Pulsars, transients and relativistic astrophysics

Abstract:

We present investigations of the interaction between the relativistic, precessing jets of the microquasar SS433 and the surrounding, expanding supernova remnant (SNR) shell, W50, and the consequent evolution in the inhomogeneous interstellar medium (ISM). We model their evolution using the hydrodynamic flash code, which uses adaptive mesh refinement. We show that the peculiar morphology of the entire nebula can be reproduced to a good approximation, due to the combined effects of (i) the evolution of the SNR shell from the free-expansion phase through the Sedov blast wave in an exponential density profile from the Milky Way disc, and (ii) the subsequent interaction of the relativistic, precessing jets of SS433. Our simulations reveal: (1) Independent measurement of the Galaxy scaleheight and density local to SS433 (as n 0 = 0.2cm -3 ,Z d = 40pc), with this scaleheight being in excellent agreement with the work of Dehnen and Binney. (2) A new mechanism for hydrodynamic refocusing of conical jets. (3) The current jet precession characteristics do not simply extrapolate back to produce the lobes of W50, but a history of episodic jet activity having at least three different outbursts with different precession characteristics would be sufficient to produce the W50 nebula. A history of intermittent episodes of jet activity from SS433 is also suggested in a kinematic study of W50 detailed in a companion paper. (4) An estimate of the age of W50, and equivalently the age of SS433's black hole created during the supernova explosion, in the range of 17000-21000yr. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

We present direct evidence, from Adaptive-Optics near-infra-red imaging, of the jets in the Galactic microquasar SS433 interacting with enhanced wind-outflow off the accretion disc that surrounds the black hole in this system. Radiant quantities of gas are transported significant distances away from the black hole approximately perpendicular to the accretion disc from which the wind emanates. We suggest that the material that comprised the resulting "bow-tie" structure is associated with a major flare that the system exhibited ten months prior to the observations. During this flare, excess matter was expelled by the accretion disc as an enhanced wind, which in turn is "snow-ploughed", or propelled, out by the much faster jets that move at approximately a quarter of the speed of light. Successive instances of such bow-ties may be responsible for the large-scale X-ray cones observed across the W50 nebula by ROSAT.

Abstract:

The Galactic microquasar SS433 occasionally exhibits a major flare when the intensity of its emission increases significantly and rapidly. We present an analysis of high-resolution, almost-nightly optical spectra obtained before, during and after a major flare, whose complex emission lines are deconstructed into single gaussians and demonstrate the different modes of mass loss in the SS433 system. During our monitoring, an initial period of quiescence was followed by increased activity which culminated in a radio flare. In the transition period the accretion disc of SS433 became visible in H-alpha and HeI emission lines and remained so until the observations were terminated; the line-of-sight velocity of the centre of the disc lines during this time behaved as though the binary orbit has significant eccentricity rather than being circular, consistent with three recent lines of evidence. After the accretion disc appeared its rotation speed increased steadily from 500 to 700 km/s. The launch speed of the jets first decreased then suddenly increased. At the same time as the jet launch speed increased, the wind from the accretion disc doubled in speed. Two days afterwards, the radio flux exhibited a flare. These data suggest that a massive ejection of material from the companion star loaded the accretion disc and the system responded with mass loss via different modes that together comprise the flare phenomena. We find that archival data reveal similar behaviour, in that when the measured jet launch speed exceeds 0.29c this is invariably simultaneous with, or a few days before, a radio flare. Thus we surmise that a major flare consists of the overloading of the accretion disc, resulting in the speeding up of the H-alpha rotation disc lines, followed by enhanced mass loss not just via its famous jets at higher-than-usual speeds but also directly from its accretion disc's wind.