Pulse Profile Research Articles

Polarization measurements of Arecibo-sky pulsars: Faraday rotations and emission-beam analyses

ABSTRACT We present Faraday rotation measure (RM) values derived at L and P bands as well as some 60 Stokes-parameter profiles, both determined from our long-standing Arecibo dual-frequency pulsar polarimetry programmes. Many of the RM measurements were carried out towards the inner Galaxy and the anticentre on pulsars with no previous determination, while others are remeasurements intended to confirm or improve the accuracy of existing values. Stokes-parameter profiles are displayed for the 58 pulsars for which no meaningful Stokes profile at lower frequency is available and 4 without a high-frequency pair. This is a population that includes many distant pulsars in the inner Galaxy. A number of these polarized pulse profiles exhibit clear interstellar-scattering tails; none the less, we have attempted to interpret the associated emission-beam structures and to provide morphological classifications and geometrical models where possible.

A study of the light bending phenomenon under full general relativity for a pulsar in a binary with a Schwarzschild black hole

ABSTRACT The values of the bending delays in the signal of a radio pulsar in a binary with a stellar mass black hole as a companion have been calculated accurately within a full general relativistic framework considering the Schwarzchid spacetime near the companion. The results match with the pre-existing approximate analytical expressions unless both of the orbital inclination angle and the orbital phase are close to 90°. For such a case, the approximate analytical expressions underestimate the value of the bending delay. On the other hand, for systems like the double pulsar, those expressions are valid throughout the orbital phase, unless its inclination angle is very close to 90°. For a pulsar-black hole binary, the bending phenomenon also increases the strength of the pulse profile and sometimes can lead to a small low intensity tail.

RX J0440.9+4431: another supercritical X-ray pulsar

ABSTRACT In the beginning of 2023, the Be transient X-ray pulsar RX J0440.9+4431 underwent a first-ever giant outburst observed from the source peaking in the beginning of February and reaching peak luminosity of ≈4.3 × 1037 erg s−1. Here, we present the results of a detailed spectral and temporal study of the source based on NuSTAR, Swift, INTEGRAL, and NICER observations performed during this period and covering wide range of energies and luminosities. We find that both the pulse profile shape and spectral hardness change abruptly around ≈2.8 × 1037 erg s−1, which we associate with a transition to supercritical accretion regime and erection of the accretion column. The observed pulsed fraction decreases gradually with energy up to 20 keV (with a local minimum around fluorescence iron line), which is unusual for an X-ray pulsar, and then rises rapidly at higher energies with the pulsations significantly detected up to ≈120 keV. The broad-band energy spectra of RX J0440.9+4431 at different luminosity states can be approximated with a two-hump model with peaks at energies of about 10–20 and 50–70 keV previously suggested for other pulsars without additional features. In particular, an absorption feature around 30 keV previously reported and interpreted as a cyclotron line in the literature appears to be absent when using this model, so the question regarding the magnetic field strength of the neutron star remains open. Instead, we attempted to estimate field using several indirect methods and conclude that all of them point to a relatively strong field of around B ∼ 1013 G.

Investigations of the High-Power, Single-Frequency, Sub-Microseconds, 1548-nm Fiber Laser Based on the Optical Pulse Modulation

High-power, single-frequency lasers are important in the applications of coherent optical communication, Doppler wind lidar, and remote sensing. Here, a 10-kHz, 353-μJ, single-frequency, 574-ns, 1548-nm fiber laser system was demonstrated based on the optical pulse modulation. The 1548-nm, single-frequency seed laser with the linewidth of 1.25 kHz was modulated by two acousto-optic modulators (AOMs) into a 10-kHz pulsed laser. Two cascaded fiber amplifiers were spliced after the AOMs to scale up the pulse energy. The amplified spontaneous emission (ASE) was inhibited by the multistage amplification construction and the optical bandpass filters. A customized pulse profile was proposed to pre-compensate the temporal modulation and inhibit the stimulated Brillouin scattering (SBS) effect. The pulse duration of the amplified single-frequency pulse was 574 ns, with the peak power of 753 W. A numerical model was also built for investigating the dynamic of the interaction process inside the power amplifier. The simulated results indicate the maximum output power of the 10-kHz, customized single-frequency laser can be 3.984 W with a pulse duration of 381 ns.

