Pulsar B1937 Research Articles

Variations in the Radiation Intensity of Pulsar B0950+08: Nine Years of Monitoring at 110 MHz

Variations in the Radiation Intensity of Pulsar B0950+08: Nine Years of Monitoring at 110 MHz

Microstructure in Radio Emission of the Pulsar B1133+16 at a Frequency of 111 MHz

Microstructure in Radio Emission of the Pulsar B1133+16 at a Frequency of 111 MHz

Radio Pulsar B0950+08: Radiation in the Magnetosphere and Sparks above the Surface

We observed the nearby radio pulsar B0950+08, which has a 100% duty cycle, using the Five-hundred-meter Aperture Spherical Radio Telescope. We obtained the polarization profile for its entire rotation, which enabled us to investigate its magnetospheric radiation geometry and the sparking pattern of the polar cap. After we excluded part of the profile in which the linear polarization factor is low (≲30%) and potentially contaminated by jumps in position angle, the rest of the swing in polarization position angle fits a classical rotating vector model (RVM) well. The best-fit RVM indicates that the inclination angle, α, and the impact angle, β, of this pulsar, are 100.°5 and −33.°2, respectively, suggesting that the radio emission comes from two poles. We find that, in such RVM geometry, either the annular vacuum gap model or the core vacuum gap model would require that the radio emissions come from a high-altitude magnetosphere with heights from ∼0.25 R LC to ∼0.56 R LC, with R LC being the light cylinder radius. Both the main and interpulses’ sparking points are located away from the magnetic pole, which could relate to the physical conditions on the pulsar surface.

Single pulse polarization study of pulsars B0950 + 08 and B1642 − 03: micropulse properties and mixing of orthogonal modes

ABSTRACT We present the results of a high-time resolution polarization study of single pulses from pulsars B0950 + 08 and B1642 − 03. Single pulses from pulsar B0950 + 08 sometimes show isolated micropulses without any significant associated subpulse emission. Assuming that the properties of such micropulses represent the intrinsic nature of micropulse emission, we characterize the width and polarization properties of these ‘intrinsic’ microstructures. Most of the ‘intrinsic’ micropulses ($\sim 90~{{\ \rm per\ cent}}$) follow common characteristic polarization properties, while the average width of these micropulses is consistent with the general micropulse population from this pulsar. Single pulses from these pulsars show a diverse range of polarization properties, including depolarization and mixing of two orthogonal modes resulting in polarization position angle jumps. We present a superposition model of the two orthogonal modes which can explain depolarization, the observed position angle jumps, and associated changes in other polarization parameters.

Plasma lensing near the eclipses of the Black Widow pulsar B1957+20

ABSTRACT Recently, several eclipsing millisecond pulsars have been shown to experience strong and apparent weak lensing from the outflow of their ionized companions. Lensing can be a powerful probe of the ionized plasma, with the strongest lenses potentially resolving emission regions of pulsars. Understanding lensing in the ‘laboratory-like’ conditions of an eclipsing pulsar may be analogously applied to fast radio bursts, many of which reside in dense, magnetized environments. We examined variable dispersion measure (DM), absorption, scattering, and flux density in the original Black Widow pulsar PSR B1957+20 through an eclipse at the Arecibo Observatory at $327\, {\rm MHz}$. We discovered clear evidence of the two regimes of lensing, strong, and apparent weak. We show that the flux density variations in the apparently weak lensing regime can be modelled directly from variations of DM, using geometric optics. The mean effective velocities in the ingress, $(954\pm 99)\, {\rm km\, s^{-1}}$, and egress $(604\pm 47)\, {\rm km\, s^{-1}}$ cannot be explained by orbital motions alone, but are consistent with significant outflow velocity of material from the companion. We also show that geometric optics can predict when and where the lensing regime-change between weak and strong occurs, and argue that the apparent weak lensing is due to averaging many images. Our framework can be applied in any source with variable electron columns, measuring their relative velocities and distances. In other eclipsing pulsars, this provides a unique opportunity to measure companion outflow velocity, predict regions of weak and strong lensing, and in principle independently constrain orbital inclinations.

