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High brightness temperature radio transients such as pulsars and fast radio bursts require the coherent radiation of particles. The antenna class of coherent radiation models require a large number of charged particles radiating in phase, therefore the particles must be spatially confined and have well-aligned velocities. Given these necessary conditions, we look at the magnetic field induced by the currents associated with coherently emitting accelerated particles and consider the interaction between the radiating particles and the induced magnetic field. We find a maximum luminosity of coherent curvature radiation that depends on source parameters such as surface magnetic field and neutron star spin period. We find that coherent radio emission across all luminosities can be explained by coherent curvature radiation and suggest it could be universally responsible for both FRBs and extreme galactic sources. Using the Crab Pulsar as an example, we constrain the emission parameters and origin of the most extreme nanoshots to within 60km of the pulsar surface assuming coherent curvature radiation. In agreement with recent observations, we also predict simultaneous X-ray emission from small-scale particle gyration due to the induced field., Comment: Accepted to MNRAS Letters

A model for the source of microwave main giant pulses (GPs) from the Crab pulsar is proposed and partly investigated. Pulse excitation takes place in a relativistic pair plasma with a strong magnetic field through the beam pulse amplifier (BPA) mechanism, in which short noise pulses of a certain type are amplified by energetic electrons at the Cherenkov resonance, even without strong anisotropy in the distribution function. The wave gain is shown to be as high as with an instability of hydrodynamic type, and wave escaping from the excitation region into the pulsar magnetosphere may not involve significant attenuation. The basic parameters of the source which explains the observed characteristics of the GP electromagnetic bursts have been analysed and are consistent with accepted ideas about physical conditions in the pulsar magnetosphere. The BPA mechanism explains the important properties of the GPs, such as the extremely short pulse duration (extreme nanoshots), the extremely high brightness temperature of the radiation source, the formation of radiation in a wide frequency range, and the possibility of radiation reaching the periphery of the pulsar magnetosphere.

In this study, we employed broadband X-rays ($6-2000$ eV) to irradiate the frozen acetone CH$_3$COCH$_3$, at the temperature of 12 K, with different photon fluences up to $2.7\times 10^{18}$ photons cm$^{-2}$. Here, we consider acetone as a representative complex organic molecule (COM) present on interstellar ice grains. The experiments were conduced at the Brazilian synchrotron facility (LNLS/CNPEN) employing infrared spectroscopy (FTIR) to monitor chemical changes induced by radiation in the ice sample. We determined the effective destruction cross-section of the acetone molecule and the effective formation cross-section for daughter species. Chemical equilibrium, obtained for fluence $2\times 10^{18}$ photons cm$^{-2}$, and molecular abundances at this stage were determined, which also includes the estimates for the abundance of unknown molecules, produced but not detected, in the ice. Timescales for ices, at hypothetical snow line distances, to reach chemical equilibrium around several compact and main-sequence X-ray sources are given. We estimate timescales of 18 days, 3.6 and 1.8 months, $1.4\times 10^9-6\times 10^{11}$ years, 600 and $1.2\times 10^7$ years, and $10^7$ years, for the Sun at 5 AU, for O/B stars at 5 AU, for white dwarfs at 1 LY, for the Crab pulsar at 2.25 LY, for Vela pulsar at 2.25 LY, and for Sagittarius A* at 3 LY, respectively. This study improves our current understanding about radiation effects on the chemistry of frozen material, in particular, focusing for the first time, the effects of X-rays produced by compact objects in their eventual surrounding ices., Comment: Accepted in MNRAS. This is a preprint. 14 pages, 7 figures

During pulsar navigation, the high-frequency noise carried by the pulsar profile signal reduces the accuracy of the pulse TOA (Time of Arrival) estimation. At present, the main method to remove signal noise by using wavelet transform is to redesign the function of the threshold and level of wavelet transform. However, the signal-to-noise ratio and other indicators of the filtered signal need to be further optimised, so a more appropriate wavelet basis needs to be designed. This paper proposes a wavelet basis design method based on frequency domain analysis to improve the denoising effect of pulsar signals. This method first analyses the pulsar contour signal in the frequency domain and then designs a Crab pulsar wavelet basis (CPn, where n represents the wavelet basis length) based on its frequency domain characteristics. In order to improve the real-time performance of the algorithm, a wavelet lifting scheme is implemented. Through simulation, this method analyses the pulsar contour signal data at home and abroad. Results show the signal-to-noise ratio can be increased by 4 dB, the mean square error is reduced by 61% and the peak error is reduced by 45%. Therefore, this method has better filtering effect.

We study the origin of quasi-harmonic emission bands with fine structure observed in the dynamic radiation spectra of high-frequency interpulses. The possible explanation of observed structure is based on the effect of double plasma resonance (DPR) at electron cyclotron harmonics realized in the magnetosphere of pulsar in a local radio emission source filled with non-relativistic plasma. The model of the source consists of neutral current sheet with a transverse magnetic field where plasma waves are generated due to DPR effect. It is shown that the emergence of emission bands and their frequency spacing are due to the inhomogeneity of the plasma and magnetic field along the current sheet, and their fine structure is due to the inhomogeneity of the current sheet in the direction orthogonal to it. Each quasi-harmonic emission band represents a system of elements of fine features of radiation that is generated by suprathermal electrons under DPR conditions. The observed upward drift of quasi-harmonic emission bands is due to the displacement of suprathermal electrons across the current sheet and an increase in the DPR frequencies with distance from the central plane of the layer.