Laser-induced breakdown spectroscopy using modulated ns-laser pulses for multi-property measurements in high-pressure combustion environments

The present work proposes a novel method to improve the calibration accuracy of laser-induced breakdown spectroscopy (LIBS) in high-pressure combustion environments. Typically, optical plasma breakdown suffers from instability in highly pressurized environments, and the plasma emits photons of noisy and broadened spectra that are unusable for extracting quantitative property information. An improved plasma emission spectrum signal is obtained by modulating or chopping the pulse width of a fundamental 10 Hz Nd:YAG laser pulse by limiting the stochastic inverse-Bremsstrahlung (IB) photon absorption process. The modulated pulse duration is decreased from 9.2 ns to 5 ns utilizing a simple optical setup prior to being focused into a high-pressure combustor. In order to evaluate the impact of the modulated temporal laser pulse profile on the plasma emission, Proper Orthogonal Decomposition (POD) is applied to the emission spectra collected over a customized flat flame burner with varied composition and pressure. POD is capable of decomposing property-sensitive spectrum components that determine the accuracy of the spectrum calibration for property measurements using LIBS. The POD-analyzed database comprises 50 flame cases with pressure and equivalence ratios ranging from 1 to 10 bars and 0.7 to 1.1, respectively. Two Reduced-Order Models (ROMs) are trained with the collected spectra; modulated and original pulse, to predict three distinct flame properties; pressure, equivalence ratio, and adiabatic flame temperature. The output model estimates pressure, equivalence ratio and adiabatic flame temperature with an improved accuracy of 8%, 7% and 55%, respectively when the ROM is trained with chopped spectra over the calibrated pressure range. This is because the reduced pulse width in general lowers the signal level of broadband plasma emission that is sensitive to pressure. The POD-aided spectrum analyses suggest that flexible pulse modulation helps to improve the calibration accuracy in a broad gas density range with varied pressure and temperature.

Research on Channelization Techniques of Radio Astronomical Wideband Signal with Oversampled Polyphase Filter Banks

Digital channelization decomposes a wideband signal into multiple adjacent sub-bands using Parallel Technology. Channelization can effectively reduce the pressure on the radio astronomy digital backends system and make wideband signal processing possible. Aiming at the problems of signal attenuation at sub-band edge, spectral leakage and aliasing encountered in wideband signal channelization, algorithms to reduce the problems are studied. We design a Critically Sampled Polyphase Filter Bank (CS-PFB) based on the Finite Impulse Response digital filter with a Hamming Window and systematically analyze the frequency response characteristics of the CS-PFB. Based on the channelized structure of the CS-PFB, an OverSampled Polyphase Filter Bank (OS-PFB) is designed by data reuse, and the filtering frequency response characteristics of CS-PFB and OS-PFB are compared and analyzed. Using the wideband baseband data generated by the CASPSR (Collaboration for Astronomy Signal processing and electronics research Parkes Swinburne Recorder), we implement sub-band division and 16-band output of these data based on the 2× oversampling OS-PFB, and the problem of spectrum inversion in the sub-bands is corrected. After removing 25% of redundant data in the head and tail of each sub-band, we recombine the sub-bands into a wideband. The wideband signal is almost identical to the original observed signal. Therefore, the experimental results show that the OS-PFB can improve the channel response. For the 400 MHz baseband data of J0437-4715, we compare the pulse profile obtained from the original baseband data with the pulse profile obtained after the channelization and recombination. The phase and amplitude information of the pulse profiles are consistent, which verifies the correctness of our channelization algorithm.

