Core Radio Flux Research Articles

Neutrino flares of radio blazars observed from TeV to PeV

ABSTRACT Radio blazars have been linked both to individual high-energy neutrino events and to excesses in likelihood sky maps constructed from lower-energy neutrino data. However, the exact mechanism by which neutrinos are produced in these sources is still unknown. Here, we demonstrate that IceCube neutrinos with energies over 200 TeV, which were previously associated with bright radio blazars, are significantly more likely to be accompanied by flares of lower-energy events, compared to those lacking blazar counterparts. The parsec-scale core radio flux density of blazars, positioned within the error regions of energetic events, is strongly correlated with the likelihood of a day-scale lower-energy neutrino flare in directional and temporal coincidence with the high-energy event, reported by IceCube. The probability of a chance correlation is 3.6 × 10−4. This confirms the neutrino-blazar connection in a new and independent way, and provides valuable clues to understanding the origin of astrophysical neutrinos.

Spectroscopic properties of radio-loud and radio-quiet quasars

AbstractSurveys have shown radio-loud (RL) quasars constitute 10%-15% of the total quasar population and rest are radio-quiet (RQ). However, it is unknown if this radio-loud fraction (RLF) remains consistent among different parameter spaces. This study shows that RLF increases for increasing full width half maximum (FWHM) velocity of the Hβ broad emission line (z < 0.75). To analyse the reason, we compared bolometric luminosity of RL and RQ quasars sample which have FWHM of Hβ broad emission line greater than 15000km/s (High Broad Line or HBL) with which have FWHM of Hβ emission line less than 2500km/s (Low Broad Line or LBL). From the distributions we can conclude for the HBL, RQ and RL quasars are peaking separately and RL quasars are having higher values whereas for the LBL the peaks are almost indistinguishable. We predicted selection effects could be the possible reason but to conclude anything more analysis is needed. Then we compared our result with Wills & Brotherton (1995) and have shown that some objects from our sample do not follow the pattern of the logR vs FWHM plot where R is the ratio of 5 GHz radio core flux density with the extended radio lobe flux density.

The Extragalactic Gamma-Ray Background from Core-dominated Radio Galaxies

Abstract Recent radio surveys have discovered a large number of low-luminosity core-dominated radio galaxies that are much more abundant than those at higher luminosities. These objects will be too faint in γ-rays to be detected individually by Fermi. Nevertheless, they may contribute significantly to the unresolved extragalactic γ-ray background. We consider here the possible contribution of these core-dominated radio galaxies to the diffuse extragalactic γ-ray background. Using published data available for all 45 of the radio galaxies listed as detected counterparts in the Fermi FL8Y source list update to the 3FGL catalog, we have searched for radio maps that can resolve the core flux from the total source flux. Using high-resolution radio maps we were able to obtain core fluxes for virtually every source. We then derived a relation between core radio flux and γ-ray flux that we extrapolated to sources with low radio luminosities that are known to be highly core-dominated. We then employed a very recent determination of the luminosity function for core-dominated radio galaxies in order to obtain the contribution of all possible γ-ray-emitting radio galaxies to the unresolved extragalactic γ-ray background. We find this contribution to be possibly non-negligible, 4%–18% of the unresolved γ-ray background observed using the Fermi-LAT telescope.

The Properties of Parsec-scale Blazar Jets

Abstract I show that, by assuming a standard Blandford–Königl jet, it is possible to determine the bulk Lorentz factor and angle to the line of sight of self-similar parsec-scale blazar jets by using five measured quantities: redshift, core radio flux, extended radio flux, the magnitude of the core shift between two frequencies, and apparent jet opening angle. From the bulk Lorentz factor and angle computed with this method, one can compute other jet properties such as the Doppler factor, magnetic field strength, and intrinsic jet opening angle. I use data taken from the literature and marginalize over nuisance parameters associated with the electron distribution and equipartition to compute these quantities, although the errors are large. Results are generally consistent with constraints from other methods. Primary sources of uncertainty are the errors on the core shift measurements and the uncertainty in the electron spectral index.

