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This paper will discuss several methods of dealing with unbalanced datasets with application to High Time Resolution Universe Survey dataset. HTRU2 is a labelled dataset with a ratio of positive to negative instances of approximately 0.1. Under sampling and oversampling methods are discussed and tested and the results are compared. It was found that Synthetic Minority Oversampling Technique provides the best performance, assessed by means of the ROC-AUC parameter. Further improvement is expected by combining oversampling and under sampling. [ABSTRACT FROM AUTHOR]

Pulsars are a class of astronomic objects that emit periodic radiation pulses with a highly stable frequency. Each pulsar has its’ own, unique emission pattern (frequency and waveform); for this reason, pulsars can be used as beacons for navigation. However, the real importance of the pulsars is their emission can be used to detect gravitational waves. Therefore, there is a high interest to identify and map new pulsars. Identifying new pulsars consists in discrimination between radio emission from genuine pulsars and from sources that are not pulsars. It is a difficult task due to the large number of spurious signals both from space and from terrestrial sources. This two-part paper will present several approaches to deal with an imbalanced labelled pulsar candidate dataset HTRU2, consisting of eight features (statistical parameters) derived from the radio spectrum. [ABSTRACT FROM AUTHOR]

Purpose: The main most pronounced events, which occurred in the initial period of the pulsars’ study at the decameter wavelength range, are presented. The example of the main scientific problems, which were formulated at the very beginning of pulsar research, shows how the emphasis and priorities of these studies have been changing over time, which tasks have finally been solved, and which are still waiting to be solved. It is shown how the ongoing modernization of the UTR-2 radio telescope have allowed to acquire new qualities in astrophysical research being made with this radio telescope and to identify new scientific directions. The example of the cited references shows how the pulsar research efforts in Ukraine have been developed and how they were integrated into the world astrophysical research of these unique objects. The purpose of this work is to show the relationship between the past and the present on the example of pulsars for longer than a semi-centennial period and to show how the scientific problems that were formulated in the past, and which could not be solved under the then-existing technical conditions, were solved by the subsequent generations of researchers. Design/methodology/approach: The methods of comparison and historical parallels show how the low-frequency studies of pulsars have been developed and evolved almost from their discovery until now. Findings: It is shown how quantitative transformations and technical development, as well as non-standard scientific approaches, unhackneyed thought and international cooperation allow to solve complex radio astronomical problems related to the low-frequency studies of pulsars. Conclusions: The paper provides a historical overview of more than half a century-long radio astronomical studies of pulsars, having been and still being made at the decameter band using the UTR-2 radio telescope. The “old” and current priorities in pulsar research are given, and it is shown how qualitatively the technical parameters of back end facility and computer performance have been changed in studying the coherent pulsar radio emission nature.

Radio frequency interference (RFI) has been an enduring concern in radio astronomy, particularly for the observations of pulsars which require high timing precision and data sensitivity. In most works of the literature, RFI mitigation has been formulated as a detection task that consists of localizing possible RFI in dynamic spectra. This strategy inevitably leads to a potential loss of information since parts of the signal identified as possibly RFI-corrupted are generally not considered in the subsequent data processing pipeline. Conversely, this work proposes to tackle RFI mitigation as a joint detection and restoration that allows parts of the dynamic spectrum affected by RFI to be not only identified but also recovered. The proposed supervised method relies on a deep convolutional network whose architecture inherits the performance reached by a recent yet popular image-denoising network. To train this network, a whole simulation framework is built to generate large data sets according to physics-inspired and statistical models of the pulsar signals and of the RFI. The relevance of the proposed approach is quantitatively assessed by conducting extensive experiments. In particular, the results show that the restored dynamic spectra are sufficiently reliable to estimate pulsar times-of-arrivals with an accuracy close to the one that would be obtained from RFI-free signals. [ABSTRACT FROM AUTHOR]

