Hintze Centre for Astrophysical Surveys

Abstract:

The well-known black-hole X-ray transient A0620-00 was a bright radio source during the first part of its outburst in 1975. We have revisited the available data and find for the first time evidence that the source exhibited multiple jet ejections. Rapid radio spectral changes indicate the addition of at least three new components which are initially optically thick. From single baseline interferometry taken about three weeks after the start of the X-ray outburst we find that the source is extended on arcsec scales and infer a relativistic expansion velocity. Some of the other (soft) X-ray transients, such as GS 1124-68 and GS 2000+25, show very similar X-ray outburst light curve shapes to that of A0620-00, while their radio outburst light curve shapes are different. We suggest that this is due to the radio emission being strongly beamed in outburst, whereas the X-ray emission remains isotropic. Since this effect is stronger at higher jet velocities, this strengthens our conclusion that the jets in A0620-00 and other soft X-ray transients move with relativistic speeds.

Abstract:

We report first results from the Streaming Motions of Abell Clusters (SMAC) project, an all-sky Fundamental Plane survey of 699 early-type galaxies in 56 clusters between ∼3000 and ∼14,000 km s-1. For this sample, with a median distance of ∼8000 km s-1, we find a bulk flow of amplitude 630 ± 200 km s-1 toward l = 260 ± 15°, b = -1 ± 12° with respect to the cosmic microwave background. The flow is robust against the effects of individual clusters and data subsets, the choice of Galactic extinction maps, Malmquist bias, and stellar population effects. The direction of the SMAC flow is ∼90° away from the flow found by Lauer & Postman, but it is in good agreement with the gravity dipole predicted from the distribution of X-ray-luminous clusters. Our detection of a high-amplitude coherent flow on such a large scale argues for excess mass density fluctuation power at wavelengths λ ≳ 60 h-1 Mpc, relative to the predictions of currently popular cosmological models.