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.

In this paper, robust algorithms of information fusion between Pulsars timing, ranging and positioning with orbital dynamical model of explorer spacecraft is demonstrated with combination to inertial navigation system. Pulsar/CNS integration is considered in this work and was recently investigated using multiple variant of nonlinear filtering approaches, providing an interesting advances and results. However, due to the colored measurement noise from pulsars time of arrival measure, robust nonlinear filter has been derived based on Gauss Quadrature Kalman filters at different degrees. Moreover, because it has been demonstrated that in the during short period of observation, and minimum photons numbers, the noise affecting the X-Ray signal becomes not a Gaussian distribution. An alternative solution to this problem is proposed using multiple quadrature Kalman filters derived in the Gaussian Sum framework. At last, as an experimental validation, the Crab pulsar data were used to demonstrate the efficiency of the novel robust filtering approach against non linearity and also colored non Gaussian measurement noises.

We discuss and summarize five results that we and various colleagues have produced over the last few years in the study of the wonderful, yet enigmatic, Crab Nebula and its pulsar. The results, in turn, have to do with the geometry inferred from Chandra X-ray observations, the surprising results of pulse phase polarimetry at 1.4 GHz, the search for an X-ray location of the γ-ray flares for which we have Agile and Fermi to thank, and seeing if the optical and infrared inner knot might be the location of these flares.

Many pulsars show sudden rotation jumps, glitches, superimposed to the gradual rotation down due to the continued loss of energy by radiation. A lot of models have been proposed to explain glitches. Most of the models are associated with layer structure of neutron stars. We try to investigate possibility of relationship between glitches of Crab pulsar and Einstein-de Haas effect. In the scenarios, spin polarization of neutron matter with Skyrme-type interactions forms a macroscopic spin angular momentum, and the Einstein-de Haas effect – transfer between the macroscopic spin and orbit angular momentum – gives rise to glitches of pulsars. It is shown that the scenario is in agreement with the observations of Crab pulsar on glitches and post-glitches relaxation.

The departure of all measured pulsar braking indexes from the "canonical" dipole value 3 has been attributed to several causes in the past. Careful monitoring of the Crab pulsar has revealed permanent changes in the spin-down rate which are most likely the accumulation of small jumps in the angle $\alpha$ between the magnetic and spin axis. Recently, a large permanent change in the braking index of the in the "Crab twin" pulsar B0540-69 has been reported, and an analogous phenomenon seen in the high-field pulsar PSR 1846-0258 has been seen following a glitch, while another similar event (in PSR J119-6127) needs to be confirmed. We argue in this work that a common physical origin of all these observations can be attributed to the counter-alignment of the axis without serious violations of the observed features and with very modest inferred values of the hypothesized jump in the $\alpha$ angle. In addition, detected increases of the X-ray luminosities after the events are an additional ingredient for this interpretation. We argue that a component of a time-dependent torque has been identified, being an important ingredient towards a full solution of observed pulsar timing behavior which is in search of a consistent modeling., Comment: 5 pages, no figures, to appear in MNRAS

The X-ray timing data for the Crab pulsar obtained by the Chinese X-ray pulsar navigation test satellite are processed and analyzed. The method to build the integrated and standard X-ray pulse profiles of the Crab pulsar by using the X-ray pulsar observation data and the satellite orbit data is described. The principle and algorithm for determining the pulsar's pulse time of arrival (toa) in the frequency domain are briefly introduced. The pulsar's pulse time of arrival is calculated by using the timing data of 50 min integration for each set of observational data. By the comparison between the observed Crab pulsar's pulse time of arrival at the solar system barycenter and that predicted with the Crab pulsar ephemeris, it is found that the timing accuracy is about 14 μs after the systematic error is removed by a quadratic polynomial fitting.

There are some similarities between bursts of repeating fast radio bursts (FRBs) and giant pulses (GPs) of pulsars. To explore possible relations between them, we study the cumulative energy distributions of these two phenomena using the observations of repeating FRB 121102 and the GPs of Crab pulsar. We find that the power-law slope of GPs (with fluence ≥130 Jy·ms) is 2.85±0.10. The energy distribution of FRB 121102 can be well fitted by a smooth broken power-law function. For the bursts of FRB 121102 above the break energy (1.22 · 1037 erg), the best-fitting slope is 2.90 −0.44 +0.55 , similar to the index of GPs at the same observing frequency (

The Crab pulsar and the surrounding nebula powered by the pulsar's rotational energy through the formation and termination of a relativistic electron-positron wind is a bright source of gamma-rays carrying crucial information about this complex conglomerate. We report the detection of $\gamma$-rays with a spectrum showing gradual steepening over three energy decades, from $5\times 10^{-4}$ to $1.1$ petaelectronvolt (PeV). The ultra-high-energy photons exhibit the presence of a PeV electron accelerator (a pevatron) with an acceleration rate exceeding 15% of the absolute theoretical limit. Assuming that unpulsed $\gamma$-rays are produced at the termination of the pulsar's wind, we constrain the pevatron's size, between $0.025$ and $0.1$ pc, and the magnetic field $\approx 110 \mu$G. The production rate of PeV electrons, $2.5 \times 10^{36}$ erg $\rm s^{-1}$, constitutes 0.5% of the pulsar's spin-down luminosity, although we do not exclude a non-negligible contribution of PeV protons to the production of the highest energy $\gamma$-rays., Comment: 43 pages, 13 figures, 2 tables; Published in Science

