The Square Kilometre Array (SKA)

Abstract:

Galactic black hole binaries produce powerful outflows which emit over almost the entire electromagnetic spectrum. Here, we report the first detection with the Herschel observatory of a variable far-infrared source associated with the compact jets of the black hole transient GX 339-4 during the decay of its recent 2010-2011 outburst, after the transition to the hard state. We also outline the results of very sensitive radio observations conducted with the Australia Telescope Compact Array, along with a series of near-infrared, optical (OIR) and X-ray observations, allowing for the first time the re-ignition of the compact jets to be observed over a wide range of wavelengths. The compact jets first turn on at radio frequencies with an optically thin spectrum that later evolves to an optically thick synchrotron emission. An OIR reflare is observed about 10 d after the onset of radio and hard X-ray emission, likely reflecting the necessary time to build up enough density, as well as to have acceleration (e.g. through shocks) along an extended region in the jets. The Herschel measurements are consistent with an extrapolation of the radio inverted power-law spectrum, but they highlight a more complex radio to OIR spectral energy distribution for the jets. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We revisit the paradigm of the dependence of jet power on black hole (BH) spin in accreting BH systems. In a previous paper, we showed that the luminosity of compact jets continuously launched due to accretion on to BHs in X-ray binaries (analogous to those that dominate the kinetic feedback from active galactic nuclei) does not appear to correlate with reported BH spin measurements. It is therefore unclear whether extraction of the BH spin energy is the main driver powering compact jets from accreting BHs. Occasionally, BH X-ray binaries produce discrete, transient (ballistic) jets for a brief time over accretion state changes. Here, we quantify the dependence of the power of these transient jets (adopting two methods to infer the jet power) on BH spin, making use of all the available data in the current literature, which include 12 BHs with both measured spin parameters and radio flares over the state transition. In several sources, regular, well-sampled radio monitoring has shown that the peak radio flux differs dramatically depending on the outburst (up to a factor of 1000), whereas the total power required to energize the flare may only differ by a factor of≲4 between outbursts. The peak flux is determined by the total energy in the flare and the time over which it is radiated (which can vary considerably between outbursts). Using a Bayesian fitting routine, we rule out a statistically significant positive correlation between transient jet power measured using these methods and current estimates of BH spin. Even when selecting sub-samples of the data that disregard some methods of BH spin measurement or jet power measurement, no correlation is found in all cases. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

LOFAR, the Low Frequency Radio Array, is a new pan-European radio telescope that is almost fully operational. One of its main drivers is to make deep images of the low frequency radio sky. To be able to do this a number of challenges need to be addressed. These include the high data rates, removal of radio frequency interference, calibration of the beams and correcting for the corrupting influence of the ionosphere. One of the key science goals is to study merger shocks, particle acceleration mechanisms and the structure of magnetic fields in nearby and distant merging clusters. Recent studies with the GMRT and WSRT radio telescopes of the "Sausage" and the "Toothbrush" clusters have given a very good demonstration of the power of radio observations to study merging clusters. Recently we discovered that both clusters contain relic and halo sources, large diffuse regions of radio emission not associated with individual galaxies. The 2 Mpc northern relic in the Sausage cluster displays highly aligned magnetic fields and and exhibits a strong spectral index gradient that is a consequence of cooling of the synchrotron emitting particles in the post-shock region. We have argued that these observations provide strong evidence that shocks in merging clusters are capable of accelerating particles. For the Toothbrush cluster we observe a puzzling linear relic that extends over 2 Mpc. The proposed scenario is that a triplemerger can lead to such a structure. With LOFAR's sensitivity it will not only be possible to trace much weaker shocks, but also to study those shocks due to merging clusters up to redshifts of at least one. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric and spectroscopic survey, using the AAOmega spectrograph on the Anglo-Australian Telescope to obtain spectra for up to ~300 000 galaxies over 280 deg2, to a limiting magnitude of rpet < 19.8 mag. The target galaxies are distributed over 0 < z ≲ 0.5 with a median redshift of z ≈ 0.2, although the redshift distribution includes a small number of systems, primarily quasars, at higher redshifts, up to and beyond z = 1. The redshift accuracy ranges from σv ≈ 50 km s-1 to σv ≈ 100 km s-1 depending on the signal-to-noise ratio of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis pipeline. We present the steps involved in taking the raw two-dimensional spectroscopic images through to flux-calibrated one-dimensional spectra. The resulting GAMA spectra cover an observed wavelength range of 3750 λ 8850Å at a resolution of R ≈ 1300. The final flux calibration is typically accurate to 10-20 per cent, although the reliability is worse at the extreme wavelength ends, and poorer in the blue than the red. We present details of the measurement of emission and absorption features in the GAMA spectra. These measurements are characterized through a variety of quality control analyses detailing the robustness and reliability of the measurements. We illustrate the quality of the measurements with a brief exploration of elementary emission line properties of the galaxies in the GAMA sample. We demonstrate the luminosity dependence of the Balmer decrement, consistent with previously published results, and explore further how Balmer decrement varies with galaxy mass and redshift. We also investigate the mass and redshift dependencies of the [NII]/Hα versus [OIII]/Hβ spectral diagnostic diagram, commonly used to discriminate between star forming and nuclear activity in galaxies. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.