Pulsar Research Articles

Searching for X-ray counterparts of degree-wide TeV halos around middle-aged pulsars with SRG/eROSITA

Context. Extended gamma-ray TeV emission (TeV halos) has been detected around middle-aged pulsars. A proposed model to explain these TeV halos is that electrons from a degree-wide pulsar wind nebula (PWN) get up-scattered by cosmic microwave background photons through inverse Compton processes. However, no X-ray degree-wide faint diffuse PWNe have been found around these middle-aged pulsars in previous X-ray observations. Aims. We performed a search for degree-wide PWNe around Geminga, PSR B0656+14, B0540+23, J0633+0632, and J0631+1036 using data from the first four consecutive Spectrum Roentgen Gamma/eROSITA all-sky surveys. In order to better understand the mechanisms underlying the formation of TeV halos, we investigated the magnetic field strength within an area of 1° in radius centred on those pulsars. Methods. To achieve our goals, we selected a list of suitable candidate pulsars in the eROSITA-DE part of the sky and applied data reduction techniques to process the eROSITA data. We then performed a spatial analysis of the regions around selected pulsars. Results. We do not detect any degree-wide diffuse emission driven by rotation-powered pulsars around Geminga, PSR B0656+14, B0540+23, J0633+0632, or J0631+1036. Indeed, close inspection of the data shows that the pulsars of interest are all embedded in diffuse emission from supernova remnants such as the Monogem Ring or the Rosetta Nebula, while PSR B0540+23 is located ~2.5° away from the Crab pulsar, which is exceptionally bright, causing its X-ray emission to spread over a significant area up to the position of PSR B0540+23 and therefore strongly diminishes our capacity to search for degree-wide bright diffuse X-ray emission. Conclusions. Despite the non-detection of any degree-wide PWN surrounding the analysed pulsars, we set flux upper limits to provide useful information on magnetic field strength and its spatial distribution around those pulsars, providing additional constraints on the proposed theory for the formation of TeV halos around pulsars.

Erratum to: The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329+54

Erratum to: The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329+54

Media educational strategies for a personality aesthetic development (using the example of the Radio Pulse of Moscow Pedagogical State University projects)

Media educational strategies for a personality aesthetic development (using the example of the Radio Pulse of Moscow Pedagogical State University projects)

The AO327 Drift Survey Catalog and Data Release of Pulsar Detections

The AO327 drift survey for radio pulsars and transients used the Arecibo telescope from 2010 until its collapse in 2020. AO327 collected ∼3100 hr of data at 327 MHz with a time resolution of 82 μs and a frequency resolution of 24 kHz. While the main motivation for such surveys is the discovery of new pulsars and new, even unforeseen, types of radio transients, they also serendipitously collect a wealth of data on known pulsars. We present an electronic catalog of data and data products of 206 pulsars whose periodic emission was detected by AO327 and are listed in the Australia Telescope National Facility catalog of all published pulsars. The AO327 data products include dedispersed time series at full time resolution, average (“folded”) pulse profiles, Gaussian pulse profile templates, and an absolute phase reference that allows phase aligning the AO327 pulse profiles in a physically meaningful manner with profiles from data taken with other instruments. We also provide machine-readable tables with uncalibrated flux measurements at 327 MHz and pulse widths at 50% and 10% of the pulse peak determined from the fitted Gaussian profile templates. The AO327 catalog data set can be used in applications like population analysis of radio pulsars, pulse profile evolution studies in time and frequency, cone and core emission of the pulsar beam, scintillation, pulse intensity distributions, and others. It also constitutes a ready-made resource for teaching signal-processing and pulsar astronomy techniques.

Spin period evolution of Vela pulsar based on the wind emission: Application to the long period radio pulsars GPM J1839‐10 (P = 21 min) and GLEAM‐X J1627 (P = 18 min)