In this paper, the possibility of periodic pulsar-like gamma-ray emission from the white dwarfs in AE Aquarii and AR Scorpii is investigated. We show that the white dwarf magnetospheres in AE Aquarii and AR Scorpii can possibly induce potentials to accelerate charged particles to energies in excess of one tera electronvolt (TeV) with associated gamma-ray emission through processes such as curvature radiation, inverse Compton, and hadronic processes such as neutral pion decay. We report here pulsed gamma-ray signatures at or close to the spin period of white dwarfs in both AE Aquarii and AR Scorpii in the Fermi-LAT dataset. This may indicate that both these white dwarfs possibly contain a particle accelerator that can produce relativistic electrons and ions and associated high energy radiation. The possibility of pair production is also investigated, which could provide a source for relativistic e± pairs in the magnetosphere. This could possibly be a driver for other forms of lepton-induced multi-wavelength pulsar-like emission from these two systems as well, for example, to explain the recently detected pulsed radio emission from AE Aquarii and R Scorpii in MeerKAT observations at the spin period of the white dwarf. The possibility of future detection of AE Aquarii and AR Scorpii with the Cherenkov Telescope Array (CTA) is also discussed. The future Vera Rubin Observatory will make a revolutionary contribution to time-domain astrophysics, which may lead to the discovery of thousands of new transient sources, possibly also many more close binaries with highly spun-up magnetized white dwarfs such as AE Aquarii and AR Scorpii for future investigation.

Since the discovery of the first fast radio burst (FRB) in 2007, and their confirmation as an abundant extragalactic population in 2013, the study of these sources has expanded at an incredible rate. In our 2019 review on the subject, we presented a growing, but still mysterious, population of FRBs—60 unique sources, 2 repeating FRBs, and only 1 identified host galaxy. However, in only a few short years, new observations and discoveries have given us a wealth of information about these sources. The total FRB population now stands at over 600 published sources, 24 repeaters, and 19 host galaxies. Higher time resolution data, sustained monitoring, and precision localisations have given us insight into repeaters, host galaxies, burst morphology, source activity, progenitor models, and the use of FRBs as cosmological probes. The recent detection of a bright FRB-like burst from the Galactic magnetar SGR 1935 + 2154 provides an important link between FRBs and magnetars. There also continue to be surprising discoveries, like periodic modulation of activity from repeaters and the localisation of one FRB source to a relatively nearby globular cluster associated with the M81 galaxy. In this review, we summarise the exciting observational results from the past few years. We also highlight their impact on our understanding of the FRB population and proposed progenitor models. We build on the introduction to FRBs in our earlier review, update our readers on recent results, and discuss interesting avenues for exploration as the field enters a new regime where hundreds to thousands of new FRBs will be discovered and reported each year. [ABSTRACT FROM AUTHOR]

A modern pulsar survey generates a large number of pulsar candidates. Filtering these pulsar candidates in a large astronomical data set is an important step towards discovering new pulsars. In this paper, a novel adaptive boosting algorithm based on deep self normalized neural network (Adaboost-DSNN) is proposed to accurately classify pulsar and non-pulsar signals. To train the proposed method on a highly imbalanced data set, the Synthetic Minority Oversampling TEchnique (SMOTE) was initially employed for balancing the data set. Then, a deep ensemble network combined with a deep self-normalized neural network and adaptive boosting was developed to train and learn the processed pulsar data. The design of the proposed Adaboost-DSNN method significantly reduced the computational time when dealing with large astronomical data sets, while also improving the classification performance. The scaled exponential liner units activation function was used to normalize the data. Considering their neighbour information and the special dropout technique (α-dropout), Adaboost-DSNN displayed good pulsar classification performance, while preserving the data properties across subsequent layers. The proposed Adaboost-DSNN method was tested on the High Time Resolution Universe Survey data sets (HTRU-1 and HTRU-2). According to experimental results, Adaboost-DSNN outperform other state-of-the-art methods with respect to training time and F1-score. The training time of the Adaboost-DSNN model is 10x times faster compared to other models of this kind. [ABSTRACT FROM AUTHOR]

Accurate measurements of the coronal plasma density profile, which varies with the solar cycle (SC), are necessary to elucidate the solar wind acceleration. In this study, the Crab pulsar is observed using the 327 MHz radio telescope at the Toyokawa Observatory of the Institute for Space-Earth Environmental Research of Nagoya University to investigate the coronal plasma density profile for radial distances between 5 and 60 solar radii at the SC24/25 minimum. We derive the dispersion measures (DMs) that represent the integration of plasma density along the line of sight (LOS) for giant radio pulses of the Crab pulsar. We find that the observed DMs increased above the interstellar background level when the LOS for the Crab pulsar approached the Sun in mid-June 2018 and 2019. This increase in DM is attributed to the effect of the coronal plasma. We determine the plasma density distribution by fitting a spherically symmetric model to the observed DM data. The flat radial slopes of the best-fit model are consistent with pulsar observations in the low-activity periods of past SCs, and they are attributed to the effect of the coronal hole over the south pole of the Sun. Our results show that the density level near the Sun is similar to those observed in the low activity periods of past SCs, implying recovery of the coronal plasma density from a significant reduction at the SC23/24 minimum. [ABSTRACT FROM AUTHOR]

