J. P. Yuan

Observations of six glitches in PSR B1737−30

Six glitches have been recently observed in the rotational frequency of the young pulsar PSR B1737-30 (J1740-3015) using the 25-m Nanshan telescope of Urumqi Observatory. With a total of 20 glitches in 20 yr, it is one of the most frequently glitching pulsars of the similar to 1750 known pulsars. Glitch amplitudes are very variable with fractional increases in rotation rate ranging from 10(-9) to 10(-6). Interglitch intervals are also very variable, but no relationship is observed between interval and the size of the preceding glitch. There is a persistent increase in vertical bar(nu) over dot vertical bar, opposite in sign to that expected from slowdown with a positive braking index, which may result from changes in the effective magnetic dipole moment of the star during the glitch.

Pulsar wind model for the spin-down behavior of intermittent pulsars

Intermittent pulsars are part-time radio pulsars. They have higher slow down rates in the on state (radio-loud) than in the off state (radio-quiet). This gives evidence that particle wind may play an important role in pulsar spindown. The effect of particle acceleration is included in modeling the rotational energy loss rate of the neutron star. Applying the pulsar wind model to the three intermittent pulsars (PSR B1931+24, PSR J1841–0500, and PSR J1832+0029) allows their magnetic fields and inclination angles to be calculated simultaneously. The theoretical braking indices of intermittent pulsars are also given. In the pulsar wind model, the density of the particle wind can always be the Goldreich-Julian density. This may ensure that different on states of intermittent pulsars are stable. The duty cycle of particle wind can be determined from timing observations. It is consistent with the duty cycle of the on state. Inclination angle and braking index observations of intermittent pulsars may help to test different models of particle acceleration. At present, the inverse Compton scattering induced space charge limited flow with field saturation model can be ruled out.

The effects of intense magnetic fields on Landau levels in a neutron star

In this paper, an approximate method of calculating the Fermi energy of electrons (EF(e)) in a high-intensity magnetic field, based on the analysis of the distribution of a neutron star magnetic field, has been proposed. In the interior of a neutron star, different forms of intense magnetic field could exist simultaneously and a high electron Fermi energy could be generated by the release of magnetic field energy. The calculation results show that: EF(e) is related to density ρ, the mean electron number per baryon Ye and magnetic field strength B.

Magnetic field decay of magnetars in supernova remnants

In this paper, we modify our previous research carefully, derive a new expression of electron energy density in superhigh magnetic fields. Based on our improved model, we re-compute the electron capture rates and the magnetic fields’ evolutionary timescales t of magnetars. According to the calculated results, the superhigh magnetic fields may evolve on timescales ∼ (106−107) yrs for common magnetars, and the maximum timescale of the field decay, t ≈ 2.9507× 10 yrs, corresponding to an initial internal magnetic field B0 = 3.0×1015 G and an initial temperature T0 = 2.6×108 K. Motivated by the results of the neutron star-supernova remnant(SNR) association of Zhang & Xie(2011), we calculate the maximum B0 of magnetar progenitors, Bmax ∼ (2.0×1014−2.93×1015) G when T0 = 2.6×108 K. When T0 ∼ 2.75×108− 1.75×108 K, the maximum B0 will also be in the range of ∼ 10 − 10 G, not exceeding the upper limit of magnetic field of a mag-

Numerical simulation of the electron capture process in a magnetar interior

In a superhigh magnetic field, direct Urca reactions can proceed for an arbitrary proton concentration. Since only the electrons with high energy E (E>Q, Q is the threshold energy of inverse β-decay) at large Landau levels can be captured, we introduce the Landau level effect coefficient q and the effective electron capture rate Γeff. By using Γeff, the values of LX and Lν are calculated, where LX and Lν are the average neutrino luminosity of AXPs and the average X-ray luminosity of AXPs LX, respectively. The complete process of electron capture inside a magnetar is simulated numerically.

