The Square Kilometre Array (SKA)

Abstract:

We present preliminary results on a global study of X-ray binaries using 14 Ms of data from the Rossi X-ray Timing Explorer RXTE satellite. Our initial study on GX 339-4 is recapped as an introduction to the methods used. We use a consistent analysis scheme for all objects, with three different spectral models to fit the powerlaw and disc components. We also take into account the possibility of a line being present in the data. The resulting almost 4000 observations allow the tracking of the spectral properties of the binaries as they evolve through an outburst. Our investigations concentrate on the disc and line properties of the binaries when in outburst. We also show the Disc-Fraction Luminosity diagram for the population of X-ray binaries studied which will enable us to further links with AGN. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

Abstract:

We describe a novel heterodyne interferometer currently under construction at Oxford. The instrument employs new techniques in heterodyne interferometry, with the aim of achieving very high brightness sensitivity in the millimetre band. It is a single-baseline tracking interferometer for operation in the frequency range 185-275 GHz with two 0.4m offset parabolic antennas separated by a 0.5 m baseline. Each antenna feeds an SIS mixer with a 2-20 GHz IF band, driven by a phase-switched LO source. The IF signals from the mixers are processed by a 2-20 GHz analogue complex correlator. The primary science goal of this instrument is to measure the spectrum of the Sunyaev-Zel'dovich effect in galaxy clusters. In particular we intend to measure the frequency of the S-Z null near 217 GHz, which allows the gas temperature of the cluster to be determined. Measuring the spectrum of the S-Z effect requires very high brightness sensitivity with moderate spatial and spectral resolution.

Abstract:

We present the design of a 230 GHz finline SIS mixer with a 2-20 GHz IF bandwidth. The mixer is intended for use in a prototype high brightness sensitivity, low spatial resolution heterodyne interferometer currently under construction at Oxford[1]. The sensitivity of the instrument will be sufficient for measuring the spectrum of the Sunyaev-Zel'dovich effect in the brightest galaxy clusters. The mixer design is based on a previously reported 230 GHz finline mixer design[2], with a number of improvements and features added to achieve the very demanding IF bandwidth requirements. An RF bandpass filter is included on the chip to isolate the IF signals from the finline transition, and the mixer tuning circuits, RF choke and IF connections have been carefully designed to exhibit very low parasitic reactances in the IF band. The first two batches of these mixers were recently fabricated at Cologne University, and are currently being tested.

Abstract:

Compact object displays drastic spectral and timing changing from the beginning to the end of an outburst, showing the different efficiencies of accretion processes. Black hole binaries hence exhibit schematically two different states in X-ray spectra: The first dominated by a thermal component and the second by a hard powerlaw shape like. Whereas the hard component is often attributed to the emission of a radiatively inefficient corona, the thermal component is interpreted as the emission of the optically thick accretion disc. The commonly accepted picture suggests that the observed transition between hard and soft states is associated by a drop in the accretion efficiency of the thermal component by a recession of the internal disc radius in hard states. However, recent studies based on relativistically broadened iron line and the thermal component strength analysis would tend to show the presence of the disc in the vicinity of the horizon. By a reanalysis of archive spectra where thermal emission is present, we tracked the values of the disc radii during outbursts among several sources. Indeed, whereas a constant inner radius would imply that the disc luminosity should monotonically depends on the temperature, we show that this relationship seems to deviate at the lowest luminosities. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

Abstract:

High energy astrophysics has made good use of combined high energy (X-ray, g-ray) and radio observations to uncover connections between outbursts, accretion, particle acceleration and kinetic feedback to the local ambient medium. In the field of microquasars the connections have been particularly important. However, radio astronomy has been relying on essentially the same facilities for the past ∼ 25 years, whereas high-energy astrophysics, in particular space-based research, has had a series of newer and more powerful missions. In the next fifteen years this imbalance is set to be redressed, with a whole familiy of new radio facilities under development en route to the Square Kilometre Array (SKA) in the 2020s. In this brief review I will summarize these future prospects for radio astronomy, and focus on possibly the most exciting of the new facilities to be built in the next decade, the Low Frequency Array LOFAR, and its uses in high energy astrophysics. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial- ShareAlike Licence.