New Features of the Pulsar B0950+08 Radiation at the Frequency of 111 MHz

Results of long time observations of the pulsar B0950+08 are given. These observations were carried out at the LPA radio telescope at the frequency of 111 MHz from January of 2016 to May of 2019 (450 days). A strong variability in emission of this pulsar has been detected with changes in signal to noise ratios hundreds of times. Part of the long-time flux density variability can be explained by refractive scintillations in the interstellar medium. The existence of radiation between the interpulse (IP) and main pulse (MP) was confirmed. It was more powerful than at high frequencies. We detected the unusual IP and precursor (Pr) radiation on 2017 August 1. On the basis of 65 strong IPs we found the correlations between energies of IP and Pr and between the phase of IP and the distance Pr–IP. It is shown that the observed peculiarities of this pulsar can be explained in the frame of the aligned rotator model. We estimated distances of radiation levels from the center of the neutron star. The calculated value of the initial period of 0.2 s means that not all pulsars are born with millisecond periods. The large age of the pulsar (6.8 million years) and the small angle between its magnetic moment and the rotation axis (less than 20°) confirm the suggestion related to pulsar evolution with respect to alignment.

Thermal and Nonthermal Emission in the Optical-UV Spectrum of PSR B0950+08*

Abstract Based on recent Hubble Space Telescope (HST) observations in the far-UV and ground-based observations in optical bands, Pavlov and colleagues have revealed a thermal component in the spectrum of the old pulsar B0950+08 (spin-down age 17.5 Myr) and estimated a neutron star (NS) surface temperature of (1–3) × 105 K. Our new HST observations in the optical have allowed us to resolve the pulsar from a close-by galaxy and measure the optical fluxes more accurately. Using the newly measured fluxes and a new calibration of the HST’s far-UV detector, we fit the optical-UV pulsar’s spectrum with a model that consists of a nonthermal power law (f ν ∝ ν α ) and thermal blackbody components. We obtained the spectral slope α = −0.3 ± 0.3, considerably flatter than found from ground-based observations, and the best-fit temperature in the range of (6–12) × 104 K (as seen by a distant observer), depending on interstellar extinction and NS radius. The temperature is lower than reported previously, but still much higher than predicted by NS passive cooling scenarios for such an old pulsar. This means that some heating mechanisms operate in NSs, e.g., caused by the interaction of the faster-rotating neutron superfluid with the slower-rotating normal matter in the inner crust of the NS.

Pulsar: physical generalization of the galactic time-space

The article considers a complex of geometric representations of space-time, based on general dynamic theories of celestial mechanics in close connection with pulsar astrometry as the physical basis of coordinate-time transformations within the solar system and galactic space as a whole. The pulsar time scale is considered as a certain material system with continuous and stable motion, representing a certain measurable parameter – the rotation period P, which changes as a function of the independent time variable – its derivative. The physical pulsar scale is a sequence of measured daily increments of the initial radiation period within any duration. According to observations at the BSA radio telescope (Pushchino) of the pulsar B0950+08, the time scale was determined with an initial period of P0=0.2530653211840410 s on the date MJD0 = 58971 (02.05.2020; 21h.58m.07s). A measured daily increment ΔP = 1.4441·10E-11 s corresponds to the measured value of the derivative P = 1.6759949886E-16, which is determined by the observational timing data. Measured ΔP are defined in the 25th decimal place. Up to 14-15 digits, Δ P there is a pulsar time scale with femtosecond resolution. From 15-16 to 25 digits Δ P is presumably sequential fixation of discrete states of microparticles during quantum-mechanical interactions of matter and electromagnetic radiation of a pulsar. According to our hypothesis, the diversity of the material world and physical processes occurring in celestial and quantum mechanics are finite and it can be generalized. This implies the inseparable unity of physical laws in four-dimensional space of celestial and quantum mechanics, detectable on pulsar time scales under the same conditions.