The AstroSat mission carries several high-energy detectors meant for fast timing studies of cosmic sources. In order to carry out high precision multi-wavelength timing studies, it is essential to calibrate the absolute time stamps of these instruments to the best possible accuracy. We present here the absolute time calibration of the AstroSat LAXPC instrument, utilising the broadband electromagnetic emission from the Crab Pulsar to cross calibrate against Fermi-LAT and ground based radio observatories Giant Metrewave Radio Telescope (GMRT) and the Ooty Radio Telescope (ORT). Using the techniques of pulsar timing, we determine the fixed timing offsets of LAXPC with respect to these different instruments and also compare the offsets with those of another AstroSat instrument, CZTI., Comment: 8 pages, 2 figures, 2 tables. Accepted for publication in the Journal of Astronomy and Astrophysics

The Cadmium Zinc Telluride Imager (CZTI) is an imaging instrument onboard AstroSat. This instrument operates as a nearly open all-sky detector above ~60 keV, making possible long integrations irrespective of the spacecraft pointing. We present a technique based on the AstroSat-CZTI data to explore the hard X-ray characteristics of the $\gamma$-ray pulsar population. We report highly significant ($\sim 30\sigma$) detection of hard X-ray (60--380 keV) pulse profile of the Crab pulsar using $\sim$5000 ks of CZTI observations within 5 to 70 degrees of Crab position in the sky, using a custom algorithm developed by us. Using Crab as our test source, we estimate the off-axis sensitivity of the instrument and establish AstroSat-CZTI as a prospective tool in investigating hard X-ray characteristics of $\gamma$-ray pulsars as faint as 10 mCrab., Comment: Accepted for publication in the Journal of Astrophysics and Astronomy, 8 pages, 3 figures, 3 tables

We used a new spectral-fitting technique to identify a subpopulation of 6 narrow-band giant pulses from the Crab pulsar out of a total of 1578. These giant pulses were detected in 77 minutes of observations with the 46-m dish at the Algonquin Radio Observatory at 400-800 MHz. The narrow-band giant pulses consist of both main- and inter-pulses, thereby being more likely to be caused by an intrinsic emission mechanism as opposed to a propagation effect. Fast Radio Bursts (FRBs) have demonstrated similar narrow-band features while only little has been observed in the giant pulses of pulsars. We report the narrow-band giant pulses with $\Delta \nu / \nu$ on the order of 0.1, which is close to the value of 0.05 reported for the repeater FRB 20190711A. Hence, the connection between FRBs and giant pulses of pulsars is further established., Comment: 7 pages, 3 figures

We present updated measurements of the Crab pulsar glitch of 2019 July 23 using a dataset of pulse arrival times spanning $\sim$5 months. On MJD 58687, the pulsar underwent its seventh largest glitch observed to date, characterised by an instantaneous spin-up of $\sim$1 $\mu$Hz. Following the glitch the pulsar's rotation frequency relaxed exponentially towards pre-glitch values over a timescale of approximately one week, resulting in a permanent frequency increment of $\sim$0.5 $\mu$Hz. Due to our semi-continuous monitoring of the Crab pulsar, we were able to partially resolve a fraction of the total spin-up. This delayed spin-up occurred exponentially over a timescale of $\sim$18 hours. This is the sixth Crab pulsar glitch for which part of the initial rise was resolved in time and this phenomenon has not been observed in any other glitching pulsars, offering a unique opportunity to study the microphysical processes governing interactions between the neutron star interior and the crust., Comment: 5 pages, 3 figures

We have developed a photo-sensor for an optical photon counting imager for astronomy with high timing resolution. We customize a Multi Pixel Photon Counter as a monolithic Geiger avalanche photodiode array with a pixel size of 100 micro-meter. The prototype model consists of 4x4 pixels. Excellent timing response is achieved as fast as an order of nanosecond. We evaluate the basic performance of the sensor and confirm the gain linearity, uniformity and low dark count rates. We observe the Crab pulsar using this system with a 35-cm telescope, and successfully detected periodic pulses with a frequency consistent with that reported by radio observatory.

Two distinct relations between QPO frequency f (Low & High frequencies) and ´black hole´ mass M have been established by observation (Smith et al, 2018). M∙f = const with different constants for the L and H relation. The ´black hole´ attributed QPOs agree at high frequencies with the spin frequency of the most rapidly rotating neutron stars of the two classes of ´ordinary´ pulsars and the ms-pulsars. ´Ordinary´ pulsars fit the L-f relation and the ms-pulsars follow the H-f relation, permitting some calculation of their neutron star mass. This is illustrated for the Crab pulsar (´ordinary´) and the ms-pulsar J1748-244ad. This observation which suggests a physical link between the spin frequency of extremely rotating neutron stars and QPO frequencies of ´black holes´ is likely to be a consequence of the ´Aschenbach´ effect, being effective at Kerr parameters of a>0.9953 (Aschenbach, 2004).

We explore here a possible consequence of crustquake, namely, the generation of bursts of gravitational waves (GWs) due to a sudden change in the quadrupole moment (QM) of a deformed pulsar as a result of crustquake. The occurrence of crustquake in a rotating neutron star can play many important roles in neutron star (NS) dynamics. Here we propose that if a pulsar undergoes crustquake, then the generation of bursts of GWs is an inevitable consequence of crustquake. We have estimated the strain amplitudes ($h_0$) for such bursts of GWs and compared with the strain amplitudes for GWs produced in various other scenarios for isolated pulsars as suggested earlier in the literature. The values we obtain are comparable to those suggestions. We also estimate the order of magnitude for characteristic strain ($h_c$) and signal to noise ratio (SNR) for such bursts. For exotic quarks stars, a multifold enhancement of strain amplitudes is expected, which makes quark stars a potential source of gravitational waves as a result of crustquake. The absence of such waves may put constraints on such hypothetical stars, Comment: 8 pages, 2 figures, 1 table. Accepted for publication in Journal of Astrophysics and Astronomy. Comments are welcome!

