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 timescales 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 ms pulsars is being observed at three radio-frequency bands, 50 cm (ß700 MHz), 20 cm (ß1400 MHz), and 10 cm (ß3100 MHz), with observations at intervals of two to three 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 10 of the 20 pulsars, rms timing residuals are less than 1 μs 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 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.

We present high signal-to-noise ratio, multi-frequency polarization pulse profiles for 24 millisecond pulsars that are being observed as part of the Parkes Pulsar Timing Array (PPTA) project. The pulsars are observed in three bands, centred close to 730, 1400 and 3100 MHz, using a dual-band 10 cm/50 cm receiver and the central beam of the 20 cm multibeam receiver. Observations spanning approximately six years have been carefully calibrated and summed to produce high S/N profiles. This allows us to study the individual profile components and in particular how they evolve with frequency. We also identify previously undetected profile features. For many pulsars we show that pulsed emission extends across almost the entire pulse profile. The pulse component widths and component separations follow a complex evolution with frequency; in some cases these parameters increase and in other cases they decrease with increasing frequency. The evolution with frequency of the polarization properties of the profile is also non-trivial. We provide evidence that the pre-and post-cursors generally have higher fractional linear polarization than the main pulse. We have obtained the spectral index and rotation measure for each pulsar by fitting across all three observing bands. For the majority of pulsars, the spectra follow a single power-law and the position angles follow a λ 2 relation, as expected. However, clear deviations are seen for some pulsars. We also present phase-resolved measurements of the spectral index, fractional linear polarization and rotation measure. All these properties are shown to vary systematically over the pulse profile.

Fast radio bursts (FRBs) are mysterious millisecond-duration radio transients 1, 2. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star magnetospheres 3-5 or relativistic shocks far from the central energy source 6-8. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters 9, 10 , or variable polarization angles in some other apparently one-off events 11, 12. Here we report observations of 15 bursts from FRB 180301 and find various polarization

Polarization profiles are presented for 20 millisecond pulsars that are being observed as part of the Parkes Pulsar Timing Array project. The observations used the Parkes multibeam receiver with a central frequency of 1369 MHz and the Parkes digital filterbank pulsar signal-processing system PDFB2. Because of the large total observing time, the summed polarization profiles have very high signal/noise ratios and show many previously undetected profile features. Thirteen of the 20 pulsars show emission over more than half of the pulse period. Polarization variations across the profiles are complex and the observed position angle variations are generally not in accord with the rotating-vector model for pulsar polarization. Never-the-less, the polarization properties are broadly similar to those of normal (non-millisecond) pulsars, suggesting that the basic radio emission mechanism is the same in both classes of pulsar. The results support the idea that radio emission from millisecond pulsars originates high in the pulsar magnetosphere, probably close to the emission regions for high-energy X-ray and gamma-ray emission. Rotation measures were obtained for all 20 pulsars, eight of which had no previously published measurements.Comment: 15pages, 21 figures, 3 tables, accepted for publication in MNRA

We derive constraints on millicharged dark matter and axion-like particles using pulsar timing and fast radio burst observations. For dark matter particles of charge e, the constraint from time of arrival (TOA) of waves is /m milli 10 −8 eV −1 , for masses m milli 10 −6 eV. For axionlike particles, the polarization of the signals from pulsars yields a bound in the axial coupling g/ma 10 −13 GeV −1 /(10 −22 eV), for ma 10 −19 eV. Both bounds scale as (ρ/ρ dm ) 1/2 for fractions of the total dark matter energy density ρ dm . We make a precise study of these bounds using TOA from several pulsars, FRB 121102 and polarization measurements of PSR J0437−4715. Our results rule out a new region of the parameter space for these dark matter models.Unraveling the nature of dark matter (DMa) is among the most urgent issues in fundamental physics. Indirect searches aim at detecting the effects of DMa in astrophysical observations, beyond its pure gravitational interaction. Given the feeble interaction of DMa with standard model fields, precise measurements are particularly promising for these searches. When one requires precision, a particular measurement stands out in astrophysics: the time of arrival (TOA) of radio waves from pulsars and fast radio bursts (FRBs). The use of pulsar timing has already been suggested to study the effects of dark matter [1][2][3][4][5][6][7][8][9]. In this Letter we present new results for DMa models directly coupled to light from the propagation of radio pulses from pulsars and FRBs. A more comprehensive exploration will be presented elsewhere [10].If DMa is coupled to the electromagnetic field, one expects modifications in the emission, propagation, and detection of radio pulses. We focus here on the effects during the propagation, which are robust under astrophysical uncertainties. In particular, we derive stringent constraints on millicharged DMa and axion-like particles (ALPs) based on dispersion measurements (DM) of radio signals from pulsars and FRBs, and on the modulation of the light polarization angle due to axion-like DMa in the Milky Way.We give a unified treatment, where the millicharged DMa and ALPs are considered as independent species. In the former case we consider that (a fraction of) the DMa is made of particles with mass m milli and electric charge q = e ( 1) [11][12][13][14][15][16][17][18]. As an example, this coupling arises in models where the DMa is charged under a dark photon, which is kinematically coupled to the visible photon [16,17]. In our analysis we remain agnostic to the origin of this term and other possible model-dependent signatures behind the charge of the DMa, and focus on constraining . Regarding ALPs, we assume the existence of axion-like [19][20][21][22][23], pseudo-scalar DMa of mass m a (represented by the field φ below).The relevant field equations readwhere g is the ALP-photon axial coupling, j ν is the ordinary electron current, whereas j ν milli is the current from millicharged particles. The role of this term in the propagation of radio-waves will...

Aims. We intend to study of the nulling and subpulse drifting in PSR J1727−2739 in detail to investigate its radiation properties. Methods. The observations were carried out on 20 March, 2004 using the Parkes 64-m radio telescope with a central frequency of 1518 MHz. A total of 5568 single pulses were analysed.Results. This pulsar shows well-defined nulls with lengths lasting from 6 to 281 pulses and separated by burst phases ranging from 2 to 133 pulses. We estimate a nulling fraction of around 68%. No emission in the average pulse profile integrated over all null pulses is detected with significance above 3σ. Most transitions from nulls to bursts are within a few pulses, whereas the transitions from bursts to nulls exhibit two patterns of decay; these transitions either decrease gradually or rapidly. In the burst phase, we find that there are two distinct subpulse drift modes with vertical spacing between the drift bands of 9.7 ± 1.6 and 5.2 ± 0.9 pulse periods, while sometimes there is a third mode with no subpulse drifting. Some mode transitions occur within a single burst, while others are separated by nulls. Different modes have different average pulse profiles. Possible physical mechanisms are discussed.

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project. It is found that the observed variations are dominated by changes in the Faraday rotation occurring in the Earth's ionosphere. Two ionospheric models are used to correct for the ionospheric contribution and it is found that one based on the International Reference Ionosphere gave the best results. Little or no significant long-term variation in interstellar RM was found with limits typically about 0.1 rad m −2 yr −1 in absolute value. In a few cases, apparently significant RM variations over timescales of a few 100 days or more were seen. These are unlikely to be due to localised magnetised regions crossing the line of sight since the implied magnetic fields are too high. Most probably they are statistical fluctuations due to random spatial and temporal variations in the interstellar electron density and magnetic field along the line of sight.