Timing and Single-pulse Study of Pulsar J1909+0122 Discovered by CRAFTS

We report the discovery of PSR J1909+0122 by the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) as part of the Commensal Radio Astronomy FAST Survey. PSR J1909+0122 has a spin period of 1.257 s and a dispersion measure of 186.2 pc cm−3. The averaged pulse profile shows two distinct components. We performed a single-pulse study based on a one-hour observation at 1.25 GHz on 2021 August 23. We used a threshold of 5σ ep to measure the nulling fraction (NF) as 63% ± 1.5%. The longitude-resolved fluctuation spectra and fast Fourier transform spectra of the binary sequences revealed the quasi-periodicity of nulling with a period of 30 rotation periods. We examined the reliability of the periodicity by comparing it to random noise injection. The NF, , and modulation periodicity P M of PSR J1909+0122 were compared with other periodic nulling pulsars, showing that the source of J1909+0122 has the second largest NF in the population. Long-term timing observations over six months were used to derive the phase-connected ephemeris of this pulsar. The measured P and values disfavor dipolar geometry for polar gap models, and the prediction for a space-charge-limited flow model in the case of inverse Compton scattering is only just above the death line. In this work, PSR J1909+0122 has revealed possible correlations between nulling behavior and pulsar properties, which will help to shed light on the pulsar emission mechanism and its temporal evolution in future observations.

PSR J0026−1955: A curious case of evolutionary subpulse drifting and nulling

ABSTRACT PSR J0026−1955 was independently discovered by the Murchison Widefield Array recently. The pulsar exhibits subpulse drifting, where the radio emission from a pulsar appears to drift in spin phase within the main pulse profile, and nulling, where the emission ceases briefly. The pulsar showcases a curious case of drift rate evolution as it exhibits rapid changes between the drift modes and a gradual evolution in the drift rate within a mode. Here, we report new analysis and results from observations of J0026−1955 made with the upgraded Giant Metrewave Radio Telescope at 300–500 MHz. We identify two distinct subpulse drifting modes: A and B, with mode A subcategorized into A0, A1, and A2, depending upon the drift rate evolutionary behaviour. Additionally, the pulsar exhibits short and long nulls, with an estimated overall nulling fraction of ∼58 per cent, which is lower than the previously reported value. Our results also provide evidence of subpulse memory across nulls and a consistent behaviour where mode A2 is often followed by a null. We investigate the drift rate modulations of J0026−1955 and put forward two different models to explain the observed drifting behaviour. We suggest that either a change in polar gap screening or a slow relaxation in the spark configuration could possibly drive the evolution in drift rates. J0026−1955 belongs to a rare subset of pulsars which exhibit subpulse drifting, nulling, mode changing, and drift rate evolution. It is therefore an ideal test bed for carousel models and to uncover the intricacies of pulsar emission physics.

Point symmetries of the Lie of the complex Ginzburg-Landau equation

A soliton is a nonlinear single moving wave that retains its shape and velocity during its movement, that is, it is a constant formation, and when it collides with isolated waves similar to itself, the phenomenon of a mutual phase shift of two waves occurs, that is, the only result of the interaction of solitons may be some kind of shift in phase. In this paper, we will study the distribution of the soliton constant in the complex Ginzburg-Landau equation (CGL) with a nonlinear regime that focuses on itself in the presence of a symmetric Gaussian potential. For many decades, nonlinear systems have attracted researchers theoretically and experimentally with their rich dynamic characteristics. Such nonlinear systems can be conservative (closed) or dissipative (open), and both support solitons. A soliton is nothing but a constant profile of light pulses in an optical system. In the case of a dissipative nonlinear system, in addition to dispersion and nonlinear equilibrium, it is possible to continuously propagate a light pulse or soliton to achieve a balance between dissipation (loss) and gain. This means that a dissipative system cannot support continuous families of solitons similar to conservative systems. In other words, in a dissipative system, the distribution of solitons can be determined by the parameters of the system, while in a conservative system it is determined by the input optical pulse. This increases the experimental feasibility of determining the area of a stable soliton in a dissipative system by simply manipulating the system.

