Since pulsars were discovered as emitters of bright coherent radio emission more than half a century ago, the cause of the emission has remained a mystery. In this Letter we demonstrate that coherent radiation can be directly generated in non-stationary pair plasma discharges which are responsible for filling the pulsar magnetosphere with plasma. By means of large-scale two-dimensional kinetic plasma simulations, we show that if pair creation is non-uniform across magnetic field lines, the screening of electric field by freshly produced pair plasma is accompanied by the emission of waves which are electromagnetic in nature. Using localized simulations of the screening process, we identify these waves as superluminal ordinary (O) modes, which should freely escape from the magnetosphere as the plasma density drops along the wave path. The spectrum of the waves is broadband and the frequency range is comparable to that of observed pulsar radio emission.
Pulsars play a crucial astrophysical role as the highly energetic compact radio, X-ray, and gamma-ray sources. Our previous works show that the radio pulsars found as the pulsing gamma sources by the Large Area Telescope (LAT) on the board of the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger comparing with the magnetic fields of radio pulsars: $\log B_{lc}$ (G) are 3.60-3.95 and 1.75. Moreover, their losses of the rotation energy are also three orders higher than the corresponding values for the main group of …
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.
The LOFAR Tied-Array All-Sky Survey (LOTAAS) is the most sensitive untargeted radio pulsar survey performed at low radio frequencies (119--151\,MHz) to date and has discovered 76 new radio pulsars, among which the 23.5-s pulsar J0250+5854, up until recently the slowest-spinning radio pulsar known. Here, we report on the timing solutions of 35 pulsars discovered by LOTAAS, which include a nulling pulsar and a mildly recycled pulsar, and thereby complete the full timing analysis of the LOTAAS pulsar discoveries. We give an overview of the findings from the full LOTAAS sample of 76 pulsars, discu…
We have used the unique low frequency sensitivity of the Large Phased Array radio telescope of Pushchino Radio Astronomy Observatory to collect dataset of the single pulse observations of second period pulsars of the Northern hemisphere. During observational sessions of 2011 - 2017 yrs. We have collected data on 71 pulsars at 111 MHz frequency using digital pulsar receiver. We have discovered Giant Radio Pulses (GRP) from pulsars B0301+09 and B1237+25, and confirmed early reported generation of anomalously strong (probable giant) pulses from B1133+16 on statistically significant dataset. Data …
We investigated the pulsar radio luminosity ($L$), emission efficiency (ratio of radio luminosity to its spin-down power $\dot{E}$), and death line in the diagram of magnetic field (B) versus spin period (P), and found that the dependence of pulsar radio luminosity on its spin-down power ($L-\dot{E}$) is very weak, shown as $L\sim\dot{E}^{0.06}$, which deduces an equivalent inverse correlation between emission efficiency and spin-down power as $ξ\sim \dot{E}^{-0.94}$. Furthermore, we examined the distributions of radio luminosity of millisecond and normal pulsars, and found that, for the simil…
The Fermi Large Area Telescope has detected over 260 gamma-ray pulsars. About one quarter of these are labeled as radio-quiet. In the population of nonrecycled gamma-ray pulsars, the fraction of radio-quiet pulsars is higher, about one half. Most radio observations of gamma-ray pulsars have been performed at frequencies between 300 MHz and 2 GHz. However, pulsar radio fluxes increase rapidly with decreasing frequency, and their radio beams often broaden at low frequencies. As a consequence, some of these pulsars might be detectable at low radio frequencies even when no radio flux is detected a…
On the basis of the PSRPOPPY software package, we developed an evolution model of population synthesis for isolated radio pulsars by incorporating the fan beam model, an alternative radio emission beam model to the widely used conal beam model. With proper choice of related models and parameters, we succesfully reproduced the observational distributions of Galactic longitude ($l$) and latitude ($b$), spin period, period derivative, dispersion measure and 1.4-GHz flux density for the 1214 isolated pulsars discovered by the Parkes multibeam and Swinburne pulsar surveys. The number of underlying …
The search for radio emission from the gamma pulsar J0357+3205 in the meter wavelength range was carried out. Periodic emission was found in one of the 1,700 observation sessions. The average pulsar profile is single-component with a half-width of 20-25 ms. Estimation of the pulsar flux density is 14 mJy.
