I review the radio to X-ray properties of gigahertz peaked-spectrum (GPS) and compact steep- spectrum (CSS) sources, the current hypotheses for their origin, and their use to constrain the evolution of powerful radio galaxies. The GPS and CSS sources are compact, powerful radio sources with well-defined peaks in their radio spectra (near 1 GHz in the GPS and near 100 MHz in the CSS). The GPS sources are entirely contained within the extent of the narrow-line region (&1 kpc), while the CSS sources are contained entirely within the host galaxy (&15 kpc). The peaks in the spectra are probably due to synchrotron self-absorption, though free-free absorption through an inhomogeneous screen may also play a role. The turnover frequency varies with linear size l as , suggesting a simple physical relationship between these parameters. The radio 20.65 n / l m morphologies are strikingly like those of the large-scale classical doubles, though some sources can have very distorted morphologies suggestive of interactions. Radio polarization tends to be low, and in some cases the Faraday rotation measures can be extremely large. The IR properties are consistent with stellar populations and active galactic nucleus (AGN) bolometric luminosity similar to that of the 3CR classical doubles. The optical host galaxy properties (absolute magnitude, Hubble diagram, evidence for interaction) are consistent with those of the 3CR classical doubles. CSS sources at all redshifts exhibit high surface brightness optical light (most likely emission-line gas) that is aligned with the radio axis. The optical emission-line properties suggest (1) interaction of the radio source with the emission-line gas and (2) the presence of dust toward the emission-line regions. X- ray observations of high-redshift GPS quasars and a couple of GPS galaxies suggest the presence of significant columns of gas toward the nuclei. Searches for cold gas in the host galaxies have revealed large amounts of molecular gas and smaller amounts of atomic gas in several sources, though probably not enough to confine the radio sources. The main competing models for the GPS and CSS sources are that (1) they are frustrated by interaction with dense gas in their environments and (2) they are young and evolving radio sources that will become large-scale sources. Combining the bright GPS and CSS samples with the 3CR results in a sample spanning a range in source size of 10 5 that can be used to study source evolution. The number density versus linear size relation is consistent with a picture in which the sources expand with constant velocity and the radio power drops with linear size l according to . This strong evolution suggests that at least some of the 20.5 P / l GPS and CSS sources evolve to become lower luminosity FR 1 radio sources. The GPS and CSS sources are important probes of their host galaxies and will provide critical clues to the origin and evolution of powerful radio sources.

https://iopscience.iop.org/article/10.1086/316162/pdf

The Compact Steep-Spectrum and Gigahertz Peaked-Spectrum Radio Sources

Aims. We have calculated variability Doppler boosting factors, Lorentz factors, and viewing angles for a large sample of sources by using total flux density observations at 22 and 37 GHz and VLBI data. Methods. We decomposed the flux curves into exponential flares and determined the variability brightness temperatures of the fastest flares. By assuming the same intrinsic brightness temperature for each source, we calculated the Doppler boosting factors for 87 sources. In addition we used new apparent jet speed data to calculate the Lorentz factors and viewing angles for 67 sources. Results. We find that all quasars in our sample are Doppler-boosted and that the Doppler boosting factors of BL Lacertae objects are lower than of quasars. The new Lorentz factors are about twice as high as in earlier studies, which is mainly due to higher apparent speeds in our analyses. The jets of BL Lacertae objects are slower than of quasars. There are some extreme sources with very high derived Lorentz factors of the order of a hundred. These high Lorentz factors could be real. It is also possible that the sources exhibit such rapid flares that the fast variations have remained undetected in monitoring programmes, or else the sources have a complicated jet structure that is not amenable to our simple analysis. Almost all the sources are seen in a small viewing angle of less than 20 degrees. Our results follow the predictions of basic unification schemes for AGN.

