available online.

Peculiarities of radio emission from new pulsars at 111 MHz

Abstract The analysis of radio emission of three new pulsars discovered at the Pushchino Radio Astronomy Observatory is presented. The detailed observations were carried out at a frequency of 111 MHz using the large phase array and the standard digital receiver with a total bandwidth of 2.245 MHz and a time resolution of 2.46 or 5.12 ms. All pulsars exhibit features of their radiation, the subpulse drift is observed in J0220+3622, the flare activity is exhibited in J0303+2248, and the nulling phenomenon has been detected in J0810+3725.

The “Bi-drifting” Subpulses of PSR J0815+0939 Observed with the Five-hundred-meter Aperture Spherical Radio Telescope

We report the “Bi-drifting” subpulses observed in PSR J0815+0939 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The observation at band from 1050 to 1450 MHz is evenly divided into two bands, i.e., the bands at center frequencies of 1150 and 1350 MHz. The mean pulse profiles and the “Bi-drifting” subpulses at these two bands are investigated. It is found that the pulse profiles at these two frequencies show four emission components, and the peak separations between four emission components decrease with the increase of frequency. In addition, the ratio of peak intensity of each component to the intensity of component IV at 1150 MHz is larger than that at 1350 MHz. We carry out an analysis of the longitude-resolved fluctuation spectrum and two-dimensional fluctuation spectrum for each emission component, and find that the P3 of components I, II and III is about 10.56, 10.57 and 10.59 s at 1150 and 1350 MHz. However, the reliable measurements of P3 of component IV and P2 for these four components were not obtained due to the low signal-to-noise ratio of observation data. The pulse energy distributions at frequencies 1150 and 1350 MHz are presented, and it is found that no nulling phenomenon has been found in this pulsar. With our observation from the FAST, the “Bi-drifting” subpulse phenomenon of PSR J0815+0939 is expanded from 400 to 1350 MHz, which is helpful for the relevant researchers to test and constrain the pulsar emission model, especially the model of “Bi-drifting” subpulse.

Dynamic Wireless Power Transfer System With an Extensible Charging Area Suitable for Moving Objects

Extensible magnetic resonance coupling-based wireless power transfer (WPT) systems are presented in this article. A transmitter (Tx) containing an 8-shape loop and two resonators is proposed to construct a bipolar Tx array. A unipolar receiver (Rx) is placed above the Tx perpendicularly to overcome the power null phenomenon. The proposed structure ensures that magnetic flux lines are confined in the vicinity of the Rx, leading to a high power transfer efficiency (PTE) over a wide range of lateral misalignment distances. Experiments demonstrated that the proposed WPT system can achieve an efficiency of 87% under perfectly aligned operating conditions, and maintain over 70% efficiency from 0 to 30 mm lateral misalignment distances. Based on the proposed Tx module, a single-feed Tx array is constructed to further increase the charging area. The PTE of a $1 \times 2$ array system is between 57.5% and 71.6% without the power null phenomenon. Meanwhile, the concern of heating due to magnetic field leakage can be significantly mitigated. These designs are proved to be very good candidates for dynamic WPT (DWPT) applications.

Radio pulsar sub-populations (I): The curious case of nulling pulsars

About 200 radio pulsars have been observed to exhibit nulling episodes - short and long. We find that the nulling fraction of a pulsar does not have any obvious correlation with any of the intrinsic pulsar parameters. It also appears that the phenomenon of nulling may be preferentially experienced by pulsars with emission coming predominantly from the polar cap region, and also having extremely curved magnetic fields.

A New Coil Structure and Its Optimization Design With Constant Output Voltage and Constant Output Current for Electric Vehicle Dynamic Wireless Charging

Dynamic wireless power transfer (DWPT) is a promising solution to address electric vehicle range anxiety and to reduce the capacity and the cost of the on-board batteries. In the traditional DWPT system, the mutual inductances among the transmitters make the design of compensation networks very complex. Besides, the power null phenomenon and the power pulsation phenomenon cause a fluctuating dc output voltage or current on the receiver side. To address these issues, this paper proposes a new magnetic coupler. Unipolar and bipolar coils are laid alternately to form segmented transmitters, which are turned on or off according to the position of the overhead receiver coil. LCC compensations, whose inputs are connected in parallel to a common inverter for cost reduction, are adopted. At the receiver side, unipolar and bipolar coils are overlapped in the same plate in order to effectively smooth out the mutual inductance variations and, hence, reduce the output voltage or current fluctuations. Also, a configurable resonant circuit is designed on the receiver side to achieve constant voltage charging and constant current charging. Moreover, an optimization design by using finite-element analysis software Maxwell is developed to choose the best turns of the receiver coil to further improve the output quality. A laboratory prototype with 4-A charging current and 96-V charging voltage, using 85 kHz operation frequency, is constructed to verify the proposed DWPT system. The experimental results show that constant and stable output voltage and current can be achieved with only ±2% fluctuation, and the overall efficiency is 90.37%.

