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The emission feature of intermittent pulsars is significant for understanding the pulsar emission mechanism. Using the observational evidence of radio emissions turning on and off and the corresponding spin-down rates in these two states of an intermittent pulsar, we will examine the polar-cap potential drop, gap height, and curvature radii of a few intermittent pulsars within the regime of the pulsar polar-cap emission theory by applying the current loss and energy flux of particle flow to pulsar braking, which are generally associated with radio emission from the polar cap. It is seen that the polar-cap parameters of the intermittent pulsars are almost equal to their maximum values, which is the main prediction of the pulsar polar-cap theory with respect to the breaking of the radio emission. It is also noticed that the intermittent pulsars are distributed near the dipole death line in the diagram, which is consistent with their emission features and the calculated polar-cap parameters. To further confirm the state switching of the intermittent pulsar, the relationships among spin-down rate, gap height, potential drop, and activity duty cycles of PSR B1931+24 are discussed. It is found that the gap height has an anticorrelation with the activity duty cycle, which indicates that the intermittency of the radio emission has a close connection to the gap height, as indicated by the pulsar polar-cap emission theory.

The braking index is an important factor when examining the pulsar braking mechanism. Measuring braking indices requires measuring the pulsar period and its first and second derivatives. Among them, the second derivative is easily contaminated by timing noise and an unresolved glitch effect. The absence of data bounding a given transition into (or out of) a radio-on phase is another disadvantage in measuring the second derivatives of intermittent pulsars, as was recently demonstrated by Young and coworkers. But, the observed period first derivatives, in the "on" and "off" states of the intermittent pulsars, give us a possible way to predict their braking indices even though they are hard to observe. In this paper, we will give a simple and useful method to study the braking indices of intermittent pulsars. As an application of our method, we will calculate the possible braking indices of three intermittent pulsars and one nulling pulsar, namely, PSR B1931 + 24, PSR J1841 0500, PSR J1832 + 0029 and PSR B0823 + 26, under three different magnetospheric conditions, which include polar cap size variation, charge density variation and the combination of the above two cases. We have found that all the braking indices we predicted are almost within the observed domain It is concluded that, in a relatively short observation period, in which the variation of the braking index can be ignored, we can accurately predict the braking indices of intermittent pulsars, under a specific magnetosphere model, by using the observed "on" and "off" state period first derivatives.

We report on radiation properties of extreme nulling pulsar J1502-5653, by analyzing the data acquired from the Parkes 64-m telescope at 1374 MHz. The radio emission from this pulsar exhibits sequences of several tens to several hundreds consecutive burst pulses, separated by null pulses, and the appearance of the emission seems quasi-periodic. The null fraction from the data is estimated to be 93.6%. No emission is detected in the integrated profile of all null pulses. Systematic modulations of pulse intensity and phase are found at the beginning of burst-pulse sequences just after null. The intensity usually rises to a maximum for the first few pulses, then declines exponentially afterwards, and becomes stable after few tens of pulse periods. The peak phase appears at later longitudes for the first pulse, then drifts to earlier longitudes rapidly, and then systematic drifting gradually vanishes while the intensity becomes stable. In this pulsar, the intensity variation and phase modulation of pulses are correlated in a short duration after the emission starts following a null. Observed properties of the pulsar are compared with other nulling pulsars published previously, and the possible explanation for phase modulation is discussed.

Interstellar scattering causes broadening and distortion to the mean pulse profiles and polarization position angle (PPA) curves, especially to the pulse profiles observed at lower frequency. This paper has implemented a method to recover the pulse profiles and the PPA curves of five pulsars which have obvious scattered pulse profiles at lower frequency. It reports a simulation to show the scattering and descattering of pulse profiles and PPA curves. As a practical application, lower-frequency profiles and PPA curves of PSR 1356-60, PSR 1831-03, PSR 1838+04, PSR 1859+03, PSR 1946+35 are obtained. It is found that the original pulse profiles and PPA curves can be recovered., 9 pages, 6 figures, accepted for publication in RAA

We present an analysis of strong single pulses from PSR J0034-0721. Our observations were made using the Urumqi 25-m radio telescope at a radio frequency of 1.54 GHz. A total of 353 strong pulses were detected during eight hours of observing. The signal-to-noise ratios of the detected pulses range from 5 to 11.5. The peak fluxes of those pulses are 17 to 39 times that of the average pulse peak. The cumulative distribution of the signal-to-noise ratios of these strong pulses has a rough power-law distribution with a slope of 4.4 ± 0.5. Ten of the strong pulses arrived approximately 23 to 40 ms earlier than the average profile peak. This suggests the possibility that there are two strong pulse-emitting regions.