AbstractThe Vela pulsar is a young neutron star with spin period of P = 89 ms and a measured low braking index (˜1.4) that is much less than the standard value of 3 predicted by the magnetic dipole radiation (MDR) model; however, its spin period evolution has been a mystery. In this article, we assume that the spin‐down of the Vela pulsar is attributed to both MDR and wind flow (hereafter MDRW), and find that the ratio of wind flow to the magnetic dipole radiation is about 80%, which is higher than that of the Crab pulsar (25%). In other words, the spin‐down torque of the Vela pulsar is dominated by the wind flow. The spin period (P) evolution of the Vela pulsar depends on its real age, where its supernova remnant age is assumed to be an indicator of its true age, estimated from 10 to 20 kyr, and then we obtain their initial spin periods of ˜53.89 and ˜20.90 ms, respectively, which are consistent with the observed initial spin period ranges of young pulsars. Furthermore, we find that the Vela‐like pulsar by MDRW can evolve to the long spin period of a thousand of seconds in less than million years, which can conveniently help the astronomers understand the recently observed ultra‐long period radio pulsars like GPM J1839‐10 (P = 21 min), GLEAM‐X J1627 (P = 18 min), as well as PSR J0901+4046 (P = 76 s).

The invisible black widow PSR J1720-0534: implications for the electron density towards the North Polar Spur

Abstract Radio emission from pulsars can be used to map out their distances through dispersion measure (DM), which quantifies the amount of radio pulse dispersion. However, this method relies on accurately modeling the free electron density in the line of sight. Here, we present a detailed study of the multi-wavelength emission from PSR J1720-0534, a black widow compact binary millisecond pulsar discovered in 2021, which the latest electron density model of the Galaxy (YMW16; Yao et al. 2017) places at only 191 pc. We obtained and analyzed deep multi-wavelength observations in the γ-ray (Fermi-LAT, 2008-2022), optical (LCO, 2.7-h), near-infrared (NOT, 3.5-h) and X-ray (Swift-XRT, 10 ksec) bands. We found no significant detection of γ-ray, optical, near-infrared, or X-ray counterparts around the radio-timing position of PSR J1720-0534, which we thus nickname ‘the invisible black widow’. Employing the most constraining near-infrared limit (J > 23.4 mag), we established a lower limit on the source distance, d > 1.1 kpc, assuming conservative properties for the black widow companion star. This distance lower limit differs drastically (by a factor of more than five) from the YMW16 DM distance estimate. We attribute this difference to the inclusion in the YMW16 model of a large and dense component towards the North Polar Spur. Considering our results and recent parallax distances to other pulsars in this direction, we argue that such a local and large component in the electron density model of the Galaxy is unnecessary.

Spin Evolution of Neutron Stars

In this paper we review the basics of magneto-rotational properties of neutron stars focusing on spin-up/spin-down behavior at different evolutionary stages. The main goal is to provide equations for the spin frequency changes in various regimes (radio pulsar, propeller, accretor, etc.). Since presently the spin behavior of neutron stars at all stages remains a subject of many uncertainties, we review different suggestions made over the years in the literature.

Studying the nulling, subpulse drifting, and moding in PSR J1921+1948 with the FAST

ABSTRACT We reported the observations of nulling, subpulse drifting, and moding of radio radiation in pulsar (PSR) B1918+19 at 1250 MHz with the Five-hundred-meter Aperture Spherical radio Telescope. The nulling fraction is 2.6 ± 0.1 per cent and no periodicity of nulling can be seen. We confirmed the existence of three different drift modes (A, B, C) and a disordered mode (N) at 1250 MHz. Unlike the other three modes where the second component of the average pulse profile dominates, the first component of the average pulse profile in mode C is brighter than the other components, the second component shifts forward and the fourth component shifts backward. The bidrifting phenomenon is observed in PSR B1918+19, the drifting of the first and second components is positive, and the drift direction of the fourth component is negative. The drifting rate of the drift bands composed of the first and second components has an obvious evolutionary trend. Mode B has a short duration and no clear trend can be seen. But for mode A, the drift rate of each drift band starts relatively fast, then slows down to a steady state, and finally increases slowly until it enters either null or mode N. Further analysis shows that the emergence and significant variation in the drifting period of multidrifting subpulse emission modes for PSR B1918+19 may be due to the aliasing effect. The interesting subpulse emission phenomenon of PSR B1918+19 at different frequencies provides a unique opportunity to understand the switching mechanism of the multidrift mode of the pulsars.