Ionospheric effects in VLBI measured with space-ground interferometer RadioAstron

ABSTRACT We report on slow phase variations of the response of the space-ground radio interferometer RadioAstron during observations of pulsar B0329+54. The phase variations are due to the ionosphere and clearly distinguishable from effects of interstellar scintillation. Observations were made in a frequency range of 316–332 MHz with the 110-m Green Bank Telescope and the 10-m RadioAstron telescope in 1-h sessions on 2012 November 26, 27, 28, and 29 with progressively increasing baseline projections of about 60, 90, 180, and 240 thousand kilometres. Quasi-periodic phase variations of interferometric scintles were detected in two observing sessions with characteristic time-scales of 12 and 10 min and amplitudes of up to 6.9 radians. We attribute the variations to the influence of medium-scale Travelling Ionospheric Disturbances. The measured amplitude corresponds to variations in vertical total electron content in ionosphere of about $0.1\times 10^{16}\, \text{m}^{-2}$. Such variations would noticeably constrain the coherent integration time in VLBI studies of compact radio sources at low frequencies.

A Synoptic VLBI Technique for Localizing Nonrepeating Fast Radio Bursts with CHIME/FRB

Abstract We demonstrate the blind interferometric detection and localization of two fast radio bursts (FRBs) with subarcminute precision on the 400 m baseline between the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the CHIME Pathfinder. In the same spirit as Very Long Baseline Interferometry (VLBI), the telescopes were synchronized to separate clocks, and the channelized voltage (herein referred to as baseband) data were saved to a disk with correlation performed offline. The simultaneous wide field of view and high sensitivity required for blind FRB searches implies a high data rate—6.5 terabits per second (Tb/s) for CHIME and 0.8 Tb s−1 for the Pathfinder. Since such high data rates cannot be continuously saved, we buffer data from both telescopes locally in memory for , and write to the disk upon receipt of a low-latency trigger from the CHIME Fast Radio Burst Instrument (CHIME/FRB). The deg2 field of view of the two telescopes allows us to use in-field calibrators to synchronize the two telescopes without needing either separate calibrator observations or an atomic timing standard. In addition to our FRB observations, we analyze bright single pulses from the pulsars B0329+54 and B0355+54 to characterize systematic localization errors. Our results demonstrate the successful implementation of key software, triggering, and calibration challenges for CHIME/FRB Outriggers: cylindrical VLBI outrigger telescopes which, along with the CHIME telescope, will localize thousands of single FRB events with sufficient precision to unambiguously associate a host galaxy with each burst.

The Northern Cross fast radio burst project – I. Overview and pilot observations at 408 MHz

ABSTRACT Fast radio bursts (FRBs) remain one of the most enigmatic astrophysical sources. Observations have significantly progressed over the last few years, due to the capabilities of new radio telescopes and the refurbishment of existing ones. Here, we describe the upgrade of the Northern Cross radio telescope, operating in the 400–416 MHz frequency band, with the ultimate goal of turning the array into a dedicated instrument to survey the sky for FRBs. We present test observations of the pulsar B0329+54 to characterize the system performance and forecast detectability. Observations with the system currently in place are still limited by modest sky coverage (∼9.4 deg2) and biased by smearing of high dispersion measure events within each frequency channels. In its final, upgraded configuration, however, the telescope will be able to carry out unbiased FRB surveys over a ∼350 deg2 instantaneous field of view up to z ∼ 5, with a (nearly constant) $\sim 760 \, (\tau /{\rm ms})^{-0.5}$ mJy rms sensitivity.

Unusually Bright Single Pulses from the Binary Pulsar B1744–24A: A Case of Strong Lensing?