We analyse the timing residuals for 50 pulsars observed using the Nanshan 25-m radio telescope at Urumqi Observatory by determining the Hurst parameter for each data set using the rescaled range method. These pulsars have been observed over a time span of 5-8 yr and have been selected to have timing residuals that resemble white noise rather than smooth curves. The results are compared with those for shuffled residual series. Despite the noise-like appearance, some timing residual series showed Hurst parameters that deviated significantly from the shuffled series. We conclude that Hurst parameter analysis is capable of detecting long-term memory in timing residuals.

Using the 25m radio telescope of the Urumqi Observatory, the strong single pulses of the pulsar PSR J0034-0721 were observed at 1.54 GHz on 6th Aug. 2007. With the technique of single-pulse detection, 116 single pulses with the signal-to-noise ratios of R SN ≥5 were detected from the observed data of 1 h. At 1.54 GHz, the signal-to-noise ratios of the detected single pulses are in the range from 5 to 10.5, and the peak flux densities of these pulses are approximately 14∼29 times that of the average pulse (AP), much less than the ratios between the intensities of typical giant pulses and the intensity of AP. The cumulative distribution of the intensities of these pulses is basically a powerlaw distribution with the spectral index α = −4.3 ± 0.4. The detection rates for the pulses of R SN ≥5 and R SN ≥10 are 3% and 0.08%, respectively. For these pulses, the half-peak width W 50 ranges from 1.6 ms to 8 ms, 3.9 ms in average. The phases of the vast majority of the strong single pulses are concentrated around the peak position of AP, but 2 strong pulses of R SN ≥8.5 are detected at the phases about 33 ms earlier than the phase of the AP peak. This implies that there probably exist two emission regions of strong pulses, and this is consistent with the previously observed results at 40 MHz and 111 MHz, except that at 1.54 GHz the profile of AP exhibits only one component.

Under the two initial 1-D one parameter velocity distribution forms ( one is normal, the other is exponential), the z direction scale height evolution of normal neutron stars in the Galaxy is studied by numerical simulation. We do statistics for the cases at different time segments, also do statistics for the cumulative cases made of each time segment. The results show in the cumulative cases the evolution curves of the scale heights are smoother than in the each time segment, i. e., the cumulation improve the signal-to-noise ratio. Certainly the evolution cases are different at different Galactic disk locations, which also have very large difference from the average cases in the whole disk. In the initial stages of z evolution of normal neutron stars, after the beginning transient states, the cumulative scale heights increase linearly with time, and the cumulative scale height increasing rates have linear relationship with the initial velocity distribution parameters, which have larger fluctuation in the vicinity of the Sun than in the whole disk. We utilize the linear relationship of the cumulative scale height increasing rates vs. the initial velocity distribution parameters in the vicinity of the Sun to make comparison with the observation near the Sun. The results show if there is no magnetic decay, then the deserved initial velocity parameters are obvious lower than the present well known results from some authors; whereas if introducing magnetic decay, for the 1-D normal case we can make consistence among concerning results using magnetic decay time values which are supported by some authors, while for the 1-D exponential case the results show the lackness of young pulsar samples in the larger z in the vicinity of the Sun. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The evolutionary scenario of neutron star binaries is still an essential enigma in both stellar astrophysics and high energy astrophysics. In order to explore the scenario, we include the accumulation of data on the orbits and spins of compact binaries in multi-wavelength ranging from radio to X-ray, such as radio pulsar binaries, HMXBs, and LMXBs, filling them into the so called "Corbet Diagram" which initially investigated the period of orbit (P (orb))similar to the period of spin (P (spin)) correlation of HMXBs. We find that the evolutionary scenario comes more clearly and makes strong confirmation of the connection between LMXBs and radio pulsar binaries, predicted by the recycle process. However, the origins of radio pulsar binaries sre still unknown. Accretion Induced Collapse (AIP) process may be a mechanism which can explain the origin of the binary millisecond pulsars with relatively longer orbital periods. A correlation of P (orb) (1/3) similar to P (spin) (-1) of LMXBs and radio pulsar binaries may exist.