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., ファイル公開：2021/06/19

The pulse profiles of the Crab pulsar (as well as some other pulsars) vary with time. They can lead to a major source of intrinsic timing noise, which lacks a detailed physical model. The phase separation Δ between the first left peak (P1) and the second right peak (P2) is a key parameter that shows the variations of pulse profiles for the Crab pulsar. It was found that the evolution of A has a tendency with increasing rates of 0.82° ± 0.25°, 0.80° ± 0.54°, and 0.77° ± 0.28° per century for the 2–6, 6–15, and 15–60 keV bands, respectively. Furthermore, the flux ratios (P2/P1) of X-ray pulse profiles in the three bands were calculated, and the derived flux ratios were consistent with the radio and X-ray measurements of the Insight-HXMT. In addition to discovering the physical origin of the pulse changes, the high-SNR X-ray pulse profiles were simulated in the annular gap model, and two model parameters (e.g., the maximum emission heights of the two peaks) were observed to slightly affect the variations of peak separation. We fitted the long-term variations of emission heights of the two peaks and discovered that the emission heights showed increasing tendencies with time. Variations of these emission heights induced a characteristic period derivative, and a complete formula for both the magnetic dipole radiation and wind-particle-induced variations of the moment of inertia was used for the pulsar’s spin-down to obtain the variation rate ά of the magnetic inclination angle, which was −1.60° per century. Intrinsic timing noise is observed to be mainly induced by the variations of pulse profiles, which might correlate with a characteristic spin period derivative arising from the fluctuations of the emission regions. This work will lay a foundation for understanding the origin of intrinsic timing noise and making high-precision timing models in the future.

Using the archival data of the Neutron star Interior Composition Explorer, we study the evolution of two-peak phase separations of the Crab pulsar’s X-ray pulse profiles, and present a possible method to predict the next glitch epochs of the Crab pulsar. The phase separations increased with time in a form of quasi-periodic fluctuation. We fit the evolution of the phase separations by using a magic wave function (MW model). It is found that the increasing rates of the phase separation are $9.798^{\circ}\pm8.997^{\circ}$ and $7.842^{\circ} \pm5.112^{\circ}$ per century at 0.3–1.2 keV and 2–6 keV bands, respectively. The fluctuation periods of the phase separation at 0.3–1.2 keV and 2–6 keV bands are $124.907\pm4.936$ and $121.478\pm3.149$ days, respectively. Using the fitting results, we predict that one to three glitch activities would be observed during January and September 2020. It could be useful for guiding the telescopes timely and effectively observe the glitch activities of the Crab pulsar in the future.

The Early Gaia Data Release 3 (EDR3) provides precise astrometry for nearly 1.5 billion sources across the entire sky. A few tens of these are associated with neutron stars in the Milky Way and Magellanic Clouds. Here, we report on a search for EDR3 counterparts to known rotation-powered pulsars using the method outlined in Antoniadis (2021). A cross-correlation between EDR3 and the ATNF pulsar catalogue identifies 41 close astrometric pairs ($< 0.5$ arcsec at the reference epoch of the pulsar position). Twenty six of these are related to previously-known optical counterparts, while the rest are candidate pairs that require further follow-up. Highlights include the Crab Pulsar (PSR B0531+21), for which EDR3 yields a distance of $2.08^{+0.78}_{-0.45}$ kpc (or $2.00_{-0.38}^{+0.56}$ kpc taking into account the dispersion-measure prior; errors indicate 95% confidence limits) and PSR J1638-4608, a pulsar thus-far considered to be isolated that lies within 0.056 arcsec of a Gaia source., To appear in RNAAS

The Virtual Telescope for X-ray Observations (VTXO) will use lightweight Phase Fresnel Lenses (PFLs) in a virtual X-ray telescope with $\sim$1 km focal length and with $\sim$50 milli-arcsecond angular resolution. VTXO is formed by using precision formation flying of two SmallSats: a smaller OpticsSat that houses the PFLs and navigation beacons while a larger DetectorSat contains an X-ray camera, a precision start tracker, and the propulsion for the formation flying. The baseline flight dynamics uses a highly elliptical supersynchronous orbit allow the formation to hold in an inertial frame around the 90,000 km apogee for 10 hours of the 32.5 hour orbit with nearly a year mission lifetime. VTXO's fine angular resolution enables measuring the environments close to the central engines of bright compact X-ray sources. This X-ray imaging capability allows for the study of the effects of dust scattering near to the central objects such as Cyg X-3 and GX 5-1, for the search for jet structure near to the compact object in X-ray novae such as Cyg X-1 and GRS 1915+105, and for the search for structure in the termination shock of in the Crab pulsar wind nebula. The VTXO SmallSat and instrument designs, mission parameters, and science performance are described. VTXO development was supported as one of the selected 2018 NASA Astrophysics SmallSat Study (AS$^3$) missions., Comment: 6 pages, 7 figures, corrected version, Proceedings Volume 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray; 114447V (2020). arXiv admin note: text overlap with arXiv:2006.12174

We report pulsar timing observations carried out in L-band with NTSC's 40-meter Haoping Radio Telescope (HRT), which was constructed in 2014. The observations were carried out using the pulsar machine we developed. Timing observations toward millisecond pulsar J0437-4715 obtains a timing residual (r.m.s) of 397ns in the time span of 284 days. And our observations successfully detected Crab pulsar's glitch that happened on July 23rd, 2019., Comment: 10 pages, 8 figures, accepted for publication in RAA (Res. Astron. Astrophys.)

