The observed polarization of radio pulsars involves several peculiar effects, such as comparable amount of orthogonal polarization modes (OPMs) which often bear the same handedness of circular polarisation V. In the average profiles of B1913+16 and B1933+16, orthogonal jumps of polarization angle (PA) are observed to occur at the maximum V, instead of V = 0. High levels of V are also observed in core components (eg. in B1237+25), where they are accompanied by strong distortions of PA from the rotating vector model. In weakly polarized emission, PA jumps by 45° are observed in B1919+21 and B0823+26. It is shown that all these peculiarities can be interpreted in a model which assumes coherent addition of waves in natural propagation modes.

We evaluated ambipolar diffusion velocity in a magnetar. Previous studies concerning ambipolar diffusion ignored the presence of the crust, although a magnetar has both core and crust. We considered both core and crust and examined the influence of the crust in this study. We found that the crustal magnetic field can accelerate the ambipolar diffusion in its core.

In this study the onset of stress-free Boussinesq thermal convection in rotating spherical shells with aspect ratio η = rinner/router = 0.9, Prandtl numbers Pr ∈ [10−4, 10−1], and Taylor numbers Ta ∈ [104, 1012] is considered. We focus on the form of the convective cell pattern that develops, and on its time scales, since this may have observational consequences for thermonuclear burning and the development of burst oscillations in the exploding oceans of accreting neutron stars (Watts (2012)).

International LOFAR stations, equipped with powerful backends, can be used as individual telescopes, and provide data sets complementary to those obtained with the LOFAR Core. Such “local mode” observations are particularly adapted to monitoring observations, where the advantage of having a high observing cadence (one observation per week) outweighs the reduced sensitivity of a single station when compared to the full array. With such observations, it is possible to monitor the temporal evolution of the pulsars’ behaviour via its dispersion, scattering, intensity, and profile shape. We present recent studies performed in the LOFAR low band (10-90 MHz).

The nearest millisecond pulsar PSR J0437–4715 is the ideal target to constrain the dense matter equation of state using the lightcurve modelling method. Our analysis combining XMM-Newton, NuSTAR, and ROSAT observations removed ambiguities in the spectral modelling of the surface emission from PSR J0437–4715. Furthermore, the NuSTAR observation demonstrated that the non-thermal hard tail emission was pulsed at the pulsar spin period. These features are crucial to model the lightcurve and to measure the radius of the neutron star. This conference proceeding is based on the publication Guillot et al. (2016).

PSR J0337+1715 is a millisecond radio pulsar in a hierarchical stellar triple system with two white dwarfs. This system is a unique and excellent laboratory in which to test the strong equivalence principle (SEP) of general relativity. An initial SEP-violation test was performed using direct 3-body numerical integration of the orbit in order to model the more than 25000 pulse times of arrival (TOAs) from three radio telescopes: Arecibo, Green Bank and Westerbork. In this work I present our efforts to quantify the effects of systematics in the TOAs and timing residuals, which limit the precision of an SEP test. In particular, we apply Fourier-based techniques to the timing residuals in order to isolate the effects of systematics that can masquerade as an SEP violation.

If the observed parallax ϖ′ has a gaussian measurement error σ, there is a 68% probability that the actual parallax ϖ is in the range ϖ′ − σ < ϖ < ϖ′ + σ (the frequentist approach). The probability distribution within this range is not known from ϖ′ and σ alone, and in particular, we cannot state that the most probable distance D is given by D = 1/ϖ′. To obtain a probability distribution, we need to know or assume a distribution of pulsar distances. Similar assumptions are also required to estimate the velocity distribution of radio pulsars.

Since the first light of the 2.4-m Thai National Telescope in 2013, Thailand foresees another great leap forward in astronomy. A project known as “Radio Astronomy Network and Geodesy for Development” (RANGD) by National Astronomical Research Institute of Thailand (NARIT) has been approved for year 2017-2021. A 40-m radio telescope has been planned to operate up to 115-GHz observation with prime-focus capability for low frequency and phased array feed receivers. The telescope’s first light is expected in late 2019 with a cryogenics K-band and L-band receivers. RFI environment at the site has been investigated and shown to be at reasonable level. A 13-m VGOS telescope is also included for geodetic applications. Early single-dish science will focus on time domain observations, such as pulsars and transients, outbursts and variability of maser and AGN sources.

We present simultaneous multi-frequency observations of PSR J1822–2256 for the first time, utilizing the unique capabilities of upgraded Giant Meterwave Radio Telescope (uGMRT). No emission is detected in about 10 % of pulses. At least two drift modes and a possibly third rare mode, occur for 66, 21 and 2 % pulses respectively (P3 ~ 17, 7.5 and 5 P0 respectively). The three drift modes and the nulls occur concurrently from 250 to 1500 MHz. Modal average profiles are distinct with their widths increasing with drift rate. These sub-pulse drift related profile mode-changes can provide independent probes of beam geometry and polar gap physics.

Sub-pulse drift related profile mode-changes provide a useful probe of pulsar radio emission. Measurements on modal profiles of PSRs B0031–07, J1822–2256 and B2319+60 are presented for different drift modes in this communication. The width of profile increases with the drift rate, while no such trend is seen for the pulsed flux density for all these pulsars. A brief discussion of implications for models is presented.