Interpreting the time variable RM observed in the core region of the TeV blazar Mrk 421

In this work we interpret and discuss the time variable rotation measure (RM) found, for the first time over a 1-yr period, in the core region of a blazar. These results are based on a one-year, multi-frequency (15, 24, and 43 GHz) Very Long Baseline Array (VLBA) monitoring of the TeV blazar Markarian 421 (Mrk 421). We investigate the Faraday screen properties and its location with respect to the jet emitting region. Given that the 43 GHz radio core flux density and the RM time evolution suggest a similar trend, we explore the possible connection between the RM and the accretion rate. Among the various scenarios that we explore, the jet sheath is the most promising candidate for being the main source of Faraday rotation. During the one-year observing period the RM trend shows two sign reversals, which may be qualitatively interpreted within the context of the magnetic tower models. We invoke the presence of two nested helical magnetic fields in the relativistic jet with opposite helicities, whose relative contribution produce the observed RM values. The inner helical field has the poloidal component ($B_{\rm p}$) oriented in the observer's direction and produces a positive RM, while the outer helical field, with $B_{\rm p}$ in the opposite direction, produces a negative RM. We assume that the external helical field dominates the contribution to the observed RM, while the internal helical field dominates when a jet perturbation arises during the second observing epoch. Being the intrinsic polarization angle parallel to the jet axis, a pitch angle of the helical magnetic field $\phi\gtrsim 70^\circ$ is required. Additional scenarios are also considered to explain the observed RM sign reversals.

RADIO PROPERTIES OF THE BAT AGNs: THE FIR–RADIO RELATION, THE FUNDAMENTAL PLANE, AND THE MAIN SEQUENCE OF STAR FORMATION

ABSTRACT We conducted 22 GHz 1″ JVLA imaging of 70 radio-quiet active galactic nuclei (AGNs) from the Swift-BAT survey. We find radio cores in all but three objects. The radio morphologies of the sample fall into three groups: compact and core-dominated, extended, and jet-like. We spatially decompose each image into core flux and extended flux, and compare the extended radio emission with that predicted from previous Herschel observations using the canonical FIR–radio relation. After removing the AGN contribution to the FIR and radio flux densities, we find that the relation holds remarkably well despite the potentially different star formation physics in the circumnuclear environment. We also compare our core radio flux densities with predictions of coronal models and scale-invariant jet models for the origin of radio emission in radio-quiet AGNs, and find general consistency with both models. However, we find that the L R/L X relation does not distinguish between star formation and non-relativistic AGN-driven outflows as the origin of radio emission in radio-quiet AGNs. Finally, we examine where objects with different radio morphologies fall in relation to the main sequence (MS) of star formation, and conclude that those AGNs that fall below the MS, as X-ray selected AGNs have been found to do, have core-dominated or jet-like 22 GHz morphologies.

The power and production efficiency of blazar jets

We use published data on the power and production efficiency of jets in blazars with double radio lobes in order to compare results obtained using different methods. In order to eliminate selection effects, we use cross-matched sub-samples containing only luminous blazars. We compare the three main existing methods, namely those based on the emission of radio lobes, on spectral fitting, and on radio core shift. We find the average jet power obtained for identical samples with the radio-lobe method is $\sim10$ times lower than that from the spectral fitting. In turn, the power from spectral fitting is compatible with that from core-shift modelling for plausible parameters of the latter. We also consider a phenomenological estimator based on the {\gamma}-ray luminosity. We examine uncertainties of those methods and discuss two alternative hypotheses. In one, the blazar-fit and core-shift methods are assumed to be correct, and the lower power from radio lobes is caused by intermittency of accretion. Long periods of quiescence cause the energy in the radio lobes, accumulated over the lifetime of the blazar, to be much less than that estimated based on the present luminous state. In addition, the power calculated using the radio lobes can be underestimated for intrinsically compact jets, in which the radio core flux can be over-subtracted. In our second hypothesis, the radio-lobe method is assumed to be correct, and the blazar-fit and core-shift powers are reduced due to the presence of $\sim15$ pairs per proton, and a larger magnetization than usually assumed, respectively.