In November 2016, China launched its first X-ray pulsar navigation satellite (XPNAV-1), in order to study the feasibility of using the regularly emitted X-ray signals from pulsars for spacecraft navigation. Over the past two years, a large amount of observations have been obtained by the XPNAV-1 satellites. The Crab pulsar (i.e. PSR0531+21) is its main observational source in which 3506627 s observations are made in 1251 orbits during 451 days. In order to study the X-ray pulsar observation performance of XPNAV-1 satellite in the past two years, those observations of Crab pulsar are processed fully. Each recovered pulse profile from daily observation have a mean similarity of 90.67% with the standard profile to be obtained from Rossi X-ray Timing Explorer (RXTE) satellite. The estimated pulse periods of Observation data of approximate to 3000 s is generally consistent with timing model of Fermi satellite and Crab ephemeris of Jodrell Bank Observatory (the mean errors of those two models are less than 10 ns). The observational results show that the pulsar data has been correctly received by the satellite, which is in good agreement with RXTE satellite and Jodrell Bank Observatory. Moreover, it is found that the X-ray detector on XPNAV-1 satellite has maintained a good technical status.

Glitches correspond to sudden jumps of rotation frequency ($\nu$) and its derivative ($\dot{\nu}$) of pulsars, the origin of which remains not well understood yet, partly because the jump processes of most glitches are not well time-resolved. There are three large glitches of the Crab pulsar, detected in 1989, 1996 and 2017, which were found to have delayed spin-up processes before the normal recovery processes. Here we report two additional glitches of the Crab pulsar occurred in 2004 and 2011 for which we discovered delayed spin up processes, and present refined parameters of the largest glitch occurred in 2017. The initial rising time of the glitch is determined as $, Comment: 25 pages, 8 figures

We present 3D full-sphere supernova simulations of non-rotating low-mass (~9 Msun) progenitors, covering the entire evolution from core collapse through bounce and shock revival, through shock breakout from the stellar surface, until fallback is completed several days later. We obtain low-energy explosions [~(0.5-1.0)x 10^{50} erg] of iron-core progenitors at the low-mass end of the core-collapse supernova (LMCCSN) domain and compare to a super-AGB (sAGB) progenitor with an oxygen-neon-magnesium core that collapses and explodes as electron-capture supernova (ECSN). The onset of the explosion in the LMCCSN models is modelled self-consistently using the Vertex-Prometheus code, whereas the ECSN explosion is modelled using parametric neutrino transport in the Prometheus-HOTB code, choosing different explosion energies in the range of previous self-consistent models. The sAGB and LMCCSN progenitors that share structural similarities have almost spherical explosions with little metal mixing into the hydrogen envelope. A LMCCSN with less 2nd dredge-up results in a highly asymmetric explosion. It shows efficient mixing and dramatic shock deceleration in the extended hydrogen envelope. Both properties allow fast nickel plumes to catch up with the shock, leading to extreme shock deformation and aspherical shock breakout. Fallback masses of 40 km/s and a NS spin period of ~30 ms, both not largely different from those of the Crab pulsar at birth., Comment: 47 pages, 27 figures, 6 tables; minor revisions, accepted by MNRAS

It is an open question whether glitch activity in individual pulsars varies on decadal time-scales. The Crab pulsar has experienced 23 spin-up glitches in the last 36 years, interrupting an otherwise monotonic deceleration. A homogeneous Poisson process, i.e. a process with constant rate, is not sufficient to describe the time-ordered distribution of glitch epochs in the Crab pulsar. There are signs of clustering at the $2\sigma$ level when testing with Ripley's $K$ function. Two alternative, inhomogeneous models with one and two step-wise rate changes are found to have higher relative evidence (Bayes factors of 1.74 and 2.86 respectively) than the homogeneous Poisson process. The distinction between clustering, where events are correlated, and rate variation is discussed. The implications for glitch microphysics, in particular trigger mechanisms based on avalanche processes, are briefly discussed., Comment: MNRAS accepted. 9 pages, 6 figures

We discusse the current X-ray observation results of Crab pulsar obtained with the Time-resolved soft X-ray spectrometer, X-ray pulsar navigation 1 satellite launched on Nov. 10, 2016, summarize the 162 observations of the TSXS from MJD 57709 to MJD 57872, and introduce the propositional method of data reduction. We compare these observation results in the 0.5–9.0 keV energy band with the radio timing parameters by folding the profiles with radio timing ephemerides derived from Jodrell Bank and estimating the phase delay results. The statistical error of post fit time correction is 55.94 μs (root mean square). These achievements verify the effectiveness of the Time-resolved soft X-ray spectrometer and laid the foundation of the future work of the X-ray pulsar navigation 1 mission.