Abstract We present a study of unusually bright single pulses (BSPs) from a millisecond pulsar in an ablating binary system, B1744−24A, based on several multiorbit observations with the Green Bank Telescope. These pulses come predominantly in time near eclipse ingress and egress, have intensities up to 40 times the average pulse intensity, and pulse widths similar to that of the average pulse profile. The average intensity, spectral index of radio emission, and the dispersion measure do not vary in connection with BSP outbursts. The average profile obtained from BSPs has the same shape as the average profile from all pulses. These properties make it difficult to explain BSPs via scintillation in the interstellar medium, as a separate emission mode, or as conventional giant pulses. BSPs from B1744−24A have similar properties to the strong pulses observed from the Black Widow binary pulsar B1957+10, which were recently attributed to strong lensing by the intrabinary material. We argue that the strong lensing likely occurs in B1744−24A as well. For this system, the sizes and locations of the lenses are not well constrained by simple 1D lensing models from Cordes et al. and Main et al. This partly stems from the poor knowledge of several important physical parameters of the system.

Investigation of the mode-switching phenomenon in pulsar B0329+54 through polarimetric analysis

The phenomenon of profile mode switching in pulsars, where the stable average pulse profile changes to another stable state on the timescale of a pulsar's period, remains poorly understood. We sought to understand how pulsars undergo profile mode switching through a comparative analysis of the polarization and geometry of the two different profile modes of PSR B0329+54. The polarization behavior and fitted parameters of the rotation-vector model remain constant between modes, and the emission height remains constant as well. These similarities lend support to a model of pair production in the surface plasma that would cause a change in the available electrons and therefore the differential emission intensity.

Braking index jumps in young pulsars

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.

A detailed study of giant pulses from PSR B1937+21 using the Large European Array for Pulsars

We have studied 4265 giant pulses (GPs) from the millisecond pulsar B1937+21; the largest-ever sample gathered for this pulsar, in observations made with the Large European Array for Pulsars. The pulse energy distribution of GPs associated with the interpulse are well-described by a power law, with index $\alpha = -3.99 \pm 0.04$, while those associated with the main pulse are best-described by a broken power law, with the break occurring at $\sim7$ Jy $\mu$s, with power law indices $\alpha_{\text{low}} = -3.48 \pm 0.04$ and $\alpha_{\text{high}} = -2.10 \pm 0.09$. The modulation indices of the GP emission are measured, which are found to vary by $\sim0.5$ at pulse phases close to the centre of the GP phase distributions. We find the frequency-resolved structure of GPs to vary significantly, and in a manner that cannot be attributed to the interstellar medium influence on the observed pulses. We examine the distribution of polarisation fractions of the GPs and find no correlation between GP emission phase and fractional polarisation. We use the GPs to time PSR B1937+21 and although the achievable time of arrival precision of the GPs is approximately a factor of two greater than that of the average pulse profile, there is a negligible difference in the precision of the overall timing solution when using the GPs.

Ages of radio pulsar: long-term magnetic field evolution

We use the Bayesian approach to write the posterior probability density for the three-dimensional velocity of a pulsar and for its kinematic age. As a prior, we use the bimodal velocity distribution found in a recent article by Verbunt, Igoshev & Cator (2017). When we compare the kinematic ages with spin-down ages, we find that in general, they agree with each other. In particular, maximum likelihood analysis sets the lower limit for the exponential magnetic field decay timescale at $8$ Myr with a slight preference of $t_\mathrm{dec} \approx 12$ Myr and compatible with no decay at all. One of the objects in the study, pulsar B0950+08 has kinematic and cooling ages $\approx 2$ Myr which is in strong contradiction with its spin-down age $\tau\approx 17$ Myr. The 68 per cent credible range for the kinematic age is 1.2--8.0 Myr. We conclude that the most probable explanation for this contradiction is a combination of magnetic field decay and long initial period. Further timing, UV and X-ray observations of B0950+08 are required to constrain its origin and evolution better.