Purpose: The studies of pulsars allow enriching our knowledge in determination of parameters of both the exotic electron-positron plasma in the pulsar magnetosphere with strong magnetic field and the ordinary ion-electron plasma of the interstellar medium, which exists in a weak magnetic field. To determine the parameters of the both plasma types it is reasonable to use polarization characteristics of a pulsed radio emission of pulsars. An accurate determination of these characteristics is quite a complex problem. For its solving, primarily we have to determine two parameters of the propagation medium – its dispersion and rotation measures. Their absolute values can be determined with the relative precision of 10-4, but the problem of rotation measure value sign determination arises. This sign depends on the interstellar magnetic field direction along the line of sight. Hear, a new method of rotation measure value sign determination is proposed. Design/methodology/approach: Muller polarization matrices are usually used for determination of such a propagation parameter as the rotation measure absolute value. When only one linear polarization is received, using of these matrices allows quite accurate determining the absolute value of the rotation measure, but not the sign of this parameter due to a certain symmetry of these matrices with respect to the direction of the linear polarization rotation plane. If we complement the system of equations, which determines the rotation measure value, with some new additional components, which take into account the contributions of the Earth ionosphere and magnetosphere to the rotation measure value, one can notice that this contribution is always positive in the Southern magnetic hemisphere (the majority of the Northern geographical hemisphere) and is always negative in the Northern magnetic hemisphere (the majority of the Southern geographical hemisphere). Moreover, the absolute value of this contribution is maximal at noon and minimal at midnight, when the concentration of ions in the Earth ionosphere is maximal and minimal, respectively. Accounting for these regularities allows to determine not only the absolute value of the rotation measure, but also its sign by means of two independent time-shifted estimations of the observed absolute value of this parameter for various ionization degrees of the Earth ionosphere. Findings: We show that using of additional equations, which take into account the contribution of the Earth ionosphere and magnetosphere to the value of the rotation measure parameter, allows full determination of this parameter accounting for the sign of this value even for the antennas, which can record a single linear polarization only. This approach allows to determine all polarization parameters of the pulsar radio emission as well as of the pulsed or continuum polarized radio emission of other cosmic sources. Conclusions: The paper presents the results of measurement of the rotation measure for the two closest to the Earth pulsars, namely J0814+7429 (B0809+74), J0953+0755 (B0950+08), and the comparison of the proposed technique for this parameter determination with other existing techniques.

A survey of the northern hemisphere at the frequency 111 MHz is carried out. The total accumulation time for each point of the survey area was at least one hour. When searching for dispersed pulses, we detected 75 sources of pulsed radiation. More than 80% of these sources are known pulsars seen in the antenna side lobes. In twelve known pulsars, from one to several hundred pulses were detected. In four pulsars (J0157+6212, J1910+5655, J2337+6151, and J2354+6155), the narrowness of the strongest pulses and the ratio of peak flux densities in the strongest pulses and in the middle profile indicate that they may be pulsars with giant pulses. We detected one new rotating radio transient (RRAT) J0812+8626 with the dispersion measure pc/cm3. [ABSTRACT FROM AUTHOR]

High sensitivity radio searches of unassociated γ-ray sources have proven to be an effective way of finding new pulsars. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during its commissioning phase, we have carried out a number of targeted deep searches of Fermi Large Area Telescope (LAT) γ-ray sources. On February 27, 2018 we discovered an isolated millisecond pulsar (MSP), PSR J0318+0253, coincident with the unassociated γ-ray source 3FGL J0318.1+0252. PSR J0318+0253 has a spin period of 5.19 ms, a dispersion measure (DM) of 26 pc cm−3 corresponding to a DM distance of about 1.3 kpc, and a period-averaged flux density of (∼11±2) µJy at L-band (1.05–1.45 GHz). Among all high energy MSPs, PSR J0318+0253 is the faintest ever detected in radio bands, by a factor of at least ∼4 in terms of L-band fluxes. With the aid of the radio ephemeris, an analysis of 9.6 years of Fermi-LAT data revealed that PSR J0318+0253 also displays strong γ-ray pulsations. Follow-up observations carried out by both Arecibo and FAST suggest a likely spectral turn-over around 350 MHz. This is the first result from the collaboration between FAST and the Fermi-LAT teams as well as the first confirmed new MSP discovery by FAST, raising hopes for the detection of many more MSPs. Such discoveries will make a significant contribution to our understanding of the neutron star zoo while potentially contributing to the future detection of gravitational waves, via pulsar timing array (PTA) experiments. [ABSTRACT FROM AUTHOR]

