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Register a new userThe Thousand-Pulsar-Array programme on MeerKAT II: observing strategy for pulsar monitoring with subarrays
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The Thousand Pulsar Array (TPA) project currently monitors about 500 pulsars with the sensitive MeerKAT radio telescope by using subarrays to observe multiple sources simultaneously. Here we define the adopted observing strategy, which guarantees that each target is observed long enough to obtain a high fidelity pulse profile, thereby reaching a sufficient precision of a simple pulse shape parameter. This precision is estimated from the contribution of the system noise of the telescope, and the pulse-to-pulse variability of each pulsar, which we quantify under some simplifying assumptions. We test the assumptions and choice of model parameters using data from the MeerKAT 64-dish array, Lovell and Parkes telescopes. We demonstrate that the observing times derived from our method produce high fidelity pulse profiles that meet the needs of the TPA in studying pulse shape variability and pulsar timing. Our method can also be used to compare strategies for observing large numbers of pulsars with telescopes capable of forming multiple subarray configurations. We find that using two 32-dish MeerKAT subarrays is the most efficient strategy for the TPA project. We also find that the ability to observe in different array configurations will become increasingly important for large observing programmes using the Square Kilometre Array telescope.
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We report here on initial results from the Thousand Pulsar Array (TPA) programme, part of the Large Survey Project MeerTime on the MeerKAT telescope. The interferometer is used in tied-array mode in the band from 856 to 1712~MHz, and the wide band coupled with the large collecting area and low receiver temperature make it an excellent telescope for the study of radio pulsars. The TPA is a 5 year project which aims to observe (a) more than 1000 pulsars to obtain high-fidelity pulse profiles, (b) some 500 of these pulsars over multiple epochs, (c) long sequences of single-pulse trains from several hundred pulsars. The scientific outcomes from the programme will include determination of pulsar geometries, the location of the radio emission within the pulsar magnetosphere, the connection between the magnetosphere and the crust and core of the star, tighter constraints on the nature of the radio emission itself as well as interstellar medium studies. First results presented here include updated dispersion measures, 26 pulsars with Faraday rotation measures derived for the first time and a description of interesting emission phenomena observed thus far.
We present observations of 35 high spin-down energy radio pulsars using the MeerKAT telescope. Polarisation profiles and associated parameters are also presented. We derive the geometry for a selection of pulsars which show interpulse emission. We point out that, in several cases, these radio pulsars should also be seen in $gamma$-rays but that improved radio timing is required to aid the high-energy detection. We discuss the relationship between the width of the radio profile and its high-energy detectability. Finally, we reflect on the correlation between the spin-down energy and the radio polarisation fraction and the implications this may have for $gamma$-ray emission.
We have measured the scattering timescale, $tau$, and the scattering spectral index, $alpha$, for 84 single-component pulsars. Observations were carried out with the MeerKAT telescope as part of the Thousand-Pulsar-Array programme in the MeerTime project at frequencies between 0.895 and 1.670 GHz. Our results give a distribution of values for $alpha$ (defined in terms of $tau$ and frequency $ u$ as $taupropto u^{-alpha}$) for which, upon fitting a Gaussian, we obtain a mean and standard deviation of $langlealpharangle = 4.0 pm 0.6$. This is due to our identification of possible causes of inaccurate measurement of $tau$, which, if not filtered out of modelling results, tend to lead to underestimation of $alpha$. The pulsars in our sample have large dispersion measures and are therefore likely to be distant. We find that a model using an isotropic scatter broadening function is consistent with the data, likely due to the averaging effect of multiple scattering screens along the line of sight. Our sample of scattering parameters provides a strong data set upon which we can build to test more complex and time-dependent scattering phenomena, such as extreme scattering events.
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.
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.
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