In this paper, we discuss a rigorous treatment of the refractive scintillation caused by a two-component interstellar scattering medium and a Kolmogorov form of density spectrum. It is assumed that the interstellar scattering medium is composed of a thin-screen interstellar medium (ISM) and an extended interstellar medium. We consider the case that the scattering of the thin screen concentrates in a thin layer represented by a δ function distribution and that the scattering density of the extended irregular medium satisfies the Gaussian distribution. We investigate and develop equations for the flux density structure function corresponding to this two-component ISM geometry in the scattering density distribution and compare our result with the observations. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation than does the single extended medium model. The level of refractive scintillation is strongly sensitive to the distribution of scattering material along the line of sight (LOS). The theoretical modulation indices are comparatively less sensitive to the scattering strength of the thin-screen medium, but they critically depend on the distance from the observer to the thin screen. The logarithmic slope of the structure function is sensitive to the scattering strength of the thin-screen medium, but is relatively insensitive to the thin-screen location. Therefore, the proposed model can be applied to interpret the structure functions of flux density observed in pulsar PSR B2111 + 46 and PSR B0136 + 57. The result suggests that the medium consists of a discontinuous distribution of plasma turbulence embedded in the interstellar medium. Thus our work provides some insight into the distribution of the scattering along the LOS to the pulsar PSR B2111 + 46 and PSR B0136 + 57.

We report the timing-analysis results obtained for RRAT J1819-1458 from regular timing observations at 1.54 GHz using the Urumqi 25 m radio telescope between 2007 April to 2008 March. RRAT J1819-1458 is a relatively young and highly magnetized neutron star discovered by its sporadic short bursts in the Parkes Multibeam Pulsar Survey data. In 94 hrs of observation data, we detected a total of 162 dispersed bursts of RRAT J1819-1458 with the signal-to-noise ratios (S/Ns) above 5-σ threshold. Among them, 5 bursts clearly show two-component structure. The S/N of the strongest burst is 13.3. The source’s DM measured through our data is 196.0±0.4 pc cm 3 . The timing position, frequency and its first derivative were determined using standard pulsar timing techniques on the arrival times of these individual bursts. The accuracy of the solved rotating parameters are improved comparing with that in previous publication. Our timing position with 2-σ error is consistent with the position of its X-ray counterpart CXOU J181934.1-145804. The effect of timing noise and the phase fluctuation of the individual short bursts on the timing residuals is briefly discussed. The distribution of the timing residuals is bimodal, which cannot be explained readily by timing irregularity.

The Crab Pulsar was observed at 1540 MHz with the 25 m radio telescope at Urumqi with a filterbank de-dispersion backend. A total of 2436 giant pulses with pulse energies larger than 4300 Jy mu s were detected in two observing sets. All of these giant pulses are located in the main pulse (MP) and inter pulse (IP) windows of the average profile of the Crab Pulsar. The ratio of the numbers of giant pulses detected in the IP and MP windows is about 0.05. Our results show that, at 1540 MHz, the emission in the IP is contributed by giant and normal pulses, while that in the MP is almost dominated by giant pulses. The distribution of energy of the 2436 giant pulses at 1540 MHz can be described by a power-law with index alpha = 3.13 +/- 0.09. The intrinsic threshold of giant pulse energy in the MP window is about 1400 Jy mu s at 1540 MHz.

