We have used the Nanshan 25-m Radio Telescope at Xinjiang Astronomical Observatory to obtain timing observations of 87 pulsars from 2002 July to 2014 March. Using the Cholesky timing analysis method we have determined positions and proper motions for
48 pulsars, 24 of which are improved positions compared to previously published values. We also present the first published proper motions for nine pulsars and improved proper motions for 21 pulsars using pulsar timing and position comparison method. The pulsar rotation parameters are derived and are more accurate than previously published values for 36 pulsars. Glitches are detected in three pulsars: PSRs J1722$-$3632, J1852$-$0635 and J1957+2831. For the first two, the glitches are large, with $Delta u_g/ u > 10^{-6}$, and they are the first detected glitches in these pulsars. PSR J1722$-$3632 is the second oldest pulsar with large glitch. For the middle-age pulsars ($tau_c > 10^5$~yr), the calculated braking indices, $|n|$, are strongly correlated with $tau_c$ and the numbers of positive and negative values of $n$ are almost equal. For young pulsars ($tau_c < 10^5$~yr), there is no correlation between $|n|$ and $tau_c$ and most have $n>0$.
By analysing the data acquired from the Parkes 64-m radio telescope at 1369 MHz, we report on the phase-stationary non-drift amplitude modulation observed in PSR J1048-5832. The high-sensitivity observations revealed that the central and trailing com
ponents of the pulse profile of this pulsar switch between a strong mode and a weak mode periodically. However, the leading component remains unchanged. Polarization properties of the strong and weak modes are investigated. Considering the similarity to mode changing, we argue that the periodic amplitude modulation in PSR J1048$-$5832 is periodic mode changing. The fluctuation spectral analysis showed that the modulation period is very short (~2.1 s or 17 P1), where P1 is the rotation period of the pulsar. We find that this periodic amplitude modulation is hard to explain by existing models that account for the periodic phenomena in pulsars like subpulse drifting.
We describe an ultra-wide-bandwidth, low-frequency receiver (UWL) recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band (~60%) the system temperature is
approximately 22K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver including its astronomical objectives, as well as the feed, receiver, digitiser and signal-processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration and timing stability.
PSR J1825$-$0935 (PSR B1822$-$09) switches between radio-quiet (Q-mode) and radio-bright (B-mode) modes. The Q-mode is known to have a periodic fluctuation that modulates both the interpulse and the main pulse with the same period. Earlier investigat
ors argued that the periodic Q-mode modulation is associated with drifting subpulses. We report on single-pulse observations of PSR J1825$-$0935 that were made using the Parkes 64-m radio telescope with a central frequency of 1369 MHz. The high-sensitivity observations revealed that the periodic Q-mode modulation is in fact a periodic longitude-stationary intensity modulation occurring in the interpulse and the main pulse. The fluctuation spectral analysis showed that the modulation period is about $43 P_1$, where $P_1$ is the rotation period of the pulsar. Furthermore, we confirm that the modulation patterns in the interpulse and the main pulse are phase-locked. Specifically, the intensities of the interpulse and the immediately following main pulse are more highly correlated than for the main pulse and interpulse at any other lag. Polarization properties of the strong and weak Q-mode states are different, even for the trailing part of the main pulse which does not show the periodic intensity modulation.
We present the measurements of Faraday rotation for 477 pulsars observed by the Parkes 64-m radio telescope and the Green Bank 100-m radio telescope. Using these results along with previous measurements for pulsars and extra-galactic sources, we anal
yse the structure of the large-scale magnetic field in the Galactic disk. Comparison of rotation measures of pulsars in the disk at different distances as well as with rotation measures of background radio sources beyond the disk reveals large-scale reversals of the field directions between spiral arms and interarm regions. We develop a model for the disk magnetic field, which can reproduce not only these reversals but also the distribution of observed rotation measures of background sources.