Discovery and timing of pulsar J2016+3711 in supernova remnant CTB 87 with FAST

ABSTRACT We report on our discovery of the radio pulsar, PSR J2016+3711, in supernova remnant (SNR) CTB 87, with a ∼10.8σ significance of pulses, which confirms the compact nature of the X-ray point source in CTB 87. It is the first pulsar discovered in SNRs using Five-hundred-meter Aperture Spherical radio Telescope (FAST). Its integrated radio pulse profile can be well described by a single component, with a width at 50 per cent of the peak flux density of about 28.1○ and an effective width of about 32.2○. The mean flux density at 1.25 GHz is estimated to be about 15.5 $\mu$Jy. Combined with the non-detection of the radio pulse at lower frequencies, the radio spectral index of the pulsar is constrained to be ≲2.3. We also present the timing solution based on 28 follow-up FAST observations. Our results reveal a period of 50.81 ms, period derivative of 7.2 × 10−14 s s−1, and dispersion measure of 428 pc cm−3. The strength of the equatorial surface magnetic dipole magnetic field is inferred to be about 1.9 × 1012 G. Using the ephemeris obtained from the radio observations, we searched Fermi-LAT data for gamma-ray pulsations but detected no pulsed signal. We also searched for radio pulses with FAST towards the X-ray counterpart of the gamma-ray binary HESS J1832−093 proximate to SNR G22.7−00.2 but found no signal.

A search for millisecond radio bursts from Messier 82

ABSTRACT Fast radio bursts (FRBs) are short-duration radio pulses of cosmological origin. Among the most common sources predicted to explain this phenomenon are bright pulses from a class of extremely highly magnetized neutron stars known as magnetars. Motivated by the discovery of an FRB-like pulse from the Galactic magnetar SGR 1935+2154, we searched for similar events in Messier 82 (M82). With a star formation rate 40 times that of the Milky Way, one might expect that the implied rate of events similar to that seen from SGR 1935+2154 from M82 should be 40 times higher than that of the Milky Way. We observed M82 at 1.4 GHz with the 20-m telescope at the Green Bank Observatory for 34.8 d. While we found many candidate events, none had a signal-to-noise ratio greater than 8. We also show that there are insufficient numbers of repeating low-significance events at similar dispersion measures to constitute a statistically significant detection. From these results, we place an upper bound for the rate of radio pulses from M82 to be 30 yr−1 above a fluence limit of 8.5 Jy ms. While this is less than nine times the rate of radio bursts from magnetars in the Milky Way inferred from the previous radio detections of SGR 1935+2154, it is possible that propagation effects from interstellar scattering are currently limiting our ability to detect sources in M82. Further searches of M82 and other nearby galaxies are encouraged to probe this putative FRB population.

Fluorescent Fe K line emission of γ Cas stars

Context. γ Cas stars are early-type Be stars that exhibit an unusually hard and bright thermal X-ray emission. One of the proposed scenarios to explain these properties postulates the existence of a neutron star companion in the propeller stage, during which the magnetosphere of a rapidly rotating neutron star repels infalling material. Aims. To test this model, we examined the fluorescent Fe Kα emission line at ~6.4keV in the X-ray spectra of γ Cas stars, which offers a powerful diagnostic of both the primary source of hard X-rays and the reprocessing material. Methods. We computed synthetic line profiles of the fluorescent Fe Kα emission line in the framework of the propelling neutron star scenario. Two reservoirs of material contribute to the fluorescence in this case: the Be circumstellar decretion disk and a shell of cool material that surrounds the shell of X-ray-emitting plasma around the putative propelling neutron star. Results. We analysed the synthetic line profiles and expected equivalent widths of the lines for three well-studied γ Cas stars. The predicted line strengths fall short of the observed values by at least an order of magnitude. Pushing the model parameters to reproduce the observed line strengths led to column densities towards the primary X-ray source that exceed the observationally determined values by typically a factor of 20, and would further imply a higher X-ray luminosity than observed. Conclusions. The strengths of the observed Fe Kα fluorescent emission lines in γ Cas stars are inconsistent with the expected properties of a propeller scenario as proposed in the literature.