We identified gigahertz-peaked spectra behavior from our radio interferometric observations at low frequencies using the Giant Metrewave Radio Telescope. We modeled the turnover spectra based on thermal free-free absorption in the interstellar medium. The free-free absorption is believed to be responsible for the inverted spectrum. Using the model, we were able to put some observational constrains on the physical parameters of the absorbing matter, which allows us to distinguish between the possible sources of absorption.

We calculate the luminosity of the synchrotron radiation from the vicinity of the light cylinder. We find that even if the thermal emission from the entire surface is included as the seed photon, the γ-ray to X-ray flux ratio for young pulsars is significantly higher than the observations. For these pulsars, most of γ-ray photons may be absorbed in the magnetosphere.

Recent studies of interstellar scattering frequency evolution indicate, that for a large number of pulsars the measured scatter time to frequency scaling does not follow predictions based upon simple scattering models. The number of such deviations suggests, that what was previously known as “anomalous scattering” is actually quite normal for a large subset of the pulsar population. New observations are needed, especially at low frequencies, to study the scattering of low-DM objects. In this regard even small telescopes, such as single LOFAR stations - like PL-612 in Bałdy, near Olsztyn, Poland - can be extremely helpful.

Both the physics of the pulsar emission mechanism and free-free absorption in the intervening interstellar medium can be tested with the pulsar radio spectra. We have built on our previous work on describing LOFAR population of millisecond pulsars (MSPs; Kondratiev et al. 2016) and HBA census of slow pulsars (Bilous et al. 2016) and present the study of radio spectra of the MSPs with a special attention on the low-frequency turnover. Using LOFAR timing data allowed us to measure flux densities of many MSPs over time span of up to three years in the frequency range 110–188 MHz. This provided more reliable estimates of mean flux densities and spectra reducing the influence of refractive scintillation, ionosphere and other factors on a single flux measurement. Together with published data at other radio frequencies we constructed pulsars’ spectra and fitted them with single or broken power-laws. We discuss the obtained spectra and their fits, paying special attention to the low-frequency turnover, and compare broadband radio spectra of MSPs to those of normal pulsars.

In this contribution, we have made use of the contemporary equation of states (EOSs) for the complete neutron star structure, and confronted them with one particular glitch constrain for the crustal moment of inertia (MOI). We find that with these EOSs, the radii of three millisecond pulsars selected by NICER: PSR J0437-4715, PSR J1614-2230, PSR J0751+1807, are all around 12.5 km. Also, a star with M ≲ 1.55M⊙ would fulfill the MOI calculation for glitch constrain with the latest neutron superfluidity density, and the glitch crisis might not be present.

The radial velocity of a pulsar induces the Doppler effect on its intrinsic spin properties. In particular, it can generate a contribution to the frequency second derivative. We estimated this effect for each of the International Pulsar Timing Array pulsars. We also assessed the possibility of measuring the frequency second derivative in the observational data.

In this paper, we present our study on multi-frequency scatter-broadening observations of a large sample of pulsars, made using the Ooty Radio Telescope (ORT) and the Giant Metrewave Radio Telescope (GMRT). For each pulsar, the scatter-broadening time scales (τsc) have been estimated at different observing frequencies and the dependence of τsc with the observing frequency, i.e., the frequency scaling index (α) has been obtained. We report estimates of α for a set of 39 pulsars, of which 31 are completely new and provide the first-time measurement on about 50% of the sample. This enhanced sample suggests that almost 65% of the pulsars have an α much lower than the conventional value of 4.4 for a Kolmogorov type turbulence spectrum, and a considerably large scattering strength. An increase in scattering strength is observed with the distance to the pulsar in the Galaxy.

Sub-pulse drifting has been regarded as one of the most insightful aspects of the pulsar radio emission. The phenomenon is generally explained with a system of emission sub-beams rotating around the magnetic axis, originating from a carousel of sparks near the pulsar surface (the carousel model). Since the observed radio emission at different frequencies is generated at different altitudes in the pulsar magnetosphere, corresponding sampling of the carousel on the polar cap differs slightly in magnetic latitude. When this aspect is considered, it is shown here that the carousel model predicts important observable effects in multi-frequency or wide-band observations. Also presented here are brief mentions of how this aspect can be exploited to probe the electrodynamics in the polar cap by estimating various physical quantities, and correctly interpret various carousel related phenomena, in addition to test the carousel model itself.

Mode changing is a phenomenon where a pulsar’s emission abruptly changes between two or more quasi-stable modes. We have discovered mode changing in the Black Widow Pulsar (PSR B1957+20), a first detection of mode changing in a millisecond pulsar. On average, a mode change occurs every 1.7 seconds. Multiple components across the pulse profile participate in the mode changing, indicating that this is likely caused by a global change in the pulsar’s magnetosphere.

The challenges of detecting and localising Fast Radio Bursts in real time can be met with the use of Phased Array Feeds. One such system, capable of creating up to 36 simultaneous beams, is currently being commissioned at the Effelsberg radio telescope in Germany following testing at the 64 m Parkes radio telescope. The PAFINDER (Phased Array Feed FRB Finder) pipeline will be used with this receiver to enable real–time single–pulse detection and localisation.