Study of recently discovered Be/X-ray pulsar MAXI J0655-013 using NuSTAR

Abstract We study the recently discovered Be/X-ray pulsar MAXI J0655–013 using the 2022 NuSTAR observations. The paper is the first detailed study of the timing and spectral properties of the source. The pulse profiles of the pulsar vary with energy. The pulsed fraction is found to increase monotonically with energy. In between the two NuSTAR observations, a large spin-up rate of ∼ -1.23 s d−1 is observed, which can be due to large spin-up torque acting on the pulsar during an outburst. Such a large spin-up rate is observed for the first time in an X-ray pulsar during an outburst. The variation of the spin period with time can be employed to obtain the orbital parameters of the binary system, and we found the orbital period to be ∼ 27.9 d. The second NuSTAR observation is done in a low luminosity state (LX ∼ 3.9 × 1034 erg s−1 ). We have detected the pulsation of the pulsar in such a low luminosity state. In such a low luminosity state, the pulsar MAXI J0655–013 might be accreting from the cold disk.

X-ray polarimetry of X-ray pulsar X Persei: another orthogonal rotator?

ABSTRACT X Persei is a persistent low-luminosity X-ray pulsar of period of ≈ 835 s in a Be binary system. The field strength at the neutron star surface is not known precisely, but indirect signs indicate a magnetic field above 1013 G, which makes the object one of the most magnetized known X-ray pulsars. Here we present the results of observations X Persei performed with the Imaging X-ray Polarimetry Explorer (IXPE). The X-ray polarization signal was found to be strongly dependent on the spin phase of the pulsar. The energy-averaged polarization degree in 3–8 keV band varied from several to ∼20 per cent over the pulse with a phase dependence resembling the pulse profile. The polarization angle shows significant variation and makes two complete revolutions during the pulse period, resulting in nearly nil pulse-phase averaged polarization. Applying the rotating vector model to the IXPE data we obtain the estimates for the rotation axis inclination and its position angle on the sky, as well as for the magnetic obliquity. The derived inclination is close to the orbital inclination, reported earlier for X Persei. The polarimetric data imply a large angle between the rotation and magnetic dipole axes, which is similar to the result reported recently for the X-ray pulsar GRO J1008−57. After eliminating the effect of polarization angle rotation over the pulsar phase using the best-fitting rotating vector model, the strong dependence of the polarization degree with energy was discovered, with its value increasing from 0 at ∼2 keV to 30per cent at 8 keV.

Hyperbolic limit on the early arrival time of bright pulses from PSR J0835−4510 (Vela)

ABSTRACT Astronomers have studied the Vela pulsar (PSR J0835−4510) for decades. This study analyses almost 100 h of single-pulse data collected over three consecutive days in 2016 and 2020. The work investigates the fascinating phenomena of the earlier arrival of brighter pulses with their increase in peak intensity. We found a hyperbolic relation between them by constructing integrated pulse profiles using flux density intervals and examining the relationship between pulse arrival time and intensity. We identified a phase limit of −0.85 ± 0.0109 ms for the earliest arrival of the brightest pulses. This study offers exciting prospects for further exploring the emission regions responsible for the Vela pulsar’s regular pulses and giant micro-pulses.