Based on the gravitational potential of an undisturbed finitely-thick disk derived by Peng et al. (1978), 3-D Monte Carlo simulations of 4 × 105 pulsars are made for the four combinations of the two parameters of gravitational potential (hz1 = 0.001 kpc , hz2 = 0.325 kpc ) and two parameters of initial velocity distribution (σv1 = 115 km/s , σv2 = 200 km/s ). The 4 × 105 pulsars are divided into 20 age-groups and the fraction of “escaped” pulsars is calculated for each group. The “not escaped” pulsars in each group, whose simulated projective positions on the Galactic plane lie in the two radial ranges 0 108yr), the Galactic disk thickness has an obvious and complex effect on the evolution of the pulsar's cumulative scale height, but for a relatively short time ( 0.325 kpc and σv2 = 200 km/s , the simulated cumulative scale height is 0.596 ± 0.005 kpc in the radial range 5

We have observed the flux densities of PSRs B0329+54 and B1508+55 for 460 days at 327 MHz using the 25 m telescope of NAOC Urumqi Observatory. The flux density time series and the corresponding structure functions are presented. Our observational results at 327 MHz and other observations at 74 MHz and 610 MHz are compared with the predictions of the refractive scintillation theory. The frequency dependence of the refractive scintillation parameters for PSR B0329+54 has been investigated. The results show that the long-term flux density modulations of PSR B0329+54 at the three frequencies are best described by a Kolmogorov spectrum for electron density inhomogeneities. For PSR B 1508+55, we suggest that the spectrum of the electron density fluctuation has a power exponent beta

The flux density structure functions of PSRs B0525+21 and B2111+46 are calculated with the refractive interstellar scintillation (RISS) theory. The theoretical curves are in good agreement with observations [Astrophys. J. 539 (2000) 300] (hereafter S2000). The spectra of the electron density fluctuations both are of Kolmogorov spectra. We suggest that the flux density variations observed for these two pulsars are attributed to refractive interstellar scintillation, not to intrinsic variability.

By means of the refractive interstellar scintillation theory (RISS), the flux density structure functions of PSRs B1642-03, B0736-40, B0740-28 and B0329+54 are calculated and compared with the observations at 610 MHz by Stinebring et al. (2000, hereafter S2000). The theoretical results are in good agreement with observations and the spectra of the electron density fluctuation are all consistent with the Kolmogorov spectra. The theoretical modulation indices m are comparatively less sensitive to the distance H from the observer to the scattering screen but critically depend on the scattering strength $\overline{C_{N}^{2}}$. The structure function does not change remarkably with the variation of H if the scattering screen is closer to the pulsar than to the observer. The results in this paper indicate that the flux density variations observed for these four pulsars are due to a propagation effect (refractive scintillation), not to the intrinsic variability.

A digital pulsar backend based on a Field Programmable Gate Array (FPGA) is developed. It is designed for incoherent de-dispersion of pulsar observations and has a maximum bandwidth of 512 MHz. The channel bandwidth is fixed to 1 MHz, and the highest time resolution is 10 μs. Testing observations were carried out using the Urumqi 25-m telescope administered by Xinjiang Astronomical Observatory and the Kunming 40-m telescope administered by Yunnan Observatories, targeting PSR J0332+5434 in the L band and PSR J0437–4715 in the S band, respectively. The successful observation of PSR J0437–4715 demonstrates its ability to observe millisecond pulsars.

This paper presents a mathematical method for de-dispersion of average pulsar profiles. We applied this method to four dispersed pulsar profiles. The results revealed that this method significantly removed the dispersion broadening and the pulse widths were reduced by about 7% to 27%, depending on the magnitude of the pulsar dispersion measure.

A flux density variation event in PSR B0809+74 over some 11 hours is presented. This event was discovered during our routine monitoring of pulsars at 327 MHz using the 25-m radio telescope of Urumqi Astronomical Observatory. The observed time scale of variation is rather different from both the time scales of diffractive and refractive interstellar scintillation. This event may be due to a new propagation effect.

A Pulsar coherent de-dispersion experiment has been carried out using the 25-m Nanshan radio telescope at Urumqi Observatory. It uses a dual polarization receiver operating at 18 cm and a VLBI back-end: Mark5A, the minimum sampling time is 5 ns. The data processing system is based on a C program on Linux and a 4-node Beowulf cluster. A high quality data acquisition system and a cluster with more processors are needed to build an on-line pulsar coherent de-dispersion system in future. The main directions for the instrument are studies of pulsar timing, scintillation monitoring, etc.

