Global Jet Watch

Abstract:

It has been proposed that the radio spectra of radio-quiet quasars is produced by free-free emission in the optically thin part of an accretion disc wind. An important observational constraint on this model is the observed X-ray luminosity. We investigate this constraint using a sample of PG radio-quiet quasars for which XMM-Newton EPIC spectra are available. Comparing the predicted and measured luminosities for 0.5, 2 and 5 keV, we conclude that all of the studied PG quasars require a large hydrogen column density absorber, requiring these quasars to be close to or Compton-thick. Such a large column density can be directly excluded for PG 0050+124, for which a high-resolution RGS spectrum exists. Further constraint on the column density for a further 19 out of the 21 studied PG quasars comes from the EPIC spectrum characteristics such as hard X-ray power-law photon index and the equivalent width of the Fe Kalpha line; and the small equivalent width of the C IV absorber present in UV spectra. For 2 sources: PG 1001+054 and PG 1411+442 we cannot exclude that they are indeed Compton-thick, and the radio and X-ray luminosity are due to a wind originating close to the super-massive black hole. We conclude that for 20 out of 22 PG quasars studied free-free emission from a wind emanating from the accretion disc cannot mutually explain the observed radio and X-ray luminosity.

Abstract:

New Chandra observations of the giant (0.5 Mpc) radio galaxy 4C23.56 at z = 2.5 show X-rays in a linear structure aligned with its radio emission, but anti-correlated with the detailed radio structure. Consistent with the powerful, high-z giant radio galaxies we have studied previously, X-rays seem to be invariably found where the lobe plasma is oldest even where the radio emission has long since faded. The hotspot complexes seem to show structures resembling the double shock structure exhibited by the largest radio quasar 4C74.26, with the X-ray shock again being offset closer to the nucleus than the radio synchrotron shock. In the current paper, the offsets between these shocks are even larger at 35kpc. Unusually for a classical double (FRII) radio source, there is smooth low surface-brightness radio emission associated with the regions beyond the hotspots (further away from the nucleus than the hotspots themselves), which seems to be symmetric for the ends of both jets. We consider possible explanations for this phenomenon, and conclude that it arises from high-energy electrons, recently accelerated in the nearby radio hotspots that are leaking into a pre-existing weakly-magnetized plasma that are symmetric relic lobes fed from a previous episode of jet activity. This contrasts with other manifestations of previous epochs of jet ejection in various examples of classical double radio sources namely (1) double-double radio galaxies by e.g. Schoenmakers et al, (2) the double-double X-ray/radio galaxies by Laskar et al and (3) the presence of a relic X-ray counter-jet in the prototypical classical double radio galaxy, Cygnus A by Steenbrugge et al. The occurrence of multi-episodic jet activity in powerful radio galaxies and quasars indicates that they may have a longer lasting influence on the on-going structure formation processes in their environs than previously presumed.

Abstract:

We present an analysis of observations of the doubly-lensed double hotspot in the giant radio galaxy J0816+5003 from MERLIN, MDM, WIYN, WHT, UKIRT and the VLA. The images of the two hotspot components span a factor of two in radius on one side of the lensing galaxy at impact parameters of less than 500pc. Hence we measure the slope of the lensing potential over a large range in radius, made possible by significant improvement in the accuracy of registration of the radio and optical frame and higher resolution imaging data than previously available. We also infer the lens and source redshifts to be 0.332 and > 1 respectively. Purely on the basis of lens modelling, and independently of stellar velocity dispersion measurements, we find the potential to be very close to isothermal.