We derive the Suns offset from the local mean Galactic plane($z_odot$) using the observed $z$ distribution of young pulsars. Pulsar distances are obtained from measurements of annual parallax, HI absorption spectra or associations where available and
otherwise from the observed pulsar dispersion and a model for the distribution of free electrons in the Galaxy. We fit the cumulative distribution function for a ${rm sech}^2(z)$ distribution function, representing an isothermal self-gravitating disk, with uncertainties being estimated using the bootstrap method. We take pulsars having characteristic age $tau_c<10^{6.5}$~yr and located within 4.5~kpc of the Sun, omitting those within the local spiral arm and those significantly affected by the Galactic warp, and solve for $z_odot$ and the scale height, $H$, for different cutoffs in $tau_c$. We compute these quantities using just the independently determined distances, and these together with DM-based distances separately using the YMW16 and NE2001 Galactic electron density models. We find that an age cutoff at $10^{5.75}$~yr with YMW16 DM-distances gives the best results with a minimum uncertainty in $z_odot$ and an asymptotically stable value for $H$ showing that, at this age and below, the observed pulsar $z$-distribution is dominated by the dispersion in their birth locations. From this sample of 115 pulsars, we obtain $z_odot=13.4pm$4.4~pc and $H=56.9pm$6.5~pc, similar to estimated scale heights for OB stars and open clusters. Consistent results are obtained using the independent-only distances and using the NE2001 model for the DM-based distances.
Timing observations from the Parkes 64-m radio telescope for 165 pulsars between 1990 and 2011 have been searched for period glitches. A total of 107 glitches were identified in 36 pulsars, where 61 have previously been reported and 46 are new discov
eries. Glitch parameters were measured by fitting the timing residual data. Observed relative glitch sizes Delta u_g/ u range between 10^-10 and 10^-5, where u = 1/P is the pulse frequency. We confirm that the distribution of Delta u_g/ u is bimodal with peaks at approximately 10^-9 and 10^-6. Glitches are mostly observed in pulsars with characteristic ages between 10^3 and 10^5 years, with large glitches mostly occurring in the younger pulsars. Exponential post-glitch recoveries were observed for 27 large glitches in 18 pulsars. The fraction Q of the glitch that recovers exponentially also has a bimodal distribution. Large glitches generally have low Q, typically a few per cent, but large Q values are observed in both large and small glitches. Observed time constants for exponential recoveries ranged between 10 and 300 days with some tendency for longer timescales in older pulsars. Shorter timescale recoveries may exist but were not revealed by our data which typically have observation intervals of 2 - 4 weeks. For most of the 36 pulsars with observed glitches, there is a persistent linear increase in dot u in the inter-glitch interval. Where an exponential recovery is also observed, the effects of this are superimposed on the linear increase in dot u. In some cases, the slope of the linear recovery changes at the time of a glitch. The ddot u values characterising the linear changes in dot u are almost always positive and, after subtracting the magnetospheric component of the braking, are approximately proportional to the ratio of |dot u| and the inter-glitch interval, as predicted by vortex-creep models.
A pulsar timing array (PTA), in which observations of a large sample of pulsars spread across the celestial sphere are combined, allows investigation of global phenomena such as a background of gravitational waves or instabilities in atomic timescale
s that produce correlated timing residuals in the pulsars of the array. The Parkes Pulsar Timing Array (PPTA) is an implementation of the PTA concept based on observations with the Parkes 64-m radio telescope. A sample of 20 millisecond pulsars is being observed at three radio-frequency bands, 50cm (~700 MHz), 20cm (~1400 MHz) and 10cm (~3100 MHz), with observations at intervals of 2 - 3 weeks. Regular observations commenced in early 2005. This paper describes the systems used for the PPTA observations and data processing, including calibration and timing analysis. The strategy behind the choice of pulsars, observing parameters and analysis methods is discussed. Results are presented for PPTA data in the three bands taken between 2005 March and 2011 March. For ten of the 20 pulsars, rms timing residuals are less than 1 microsec for the best band after fitting for pulse frequency and its first time derivative. Significant red timing noise is detected in about half of the sample. We discuss the implications of these results on future projects including the International Pulsar Timing Array (IPTA) and a PTA based on the Square Kilometre Array. We also present an extended PPTA data set that combines PPTA data with earlier Parkes timing data for these pulsars.
Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based timescale that has a precision comparable to the uncertainties in international atomic timescales. Our ensemble of pulsars provides an
Ensemble Pulsar Scale (EPS) analogous to the free atomic timescale Echelle Atomique Libre (EAL). The EPS can be used to detect fluctuations in atomic timescales and therefore can lead to a new realisation of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the International Atomic Timescale (TAI) and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar timescale.
The Parkes Pulsar Data Archive currently provides access to 165,755 data files obtained from observations carried out at the Parkes Observatory since the year 1991. Data files and access methods are compliant with the Virtual Observatory protocol. Th
is paper provides a tutorial on how to make use of the Parkes Pulsar Data Archive and provides example queries using on-line interfaces.