The recent use of the tail-tip bleeding approach in mice has enabled researchers to generate detailed pulse and surge profiles of luteinizing hormone (LH) secretion in mice. However, the analysis of pulsatile LH secretion is piecemeal across the field with each laboratory using their own methodology. We have reformulated the once-popular PULSAR algorithm of Merriam and Wachter to operate on contemporary computer systems and provide downloadable and online pulse analysis platforms. As it is now possible to record the activity of the gonadotropin-releasing hormone pulse generator in freely behaving mice, we have been able to unambiguously define LH pulses in intact and gonadectomized male and female mice. These data sets were used to determine the appropriate PULSAR parameter sets for analyzing pulsatile LH secretion in the mouse. This was then used to establish an accurate model of estrogen negative feedback in the mouse. Intact and ovariectomized mice given Silastic capsules containing 1, 2, and 4 μg 17-β-estradiol/20 g body weight were tail-tip bled at 6-min intervals, and the resultant LH profiles were analyzed with PULSAR. Only the 4 μg 17-β-estradiol capsule treatment was found to return LH pulse amplitude and frequency to that of intact diestrous mice. Ultrasensitive mass spectrometry analysis showed that the 4 μg 17-β-estradiol capsule generated circulating estradiol levels equivalent to that of diestrous mice. It is hoped that the reformulation of PULSAR and generation of a realistic model of estrogen-negative feedback will provide a platform for the more uniform assessment of pulsatile hormone secretion in mice. [ABSTRACT FROM AUTHOR]

Purpose: Due to the significant increase of a number of pulsars discovered with high-frequency radio telescopes over the last ten years and the necessity to obtain accurate parameters of their decameter radiation (as well as to identify single pulses detected with the UTR-2), the second decameter census of these sources with the UTR-2 radio telescope became needed. Design/methodology/approach: Single pulses detected as a result of the first decameter survey of pulsars and transient emission sources can be anomalously intense pulses of the recently discovered pulsars. Identification is only possible with an accurate information on the dispersion measure (DM) of each of these sources. Given that the new pulsars are likely to have a low radiant flux density, in contrast to the first decameter pulsar census [1], the second one plans to increase the signal-to-noiseratio by increasing the observation time of each pulsar. This paper gives a complete list of the studied sources, limited by the dispersion measure (DM< 30 pc·cm-³), period (P> 0.1 s) and declination (δ>-10º), known for the beginning of 2020, as well as some examples of the decameter pulsar radio emission detected by means of pipeline data processing with the possibility of flexible adjustment of search parameters. Findings: For the first time in the low-frequency wavelength range, the radio emission from the PSR J2325-0530, PSR J0613+3731, and PSR J1426+52 pulsars has been detected. The main result of present work is specified period for the latter pulsar (PSR J1426+52), being 0.995866 s ± 5 µs, the other parameters of its radio emission are also specified. Conclusions: High sensitivity of the UTR-2 radio telescope, its receiving equipment and efficient data processing and analysis pipeline allow detecting the decameter radiation of weak pulsars, as well as obtaining their parameters with the accuracy sufficient for identification of previously discovered transient signals.

Large-scale beamforming with radio interferometers has the potential to revolutionize the science done with pulsars and fast radio bursts by improving the survey efficiency for these sources. We describe a wide-field beamformer for the MeerKAT radio telescope and outline strategies to optimally design such surveys. For software implementation of these techniques, Mosaic is introduced and its application in the MeerKAT telescope is presented. We show initial results using the beamformer by observing a globular cluster to track several pulsars simultaneously and demonstrate the source localization capability of this observation. [ABSTRACT FROM AUTHOR]