On the Maximum Mass and Oblateness of Rotating Neutron Stars with Generic Equations of State

A considerable effort has been dedicated recently to the construction of generic equations of state (EOSs) for matter in neutron stars. The advantage of these approaches is that they can provide model-independent information on the interior structure and global properties of neutron stars. Making use of more than 106 generic EOSs, we assess the validity of quasi-universal relations of neutron-star properties for a broad range of rotation rates, from slow rotation up to the mass-shedding limit. In this way, we are able to determine with unprecedented accuracy the quasi-universal maximum-mass ratio between rotating and nonrotating stars and reveal the existence of a new relation for the surface oblateness, i.e., the ratio between the polar and equatorial proper radii. We discuss the impact that our findings have on the imminent detection of new binary neutron-star mergers and how they can be used to set new and more stringent limits on the maximum mass of nonrotating neutron stars, as well as to improve the modeling of the X-ray emission from the surface of rotating stars.

The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329#

The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329#

Redeveloping a CLEAN Deconvolution Algorithm for Scatter-broadened Radio Pulsar Signals

Broadband radio waves emitted from pulsars are distorted and delayed as they propagate toward the Earth due to interactions with the free electrons that compose the interstellar medium (ISM), with lower radio frequencies being more impacted than higher frequencies. Multipath propagation in the ISM results in both later times of arrival for the lower frequencies and causes the observed pulse to arrive with a broadened tail described via the pulse broadening function. We employ the CLEAN deconvolution technique to recover the pulse broadening timescale and by proxy the intrinsic pulse shape. This work expands upon previous descriptions of CLEAN deconvolution used in pulse broadening analyses by parameterizing the efficacy on simulated data and developing a suite of tests to establish which of a set of figures of merit leads to an automatic and consistent determination of the scattering timescale and its uncertainty. We compare our algorithm to the cyclic spectroscopy method of estimating the scattering timescale, specifically to the simulations performed in Dolch et al. (2021). We test our improved algorithm on the highly scattered millisecond pulsar J1903+0327, showing the scattering timescale to change over years, consistent with estimates of the refractive timescale of the pulsar.

A MeerKAT view of the double pulsar eclipses

The double pulsar system, PSR J0737−3039A/B, consists of two neutron stars bound together in a highly relativistic orbit that is viewed nearly edge-on from the Earth. This alignment results in brief radio eclipses of the fast-rotating pulsar A when it passes behind the toroidal magnetosphere of the slow-rotating pulsar B. The morphology of these eclipses is strongly dependent on the geometric orientation and rotation phase of pulsar B, and their time evolution can be used to constrain the geodetic precession rate of the pulsar. We demonstrate a Bayesian inference framework for modelling high-sensitivity eclipse light curves obtained with MeerKAT between 2019 and 2023. Using a hierarchical inference approach, we obtained a precession rate of ΩSOB = 5.16°−0.34°+0.32° yr−1 (68% confidence intervals) for pulsar B, consistent with predictions from general relativity to a relative uncertainty of 6.5%. This updated measurement provides a 6.1% test of relativistic spin-orbit coupling in the strong-field regime. We show that a simultaneous fit to all of our observed eclipses can in principle return a ∼1.5% test of spin-orbit coupling. However, systematic effects introduced by the current geometric orientation of pulsar B along with inconsistencies between the observed and predicted eclipse light curves result in difficult to quantify uncertainties when using this approach. Assuming the validity of general relativity, we definitively show that the spin axis of pulsar B is misaligned from the total angular momentum vector by 40.6° ±0.1° and that the orbit of the system is inclined by approximately 90.5° from the direction of our line of sight. Our measured geometry for pulsar B suggests the largely empty emission cone contains an elongated horseshoe-shaped beam centred on the magnetic axis, and that it may not be re-detected as a radio pulsar until early 2035.

Non-detection of Radio Pulsations in the High-mass X-Ray Binary V0332+53 During Quiescence

Following recent discoveries of ultra-long-period radio-loud neutron stars located beyond death line models in the pulsar period-period derivative diagram, we performed a radio pulsation search in the high-mass X-ray binary V0332+53 during quiescence. Although the period and magnetic field of the neutron star in this binary make it the most promising high-mass X-ray binary to explore for this purpose, the GBT observations do not reveal radio pulsations. Here, We present the duty-cycle-dependent flux density limits on the presence of any pulsations and briefly discuss its possible origins: the intrinsic absence or faintness of pulsations, the presence of low-level residual accretion, or eclipses and/or pulse scattering due to the presence of a massive binary companion.