A comprehensive long-term study of the radio and X-ray variability of NGC 4051 Paper II

The origin of the low luminosity radio emission in radio-quiet AGN, is unknown. The detection of a positive correlation between the radio and X-ray emission would imply a jet-like origin, similar to that seen in `hard state' X-ray binary systems. In our previous work, we found no believable radio variability in the well known X-ray bright Seyfert 1 galaxy NGC 4051, despite large amplitude X-ray variability. In this study we have carefully re-analysed radio and X-ray observations using the same methods as our previous work, we again find no evidence for core radio variability. In direct contrast to our findings, another study claim significant radio variability and a distinctive anti-correlation between radio and X-ray data for the same source. The other study report only integral flux values and do not consider the effect of the changing array on the synthesised beam. In both our studies of NGC 4051 we have taken great care to account for the effect that the changing beam size has on the measured radio flux and as a result we are confident that our method gives more accurate values for the intrinsic core radio flux. However, the lack of radio variability we find is hard to reconcile because radio images of NGC 4051 do show jet-like structure. We suggest that the radio structures observed are likely the result of a previous period of higher radio activity and that the current level of radio emission from a compact nuclear jet is low.

A ROBUST DERIVATION OF THE TIGHT RELATIONSHIP OF RADIO CORE DOMINANCE TO INCLINATION ANGLE IN HIGH REDSHIFT 3CRR SOURCES

ABSTRACT It is believed that, in radio-loud active galactic nuclei (AGNs), the core radio flux density can be normalized to the flux density of the extended lobe emission to infer the orientation of a radio source. However, very little is known about the reliability and precision of this method, and we are unaware of any robust conversion recipe to infer the inclination from the core dominance. Investigating whether or not the radio core dominance parameter R separates the quasars from the radio galaxies in the 1 3CRR catalog, we found excellent agreement of R with optical type, infrared flux ratios, and optical polarization. This indicates that probably both R and optical classification are very good orientation indicators, and the unified model is strongly predictive for these objects. The relative number densities indicate half-opening angles close to 60°, as expected from large surveys. The separations of optical types according to radio core dominance as well as near-infrared/MIR ratios, which are essentially perfect, mean that there can be only a small dispersion of torus half-opening angles. Also, even though torus dust is thought to be clumpy, there is an almost zero probability to see a type-1 source at high inclination. Finally, using only the Copernican Principle, i.e., the assumption that solid angle is filled uniformly with source axis orientations, we estimated a semi-empirical relation between core dominance and AGN inclination. This makes it possible to use R to infer the inclination of a source to an accuracy of ∼10° or less, at least for this type of object.

Why are some BL Lacertaes detected byFermi, but others not?

By cross-correlating an archival sample of 170 BL Lacs with 2 year \fermilat AGN sample, we have compiled a sample of 100 BL Lacs with \fermi detection (FBLs), and a sample of 70 non-\fermi BL Lacs (NFBLs). We compared various parameters of FBLs with those of NFBLs, including the redshift, the low frequency radio luminosity at 408 MHz ($L_{\rm 408MHz}$), the absolute magnitude of host galaxies ($M_{\rm host}$), the polarization fraction from NVSS survey ($P_{\rm NVSS}$), the observed arcsecond scale radio core flux at 5 GHz ($F_{\rm core}$) and jet Doppler factor; all the parameters are directly \textbf{measured} or derived from available data from literatures. We found that the Doppler factor is on average larger in FBLs than in NFBLs, and the $Fermi~ \gamma$-ray detection rate is higher in sources with higher Doppler factor. In contrast, there are no significant differences in terms of the intrinsic parameters of redshift, $ L_{\rm 408MHz}$, $ M_{\rm host}$ and $ P_{\rm NVSS}$. FBLs seem to have a higher probability of exhibiting measurable proper motion. These results strongly indicate a higher beaming effect in FBLs compared to NFBLs. The radio core flux is found to be strongly correlated with $\gamma$-ray flux, which remains after excluding the common dependence of the Doppler factor. At the fixed Doppler factor, FBLs have systematically larger radio core flux than NFBLs, implying lower $\gamma$-ray emission in NFBLs since the radio and $\gamma$-ray flux are significantly correlated. Our results indicate that the Doppler factor is an important parameter of $\gamma$-ray detection, the non-detection of $\gamma$-ray emission in NFBLs is likely due to low beaming effect, and/or low intrinsic $\gamma$-ray flux, and the gamma-rays are likely produced co-spatially with the arcsecond-scale radio core radiation and mainly through the SSC process.