Although fifty years have passed since the discovery of radio pulsars, there is still no satisfactory understanding of how these amazing objects operate. While there has been significant progress in understanding the basic properties of radio pulsars, there is as yet no consensus on key issues, such as the nature of coherent radio emission or the conversion mechanism of the electromagnetic energy of the pulsar wind into particle energy. In this review, we present the main theoretical results on the magnetosphere of neutron stars. We formulate a number of apparently simple questions, which neve…
Binary pulsars are affected by general relativity (GR), causing the spin axes of each pulsar to precess. We present polarimetric radio observations of PSR J1906+0746 that demonstrate the validity of the geometrical model of pulsar polarisation. We reconstruct the (sky-projected) polarisation emission map over the pulsar's magnetic pole and predict the disappearance of the detectable emission by 2028. Two additional tests of GR are performed in this system, including the spin-precession for strongly self-gravitating bodies. We constrain the relativistic treatment of the pulsar polarisation mode…
We have conducted the largest investigation to date into the origin of phase resolved, apparent RM variations in the polarized signals of radio pulsars. From a sample of 98 pulsars based on observations at 1.4 GHz with the Parkes radio telescope, we carefully quantified systematic and statistical errors on the measured RMs. A total of 42 pulsars showed significant phase resolved RM variations. We show that both magnetospheric and scattering effects can cause these apparent variations. There is a clear correlation between complex profiles and the degree of RM variability, in addition to deviati…
We summarize the state of the art and future directions in using millisecond radio pulsars to test gravitation and measure intrinsic, fundamental parameters of the pulsar systems. As discussed below, such measurements continue to yield high-impact constraints on viable nuclear processes that govern the theoretically-elusive interior of neutron stars, and place the most stringent limits on the validity of general relativity in extreme environments. Ongoing and planned pulsar-timing measurements provide the greatest opportunities for measurements of compact-object masses and new general-relativi…
Distance versus dispersion measure relations are constructed for Galactic radio pulsars in small solid angle intervals. The calculations are based on some basic criteria as well as using the independent distance measurements of well examined pulsars for the first Galactic quadrant including Galactic central directions. Values of average free electron density for these regions are derived from the fits to distance versus dispersion measure relations and checked for consistency and smoothness. The effects of plasma in the Galactic arms and within the central parts of the Galactic bulge region ar…
Over the past 13 years, the Parkes radio telescope has observed a large number of pulsars using digital filterbank backends with high time and frequency resolution and the capability for Stokes recording. Here we use archival data to present polarimetry data at an observing frequency of 1.4 GHz for 600 pulsars with spin-periods ranging from 0.036 to 8.5 s. We comment briefly on some of the statistical implications from the data and highlight the differences between pulsars with high and low spin-down energy. The dataset, images and table of properties for all 600 pulsars are made available in …
We present the results of modelling of the radio spectrum evolution and dispersion measure variations of PSR B1259-63, a pulsar in a binary system with Be star LS 2883. We base our model on a hypothesis that the observed variations of the spectrum are caused by thermal free-free absorption occurring in the pulsar surroundings. We reproduce the observed pulsar spectral shapes in order to examine the influence of the stellar wind of LS 2883 and the equatorial disc on the pulsar's radiation. The simulations of the pulsar's radio emission and its consequent free-free absorption give us an insight …
Our paper presents the results of the second census of pulsars in decametre wave range at UTR-2 radio telescope. Over the past ten years, the number of discovered nearby pulsars in the world has doubled, which has made it urgent to search for a low-frequency radio emission from newly discovered sources. To increase this census sensitivity, the integration time was doubled compared with the first census of 2010-2013. As a result, the decametre radio emission of 20 pulsars was detected, their flux densities and the shape of pulses were obtained. The dispersion measure for 10 pulsars and the rota…
We report on a time-domain search for pulsars in 44 steep spectrum radio sources originally identified from recent imaging surveys. The time-domain search was conducted at 327 MHz using the Ooty radio telescope, and utilized a semi-coherent dedispersion scheme retaining the sensitivity even for sub-millisecond periods up to reasonably high dispersion measures. No new pulsars were found. We discuss the nature of these steep spectrum sources and argue that majority of the sources in our sample should either be pulsars or a new category of Galactic sources. Several possibilities that could hinder…
Recent multi-frequency measurements of pulse widths W50 for the long-period pulsar J0250+5854 by Agar et al provide a unique insight to the emission process owing to its small polar-cap radius. The frequency-dependence of W50 can be simply understood as a consequence of the emitting plasma remaining under acceleration during the interval of radio emission. This is possible in a plasma of ions and protons but not in one of high-multiplicity electron-positron pairs. Extension of the model to the pulse profiles of the general pulsar population is considered briefly.
In this Letter we propose that coherent radio emission of Crab, other young energetic pulsars, and millisecond pulsars is produced in the magnetospheric current sheet beyond the light cylinder. We carry out global and local two-dimensional kinetic plasma simulations of reconnection to illustrate the coherent emission mechanism. Reconnection in the current sheet beyond the light cylinder proceeds in the very efficient plasmoid-dominated regime, and current layer gets fragmented into a dynamic chain of plasmoids which undergo successive coalescence. Mergers of sufficiently large plasmoids produc…
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 Phased Array (LPA) and the standard digital receiver with a total bandwidth is 2.245 MHz and time resolution is 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.
Synchronous X-ray and Radio Mode Switches: a Rapid Global Transformation of the Pulsar Magnetosphere
脉冲星发射低频无线电波，直到高能伽马射线，这些伽马射线产生于从表面到磁层边缘的任何地方。因此，检测多波长发射中的相关模式变化是理解这些发射位点之间的物理关系的关键。通过同步观测，我们探测到PSR B 0943 +10的射电和X射线发射特性的同步开关。当脉冲星处于持续的无线电“明亮”模式时，X射线只显示非脉冲，非热成分。相反，当脉冲星处于无线电“安静”模式时，X射线亮度增加一倍以上，并且观察到100%的脉冲热分量以及非热分量。这表明磁层的条件发生了快速的全球性变化，这对所有提出的脉冲星发射理论提出了挑战。
Radio timing observations of a millisecond pulsar in orbit around the Galactic centre black hole (BH) or a BH at the centre of globular clusters could answer foundational questions in astrophysics and fundamental physics. Pulsar radio astronomy typically employs the post-Keplerian approximation to determine the system parameters. However, in the strong gravitational field around the central BH, higher order relativistic effects may become important. We compare the pulsar timing delays given by the post-Keplerian approximation with those given by a relativistic timing model. We find significant…
The SUrvey for Pulsars and Extragalactic Radio Bursts ran from 2014 April to 2019 August, covering a large fraction of the southern hemisphere at mid- to high-galactic latitudes, and consisting of 9-minute pointings taken with the 20-cm multibeam receiver on the Parkes Radio Telescope. Data up to 2017 September 21 have been searched using standard Fourier techniques, single-pulse searches, and Fast Folding Algorithm searches. We present 19 new discoveries, bringing the total to 27 discoveries in the programme, and we report the results of follow-up timing observations at Parkes for 26 of these…