Purpose: Harnessing the immune-stimulatory effects of radiation by combining it with immunotherapy is a promising new treatment strategy. However, more studies characterizing immunotherapy and radiation dose scheduling for the optimal therapeutic effect is essential for designing clinical trials.Methods and Materials: A new ablative radiation dosing scheme, personalized ultrafractionated stereotactic adaptive radiation therapy (PULSAR), was tested in combination with α-PD-L1 therapy in immune-activated and resistant syngeneic immunocompetent mouse models of cancer. Specifically, tumor growth curves comparing immunotherapy and radiation therapy dose sequencing were evaluated in immunologically cold and hot tumor models. The response relative to cytotoxic killer T cells was evaluated using an α-CD8 depleting antibody, and immunologic memory was tested by tumor rechallenge of cured mice.Results: We report that both radiation and immunotherapy sequencing, as well as radiation therapy fraction spacing, affect the combination treatment response. Better tumor control was achieved by giving α-PD-L1 therapy during or after radiation, and spacing fractions 10 days apart (PULSAR) achieved better tumor control than traditional daily fractions. We showed that CD8+ depleting antibody abrogated tumor control in the PULSAR combination treatment, and certain treatment schedules induced immunologic memory.Conclusions: These results illustrate that radiation therapy dosing and scheduling affect tumor control, in combination with checkpoint blockade therapies. PULSAR-style radiation dosing is more complementary in combination with single-agent immunotherapy than traditional daily fractions in this preclinical model. Preclinical investigation could prove helpful in designing clinical trials investigating combination therapy. [ABSTRACT FROM AUTHOR]

In this commentary, we describe the potential of highly ablative doses utilizing Stereotactic Body Radiation Therapy (SBRT) in single or few fractions to enhance immune-responsiveness, how timing of this approach in combination with immune-checkpoint inhibitors may augment treatment-effect, and whether Personalized Ultrafractionated Stereotactic Adaptive Radiation Therapy (PULSAR) is an avenue for future advancement in the continued endeavor to foster a systemic effect of therapy beyond the radiation treatment field. The ablative potential of SBRT may support an increase in tumor-antigen presentation, enhancement of immune-stimulatory components, and an improvement in tumor-microenvironment immune cell infiltration. Furthermore, the latest advancement of ablative radiation delivery is PULSAR-based therapy, whereby ablative doses are delivered in pulses of treatment that may be several weeks apart, combined with adaptive treatment to tumor changes across time. The benefits of this novel approach include the ability to optimize direct tumor control by assessment of tumor size and location via dedicated imaging acquired prior to each delivered pulse, and further potentiation of immune recognition through combination with concurrent immune-checkpoint blockade.

Non-local theories of gravity are considered extended theories of gravity, meaning that when the non-local terms are canceled out, the limit of General Relativity (GR) is obtained. Several reasons have led us to consider this theory with increasing interest, but primarily non-locality emerges in a natural way as a 'side' effect of the introduction of quantum corrections to GR, the purpose of which was to cure the singularity problem, both at astrophysical and cosmological level. In this paper we studied a peculiar case of the so called Deser-Woodard theory consisting in the addition of a non-local term of the form R □ − 1 R to the Hilbert-Einstein lagrangian, where R is the Ricci scalar, and derived, for the first time, constraints on the dimensionaless non-local parameter A by exploiting the predicted gravitational wave emission in three binary pulsars, namely PSR J1012+5307, PSR J0348+0432 and PSR J1738+0333. We discovered that the instantaneous flux strongly depends on A and that the best constraints (0.12 < A < 0.16) come from PSR J1012+5307, for which the GR prediction is outside the observational ranges. However, since for PSR J 1012 + 5307 scintillation is suspected, as emerged in a recent census by LOFAR corruptions in pulsar timing could be hidden. We finally comment on the usability and reliability of this type of test for extended theories of gravity. [ABSTRACT FROM AUTHOR]

We calculate the time delay for photons propagating in a charged electron‐positron gas at finite temperature and in an external magnetic field with the final aim of studying the effect for photons in a neutron star magnetosphere. The dispersion relations are solved in terms of analytic functions, in the degenerate, strong magnetic field, and ultra‐relativistic limit. For fixed values of frequency, temperature, and chemical potential, we study the dependence of photon time delay with the magnetic field strength, as well as with distance. For the latter, we adopt a magnetic dipole configuration and obtain that, according to the expectation, photons of higher energy experience a minor time delay. Obtained results are compared with the previous ones obtained for the photon time delay in vacuum magnetosphere. [ABSTRACT FROM AUTHOR]

