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We report a study of the transitional intervals between pulsar B0943+10’s two primary Q and B emission modes using Arecibo 327-MHz observations. The goal of this study was to detect signs of a ‘transitional’ mode at 327 MHz, discovered recently at lower frequencies. We have found subpulse drift and profile form patterns at 327 MHz similar to those identified at lower frequencies in the Q-to-B mode transition process. Pulse fading during about 15 stellar rotations preceding the appearance of subpulse drift was observed as well. Another part of the work is devoted to a detailed study of the pulse polarization variations in the main modes. A complex behaviour of the linear polarization percentage (LPP) of the dominant first component of the average profile with B-mode age has been found: during the first 4 h, the LPP continuously increases from 5 to 40 per cent, and over the next 1.5 h gradually decreases down to 30 per cent until the subsequent onset of the Q mode. In contrast, the LPP of the second component does not change over the B-mode lifetime, remaining at the level of 22 per cent. A non-instantaneous decrease in the LPP was detected at Q-mode onset. No systematic change of the LPP of the averaged Q-mode pulses over several hours of age was found. The results are discussed within the framework of the core–cone beam model and orthogonal polarization modes.

 

This paper continues our study of radio pulsar emission-beam configurations with the primary intent of extending study to the lowest possible frequencies. Here, we focus on a group of 133 more recently discovered pulsars, most of which were included in the (100–200 MHz) LOFAR High-Band Survey, observed with Arecibo at 1.4 GHz and 327 MHz, and some observed at decametre wavelengths. Our analysis framework is the core/double-cone beam model, and we took opportunity to apply it as widely as possible, both conceptually and quantitatively, while highlighting situations where modelling is difficult, or where its premises may be violated. In the great majority of pulsars, beam forms consistent with the core/double-cone model were identified. Moreover, we found that each pulsar’s beam structure remained largely constant over the frequency range available; where profile variations were observed, they were attributable to different component spectra and in some instances to varying conal beam sizes. As an Arecibo population, many or most of the objects tend to fall in the Galactic anticenter region and/or at high Galactic latitudes, so overall it includes a number of nearer, older pulsars. We found a number of interesting or unusual characteristics in some of the pulsars that would benefit from additional study. The scattering levels encountered for this group are low to moderate, apart from a few pulsars lying in directions more towards the inner Galaxy.

 

We present pulsar emission beam analyses and models in an effort to examine pulsar geometry and physics at the lowest frequencies scattering permits. We consider two populations of well-studied pulsars that lie outside the Arecibo sky, the first drawing on the Jodrell Bank Gould & Lyne survey down to –35° declination and a second using Parkes surveys in the far south. These assemble the full sky population of 487 pulsars known before the late 1990s which conveniently all have ‘B’ names. We make full use of the core/double-cone emission beam model to assess its efficacy at lower frequencies, and we outline how different pair plasma sources probably underlie its validity. The analysis shows that with a very few exceptions pulsar radio emission beams can be modeled quantitatively with two concentric conal beams and a core beam of regular angular dimensions at 1 GHz. Further, the beamforms at lower frequencies change progressively in size but not in configuration. Pulsar emission-beam properties divide strongly depending on whether the plasma excitation is central within the polar fluxtube producing a core beam or peripheral along the edges generating conal beams, and this seems largely determined by whether their spin-down energy is greater or less than about 1032.5 ergs s−1. Core emission dominated pulsars tend concentrate closely along the Galactic plane and in the direction of the Galactic center; whereas conal pulsars are somewhat more uniformly distributed both in Galactic longitude and latitude. Core dominated pulsars also tend to be more distant and particularly so in the inner Galaxy region.

 

ABSTRACT Since their discovery more than 50 years ago, broad-band radio studies of pulsars have generated a wealth of information about the underlying physics of radio emission. In order to gain some further insights into this elusive emission mechanism, we performed a multifrequency study of two very well-known pulsars, PSR B0919+06 and PSR B1859+07. These pulsars show peculiar radio emission properties whereby the emission shifts to an earlier rotation phase before returning to the nominal emission phase in a few tens of pulsar rotations (also known as ‘swooshes’). We confirm the previous claim that the emission during the swoosh is not necessarily absent at low frequencies and the single pulses during a swoosh show varied behaviour at 220 MHz. We also confirm that in PSR B0919+06, the pulses during the swoosh show a chromatic dependence of the maximum offset from the normal emission phase with the offset following a consistent relationship with observing frequency. We also observe that the flux density spectrum of the radio profile during the swoosh is inverted compared to the normal emission. For PSR B1859+07, we have discovered a new mode of emission in the pulsar that is potentially quasi-periodic with a different periodicity than is seen in its swooshes. We invoke an emission model previously proposed in the literature and show that this simple model can explain the macroscopic observed characteristics in both pulsars. We also argue that pulsars that exhibit similar variability on short time-scales may have the same underlying emission mechanism. 

ABSTRACT We report the result of measurements of a gradual shift of the integrated pulses towards later spin phase of the anomalous pulsar B0943+10 at high radio frequencies. We have used observations from the Arecibo Observatory and the GMRT at 327 and 325 MHz correspondingly. For the measurements, we have proposed a special method for calculating the correct positions of the partially merged two components of the pulse profile shape with significant temporal changes in their amplitude ratio. The exponential change in the pulse phase with an amplitude of 4 ms and characteristic time of about 1 h has been found. Comparison of our measurements at 325 and 327 MHz with those at the lower frequencies of 25–80, 62 and 112 MHz have shown that the character of the process does not depend on frequency across a wide frequency range. The result is very important for constraining the nature of the delay. It supports the assumption that the process results from changes in the vacuum gap near the surface of the pulsar. The further correlation between changes in the pulse phase and its intensity is discussed.