EVOLUTION OF THE X-RAY PROFILE OF THE CRAB PULSAR

Using the archival data from the Rossi X-ray Timing Explorer, we study the evolution of the Crab pulsars X-ray profile in a time span of 11 years. The X-ray profiles, as characterized by a few parameters, changed slightly, but with high statistical significance in these years: the separation of the two peaks increased with a rate of 088 ± 020 per century, the flux ratio of the second pulse to the first pulse decreased by per century, and the pulse widths of the two pulses represented by their full widths at half maxima decreased by and per century, respectively. The evolutionary trends of the X-ray profile are similar to that observed in radio, but with quantitative differences. Finally, we briefly discuss the constraints of these X-ray properties on the geometry of the emission region of this pulsar.

Comparison of pulsar positions from timing and very long baseline astrometry

Pulsar positions can be measured with high precision using both pulsar timing methods and very long baseline interferometry (VLBI). Pulsar timing positions are referenced to a solar-system ephemeris, whereas VLBI positions are referenced to distant quasars. Here, we compare pulsar positions from published VLBI measurements with those obtained from pulsar timing data from the Nanshan and Parkes radio telescopes in order to relate the two reference frames. We find that the timing positions differ significantly from the VLBI positions (and also differ between different ephemerides). A statistically significant change in the obliquity of the ecliptic of 2.16 ± 0.33 mas is found for the JPL ephemeris DE405, but no significant rotation is found in subsequent JPL ephemerides. The accuracy with which we can relate the two frames is limited by the current uncertainties in the VLBI reference source positions and in matching the pulsars to their reference source. Not only do the timing positions depend on the ephemeris used in computing them, but also different segments of the timing data lead to varying position estimates. These variations are mostly common to all ephemerides, but slight changes are seen at the 10 μas level between ephemerides.

Strong pulses detected from rotating radio transient J1819 − 1458

Aims. We analyze individual pulses detected from RRAT J1819-1458. Methods. From April 2007 to April 2010, we carried out observations using the Nanshan 25-m radio telescope of Urumqi Observatory at a central frequency of 1541.25 MHz. Results. We obtain a dispersion measure DM = 195.7 +/- 0.3 pc cm(-3) by analyzing all the 423 detected bursts. The tri-band pattern of arrival time residuals is confirmed by a single pulse timing analysis. Twenty-seven bimodal bursts located in the middle residual band are detected, and, profiles of two typical bimodal bursts and two individual single-peak pulses are presented. We determine the statistical properties of SNR and W-50 of bursts in different residual bands. The W50 variation with SNR shows that the shapes of bursts are quite different from each other. The cumulative probability distribution of intensity for a possible power law with index alpha = 1.6 +/- 0.2 is inferred from the number of those bursts with SNR >= 6 and high intensities.

Interstellar Scintillation observations for PSR B0355+54

In this paper, we report our investigation of pulsar scintillation phenomena by monitoring PSR B0355+54 at 2.25 GHz for three successive months using the Kunming 40-m radio telescope. We measured the dynamic spectrum, the two-dimensional correlation function and the secondary spectrum. These observations have a high signal-to-noise ratio (S/N >= 100). We detected scintillation arcs, which are rarely observable using such a small telescope. The submicrosecond scale width of the scintillation arc indicates that the transverse scale of the structures on the scattering screen is as compact as astronomical unit size. Our monitoring shows that the scintillation bandwidth, the time-scale and the arc curvature of PSR B0355+54 were varying temporally. A plausible explanation would need to invoke a multiple-scattering-screen or multiple-scattering-structure scenario, in which different screens or ray paths dominate the scintillation process at different epochs.

Proper motions of 15 pulsars: a comparison between Bayesian and frequentist algorithms

We present proper motions for 15 pulsars which are observed regularly by the Nanshan 25-m radio telescope. Two methods, the frequentist method and the Bayesian method, are used and the results are compared. We demonstrate that the two methods can be applied to young pulsar data sets that exhibit large amounts of timing noise with steep spectral exponents and give consistent results. The measured positions also agree with very long baseline interferometric positions. Proper motions for four pulsars are obtained for the first time, and improved values are obtained for five pulsars.