What if normal baryonic matter is compressed so tightly that atomic nuclei come into close contact? This question has been asked since 1930s. The first answer was presented by Lev Landau whose speculation has been developed, and the concept of neutron star is then popularized. However, another answer is related to strange star, which becomes worthy of attention especially after the establishment of the standard model of particle physics in 1960s. The basic ideas of this study are introduced pedagogically. We must point out emphatically that flavor symmetry and strong coupling between quarks would be essential in seeking true answer to the question. The final answer is expected to appear in the era of multimessenger astronomy. It is emphasized too that, besides the differences of global properties (e.g., mass‐radius relation, maximum mass, tidal deformability), the strong‐bound surface of strange star (rather than the gravity‐bound one for conventional neutron star) could play an important role in identifying a strange star by astronomical observations. [ABSTRACT FROM AUTHOR]

Fractionated radiotherapy was established in the 1920s based upon two principles: (1) delivering daily treatments of equal quantity, unless the clinical situation requires adjustment, and (2) defining a specific treatment period to deliver a total dosage. Modern fractionated radiotherapy continues to adhere to these century-old principles, despite significant advancements in our understanding of radiobiology. At UT Southwestern, we are exploring a novel treatment approach called PULSAR (Personalized Ultra-Fractionated Stereotactic Adaptive Radiotherapy). This method involves administering tumoricidal doses in a pulse mode with extended intervals, typically spanning weeks or even a month. Extended intervals permit substantial recovery of normal tissues and afford the tumor and tumor microenvironment ample time to undergo significant changes, enabling more meaningful adaptation in response to the evolving characteristics of the tumor. The notion of dose painting in the realm of radiation therapy has long been a subject of contention. The debate primarily revolves around its clinical effectiveness and optimal methods of implementation. In this perspective, we discuss two facets concerning the potential integration of dose painting with PULSAR, along with several practical considerations. If successful, the combination of the two may not only provide another level of personal adaptation ("adaptive dose painting"), but also contribute to the establishment of a timely feedback loop throughout the treatment process. To substantiate our perspective, we conducted a fundamental modeling study focusing on PET-guided dose painting, incorporating tumor heterogeneity and tumor control probability (TCP)., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Peng, Deng, Jiang and Timmerman.)

Purpose: The subject of the paper is discussion of reflected radiation from the neutron star surface. Such radiation, as was shown earlier by S. V. Trofymenko and one of the authors, occurs when reflects the radiation of relativistic positrons flying from the magnetosphere to a star in the accelerating electric field of the polar gap. This gave an explanation of both the interpulse shift in the Crab pulsar (mirror reflection in an inclined magnetic field) and the appearance of additional HF components (diffraction on the periodic structure excited by the incident radiation) discovered by Moffett and Hankins. The aim of the paper is to study the effect on the HF components of a resonance with a surface electromagnetic wave. Design/methodology/approach: Since the HF components occur at the same frequencies as the interpulse shift, we believe that they are a consequence of the same physical process. Such a process is the reflection from the surface of a neutron star of the radiation of the return positrons. The appearance of HF components is considered as a manifestation of stimulated scattering by surface waves. For comparison, the data of laboratory experiments on the diffraction of laser radiation on a metal diffraction grating are presented. They demonstrate the appearance of a bright near-surface wave under resonance conditions, which can serve as an analog of the HF component in the Crab pulsar. Findings: In the formation of HF components, such phenomena as Wood’s anomalies are significant, leading to considerable essential increase of the increment of stimulated scattering at the resonance with the surface electromagnetic wave. The surface wave excited with the resonance leads to reflected Raman scattering of higher frequencies of the continuous spectrum of the incident radiation. Conclusions: The radiation of a pulsar is determined, among others, by the reflecting properties of the surface of the neutron star, i.e. its conductivity (surface impedance). The resonance substantially reduces the stimulated scattering threshold. The continuous spectrum of the radiation incident on the surface provides a large width of the HF-components.