Pulsar glitches are attributed to the sudden re-coupling of very weakly coupled large scale superfluid components in the neutron star interior. This process leads to rapid exchange of angular momentum and an increase in spin frequency. The transfer of angular momentum is regulated by a dissipative mutual friction, whose strength defines the spin-up timescale of a glitch. Hence, observations of glitch rises can be used to shed light on the dominant microphysical interactions at work in the high density interior of the star. We present a simple analytical model, complemented with more detailed numerical simulations, which produces a fast spin-up followed by a more gradual rise. Such features are observed in some large glitches of the Crab pulsar, including the largest recent glitch of 2017. We also use observations to constrain the mutual friction coefficient of the glitch-driving region for two possible locations: the inner crust and outer core of the star. We find that the features of Crab glitches require smaller values of the mutual friction coefficient than those needed to explain the much faster Vela spin-ups. This suggests a crustal origin for the former but an outer core contribution for the latter.

A model for the source of microwave bursts from the Crab pulsar in the form of a current sheet with a transversemagnetic field has been investigated. The emission generation mechanism is based on the excitation of plasma waves at the double plasma resonance frequencies in a nonrelativistic nonequilibrium plasma followed by their scattering into electromagnetic waves that escape from the current sheet into the neutron star magnetosphere. The basic parameters of the source explaining the observed characteristics of quasi-harmonic bursts in the interpulses of radio emission from this pulsar have been established.

This paper develops a timing solution for the X-ray pulsar timing model without the use of the initial radio model parameters. First, we address the problem of phase ambiguities for the pre-fit residuals in the construction of pulsar timing model. To improve the estimation accuracy of the pulse time of arrival (TOA), we have deduced the general form of test statistics in Fourier transform, and discussed their estimation performances. Meanwhile, a fast maximum likelihood (FML) technique is presented to estimate the pulse TOA, which outperforms cross correlation (CC) estimator and exhibits a performance comparable with maximum likelihood (ML) estimator in spite of a much less reduced computational complexity. Depending on the strategy of the difference minimum of pre-fit residuals, we present an effective forced phase-connected technique to achieve initial model parameters. Then, we use the observations with the Rossi X-Ray Timing Explorer (RXTE) and X-ray pulsar navigation-I (XPNAV-1) satellites for experimental studies, and discuss main differences for the root mean square (RMS) residuals calculated with the X-ray and radio ephemerides. Finally, a chi-square value (CSV) of pulse profiles is presented as a complementary indicator to the RMS residuals for evaluating the model parameters. The results show that the proposed timing solution is valid and effective, and the obtained model parameters can be a reasonable alternative to the radio ephemeris.

Additional relative to the main pulse and interpulse HF-components in the radiation of a Crab pulsar are observed in the same range where the interpulse shift occurs (Moffett, Hankins, 1996; Hankins, Jones and Eilek, 2015). The latter is explained by the specular reflection from a neutron star surface of returned positron radiation in an inclined magnetic field (Kontorovich, Trofimenko, 2017). Therefore the additional HF-components, which are substantially shifted in the rotation phase of the pulsar, can be naturally associated with (nonlinear) reflection – diffraction on the surface periodic structure. It is significant that such a structure can arise as a result of stimulated scattering on surface waves, and this scattering can occur under conditions of plasmon-polariton resonance associated with the diffraction spectrum sliding along the surface, which significantly reduces the stimulated scattering threshold. The large width of the components is explained by the continuous radiation spectrum of returned positrons incident on the surface. Although this mechanism found itself in the Crab pulsar due to a unique combination of parameters at centimeter wavelengths, it is completely common to pulsars. Another possibility – diffraction by a periodic structure due to the action of constant fields (electric or magnetic) − requires some separate consideration. The content of the report corresponds to publications (Kontorovich et al., 2018).

Slightly more than 30 years ago, Whipple detection of the Crab Nebula was the start of Very High Energy gamma-ray astronomy. Since then, gamma-ray observations of this source have continued to provide new surprises and challenges to theories, with the detection of fast variability, pulsed emission up to unexpectedly high energy, and the very recent detection of photons with energy exceeding 1 PeV. In this article we review the impact of gamma-ray observations on our understanding of this extraordinary accelerator., 27 Pages, 8 Figures

The Crab pulsar is a typical example of a young, rapidly spinning, strongly magnetized neutron star that generates broadband electromagnetic radiation by accelerating charged particles to near light speeds in its magnetosphere 1 . Details of this emission process so far remain poorly understood. Measurement of polarization in X-rays, particularly as a function of pulse phase, is thought to be a key element necessary to unravel the mystery of pulsar radiation2–4. Such measurements are extremely difficult, however: to date, Crab is the only pulsar to have been detected in polarized X-rays5–8 and the measurements have not been sensitive enough to adequately reveal the variation of polarization characteristics across the pulse 7 . Here, we present the most sensitive measurement to date of polarized hard X-ray emission from the Crab pulsar and nebula in the 100–380 keV band, using the Cadmium–Zinc–Telluride Imager 9 instrument on-board the Indian astronomy satellite AstroSat 10 . We confirm with high significance the earlier indication6,7 of a strongly polarized off-pulse emission. However, we also find a variation in polarization properties within the off-pulse region. In addition, our data hint at a swing of the polarization angle across the pulse peaks. This behaviour cannot be fully explained by the existing theoretical models of high-energy emission from pulsars.