The observing signals from pulsar are always influenced by the interstellar medium (ISM) scattering. In the lower frequency observation, the intensity profiles are broadened and the plane of polarization angle (PPA) curves are flattened by the scattering effect of the ISM. So before we analyze the scattered signal, we should take a proper approach to clear scattering effect from it. Observing data and simulation have shown that the Stokes phase portraits $I$-$U$, $I$-$Q$ and $Q$-$U$ are also distorted by the ISM scattering. In this paper, a simulation is held to demonstrate a scattering and a descattering of the Stokes phase portraits of a single pulse profile of a pulsar. As a realization of the simulation method, this paper has studied the descattering of Stokes phase portraits of lower frequency observation of PSR B1356$-$60, PSR B1831$-$03, PSR B1859+03, PSR B1946+35., Comment: 9 pages, 5 figures, accepted by astrophysics and space science

We report on the detection of sporadic, strong single pulses co-existing with a periodic weak emission in the duration of weak mode of PSR B0826-34. The intensities and durations of these pulses are comparable with that of the sub-pulses in the strong mode, and these pulses are distributed within the phase ranges of the main-pulse and interpulse of the strong-mode average profile. These results suggest that there are most possibly sporadic, very short timescale turn-on of strong-mode emission during the weak-mode state of the pulsar. The emission features of the bursts of strong pulses of PSR B0826-34 during its weak-mode state are similar to those of the rotating radio transients (RRATs). PSR B0826-34 is the second pulsar known which oscillates between pulsar-like and RRAT-like modes., Comment: 11 pages, 4 figures; 2012, ApJ, 759, L3

Using the Kunming 40-m radio telescope at Yunnan Observatory, a Pulsar coherent de-dispersion experiment has been carried out, which uses a dual polarization receiver operating at s-band and a VLBA back-end: Mark5B+, whose highest sampling rate is 64MHz. The data processing system is based on the C programs on Linux. Some pulsar profiles had been carried out using the DBBC and Mark5B+ record system. In this paper we will discuss the application of the DBBC platform in pulsar observation domain and the algorithm of de-dispersion. The main purposes for the instrument are studies of pulsar mode changing, pulsar timing, scintillation monitoring, glitches, GPs (Giant Pulsars), etc.

We present high-quality observations of PSR B0826-34 at 1374 MHz. The emission from this pulsar exhibits strong bursts of pulses followed by long periods of `null' pulses. When it is strong, the radiation extends through the whole pulse period. We show for the first time that there is weak emission during the `null' phases, which should therefore be considered to be a different mode rather than a null. During this weak mode the profile is similar to that observed in the strong mode at low radio frequency. Using a phase-tracking method, the pattern of drifting subpulses during the strong mode is seen to be coherent across the whole profile. The drift rate is variable and includes positive and negative values. Thirteen subpulse bands have been directly observed, covering the whole longitude range. The subpulses and their spacings ($P_2$) are wider in one half of the profile than those in the other half. This difference, and the variation of observed $P_2$ within the two regions, can be accounted for if the magnetic pole is inclined to the rotation axis by about 0.5 degrees. These two regions appear to represent radiation from outer and inner cones. The intensity modulation of subpulses in all longitude ranges is related to the magnitude of the drift rate., 8 pages, 10 figures. Accepted for publication in MNRAS

The pulsar’s observation is being developed using the 25m radio telescope at Urumqi Astronomical Observatory (UAO). A pulsar timing system has been set up. It uses a dual polarization receiver operating at 18cm and a filterbank receiver. Timing properties of about 100 pulsars will be monitored with this system. The single channel system at 92 cm works since 1996 for the program of mean pulse profile and long term variation of intensity about 18 pulsars. The observation of spectrum properties for few strong pulsars at 92cm, 18cm, 13cm, 6cm, and 3.6cm is in progress.

A rigorous treatment of the refractive scintillation caused by a two-component interstellar scattering medium and a Kolmogorov form of density spectrum is discussed. It is assumed that the interstellar scattering medium is composed of a thin screen ISM and an extended interstellar medium. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation than the single extended medium model along the line of sight to the pulsar PSR B0136+57.