Optimal population transfer using adiabatic rapid passage in the presence of drive-induced dissipation

Adiabatic rapid passage (ARP) is extensively used to achieve efficient transfer or inversion of populations in quantum systems. Landau and Zener accurately estimated the transfer probability of ARP for a closed system and showed that this probability improved with higher drive amplitude. Recently, we found that, in open quantum systems, applying a strong drive can give rise to significant drive-induced dissipation (DID). Here, we investigate the effect of DID on the performance of ARP that is implemented using a linearly chirped pulse on a two-level system. From the Landau-Zener formula, the population transfer was known to be enhanced with increasing drive amplitude. However, here we show that, beyond a threshold value of the drive amplitude, the transfer probability is reduced because of the detrimental effect of DID. We show that the competition between the two processes results in an optimal behavior of the population transfer. We also propose a phenomenological model that helps explain such nonmonotonic behavior of the transfer. Using this model, we estimate the optimum time at which the maximum population transfer occurs. We extend the analysis for rectangular as well as Gaussian pulse profiles and conclude that a Gaussian pulse outperforms a rectangular pulse.

Key Modes of Ignition and Maintenance of Corona Discharge in Air

Theoretical and experimental studies of various modes of corona discharge operation in atmospheric pressure air are presented in this short review. The original results of modeling negative corona discharges are presented, taking into account the non-stationary plasma-chemical kinetics of charged particles in air plasma. The space–time evolution of the discharge in needle-to-plane geometry is investigated and analyzed. Several stages of discharge development are revealed from the moment of initiation of a low-negative current corona to the quasi-stationary mode of a glow discharge. Experimental data of the authors are presented. Modern technology and diagnostic equipment with a wide variation of the main parameters (the shape and polarity of the applied voltage, the type of gap, etc.) was used. The measurement of the optical characteristics of the plasma glow was carried out with high spatial resolution. Corona discharge current pulse profiles in the air at atmospheric pressure have been recorded with subnanosecond time resolution. With a positive polarity of the pin electrode and high voltage, a transition from a spherical streamer initiating a corona discharge to a cylindrical streamer is shown. The author’s results are rigorously evaluated through a critical comparison with findings from other research groups.

Temporal and spectral study of the X-ray pulsar 2S 1553–542 during the 2021 outburst

We study the timing and spectral properties of the X-ray pulsar 2S 1553–542 using the NuSTAR and NICER during the outburst in January–February 2021. During the outburst, the spin period of the neutron star was $$P\sim 9.2822$$ s based on NuSTAR data. The pulse profiles are studied using different NICER observations, which implies that the profile is more or less sinusoidal with a single peak and the beaming patterns are dominated mainly by the pencil beam. The NICER spectra of the source are studied for different days of the outburst. They can be well described by a model consisting of a blackbody emission, power law and photoelectric absorption component. The variation of spectral parameters with luminosity is studied over the outburst. The photon index shows anti-correlation with luminosity below the critical luminosity, which implies that the source was accreting in the sub-critical accretion regime during the NICER observations. We also report the anti-correlation between pulsed fraction (PF) and luminosity of the 2S 1553–542 using NICER observations. The evolution of spin-up rate with luminosity is studied during the outburst, which implies that both are strongly correlated. The torque-luminosity model is applied to estimate the magnetic field at different spin-up rates. The magnetic field is estimated to be $${\simeq }2.56 \times 10^{12}$$ G from the torque-luminosity model using the source distance of 20 kpc. The magnetic field is also estimated using the critical luminosity, consistent with our findings.

Single-pulse Emission Variation of Two Pulsars Discovered by FAST

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

NuSTAR investigation of X-ray variability and hard X-ray spectral properties in IGR J16320-4751 and IGR J16479-4514