A statistical study of the glitch population and the behavior of the glitch activity across the known population of neutron stars is presented. A constant ratio between the glitch activity and the spin-down rate $\dot{\nu }_{\rm {g}}$/|$\dot{\nu }$| = 0.010 ± 0.001 is consistent with the behavior of all rotation-powered pulsars and magnetars. This relation is dominated by large glitches (Δν ≳ 10 μ Hz), which occur at a rate directly proportional to |$\dot{\nu }$|. The only exception are the rotation-powered pulsars with the highest values of |$\dot{\nu }$|, such as the Crab pulsar and PSR B0540–69, which exhibit a much smaller glitch activity, intrinsically different from each other and from the rest of the population. This contribution is based on the work done by Fuentes et al. (2017) “The glitch activity of neutron stars”, accepted for publication in A&A.

The pulsed radiation from the Crab pulsar consists of the main pulse (MP) and inter pulse (IP), as well as of the extra pulse components appearing at certain frequencies. It has been studied in many frequencies and contains unique information, which is not available for the majority of the pulsars. One of the mysteries of these data, found by Moffett and Hankins twenty years ago, is the shift of the IP at high radio frequencies compared to lower ones and return to its previous position in the more high-frequency optical and X-ray range. We propose the explanation of these mysterious changes with the frequency as a reflection of radiation by relativistic positrons from the stellar surface. The magnetic field of the pulsar in the pole must be inclined to the surface of the star and affects on the discussed processes.

Measurements with a CubeSat gas pixel detector reveal a change in the Crab pulsar polarization after a glitch in the spin period, suggesting that starquakes alter the magnetosphere.

This work questions our relationship to time and cosmic phenomena that occur on scales in space and time far beyond human perception. In UNRESOLVED SUN / SOLEIL IRRESOLU, these phenomena are made tangible by a thin disc of green fluorescent liquid inhabited by mobile and ephemeral vibrations, in an unusual visual and sound landscape. Thanks to a complex optical device and precise adjustment, the light that passes through the layer is projected onto the adjacent wall in the form of a large orange disc deformed by storms. The space deployed in the imagination results more from music than from choreography. The small green fluorescent disc and the large projection then behave like a sound material composed of textures and rhythms. The sonic material is derived from the real and historical astrophysical observation of the crab Pulsar, a remnant neutron star of the gigantic explosion of a supernova never reported, the first object in space observed with a radio telescope to pulse at audible frequency.

The Crab Nebula is the most studied object in the gamma-ray sky. Yet there are many important unanswered questions on the interrelation between the gamma-ray emission from the Pulsar and the Nebula. We present the results of 112 hours of observations conducted with the MAGIC Telescopes by using the stereoscopic Sum-Trigger-II, a novel trigger system essentially halving the lower energy threshold of the telescopes. In order to process the data, a dedicated analysis aiming for the lowest energies is applied. From these observations, we detect pulsed gamma-ray emission down to 27 GeV, which allows us to perform a detailed spectral study. Due to the sound statistical basis, we perform short-time variability studies of the Pulsar and test possible correlations with the nebular flares detected by Fermi-LAT.

Giant pulses (GPs) are extremely bright individual pulses of radio pulsar. In microbursts of Crab pulsar, which is an active GP emitter, zebra-pattern-like spectral structures are observed, which are reminiscent of the “zebra bands” that are observed in type IV solar radio flares. However, band spacing linearly increases with the band center frequency of ∼5-30 GHz. In this study, we propose that the Crab pulsar GP can originate from the coherent instability of plasma near a light cylinder. Further, the growth of coherent instability can be attributed to the resonance observed between the cyclotron-resonant-excited wave and the background plasma oscillation. The particles can be injected into the closed-field line regions owing to magnetic reconnection near a light cylinder. These particles introduce a large amount of free energy that further causes cyclotron-resonant instability, which grows and amplifies radiative waves at frequencies close to the electron cyclotron harmonics that exhibit zebra-pattern-like spectral band structures. Further, these structures can be modulated by the resonance between the cyclotron-resonant-excited wave and the background plasma oscillation. In this scenario, the band structures of the Crab pulsar can be well fitted by a coherent instability model, where the plasma density of a light cylinder should be ~1013-15 cm−3, with an estimated gradient of >5:5 × 105 cm−4. This process may be accompanied by high-energy emissions. Similar phenomena are expected to be detected in other types of GP sources that have magnetic fields of ≃ 106 G in a light cylinder.

Gravitational waves (GWs) can offer a novel window into the structure and dynamics of neutron stars. Here we present the first search for long-duration quasi-monochromatic GW transients triggered by pulsar glitches. We focus on two glitches observed in radio timing of the Vela pulsar (PSR J0835-4510) on 12 December 2016 and the Crab pulsar (PSR J0534+2200) on 27 March 2017, during the Advanced LIGO second observing run (O2). We assume the GW frequency lies within a narrow band around twice the spin frequency as known from radio observatons. Using the fully-coherent transient-enabled F-statistic method to search for transients of up to four months in length. We find no credible GW candidates for either target, and through simulated signal injections we set 90% upper limits on (constant) GW strain as a function of transient duration. For the larger Vela glitch, we come close to beating an indirect upper limit for when the total energy liberated in the glitch would be emitted as GWs, thus demonstrating that similar post-glitch searches at improved detector sensitivity can soon yield physical constraints on glitch models., Comment: 10 pages, 3 figures (incl. appendices). Updated to match version accepted by PRD and fixed a few references

