The physical origin of radio emission in Radio Quiet Active Galactic Nuclei (RQ AGN) remains unclear, whether it is a downscaled version of the relativistic jets typical of Radio Loud (RL) AGN, or whether it originates from the accretion disk. The co
rrelation between 5 GHz and X-ray luminosities of RQ AGN, which follows $L_R = 10^{-5}L_X$ observed also in stellar coronae, suggests an association of both X-ray and radio sources with the accretion disk corona. Observing RQ AGN at higher (mm-wave) frequencies, where synchrotron self absorption is diminished, and smaller regions can be probed, is key to exploring this association. Eight RQ AGN, selected based on their high X-ray brightness and variability, were observed at 95 GHz with the CARMA and ATCA telescopes. All targets were detected at the $1-10$ mJy level. Emission excess at 95~GHz of up to $times 7$ is found with respect to archival low-frequency steep spectra, suggesting a compact, optically-thick core superimposed on the more extended structures that dominate at low frequencies. Though unresolved, the 95 GHz fluxes imply optically thick source sizes of $10^{-4}-10^{-3}$ pc, or $sim 10 - 1000$ gravitational radii. The present sources lie tightly along an $L_R$ (95 GHz) = $10^{-4}L_X$ (2$-$10 keV) correlation, analogous to that of stellar coronae and RQ AGN at 5 GHz, while RL AGN are shown to have higher $L_R / L_X$ ratios. The present observations argue that simultaneous mm-wave and X-ray monitoring of RQ AGN features a promising method for understanding accretion disk coronal emission.
Observations with the Swift satellite of X-ray afterglows of more than a hundred gamma ray bursts (GRBs) with known redshift reveal ubiquitous soft X-ray absorption. The directly measured optical depth tau at a given observed energy is found to be co
nstant on average at redshift z > 2, i.e., <tau (0.5 keV) >_{z > 2} = 0.40+/- 0.02. Such an asymptotic optical depth is expected if the foreground diffuse intergalactic medium (IGM) dominates the absorption effect, and if the metallicity of the diffuse IGM reaches ~ 0.2 - 0.4 solar at z = 0. To further test the IGM absorption hypothesis, we analyze the 12 highest S/N (> 5000 photon) z > 2 quasar spectra from the XMM-Newton archive, which are all extremely radio loud (RLQs). The quasar optical depths are found to be consistent with the mean GRB value. The four lowest-z quasars (2 < z < 2.5), however, do not show significant absorption. The best X-ray spectra of radio-quiet quasars (RQQs) at z > 2 provide only upper limits to the absorption, which are still consistent with the RLQs, albeit with much lower S/N (< 1000 photons at z ~ 4). Lack of quasar absorption poses a challenge to the smooth IGM interpretation, and could allude to the opacity being rather due to the jets in RLQs and GRBs. However, the jet absorbing column would need to appear in RLQs only at z > 2.5, and in GRBs to strongly increase with z in order to produce the observed tendency to a constant mean tau. High X-ray spectral resolution can differentiate between an absorber intrinsic to the source that produces discernible spectral lines, and the diffuse IGM that produces significant absorption, but no discrete features.
We report on the highest to date signal-to-noise-ratio X-ray spectrum of the luminous quasar PDS 456, as obtained during two XMM-Newton orbits in September 2007. The present spectrum is considerably different from several previous X-ray spectra recor
ded for PDS 456 since 1998. The ultra-high-velocity outflow seen as recently as February 2007 is not detected in absorption. Conversely, a significant reflection component is detected. The reflection model suggests the reflecting medium may be outflowing at a velocity v/c = -0.06 +/- 0.02. The present spectrum is analyzed in the context of the previous ones in an attempt to understand all spectra within the framework of a single model. We examine whether an outflow with variable partial covering of the X-ray source along the line of sight that also reflects the source from other lines of sight can explain the dramatic variations in the broad-band spectral curvature of PDS 456. It is established that absorption plays a major role in shaping the spectrum of other epochs, while the 2007 XMM-Newton spectrum is dominated by reflection, and the coverage of the source by the putative outflow is small (< 20%).
For the past decade, ionized outflows of a few 100 km/s from nearby Seyfert galaxies have been studied in great detail using high resolution X-ray absorption spectra. A recurring feature of these outflows is their broad ionization distribution includ
ing essentially ions (e.g., of Fe) from neutral to fully ionized. The absorption measure distribution (AMD) is defined as the distribution of column density with ionization parameter |d N_H/d (log xi)|. AMDs of Seyfert outflows can span up to five orders of magnitude in xi. We present the AMD of five outflows and show that they are all rather flat, perhaps slightly rising towards high ionization. More quantitatively, a power-law fit for log AMD ~ (log xi)^a yields slopes of 0 < a < 0.4. These slopes tightly constrain the density profiles of the wind, which until now could be addressed only by theory. If the wind is distributed on large scales, the measured slopes imply a generic density radial profile of n ~ r^{-alpha} with 1 < alpha < 1.3. This scaling rules out a mass conserving radial flow of n ~ r^{-2}, or a constant density absorber, but is consistent with a non-spherical MHD outflow model in which n ~ r^{-1} along any given line of sight. On the other hand, if ionization variations are a result of local (delta r) density gradients, e.g. as in the turbulent interstellar medium (ISM), the AMD slopes imply density scaling of n ~ delta r^{-alpha} with 0.7 < alpha < 1.0, which is quite different from the scaling of approximately n ~ delta r^{0.4} found in the Milky Way ISM and typical of incompressible turbulence.