Observations of the Crab pulsar at 327 MHz were made at the Toyokawa Observatory of the Institute for Space-Earth Environmental Research, during the solar occultation in mid-June 2018 to investigate the coronal plasma density in the weak sunspot cycle, Cycle 24. The dispersion measurements (DMs) were determined using giant pulses detected from observations of the Crab pulsar. The systematic increase in DM over the background level, observed during the period of the closest approach of the Crab pulsar's line-of-sight to the Sun, was ascribed to the effect of the coronal plasma. A coronal density model assuming spherical symmetry was determined by fitting it to the DM data, and was compared with those determined in past solar cycles. The best-fit model had large errors, and indicated a systematically higher value than those derived from past observations. The results obtained here are likely to be significantly affected by latitude/longitude variation in coronal plasma density, the time variation of the interstellar medium, mainly the Crab nebula, and increased measurement errors due to the reduced occurrence of giant pulses. Hence, further observations are needed to derive conclusions about a change of coronal density in the current cycle. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of pulsar-based navigation in deep space mission applications. The noise properties of X-ray based and radio-baspulsar measurements are examined and compared. A closed form parametric covariance analysis tool was developed in this study. It provides a rough estimate of the navigation performance associated with a deep space cruise that makes use of ion thrusters and sequential pulsar observations. In addition, the flight trajectory of the Dawn spacecraft was used to form a hypothetical deep space mission scenario that utilizes pulsars as navigation beacons. This simulated scenario accounts for clock uncertainty, pulsar timing noise, maneuver execution errors, sequential observation and interruptions between pulsar observations. A particle filter was implemented to reduce the large initial position uncertainty by resolving the number of pulsar wavelengths between the spacecraft and the Solar System Barycenter. The resulting position and velocity uncertainties from the particle filter can be used to initialize an Extended Kalman Filter, which estimates the spacecraft position and velocity for steady state operations. [ABSTRACT FROM AUTHOR]

We use radio millisecond pulsars (MSPs) to determine the position of the Parkes telescope to explore the feasibility of pulsar navigation for terrestrial application, as well to investigate the relations between pulsar observations and the positional errors for potential X-ray pulsar navigation (XNAV). Different from the analytical algorithm (Han et al. Astrophys. Space Sci. 364, 3, 2018) which derives the relations between observatory coordinates and pulsar timing residuals, a grid search method is used in our work. The method divides the space adjacent to the radio telescope into small grids, from which we form the rms timing residuals and fit pulsar parameters to find the position with minimal χ2 value. Six pulsars from the Parkes Pulsar Timing Array (PPTA) are selected to perform position determinations. The positional errors are analyzed together with the pulsar reference phase, timing residuals, and observation numbers. Using a hybrid database of pulsar timing and cartographic data, we obtained best positional accuracy of around 10 m by PSR J0437 − 4715. To investigate the feasibility of pulsar terrestrial navigation, only few observations from PSR J0437 − 4715 are used for position determinations. The results show that the precision of about 100 m is achievable with only 3 or 4 observations. In this paper, we introduce our method in detail and discuss the positioning performance in different scenarios. [ABSTRACT FROM AUTHOR]

Pulsars are magnetized neutron stars. They are not resolved by modern radio telescopes and are studied only by radiation coming from the regions of the magnetic poles. Because of the rotation, this narrow radiation is received as pulses. In a few pulsars whose magnetic axis is almost orthogonal to the rotation axis (the simplest hypothesis), pulses are observed from both poles: the (main) pulse and the interpulse. Such objects primarily include a pulsar in the Crab nebula, observed at many frequencies of the electromagnetic spectrum. In the remarkable work of Hankins and Eilek, a striking difference between the spectra of the main pulse and the interpulse in the Crab nebula in the centimeter wavelength range at microsecond resolution was found (surprising the authors: "In traditional pulsar models... the MP and IP should be the same in their observable quantities (such as spectrum, time signature, or dispersion). We were—and remain—quite surprised that this turns out not to be the case in the Crab pulsar." See T. H. Hankins and J. A. Eilek, "Radio emission signatures in the Crab pulsar," Astrophys. J., 670:693–701, 2007). In particular, a wide range of frequencies was observed in the spectra of the main pulse forming "vertical structures," while "horizontal structures" with distinguished frequencies were observed in the spectra of the interpulse at the same frequencies. Such a difference, related to different radiation mechanisms (nonrelativistic electron emission in a longitudinal accelerating field for the main pulse and relativistic positron radiation due to the curvature of magnetic field lines for the interpulse), is explained by the change from the nonrelativistic to the relativistic mechanism as the frequency increases. Therefore, the frequencies at which the mechanism changes differ for the main pulse and the interpulse. The frequency of observation in the work of Hankins and Eilek is just between these frequencies with which the difference in the microstructure is connected. [ABSTRACT FROM AUTHOR]

