The Square Kilometre Array (SKA)

Abstract:

We discuss the relative merits of mid-infrared and X-ray selection of type 2 quasars. We describe the mid-infrared, near-infrared and radio selection criteria used to find a population of redshift z ∼ 2 type 2 quasars which we previously argued suggests that most supermassive black hole growth in the Universe is obscured. We present the optical spectra obtained from the William Herschel Telescope, and we compare the narrow emission-line luminosity, radio luminosity and maximum size of jets to those of objects from radio-selected samples. This analysis suggests that these are genuine radio-quiet type 2 quasars, albeit the radio-bright end of this population. We also discuss the possibility of two different types of quasar obscuration, which could explain how the ∼2-3:1 ratio of type 2 to type 1 quasars preferred by modelling our population can be reconciled with the ∼1:1 ratio predicted by unified schemes. © 2006 RAS.

Abstract:

We present here a direct comparison of the polarization position angle (PA) profiles of 17 pulsars, observed at 1.4 and 3.1 GHz. Absolute PAs are obtained at each frequency, permitting a measurement of the difference in the profiles. By doing this, we obtain more precise rotation measure (RM) values for some of the pulsars in the current catalogue. We find that, apart from RM corrections, there are small, pulse-longitude-dependent differences in PA with frequency. Such differences go beyond the interpretation of a geometrical origin. We describe in detail the PA evolution between the two frequencies and discuss possible causes, such as orthogonal and nonorthogonal polarization modes of emission. We also use the PA and total power profiles to estimate the difference in emission height at which the two frequencies originate. In our data sample, there are changes in the relative strengths of different pulse components, especially overlapping linearly polarized components, which coincide with intrinsic changes of the PA profile, resulting in interesting PA differences between the two frequencies. © 2005 RAS.

Abstract:

We present an empirical model for single pulses of radio emission from pulsars based on Gaussian probability distributions for relevant variables. The radiation at a specific pulse phase is represented as the superposition of radiation in two (approximately) orthogonally polarized modes (OPMs) from one or more subsources in the emission region of the pulsar. For each subsource, the polarization states are drawn randomly from statistical distributions, with the mean and the variance on the Poincaré sphere as free parameters. The intensity of one OPM is chosen from a lognormal distribution, and the intensity of the other OPM is assumed to be partially correlated, with the degree of correlation also chosen from a Gaussian distribution. The model is used to construct simulated data described in the same format as real data: distributions of the polarization of pulses on the Poincaré sphere and histograms of the intensity and other parameters. We concentrate on the interpretation of data for specific phases of PSR B0329+54 for which the OPMs are not orthogonal, with one well defined and the other spread out around an annulus on the Poincaré sphere at some phases. The results support the assumption that the radiation emerges in two OPMs with closely correlated intensities, and that in a statistical fraction of pulses one OPM is invisible. © 2005 RAS.

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:

The Faulkes Telescope Project is the educational arm of the Las Cumbres Observatory Global Telescope Network (LCOGT). It currently has two 2-metre robotic telescopes, located at Haleakala on Maui (FT North) and Siding Spring in Australia (FT South). It is planned to increase this to six 2-metre telescopes in the future, complemented by a network of 30-40 smaller (0.4 - 1 metre) telescopes providing 24 hour coverage of both northern and southern hemispheres. We are undertaking a monitoring project of 10 low-mass X-ray binaries (LMXBs) using FT North to study the optical continuum behaviour of X-ray transients in quiescence. The introduction of FT South in September 2006 allows us to extend this monitoring to include 17 southern hemisphere LMXBs. With new instrumentation, we also intend to expand this monitoring to include both infrared wavelengths and spectroscopy.