Simulating radio-off fractions in rotating radio transients

We aim to simulate the proportions of non-detectable emission, measured as radio-off fractions ($f_ off $), in rotating radio transients (RRATs). We also investigate the properties related to the underlying mechanism for such sporadic emission. From observations of intermittent pulsars, radio emission originates from two distinct emission states and it becomes non-detectable when the pulsar switches to an emission state characterized by magnetospheric plasma density of zero. We performed simulations of $f_ off $ based on 10,000 samples, each with 10,000 rotations and using a model that tracks changes in the plasma density in a pulsar magnetosphere with multiple emission states. We assumed that (i) RRATs are radio pulsars, (ii) radio pulse intensity is correlated with the emitting plasma density as stated in the conventional models, and (iii) a pulse emission corresponds to a change in the plasma density under favorable conditions. A best-fit distribution for $f_ off $ is obtained when emission from RRATs is defaulted to radio-off. The resulting wait time distribution can be fitted by two functions of an exponential and a Gaussian, which is consistent with the observations. We demonstrate that the switch rate is low and that the burst rate is dependent on rotation period. In addition, the switch rate is related to the obliquity angle, which implies that the mechanism varies over time. Our results suggest that switching to radio-on is a random process, which implies that the burst rate is different for different RRATs. We show that RRAT emission and pulse nulling may share similar origins, but with different default emission. We discuss how the emission may change from that of RRAT to pulse nulling (or vice versa) as a pulsar evolves.

Effect of variable crustal density on the surface magnetic field of radio pulsars

ABSTRACT We study the surface magnetic field fluctuations due to radial oscillations as a viable cause for the microstructures of the radio pulsar pulse patterns. The electrical conductivity of matter in the outer layer of the crust of a neutron star (NS) plays a crucial role in the resulting surface magnetic field if we assume that the magnetic field is confined to this layer. This outer layer has a rapidly varying matter density that changes the microphysics of the material, affecting the electrical conductivity at every stage of the density change. In this study, the varying electrical conductivity in this rapidly varying density regime of the outer layer of the NS crust – from ∼1011 to about 104 g cm−3 – has been used to calculate the surface magnetic field using the induction equation. A finite effect of the strong gravitational field at the NS surface has also been taken into account. The equations have been solved in MATLAB using the method of lines. Any minor radial fluctuation due to stellar oscillation, in particular the radial oscillations, leads to a fluctuation of the electrical conductivity in the outer layer of the crust. This leads to fluctuations in the surface magnetic field with a frequency equal to the frequency of the stellar oscillation. We find that not only is the variation of the surface magnetic field substantial, but also it does not remain constant throughout the lifetime of the NS.

Radio pulse profile evolution of magnetar Swift J1818.0−1607

ABSTRACT The shape and polarization properties of the radio pulse profiles of radio-loud magnetars provide a unique opportunity to investigate their magnetospheric properties. Gaussian process regression analysis was used to investigate the variation in the total intensity shape of the radio pulse profiles of the magnetar Swift J1818.0–1607. The observed profile shape was found to evolve through three modes between MJDs 59104 and 59365. The times at which these transitions occurred coincided with changes in the amplitude of modulations in the spin-down rate. The amount of linear and circular polarization was also found to vary significantly with time. Lomb–Scargle periodogram analysis of the spin-down rate revealed three possibly harmonically related frequencies. This could point to the magnetar experiencing seismic activity. However, no profile features exhibited significant periodicity, suggesting no simple correlations between the profile variability and fluctuations of the spin-down on shorter time-scales within the modes. Overall, this implies that the mode changes seen are a result of local magnetospheric changes, with other theories, such as precession, less able to explain these observations.

An Examination of Polarization Mode Transitions in Pulsar Radio Emission

A statistical model is used to determine how stochastic fluctuations in the intensities of orthogonal polarization modes contribute to the modulation and depolarization of pulsar radio emission. General expressions for the distributions of the Stokes parameters, linear polarization, polarization position angle, and fractional polarization are derived when the mode intensities follow the same or different probability distributions. The transition between modes is examined. When the mode intensities follow the same distribution, the fractional linear polarization and modulation index are symmetric about the transition. The symmetry is disrupted when the mode intensities follow different distributions. The fractional linear polarization is minimum and the mode frequency of occurrence changes rapidly at transitions where the mode intensity distributions are the same and the modulation index is small. A lower limit on the fractional linear polarization that can be attained via the simultaneous occurrence of the modes as a function of modulation index is quantified.