Abstract We present the results obtained from a comprehensive timing and spectral study of two high mass X-ray binary sources using NuSTAR observations. These two sources, IGR J16320-4751 and IGR J16479-4514 were discovered by INTEGRAL and have been characterizated for the first time in the hard X-ray band (beyond 10 keV) in this work. In these sources, we observe the occurrence of intense X-ray flares, with average luminosities exceeding 1036 erg s−1. Our analysis reveals that these flares can be described consistently in the quasi-spherical accretion regime. The orbital phase of the first flare in NuSTAR observation of IGR J16479-4514 matches with the orbital phases of previous flares (φ = 0.35) in this source detected by other telescopes. We conclude that this flare occurs as a result of the periastron passage of the neutron star, rather than due to the presence of a corotating interaction region (CIR). Furthermore, from the energy-resolved pulse profile analysis of IGR J16320-4751, we find that the pulse fraction is lower in hard X-rays compared to the soft X-rays. We present the hard X-ray spectral parameters of these two sources using several standard spectral model components. We do not detect a cyclotron absorption feature in either target. We provide estimates to the surface magnetic field strength of NS in IGR J16320-4751 using two indirect methods. Lastly, we observe spectral hardening during flaring segments compared to the off-flaring segments which indicates that comptonization is more effective during the flaring segments.

Improving pulsar-timing solutions through dynamic pulse fitting

ABSTRACT Precision pulsar timing is integral to the detection of the nanohertz stochastic gravitational-wave background as well as understanding the physics of neutron stars. Conventional pulsar timing often uses fixed time and frequency-averaged templates to determine the pulse times of arrival, which can lead to reduced accuracy when the pulse profile evolves over time. We illustrate a dynamic timing method that fits each observing epoch using basis functions. By fitting each epoch separately, we allow for the evolution of the pulse shape epoch to epoch. We apply our method to PSR J1103−5403 and find evidence that it undergoes mode changing, making it the fourth millisecond pulsar to exhibit such behaviour. Our method, which is able to identify and time a single mode, yields a timing solution with a root-mean-square error of $1.343$ µs, a factor of 1.78 improvement over template fitting on both modes. In addition, the white-noise amplitude is reduced 4.3 times, suggesting that fitting the full data set causes the mode changing to be incorrectly classified as white noise. This reduction in white noise boosts the signal-to-noise ratio of a gravitational-wave background signal for this particular pulsar by 32 per cent. We discuss the possible applications for this method of timing to study pulsar magnetospheres and further improve the sensitivity of searches for nanohertz gravitational waves.

Significant texture and wear resistance improvement of TiN coatings using pulsed DC magnetron sputtering

Titanium nitride (TiN) coatings fabricated through reactive sputtering feature a suite of parameters capable of altering the microstructure and properties. Here, we explore the influence of bipolar pulsed direct current (DC) magnetron sputtering on microstructure evolution of TiN coating, in comparison to conventional DC sputtering. The implementation of a pulsed DC voltage profile promotes a drastic texture change from randomly oriented polycrystals to (111) textured TiN coatings across the full range of pulse frequencies on various Si substrates, including amorphous SiO2. Additionally, higher pulse frequencies promote significant grain size reduction, accompanied with corresponding increases in hardness and wear resistance. The potential mechanism for this microstructural and texture evolution is also explored.

The Spin-down Accretion Regime of Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124

The relatively high fluxes of the Galactic ultraluminous X-ray pulsar Swift J0243 allow a detailed study of its spin-down regime in the quiescent state for the first time. After the 2017 giant outburst, its spin frequency shows a linearly decreasing trend with some variations due to minor outbursts. The linear spin-down rate is ∼ −1.9 × 10−12 Hz s−1 during the period of lowest luminosity, from which one can infer a dipole field of ∼1.75 × 1013 G. The relation during the spin-down regime is complex, and is close to zero when the luminosity reaches both the high end (L 38 ∼ 0.3) and the lowest value (L 38 ∼ 0.03). The luminosity of zero torque is different for the giant outburst and other minor outbursts. This is likely due to different accretion flows for different types of outburst, as evidenced by the differences in the spectra and pulse profiles at a similar luminosity for different types of outburst (giant or not). The pulse profile changes from double peaks in the spin-up state to a single broad peak in the low spin-down regime, indicating the emission beam/region is larger in the low spin-down regime. These results show that accretion is still ongoing in the low spin-down regime, for which the neutron star is supposed to be in a propeller state.