/pdf/doppler-factors-lorentz-factors-and-viewing-angles-for-194npcs1p1.pdf

Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies

We present results from a monitoring programme of 42 quasars from the Palomar–Green sample. The objects were observed for seven years at the Wise Observatory, as part of a long-term effort to monitor AGN of various types. This is the most extensive programme of its kind carried out to date on a well-defined, optically selected quasar sample. The typical sampling interval is ∼ 40 d. One-third of the quasars were observed at ∼ 60 epochs, and the rest at ∼ 30 epochs in two bands (B and R) with a photometric accuracy of ∼ 0.01 mag. We present light curves for all of the sources, and discuss the sample variability properties. All of the quasars in the sample varied during the campaign with intrinsic rms amplitudes of 5 <σB<34 per cent and 4 <σR<26 per cent. The rms amplitude and colour for the entire sample are σB=14 per cent, σR=12 per cent and σB-R=5 per cent. On time-scales of 100 to 1000 d the power spectra of the sources have a power-law shape, Pν≺ν−γ, with γ≈ 2.0 and a spread ≲ 0.6. At least half of the quasars, particularly those that are most variable, become bluer when they brighten, and the rest do not show this behaviour. We quantify this phenomenon, which has been observed previously mainly in Seyfert galaxies. The quasars which are most variable tend also to exhibit asymmetry in their variations, in the sense that the brightening phases last longer than the fading phases. We have searched for correlations between the measured variability properties and other parameters of the quasars, such as luminosity, redshift, radio loudness and X-ray slope. We find several new correlations, and reproduce some of the correlations reported by previous studies. Among them are an anticorrelation of variability amplitude with luminosity, a trend of the autocorrelation time-scale with luminosity, and an increase in variability amplitude with Hβ equivalent width. However, all of these trends have a large scatter despite the low observational uncertainties.

/pdf/long-term-optical-variability-properties-of-the-palomar-4t435s799g.pdf

Long-term optical variability properties of the Palomar–Green quasars

We have considered all blazars observed in the X{ray band and for which the slope of the X{ray spectrum is available. We have collected 421 spectra of 268 blazars, including 12 archival unpublished ASCA spectra of 7 blazars whose analysis is presented here. The X{ray spectra of blazars show trends as a function of their power, conrming that the blazar overall energy distribution can be parameterized on the basis of one parameter only, i.e. the bolometric luminosity. This is conrmed by the relatively new hard (2{10 keV) X{ray data. Our results conrm the idea that in low power objects the X{ray emission mechanism is the synchrotron process, dominating both the soft and the hard X{ray emissions. Low energy peaked BL Lac objects are intermediate, often showing harder spectra in the hard X{ray band, suggesting that the synchrotron process dominates in the soft band, with the inverse Compton process dominating at high energies. The most powerful objects have X{ray spectra that are flat both in the soft and in the hard band, consistent with a dominating inverse Compton component.

/pdf/hard-x-ray-properties-of-blazars-2uao36tgay.pdf

Hard X-ray properties of blazars

We have undertaken a survey, the Deep X-Ray Radio Blazar Survey (DXRBS), of archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the ROSAT WGACAT database with several publicly available radio catalogs, restricting our candidate list to serendipitous flat radio spectrum sources (αr ≤ 0.70, where Sν ∝ ν). We discuss our survey methods, identification procedure, and first results. Our survey is found to be ~95% efficient at finding flat-spectrum radio-loud quasars (FSRQs; 59 of our first 85 identifications) and BL Lacertae objects (22 of our first 85 identifications), a figure that is comparable to or greater than that achieved by other radio and X-ray survey techniques. The identifications presented here show that all previous samples of blazars (even when taken together) did not representatively survey the blazar population, missing critical regions of (LX, LR) parameter space within which large fractions of the blazar population lie. Particularly important is the identification of a large population of FSRQs (25% of DXRBS FSRQs) with ratios of X-ray to radio luminosity 10-6 (αrx 0.78). In addition, as a result of our greater sensitivity, the DXRBS has already more than doubled the number of FSRQs in complete samples with 5 GHz (radio) luminosities between 1031.5 and 1033.5 ergs s-1 Hz-1, and fills in the region of parameter space between X-ray–selected and radio-selected samples of BL Lac objects. The DXRBS is the very first sample to contain statistically significant numbers of blazars at low luminosities, approaching what should be the lower end of the FSRQ luminosity function.

https://iopscience.iop.org/article/10.1086/300283/pdf

The Deep X-Ray Radio Blazar Survey. I. Methods and First Results*

The radio and optical properties of a complete 5 GHz sample of strong radio sources are studied. High polarization is strongly correlated with the fraction of the total 5 GHz flux density found in a milliarcsec core. The detection rate of radio galaxies containing optical cores with high polarization is consistent with the hypothesis that all radio sources contain optically polarized cores, with strength proportional to the core radio flux density. High optical polarization, optical power-law fraction, line-to-continuum ratio, emission lines of small equivalent widths, and large amplitude flux variability are all strongly correlated with the fraction of the 5 GHz radio flux density that is unresolved on VLBI scales. The distributions of these properties are well matched by a model where radio and optical radiation have the same beaming geometry and with Doppler boosting of a factor of 10-100 in the optical. A striking alignment of the position angle of the VLBI structure axis and the position angle of optical polarization in highly polarized sources is confirmed.

C. R. Lawrence

Papers

Optical polarization of a complete sample of radio sources