Sample Of Flat-spectrum Radio Quasars Research Articles

Jet Mechanism and γ-Ray-emitting Region for Fermi Flat-spectrum Radio Quasars with Broad-line Emissions

Blazars are a subject of intense debate, specifically regarding their jet launch and emission mechanisms, and the origins of their γ-ray radiation. To explore these issues, we have built a comprehensive sample of flat-spectrum radio quasars (FSRQs), with well-characterized spectral energy distribution. This study aims to elucidate the dominant jet launch mechanism and the main processes behind the inverse Compton (IC) component. Additionally, we seek to pinpoint the location of the γ-ray dissipation region relative to the central black hole, denoted as R γ . Our approach involves a detailed analysis of broad-line region (BLR) emission, from which we derive robust estimates of the black hole masses using two distinct virial techniques. This enables us to constrain the jet power across a wide array of FSRQs. Our findings lead to several significant conclusions: (i) The correlation of jet power with black hole mass allows us to test the Blandford–Znajek, Blandford–Payne, and hybrid mechanisms. We find that the hybrid mechanism is most effective in explaining the jet power observed in the majority of FSRQs; (ii) The IC component of the γ-rays in FSRQs is predominantly due to the external Compton process. (iii) Through simulations, we determine the minimum and maximum values of R γ (the γ-ray dissipation region) and conclude it is located outside the BLR. This conclusion is derived from the variability timescale analysis.

The space density ofz > 4 blazars

High redshift blazars are an important class of Active Galactic Nuclei (AGN) that can provide an independent estimate of the supermassive black-hole mass function in high redshift radio-loud AGN without the bias due to absorption along the line-of-sight. Using the Cosmic Lens All Sky Survey (CLASS) we built a complete radio flux-limited sample of high redshift (z>4) blazars suitable for statistical studies. By combining dedicated optical observations and the SDSS spectroscopic database, we obtained a sample of 26 blazar candidates with a spectroscopic redshift above 4. On the basis of their radio spectrum we distinguish between blazars and QSO with a Gigahertz Peaked Spectrum (GPS) like spectrum. Out of the 18 confirmed blazars 14 constitute a completely identified, flux-limited sample down to a magnitude of 21 (AB). Using this complete sample we derive a space density of blazars with 4<z<5.5 of rho=0.13 (+0.05,-0.03) Gpc^-3. This is the first actual estimate of the blazar space density in this range of redshift. This value is in good agreement with the extrapolation of the luminosity function and cosmological evolution based on a sample of flat-spectrum radio quasars selected at lower redshifts and it is consistent with a cosmological evolution peaking at z$\sim$2 similar to radio-quiet QSO. We do not confirm, instead, the presence of a peak at z~4 in the space density evolution, recently suggested using an X-ray selected sample of blazars. It is possible that this extreme peak of the evolution is present only among the most luminous blazars.

Black-hole mass estimates for a homogeneous sample of bright flat-spectrum radio quasars

We have selected a complete sample of flat-spectrum radio quasars (FSRQs) from the WMAP 7-yr catalog within the SDSS area, all with measured redshift, and have compared the black hole mass estimates based on fitting a standard accretion disk model to the `blue bump' with those obtained from the commonly used single epoch virial method. The sample comprises 79 objects with a flux density limit of 1 Jy at 23 GHz, 54 of which (68%) have a clearly detected `blue bump'. Thirty-four of the latter have, in the literature, black hole mass estimates obtained with the virial method. The mass estimates obtained from the two methods are well correlated. If the calibration factor of the virial relation is set to $f=4.5$, well within the range of recent estimates, the mean logarithmic ratio of the two mass estimates is equal to zero with a dispersion close to the estimated uncertainty of the virial method. The fact that the two independent methods agree so closely in spite of the potentially large uncertainties associated with each lends strong support to both of them. The distribution of black-hole masses for the 54 FSRQs in our sample with a well detected blue bump has a median value of $7.4\times 10^{8}\,M_\odot$. It declines at the low mass end, consistent with other indications that radio loud AGNs are generally associated with the most massive black holes, although the decline may be, at least partly, due to the source selection. The distribution drops above $\log(M_\bullet/M_\odot) = 9.4$, implying that ultra-massive black holes associated with FSRQs must be rare.

DEEP MULTIWAVEBAND OBSERVATIONS OF THE JETS OF 0208-512 AND 1202-262

We present deep {\it HST, Chandra, VLA} and {\it ATCA} images of the jets of PKS 0208--512 and PKS 1202--262, which were found in a {\it Chandra} survey of a flux-limited sample of flat-spectrum radio quasars with jets (see Marshall et al., 2005). We discuss in detail their X-ray morphologies and spectra. We find optical emission from one knot in the jet of PKS 1202--262 and two regions in the jet of PKS 0208--512. The X-ray emission of both jets is most consistent with external Comptonization of cosmic microwave background photons by particles within the jet, while the optical emission is most consistent with the synchrotron process. We model the emission from the jet in this context and discuss implications for jet emission models, including magnetic field and beaming parameters.

The Two-Color Diagram: The "Double-Hump" Behavior at the Radio Band and the Evolution of Blazars

We compiled a sample of 29 flat-spectrum radio quasars (FSRQs) and 48 BL Lac objects for which both B - V and U - B are available. The two-color (U - B, B - V) stellar evolution diagram of FSRQs and BL Lac objects in this sample shows that FSRQs and BL Lac objects can be considered to be in the same family, but they occupy different extreme regions in the diagram. The result of the two- color diagram of FSRQs and BL Lac objects in this paper is consistent with the intrinsic accretion rate - luminosity relation for FSRQs and BL Lac objects that was obtained in a previous paper. In addition, based on the quasi-simultaneous spectral properties of core-dominated radio sources observed by Punsly, we compiled another sample of FSRQs and BL Lac objects for which the quantities Delta log [(F-nu)(cm)/(F-nu)(mm)] have been well obtained. We found that there is a significant correlation between the intrinsic bolometric luminosity log L-bol(in) and the quantity Delta. We also found that FSRQs have a relatively higher bolometric luminosity and larger Delta than BL Lac objects. This result is also consistent with the intrinsic accretion rate - luminosity relation because the physical parameters Delta are strongly correlated with the accretion rates (M) and nuclear gas densities.

Is there a relationship between BL Lacertae objects and flat-spectrum radio quasars?

The properties of a complete sample of flat-spectrum radio quasars are analysed and compared to those of radio-selected BL Lacs, studied in a previous paper, to look for any relationship between the two classes. It is shown that microlensing of quasars by stars in foreground galaxies can probably be ruled out as an explanation for the BL Lac phenomenon, while an evolutionary connection between flat-spectrum radio quasars and BL Lacs does not seem to be supported by the present data. The intrinsic properties of the two classes, that is extended radio emission and line luminosities, are significantly different