We revisit here a possibility of generation of gravitational wave (GW) bursts due to a very quick change in the quadrupole moment (QM) of a deformed spheroidal pulsar as a result of crustquake. Since it was originally proposed as a possible explanation for sudden spin-up (glitch) of pulsars, the occurrence of crustquake and its various consequences have been studied and discussed quite often in the literature. Encouraged by recent development in gravitational wave (GW) astronomy, we re-investigate the role of crustquake in the emission of GWs. Assuming exponential decay of excitation caused by crustquake, we have performed a Fourier analysis to estimate the GW strain amplitude h(t), characteristic signal amplitude h c (f) and signal-to-noise ratio (SNR) of the burst for the Crab pulsar. For exotic quark stars, multifold enhancement of these quantities are expected, which might make quark star a potential source of gravitational waves. The absence of such bursts may put several constraints on pulsars and such hypothetical stars. [ABSTRACT FROM AUTHOR]

The pulsar is a highly magnetized rotating neutron star that provides the first indirect evidence for the existence of gravitational waves and also provides the possibility to reveal extreme phenomena in neutron star astrophysics. Therefore, the identification of pulsars in the universe is a prerequisite for the study of pulsars and gravitational waves. At present, a large number of pulsar searches have produced millions of pulsar candidates. In the face of these large-scale data, if only relying on manual visual classification by experts in related fields, it will be a huge project. Since the emergence of machine learning, its theory and technology have become increasingly mature, and has been successfully applied to astronomical research fields such as pulsar candidate screening. This paper introduces the related machine learning theory of pulsar candidate recognition firstly, and then reviews the research status of pulsar candidate recognition based on machine learning in recent years. Finally, we discuss and prospect the identification of pulsars in the future. [ABSTRACT FROM AUTHOR]

The discovery of radio pulsars over a half century ago was a seminal moment in astronomy. It demonstrated the existence of neutron stars, gave a powerful observational tool to study them, and has allowed us to probe strong gravity, dense matter, and the interstellar medium. More recently, pulsar surveys have led to the serendipitous discovery of fast radio bursts (FRBs). While FRBs appear similar to the individual pulses from pulsars, their large dispersive delays suggest that they originate from far outside the Milky Way and hence are many orders-of-magnitude more luminous. While most FRBs appear to be one-off, perhaps cataclysmic events, two sources are now known to repeat and thus clearly have a longer lived central engine. Beyond understanding how they are created, there is also the prospect of using FRBs—as with pulsars—to probe the extremes of the Universe as well as the otherwise invisible intervening medium. Such studies will be aided by the high-implied all-sky event rate: there is a detectable FRB roughly once every minute occurring somewhere on the sky. The fact that less than a hundred FRB sources have been discovered in the last decade is largely due to the small fields-of-view of current radio telescopes. A new generation of wide-field instruments is now coming online, however, and these will be capable of detecting multiple FRBs per day. We are thus on the brink of further breakthroughs in the short-duration radio transient phase space, which will be critical for differentiating between the many proposed theories for the origin of FRBs. In this review, we give an observational and theoretical introduction at a level that is accessible to astronomers entering the field. [ABSTRACT FROM AUTHOR]

In this short-note, I have discussed spherical deformation in rotationally perturbed spacetime which is valid for strong gravitational fields assuming star is homogenous and spherically symmetric. I have considered a photon emitted by a rapidly rotating star (pulsar) and calculated net deflection angle. In this case, we observed that rapidly emitted photon has shown bending under inertial frame drag effect which is opposite to non rotational case. I have also considered red-shift effect in this situation and observed that the red shift of a line emission shifted towards lower frequency with the effect of broadening. The rotation effect is also maximum on tangentially backward emitted photon which causes limbs of the stars moves away from observer [ABSTRACT FROM AUTHOR]

We study the transverse propagation of photons in a magnetized vacuum considering radiative corrections in the one‐loop approximation. The dispersion equation is modified due to the magnetized photon self‐energy in the transparency region (0 < ω < 2me). The aim of our study is to explore the propagation of photons in a neutron star magnetosphere (described by a magnetized vacuum). The solution of the dispersion equation is obtained in terms of analytic functions. The larger the magnetic field, the higher the phase velocity and the more the dispersion curve deviates from the light‐cone. For fixed values of the frequency, we study the dependence of photons time delay with the magnetic field strength, as well as with distance. For the latter, we adopt a magnetic dipole configuration and obtain that, contrary to the expectation, photons of higher energy experience a longer time delay. A discussion of potential causes of this behavior is presented. [ABSTRACT FROM AUTHOR]