Pulsars, transients and relativistic astrophysics

Abstract:

ABRIDGED We present new results on the variations in speed and direction of the jet bolides in the Galactic microquasar SS433, from high resolution spectra, taken with the ESO 3.6-m New Technology Telescope almost nightly over 0.4 of a precession cycle. We find: (i) These data exhibit multiple ejections within most 24-hour periods and, throughout the duration of the observing campaign, the weighted means of the individual bolides, in both the red jet and the blue jet, clearly exhibit the pronounced nodding known in this system. (ii) We present further evidence for a 13-day periodicity in the jet speed, and show this cannot be dominated by Doppler shifts from orbital motion. (iii) We show the phase of this peak jet speed has shifted by a quarter of a cycle in the last quarter-century. (iv) We show that the two jets ejected by SS433 are highly symmetric on timescales measured thus far. (v) We demonstrate that the anti-correlation between variations in direction and in speed is not an artifact of an assumption of symmetry. (vi) We show that a recently proposed mechanism (Begelman et al 2006) for varying the ejection speed and anti-correlating it with polar angle variations is ruled out. (vii) The speed of expansion of the plasma bolides in the jets is approximately 0.0024c. These novel data carry a clear signature of speed variations. They have a simple and natural interpretation in terms of both angular and speed fluctuations which are identical on average in the two jets. They complement archival optical data and recent radio imaging.

Abstract:

We present a model for the radio emission from radio-quiet quasar nuclei. We show that a thermal origin for the high brightness temperature, flat spectrum point sources (known as radio ``cores'') is possible provided the emitting region is hot and optically-thin. We hence demonstrate that optically-thin bremsstrahlung from a slow, dense disk wind can make a significant contribution to the observed levels of radio core emission. This is a much more satisfactory explanation, particularly for sources where there is no evidence of a jet, than a sequence of self-absorbed synchrotron components which collectively conspire to give a flat spectrum. Furthermore, such core phenomena are already observed directly via milli-arcsecond radio imaging of the Galactic microquasar SS433 and the active galaxy NGC1068. We contend that radio-emitting disk winds must be operating at some level in radio-loud quasars and radio galaxies as well (although in these cases, observations of the radio cores are frequently contaminated/dominated by synchrotron emission from jet knots). This interpretation of radio core emission mandates mass accretion rates that are substantially higher than Eddington. Moreover, acknowledgment of this mass-loss mechanism as an AGN feedback process has important implications for the input of energy and hot gas into the inter-galactic medium (IGM) since it is considerably less directional than that from jets.