Two modes of partially screened gap

The analysis of X-ray observations suggest an ultrastrong ($B\gtrsim 10^{14} \,{\rm G}$) surface magnetic field at the polar cap of pulsars (Szary, 2013). On the other hand, the temperature of the polar caps is about a few millions Kelvin. Based on these two facts we use the Partially Screened Gap (PSG) model to describe the Inner Acceleration Region (IAR). The PSG model assumes that the temperature of the actual polar cap is equal to the so-called critical value, i.e. the temperature at which the outflow of thermal ions from the surface screens the gap completely. We have found that, depending on the conditions above the polar cap, the generation of high energetic photons in IAR can be caused either by Curvature Radiation (CR) or by Inverse Compton Scattering (ICS). Completely different properties of both processes result in two different scenarios of breaking the acceleration gap: the so-called PSG-off mode for the gap dominated by CR and the PSG-on mode for the gap dominated by ICS. The existence of two different mechanisms of gap breakdown naturally explains the mode-changing phenomenon. Different characteristics of plasma generated in the acceleration region for both modes also explain the pulse nulling phenomenon.

FREQUENCY INDEPENDENT QUENCHING OF PULSED EMISSION

Simultaneous observations at four different frequencies viz. 313, 607, 1380 and 4850 MHz, for three pulsars, PSRs B0031-07, B0809+74 and B2319+60, are reported in this paper. Identified null and burst pulses are highly concurrent across more than decade of frequency. Small fraction of non-concurrent pulses (less than or equal to 3%) are observed, most of which occur at the transition instances. We report, with very high significance for the first time, full broadband nature of the nulling phenomenon in these three pulsars. These results suggest that nulling invokes changes on the global magnetospheric scale.

A new method to analyse pulsar nulling phenomenon

Pulsar nulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar nulling phenomenon, by involving two key parameters, the nulling degree, χ, which is defined as the angle in a rectangular coordinates for the numbers of nulling periods and bursting periods, and the nulling scale, N, which is defined as the effective length of the consecutive nulling periods and bursting periods. The nulling degree χ can be calculated by tan χ = N nulling/N bursting and the mean is related to the nulling fraction, while the nulling scale, N, is also a newly defined fundamental parameter which indicates how often the nulling occurs. We determined the distributions of χ and N for 10 pulsars by using the data in literature. We found that the nulling degree χ indicates the relative length of nulling to that of bursting, and the nulling scale N is found to be related to the derivative of rotation frequency and hence the loss rate of rotational energy of pulsars. Their deviations reflect the randomness of the nulling process.

Investigation of the unique nulling properties of PSR B0818−41

We report on the unique nulling properties of PSR B0818-41, using the GMRT at 325 and 610 MHz. We find following interesting behaviour just before and after the nulls: (i) The pulsar's intensity does not switch off abruptly at the null, but fades gradually, taking ~ 10 P1. Just after nulls intensity rises to a maximum over a short (less than one period) time scale. (ii) While the last active pulses before nulls are dimmer, the first few active pulses just after nulls outshine normal ones. This effect is very clear for inner region of pulsar profile, where mean intensity of last few active pulses just after nulls is ~ 2.8 times more than that for last active pulses just before nulls. (iii) There is a significant evolution of shape of the pulsar's profile, around nulls, especially at beginning of bursts: an enhanced bump of intensity in inner region, a change in ratio of strengths of the leading and trailing peaks towards a more symmetric profile, an increase in profile width of about 10%, and a shift of profile centre towards later longitudes. (iv) Just before nulls, the apparent drift rate becomes slower, transitioning to an almost phase stationary drift pattern. Further, when the pulsar comes out of null, the increased intensity is very often accompanied by what looks like a disturbed drift rate behaviour, which settles down to the regular drift pattern as the pulsar intensity returns to normal. Thus, we find some very specific and well correlated changes in the radio emission properties of PSR B0818-41 when the emission restarts after a null. These could imply that the phenomenon of nulling is associated with some kind of a "reset" of the pulsar radio emission engine. We also present plausible explanations for some of the observed behaviour, using the Partially Screened Gap model of the inner pulsar accelerator.

On the randomness of pulsar nulls

Pulsar nulling is not always a random process; most pulsars, in fact, null non-randomly. The Wald-Wolfowitz statistical runs test is a simple diagnostic that pulsar astronomers can use to identify pulsars that have non-random nulls. It is not clear at this point how the dichotomy in pulsar nulling randomness is related to the underlying nulling phenomenon, but its nature suggests that there are at least two distinct reasons that pulsars null.

The PULSE@Parkes Project: a New Observing Technique for Long-Term Pulsar Monitoring

AbstractThe PULSE@Parkes project has been designed to monitor the rotation of radio pulsars over time spans of days to years. The observations are obtained using the Parkes 64-m and 12-m radio telescopes by Australian and international high school students. These students learn the basis of radio astronomy and undertake small projects with their observations. The data are fully calibrated and obtained with the state-of-the-art pulsar hardware available at Parkes. The final data sets are archived and are currently being used to carry out studies of 1) pulsar glitches, 2) timing noise, 3) pulse profile stability over long time scales and 4) the extreme nulling phenomenon. The data are also included in other projects such as gamma-ray observatory support and for the Parkes Pulsar Timing Array project. In this paper we describe the current status of the project and present the first scientific results from the Parkes 12-m radio telescope. We emphasise that this project offers a straightforward means to enthuse high school students and the general public about radio astronomy while obtaining scientifically valuable data sets.

On the origin of pulsar ?nulling?

We show that depending on the type of pulsar evolutional model one adopts, the phenomenon of nulling is found to be either intrinsic to all pulsars, occurring during a particular stage of its life, or may be peculiar to only a class of pulsars.