GAMMA RAYS FROM RADIO GALAXIES: FERMI/LAT OBSERVATIONS

We review the high energy properties of Misaligned AGNs associated with γ-ray sources detected by Fermi in 24 months of survey. Most of them are nearby emission low power radio galaxies (i.e FRIs) which probably have structured jets. On the contrary, high power radio sources (i.e FRIIs) with GeV emission are rare. The small number of FRIIs does not seem to be related to their higher redshifts. Assuming proportionality between the radio core flux and the γ-ray flux, several of them are expected to be bright enough to be detected above 100 MeV in spite of their distance. We suggest that beaming/jet structural differences are responsible for the detection rate discrepancy observed between FRIs and FRIIs.

Accretion states of the Galactic microquasar GRS 1758−258

We present the results of a radio and X-ray study of the Galactic microquasar GRS 1758-258, using unpublished archival data and new observations. We focus in particular on the 2000-2002 state transitions, and on its more quiet behaviour in 2008-2009. Our spectral and timing analysis of the XMM-Newton data shows that the source was in the canonical intermediate, soft and hard states in 2000 September 19, 2001 March 22 and 2002 September 28, respectively. We estimate the disk size, luminosity and temperature, which are consistent with a black hole mass ~10 M_{sun}. There is much overlap between the range of total X-ray luminosities (on average ~0.02 L_{Edd}) in the hard and soft states, and probably between the corresponding mass accretion rates; in fact, the hard state is often more luminous. The extended radio lobes seen in 1992 and 1997 are still present in 2008-2009. The 5-GHz radio core flux density has shown variability between ~0.1-0.5 mJy over the last two decades. This firmly places GRS 1758-258 in the radio-quiet sequence of Galactic black holes, in the radio/X-ray plane. We note that this dichotomy is similar to the dichotomy between the radio/X-ray sequences of Seyfert and radio galaxies. We propose that the different radio efficiency of the two sequences is due to relativistic electron/positron jets in radio-loud black holes, and sub-relativistic, thermally dominated outflows in radio-quiet sources.

MULTIWAVELENGTH OBSERVATIONS OF 3C 454.3. III. EIGHTEEN MONTHS OF AGILE MONITORING OF THE “CRAZY DIAMOND”

ABSTRACT We report on 18 months of multiwavelength observations of the blazar 3C 454.3 (Crazy Diamond) carried out in the period 2007 July–2009 January. In particular, we show the results of the AGILE campaigns which took place on 2008 May–June, 2008 July–August, and 2008 October–2009 January. During the 2008 May–2009 January period, the source average flux was highly variable, with a clear fading trend toward the end of the period, from an average γ-ray flux F E>100 MeV ≳ 200 × 10−8 photons cm−2 s−1 in 2008 May–June, to F E>100 MeV ∼ 80 × 10−8 photons cm−2 s−1 in 2008 October–2009 January. The average γ-ray spectrum between 100 MeV and 1 GeV can be fit by a simple power law, showing a moderate softening (from ΓGRID ∼ 2.0 to ΓGRID ∼ 2.2) toward the end of the observing campaign. Only 3σ upper limits can be derived in the 20–60 keV energy band with Super-AGILE, because the source was considerably off-axis during the whole time period. In 2007 July–August and 2008 May–June, 3C 454.3 was monitored by Rossi X-ray Timing Explorer (RXTE). The RXTE/Proportional Counter Array (PCA) light curve in the 3–20 keV energy band shows variability correlated with the γ-ray one. The RXTE/PCA average flux during the two time periods is F 3-20 keV = 8.4 × 10−11 erg cm−2 s−1, and F 3-20 keV = 4.5 × 10−11 erg cm−2 s−1, respectively, while the spectrum (a power law with photon index ΓPCA = 1.65 ± 0.02) does not show any significant variability. Consistent results are obtained with the analysis of the RXTE/High-Energy X-Ray Timing Experiment quasi-simultaneous data. We also carried out simultaneous Swift observations during all AGILE campaigns. Swift/XRT detected 3C 454.3 with an observed flux in the 2–10 keV energy band in the range (0.9–7.5) × 10−11 erg cm−2 s−1 and a photon index in the range ΓXRT = 1.33–2.04. In the 15–150 keV energy band, when detected, the source has an average flux of about 5 mCrab. GASP-WEBT monitored 3C 454.3 during the whole 2007–2008 period in the radio, millimeter, near-IR, and optical bands. The observations show an extremely variable behavior at all frequencies, with flux peaks almost simultaneous with those at higher energies. A correlation analysis between the optical and the γ-ray fluxes shows that the γ-optical correlation occurs with a time lag of τ = −0.4+0.6 −0.8 days, consistent with previous findings for this source. An analysis of 15 GHz and 43 GHz VLBI core radio flux observations in the period 2007 July–2009 February shows an increasing trend of the core radio flux, anti-correlated with the higher frequency data, allowing us to derive the value of the source magnetic field. Finally, the modeling of the broadband spectral energy distributions for the still unpublished data, and the behavior of the long-term light curves in different energy bands, allow us to compare the jet properties during different emission states, and to study the geometrical properties of the jet on a time-span longer than one year.

