Aris Karastergiou

Abstract:

We present polarization data for 32 mainly southern pulsars at 8.4 GHz. The observations show that the polarization fraction is low in most pulsars at this frequency except for the young, energetic pulsars which continue to show polarization fractions in excess of 60 per cent. All the pulsars in the sample show evidence for conal emission with only one-third also showing core emission. Many profiles are asymmetric, with either the leading or the trailing part of the cone not detectable. Somewhat surprisingly, the asymmetric profiles tend to be more polarized than the symmetrical profiles. Little or no pulse narrowing is seen between 1 and 8.4 GHz. The spectral behaviour of the orthogonal polarization modes and radius to frequency mapping can likely account for much of the observational phenomenology. Highly polarized components may originate from higher in the magnetosphere than unpolarized components. © 2006 RAS.

Abstract:

We present polarization profiles for 48 southern pulsars observed with the new 10-cm receiver at the Parkes telescope. We have exploited the low system temperature and high bandwidth of the receiver to obtain profiles which have good signal-to-noise for most of our sample at this relatively high frequency. Although, as expected, a number of profiles are less linearly polarized at 3.1 GHz than at lower frequencies, we identify some pulsars and particular components of profiles in other pulsars which have increased linear polarization at this frequency. We discuss the dependence of linear polarization with frequency in the context of a model in which emission consists of the superposition of two, orthogonally polarized modes. We show that a simple model, in which the orthogonal modes have different spectral indices, can explain many of the observed properties of the frequency evolution of both the linear polarization and the total power, such as the high degree of linear polarization seen at all frequencies in some high spin-down, young pulsars. Nearly all the position angle profiles show deviations from the rotating vector model; this appears to be a general feature of high-frequency polarization observations. © 2005 RAS.

Abstract:

We present polarisation profiles for 48 southern pulsars observed with the new 10-cm receiver at the Parkes telescope. We have exploited the low system temperature and high bandwidth of the receiver to obtain profiles which have good signal to noise for most of our sample at this relatively high frequency. Although, as expected, a number of profiles are less linearly polarised at 3.1 GHz than at lower frequencies, we identify some pulsars and particular components of profiles in other pulsars which have increased linear polarisation at this frequency. We discuss the dependence of linear polarisation with frequency in the context of a model in which emission consists of the superposition of two, orthogonally polarised modes. We show that a simple model, in which the orthogonal modes have different spectral indices, can explain many of the observed properties of the frequency evolution of both the linear polarisation and the total power, such as the high degree of linear polarisation seen at all frequencies in some high spin-down, young pulsars. Nearly all the position angle profiles show deviations from the rotating vector model; this appears to be a general feature of high-frequency polarisation observations.

Abstract:

In most pulsars, the circularly polarized component, Stokes V, is weak in the average pulse profiles. By forming the average profile of |V| from single pulses we can distinguish between pulsars where V is weak in the individual pulses and those where large V of variable handedness is observed from one pulse to the other. We show how |V| profiles depend on the signal-to-noise ratio of V in the single pulses and demonstrate that it is possible to simulate the observed, broad distributions of V by assuming a model where |V| is distributed around a mean value and the handedness of V is permitted to change randomly. The |V| enhanced profiles of 1.3 pulsars are shown, five observed at 1.41 GHz and eight observed at 4.85 GHz, to complement the set in Karastergiou et al. (2003b). It is argued that the degree of circular polarization in the single pulses is related to the orthogonal polarization mode phenomenon and not to the classification of the pulse components as cone or core.

Abstract:

In most pulsars, the circularly polarized component, Stokes $V$, is weak in the average pulse profiles. By forming the average profile of $|V|$ from single pulses we can distinguish between pulsars where $V$ is weak in the individual pulses and those where large $V$ of variable handedness is observed from one pulse to the other. We show how $|V|$ profiles depend on the signal-to-noise ratio of $V$ in the single pulses and demonstrate that it is possible to simulate the observed, broad distributions of $V$ by assuming a model where $|V|$ is distributed around a mean value and the handedness of $V$ is permitted to change randomly. The $|V|$ enhanced profiles of 13 pulsars are shown, 5 observed at 1.41 GHz and 8 observed at 4.85 GHz, to complement the set in Karastergiou et al. (2003b). It is argued that the degree of circular polarization in the single pulses is related to the orthogonal polarization mode phenomenon and not to the classification of the pulse components as cone or core.