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Register a new userResults of 12 Years of Pulsar Timing at Nanshan -- I
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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 $n>0$.
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We present an overview and the first results from a large-scale pulsar timing programme that is part of the UTMOST project at the refurbished Molonglo Observatory Synthesis Radio Telescope (MOST) near Canberra, Australia. We currently observe more than 400 mainly bright southern radio pulsars with up to daily cadences. For 205 (8 in binaries, 4 millisecond pulsars) we publish updated timing models, together with their flux densities, flux density variability, and pulse widths at 843 MHz, derived from observations spanning between 1.4 and 3 yr. In comparison with the ATNF pulsar catalogue, we improve the precision of the rotational and astrometric parameters for 123 pulsars, for 47 by at least an order of magnitude. The time spans between our measurements and those in the literature are up to 48 yr, which allows us to investigate their long-term spin-down history and to estimate proper motions for 60 pulsars, of which 24 are newly determined and most are major improvements. The results are consistent with interferometric measurements from the literature. A model with two Gaussian components centred at 139 and $463~text{km} : text{s}^{-1}$ fits the transverse velocity distribution best. The pulse duty cycle distributions at 50 and 10 per cent maximum are best described by log-normal distributions with medians of 2.3 and 4.4 per cent, respectively. We discuss two pulsars that exhibit spin-down rate changes and drifting subpulses. Finally, we describe the autonomous observing system and the dynamic scheduler that has increased the observing efficiency by a factor of 2-3 in comparison with static scheduling.
In this paper we study a set of twelve pulsars that previously had not been characterized. Our timing shows that eleven of them are normal isolated pulsars, with rotation periods between 0.22 and 2.65 s, characteristic ages between 0.25 Myr and 0.63 Gyr, and estimated magnetic fields ranging from 0.05 to 3.8x 10^{12} G. The youngest pulsar in our sample, PSR~J0627+0706, is located near the Monoceros supernova remnant (SNR G205.5+0.5), but it is not the pulsar most likely to be associated with it. We also confirmed the existence of a candidate from an early Arecibo survey, PSR~J2053+1718, its subsequent timing and polarimetry are also presented here. It is an isolated pulsar with a spin period of 119 ms, a relatively small magnetic field of 5.8x10^9 G and a characteristic age of 6.7 Gyr; this suggests the pulsar was mildly recycled by accretion from a companion star which became unbound when that companion became a supernova. We report the results of single-pulse and average Arecibo polarimetry at both 327 and 1400 MHz aimed at understanding the basic emission properties and beaming geometry of these pulsars. Three of them (PSRs~J0943+2253, J1935+1159 and J2050+1259) have strong nulls and sporadic radio emission, several others exhibit interpulses (PSRs J0627+0706 and J0927+2345) and one shows regular drifting subpulses (J1404+1159).
In May 1982, when Italy joined ESO, only two isolated neutron stars (INSs) had been identified in the optical: the Crab and Vela pulsars. Thanks to the ESO telescopes and the perseverance of a few Italian astronomers, now about 30 INSs have been identified in the optical/IR, and a new important channel in their multi-wavelength studies has been opened. In this contribution, I review the major steps in 30 years of INS studies at ESO, highlight the role of Italian astronomers, and introduce future perspectives with the E-ELT.
The 30-Hz rotation rate of the Crab pulsar has been monitored at Jodrell Bank Observatory since 1984 and by other observatories before then. Since 1968, the rotation rate has decreased by about $0.5$,Hz, interrupted only by sporadic and small spin up events (glitches). 24 of these events have been observed, including a significant concentration of 15 occurring over an interval of 11 years following MJD 50000. The monotonic decrease of the slowdown rate is partially reversed at glitches. This reversal comprises a step and an asymptotic exponential with a 320-day time constant, as determined in the three best-isolated glitches. The cumulative effect of all glitches is to reduce the decrease in slowdown rate by about 6%. Overall, a low mean braking index of $2.342(1)$ is measured for the whole period, compared with values close to $2.5$ in intervals between glitches. Removing the effects of individual glitches reveals an underlying power law slowdown with the same braking index of 2.5. We interpret this value in terms of a braking torque due to a dipolar magnetic field in which the inclination angle between the dipole and rotation axes is increasing. There may also be further effects due to a monopolar particle wind or infalling supernova debris.
While pulsars possess exceptional rotational stability, large scale timing studies have revealed at least two distinct types of irregularities in their rotation: red timing noise and glitches. Using modern Bayesian techniques, we investigated the timing noise properties of 300 bright southern-sky radio pulsars that have been observed over 1.0-4.8 years by the upgraded Molonglo Observatory Synthesis Telescope (MOST). We reanalysed the spin and spin-down changes associated with nine previously reported pulsar glitches, report the discovery of three new glitches and four unusual glitch-like events in the rotational evolution of PSR J1825$-$0935. We develop a refined Bayesian framework for determining how red noise strength scales with pulsar spin frequency ($ u$) and spin-down frequency ($dot{ u}$), which we apply to a sample of 280 non-recycled pulsars. With this new method and a simple power-law scaling relation, we show that red noise strength scales across the non-recycled pulsar population as $ u^{a} |dot{ u}|^{b}$, where $a = -0.84^{+0.47}_{-0.49}$ and $b = 0.97^{+0.16}_{-0.19}$. This method can be easily adapted to utilise more complex, astrophysically motivated red noise models. Lastly, we highlight our timing of the double neutron star PSR J0737$-$3039, and the rediscovery of a bright radio pulsar originally found during the first Molonglo pulsar surveys with an incorrectly catalogued position.
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