An X‐Ray Image of the Composite Supernova Remnant SNR G16.7+0.1

We have observed the Galactic supernova remnant G16.7+0.1 for 13 ks using the EPIC cameras on board the XMM-Newton X-Ray Observatory, producing the first X-ray image of the remnant. This composite radio remnant has a core radio flux density of only 100 mJy, making it one of the faintest radio synchrotron nebulae yet detected, although the core-to-shell flux ratio at 6 cm is typical of the growing class of composite remnants. Our image is seriously contaminated by bright arcs produced by singly reflected X-rays from the X-ray binary GX 17+2, which lies just outside the field of view, providing an interesting data analysis challenge. Nonetheless, the remnant's synchrotron core is clearly detected. We report on the spectrum and intensity of the core emission as well as on our search for emission from the thermal shell and describe the constraints these observations provide on the remnant's distance, age, and central pulsar properties.

Clues to Quasar Broad-Line Region Geometry and Kinematics

We present evidence that the high-velocity C IV λ1549 emission-line gas of radio-loud quasars may originate in a disklike configuration, in close proximity to the accretion disk often assumed to emit the low-ionization lines. For a sample of 36 radio-loud z ≈ 2 quasars, we find the 20%-30% peak widths to show significant inverse correlations with the fractional radio core-flux density R, which is the radio axis inclination indicator. Highly inclined systems have broader line wings, consistent with a high-velocity field perpendicular to the radio axis. By contrast, the narrow line core shows no such relation with R, so the lowest velocity C IV-emitting gas has an inclination-independent velocity field. We propose that this low-velocity gas is located at higher disk altitudes than the high-velocity gas. A planar origin of the high-velocity C IV emission is consistent with the current results and with an accretion disk wind emitting the broad lines. A spherical distribution of randomly orbiting broad-line clouds and a polar high-ionization outflow are ruled out.

Extended and Compact X‐Ray Emission from the Powerful Radio Galaxy 3C 220.1

We report on ROSAT HRI observations of the z = 0.61 radio galaxy 3C 220.1. The X-ray emission from this object consists of an extended component, which we attribute to luminous cluster emission, and a compact central source. The compact component is too bright to be modeled as a cooling flow under some plausible assumptions for the hot gas temperature and distribution; we suggest instead that it is directly related to the core of the radio source. The X-ray flux of the compact component is consistent with the prediction of Worrall et al. that all powerful radio galaxies should have a central jet-related X-ray emission component that is proportional in strength to the radio-core flux density. Other observations of distant 3CR radio sources are consistent with this model.