We present statistical analysis of a fluence limited sample of over 1100 giant pulses from the Crab pulsar, with fluence > 130 Jy ms at ~1330 MHz. These were detected in ~260 hours of observation with the National Centre for Radio Astrophysics (NCRA)-15m radio telescope. We find that the pulse energy distribution follows a power law with index $\alpha\approx$-3 at least up to a fluence of ~5 Jy s. The power law index agrees well with that found for lower energy pulses in the range 3-30 Jy ms. The fluence distribution of the Crab pulsar hence appears to follow a single power law over ~3 orders of magnitude in fluence. We do not see any evidence for the flattening at high fluences reported by earlier studies. We also find that at these fluence levels, the rate of giant-pulse emission varies by as much as a factor of ~5 on time-scales of a few days, although the power law index of the pulse-energy distribution remains unchanged. The slope of the fluence distribution for Crab giant pulses is similar to that recently determined for the repeating FRB 121102. We also find an anti-correlation between the pulse fluence and the pulse width, so that more energetic pulses are preferentially shorter., Comment: 5 pages, 6 figures

A low dispersion spectrograph-cum-imager has been developed and assembled in ARIES, Nainital. The optical design of the spectrograph consists of a collimator and a focal reducer converting the f/9 beam from the 3.6-m Devasthal optical telescope to a nearly f/4.3 beam. The instrument is capable of carrying out broad-band imaging, narrow-band imaging and low-resolution ({\lambda}/{\Delta}{\lambda}, Comment: 8 pages, 6 figures, Accepted in Current Science (CSci; Indian Academy of Sciences)

[Aims] The aim of this study is to search for evidence of a common emission engine between radio giant pulses (GPs) and very-high-energy (VHE, E > 100 GeV) γ-rays from the Crab pulsar., [Methods] We performed 16 h of simultaneous observations of the Crab pulsar at 1.4 GHz with the Effelsberg radio telescope and the Westerbork Synthesis Radio Telescope (WSRT), and at energies above 60 GeV we used the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes. We searched for a statistical correlation between the radio and VHE γ-ray emission with search windows of different lengths and different time lags to the arrival times of a radio GP. A dedicated search for an enhancement in the number of VHE γ-rays correlated with the occurrence of radio GPs was carried out separately for the P1 and P2 phase ranges, respectively., [Results] In the radio data sample, 99444 radio GPs were detected. We find no significant correlation between the GPs and VHE photons in any of the search windows. Depending on phase cuts and the chosen search windows, we find upper limits at a 95% confidence level on an increase in VHE γ-ray events correlated with radio GPs between 7% and 61% of the average Crab pulsar VHE flux for the P1 and P2 phase ranges, respectively. This puts upper limits on the flux increase during a radio GP between 12% and 2900% of the pulsed VHE flux, depending on the search window duration and phase cuts. This is the most stringent upper limit on a correlation between γ-ray emission and radio GPs reported so far., The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2015-69818-P, FPA2012-36668, FPA2015-68378-P, FPA2015-69210-C6-2-R, FPA2015-69210-C6-4-R, FPA2015-69210-C6-6-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2015-71662-C2-2-P, CSD2009-00064), and the Japanese JSPS and MEXT is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia “Severo Ochoa” SEV-2012-0234 and SEV-2015-0548, and Unidad de Excelencia “María de Maeztu” MDM-2014-0369, by the Croatian Science Foundation (HrZZ) Project 09/176 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq and FAPERJ.

We report on X-ray emission properties of the Crab pulsar(PSR B0531+21) using observations by Insight-HXMT during its first year after launch. We obtained high signal-to-noise profiles in the X-ray energy band 11-250 keV. We have confirmed an increase in the flux ratio of the second peak over the main peak with increasing energy, consistent with other missions. The separation of the two peaks shows no significant trend with increasing energy. The phase-averaged spectrum, fitted by a logpar model, and the phase-resolved spectra of the Crab pulsar, fitted by a powerlaw in the different energy bands of HXMT, are consistent with RXTE and NuSTAR in that photon indices evolve as a function of phase as well as a function of energy contributing to a broadband modeling., Comment: 10 pages, 5 figures, accepted for publication in RAA

Isolated pulsars are ideal sources for polarisation studies since the radiation from pulsars generally covers a wide range of wavelengths from radio to very-high-energy γ-rays and the pulsed emission is closely tied to the local magnetic field direction. Although radio polarisation data exist for many pulsars, polarisation measurements at higher energies exist for only six sources. All six of these have optical polarisation measurements while only the Crab pulsar has measured polarisation in the X-ray band. One member of a small group of pulsars only visible at optical and X-ray wavelengths, thought to be powered by thermal emission from the cooling neutron star surface, has detected optical polarisation. This chapter will review the current multi-wavelength polarisation observations and the theoretical modelling by which we can probe the pulsar magnetosphere structure and emission mechanisms.

Using the archive data from the Rossi X-ray Timing Explorer ({\sl RXTE}), we have studied the evolution of the X-ray profile of the Crab pulsar in a time span of 11 years. The X-ray profiles, as characterized by a few parameters, changed slightly but significantly in these years: the separation of the two peaks increased with a rate $0.88\pm0.20\,\textordmasculine$\,per century, the flux ratio of the second pulse to the first pulse decreased with $(3.64\pm0.86)\times10^{-2}$\,per century, and the pulse widths of the two pulses descended with $1.44\pm0.15\,\textordmasculine$\, and $1.09\pm0.73\,\textordmasculine$\,per century, respectively. The evolutionary trends of the above parameters are similar to the radio results, but the values are different. We briefly discussed the constraints of these X-ray properties on the geometry of the emission region of this pulsar.