A VLBI Distance and Transverse Velocity for PSR B1913+16

Abstract Using the Very Long Baseline Array, we have made astrometric observations of the binary pulsar B1913+16 spanning an 18-month period in 2014–2015. From these observations we make the first determination of the annual geometric parallax of B1913+16, measuring mas (68% confidence interval). The inferred parallax probability distribution differs significantly from a Gaussian. Using our parallax measurement and prior information on the spatial and luminosity distributions of the millisecond pulsar population, we infer a distance of kpc, which is significantly closer than the 9.8 ± 3.1 kpc suggested by the pulsar’s dispersion measure (DM) and analyses of the ionized interstellar medium. While the relatively low significance of the parallax detection (∼3σ) currently precludes an improved test of general relativity using the orbital decay of PSR B1913+16, ongoing observations with improved control of systematic astrometric errors could reach the 10% distance uncertainty required for this goal. The proper motion measured by our Very Long Baseline Interferometry astrometry differs substantially from that obtained by pulsar timing, a discrepancy that has also been found between the proper motion measurements made by interferometers and pulsar timing for some other pulsars, which we speculate is the result of timing noise or DM variations in the timing data set. Our parallax and proper motion measurements yield a transverse velocity of km s−1 in the solar reference frame. Analysis incorporating galactic rotation and solar motion finds that the space velocity of the pulsar relative to its standard of rest has a component km s−1 perpendicular to the galactic plane and components on the order of 100 km s−1 parallel to the galactic plane.

Modelling the thermal absorption and radio spectra of the binary pulsar B1259–63

We present the results of modelling of the radio spectrum evolution and dispersion measure variations of PSR B1259-63, a pulsar in a binary system with Be star LS 2883. We base our model on a hypothesis that the observed variations of the spectrum are caused by thermal free-free absorption occurring in the pulsar surroundings. We reproduce the observed pulsar spectral shapes in order to examine the influence of the stellar wind of LS 2883 and the equatorial disc on the pulsar's radiation. The simulations of the pulsar's radio emission and its consequent free-free absorption give us an insight into the impact of stellar wind and equatorial disc of LS 2883 has on the shapes of PSR B1259-63 radio spectra, providing an evidence for the connection between gigahertz-peaked spectra phenomenon and the close environment of the pulsar. Additionally, we supplement our model with an external absorbing medium, which results in a good agreement between simulated and observational data.

Performance of a Highly Sensitive, 19-element, Dual-polarization, Cryogenic L-band Phased-array Feed on the Green Bank Telescope

Abstract A new 1.4 GHz, 19-element, dual-polarization, cryogenic phased-array feed (PAF) radio astronomy receiver has been developed for the Robert C. Byrd Green Bank Telescope (GBT) as part of the Focal L-band Array for the GBT (FLAG) project. Commissioning observations of calibrator radio sources show that this receiver has the lowest reported beam-formed system temperature (T sys) normalized by aperture efficiency (η) of any phased-array receiver to date. The measured T sys/η is 25.4 ± 2.5 K near 1350 MHz for the boresight beam, which is comparable to the performance of the current 1.4 GHz cryogenic single-feed receiver on the GBT. The degradation in T sys/η at ∼4′ (required for Nyquist sampling) and ∼8′ offsets from the boresight is, respectively, ∼1% and ∼20% of the boresight value. The survey speed of the PAF with seven formed beams is larger by a factor between 2.1 and 7 compared to a single-beam system, depending on the observing application. The measured performance, both in frequency and offset from the boresight, qualitatively agrees with predictions from a rigorous electromagnetic model of the PAF. The astronomical utility of the receiver is demonstrated by observations of the pulsar B0329+54 and an extended H ii region, the Rosette Nebula. The enhanced survey speed with the new PAF receiver will enable the GBT to carry out exciting new science, such as more efficient observations of diffuse, extended neutral hydrogen emission from galactic inflows and searches for fast radio bursts.

Neutron star planets: Atmospheric processes and irradiation

Of the roughly 3000 neutron stars known, only a handful have sub-stellar companions. The most famous of these are the low-mass planets around the millisecond pulsar B1257+12. New evidence indicates that observational biases could still hide a wide variety of planetary systems around most neutron stars. We consider the environment and physical processes relevant to neutron star planets, in particular the effect of X-ray irradiation and the relativistic pulsar wind on the planetary atmosphere. We discuss the survival time of planet atmospheres and the planetary surface conditions around different classes of neutron stars, and define a neutron star habitable zone. Depending on as-yet poorly constrained aspects of the pulsar wind, both Super-Earths around B1257+12 could lie within its habitable zone.