The Emission‐Line Properties of Low‐Redshift Quasi‐stellar Objects. II. The Relation to Radio Type

We present optical spectrophotometry of 45 quasars in the redshift range 0.045-0.592. These data are combined with the sample of 87 low-redshift quasar and QSO spectra obtained by Boroson & Green for a more extensive investigation of the relation of the properties of the broad Hβ, [O III] λ5007, and optical Fe II emission lines to the objects' radio, optical, and X-ray continuum parameters. We derive a complete correlation matrix for the quasars and perform two-sample tests on the subsamples of flat radio spectrum (FRS) quasars, steep radio spectrum (SRS) quasars, and radio-quiet objects (QSOs). Our principal findings are as follows: 1. We confirm that the width of the Hβ profile at quarter-maximum and half-maximum points is inversely correlated with the ratio of the 6 cm radio core flux to that measured from the optical continuum at 5500 A, which has been argued to be an indicator of the orientation of the objects' radio axis under beaming models. The Hβ profile widths do not correlate strongly with any line or continuum parameter likely to be an indicator of the intrinsic power of the central engine, including the extended radio luminosity. A principal components analysis of the correlation matrix does not reveal any clear trends separate from the dependence of Hβ profile width on the orientation indicator, and we find no evidence of a decrease in the strength of the profile base component in FRS quasars relative to SRS quasars from a simple line deblending procedure. 2. The two-sample tests reveal several strong differences between the quasar and QSO subsamples, including differences between samples closely matched in optical luminosity. While QSOs are statistically closer to FRS quasars than SRS quasars in their emission-line properties, the FRS quasars still have significantly wider and more redward asymmetric Hβ profiles, stronger [O III] λ5007 emission, and weaker optical Fe II emission. The variance of the Hβ profile width and asymmetry parameters is also significantly larger among the combined sample of FRS and SRS quasars than among the QSOs. From the combined quasar and QSO sample, we confirm that there is an inverse correlation between soft X-ray luminosity and the equivalent width of the optical Fe II emission complex in the range ~λλ4434-4684. 3. The Balmer line profiles of several of the quasars show a division into two components, a core of intermediate (~103 km s-1) velocity width, and a very broad (~104 km s-1) base that is typically redshifted with respect to systemic velocity. This supports evidence that the broad-line region is divided into an inner Very Broad Line Region and an outer Intermediate Line Region. A few objects also display unusually strong emission in He II λ4686 and/or He I λ5876, while in other objects these lines are weak or absent. It is presently unclear whether these differences are intrinsic to the objects or else represent transient events caused by the dynamical evolution of the broad-line gas. The results for the quasar sample are consistent with unified models of FRS and SRS quasars and the interpretation that the change in profile widths arises from differing views of a flattened broad-line region with a strong component of planar motion. Under a unified model we estimate the ratio of planar to random BLR motions to be ~7:1. Assuming that the profile width and asymmetry parameters trace the mass of the central black hole, the distributions of these parameters indicate a larger average hole mass and a larger range of hole masses among the quasars than the QSOs, consistent with the model in which quasar black holes are the rapidly spinning product of the coalescence of two or more black holes at the centers of merged galaxies.

A survey for high optical polarization in quasars with core-dominant radio structure - Is there a beamed optical continuum?

view Abstract Citations (216) References (84) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Survey for High Optical Polarization in Quasars with Core-dominant Radio Structure: Is There a Beamed Optical Continuum? Wills, Beverley J. ; Wills, D. ; Breger, Michel ; Antonucci, R. R. J. ; Barvainis, Richard Abstract We present 129 new optical linear polarization measurements of 84 quasars (defined as starlike on Sky Survey prints). We have discovered 23 new highly polarized objects (p> 3%), of which 14 are known to have broad emission lines. This represents a significant increase in the numbers of these objects that were known. With the addition of data from the literature, our measurements constitute well-defined samples of flat-spectrum core-dominant radio quasars brighter than about 18 mag, one selected from the list published by Perley (1982) and another from that by Kuhr et al. (1981). The results of this survey of 123 quasars and BL Lac objects are the following: 1. The fraction of objects that have been found to be highly polarized on at least one measurement is 45% +/- 5%. This is a lower limit to the total fraction of highly polarized quasars because the well-observed highly polarized objects of this class have p <3% some of the time. 2. There is a highly significant correlation between percentage polarization and the dominance of a compact radio core as measured by R, the ratio of radio core flux density to flux density in the extended lobes. In order to include low-R objects and to increase the sample size, we have added data from the literature. We find that all 13 quasars (including 10 BL Lac objects) with log R> 2 are highly polarized while for log R < 0 this fraction is only 5%. If relativistic beaming is the explanation for the strong synchrotron emission of the radio core, then the strength of the polarized component of the optical continuum also has a strong angle dependence, suggesting that the optical flux is beamed as well. 3. The fraction of quasars with p> 3% in a fixed observed passband apparently decreases with increasing redshift. Using the maximum observed values of p for each object, we find that for z < 1, 59% +/- 6% of the sample have p > 3%, compared with 24% +/- 6% for z > 1. A likely interpretation is that many of these highly polarized quasars show decreasing percentage polarization at shorter rest wavelengths where a very low polarization flat-spectrum "Big Blue Bump" component dominates over a highly polarized- steep-spectrum "synchrotron" component. Shorter rest wavelengths shift through our observing window with increasing quasar redshift. We present a simple spectrum model consisting of a steep polarized optical synchrotron component related to the radio core, and a flat, unpolarized Big Blue Bump, which explains results 1,2, and 3. The combined R and redshift dependence of polarization (or of fraction of highly polarized objects) results in a very high incidence of highly polarized objects, at least 74% +/- 8%, among those 36 objects with log R > 1.25 and z < 1. This has two immediate consequences. High optical polarization quasars and flat-spectrum core-dominant quasars are essentially the same objects. Therefore, the blazar unified scheme advocated by Blandford & Rees, and by Antonucci & Ulvestad, and the generalized unified scheme of Blandford & Konigl, Orr & Browne, and Wills & Browne, are approximately equivalent. Also, the apparent similarity in the radio and optical "beaming cones" suggests that the corresponding emission regions are closely related. The optical synchrotron radiation may originate in the radio core and in unresolved superluminal radio components producing the radio emission. There is a significantly lower incidence of high polarization among the intrinsically small compact steep-spectrum (CSS) and gigahertz peaked spectrum (GPS) sources - only two out of 23. Either their structure cannot be unified by relativistic beaming geometry, the core spectra are too steep for significant optical synchrotron emission, or the selection criteria for these sources eliminate the highly beamed examples. Finally, fewer than about 2% of the 3CR population of all FR II and compact sources are beamed in our direction, as indicated by the upper limit to the fraction of highly polarized quasars and core-dominant objects among those sources with S_ext_ > 10 Jy. If this fraction represents the radiation angle of a simple relativistic jet, the Lorentz factor, γ >= 5, is consistent with that deduced from other methods. Publication: The Astrophysical Journal Pub Date: October 1992 DOI: 10.1086/171869 Bibcode: 1992ApJ...398..454W Keywords: Bl Lacertae Objects; Galactic Structure; Optical Polarization; Quasars; Sky Surveys (Astronomy); Astronomical Models; Astronomical Spectroscopy; Radio Emission; Red Shift; Spectral Line Width; Very Large Array (Vla); Astrophysics; GALAXIES: QUASARS: GENERAL; POLARIZATION; GALAXIES: BL LACERTAE OBJECTS: GENERAL full text sources ADS | data products NED (268) SIMBAD (267)

Optical polarization of a complete sample of radio sources

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.

Compact radio cores in three Seyfert galaxies - High resolution studies of MKN 3, MKN 231, and MKN 463

The small-scale morphologies of Mkn 231 and Mkn 463 have been investigated using the European VLBI Network (EVN) at 1.6 GHz and the VLA at 15 and 22 GHz. Mkn 3 has been studied using the EVN at 1.4 and 1.6 GHz. All of the galaxies have a substantial fraction of their core radio flux in linear or elongated structures, typically tens of parsecs in extent. Agreement between the parsec- and kiloparsec-scale position angles of continuum radio emission suggests collimated outflow from the galaxy centers that continues over several orders of magnitude in scale. Supernova rates of order one hundred per year on scales of tens of parsecs are required to explain the nuclear radio emission as the result of bursts of star formation. The luminosities, small extents, and linear morphologies of the radio sources all support the idea that the nuclear radio sources are energized by active galactic nuclei and therefore support the more general picture of Seyfert galaxy nuclei being low-luminosity quasars. All of the galaxies appear to have undergone violent interactions in the recent past.