scholarly journals Arcsecond Scale Polarization of BL Lac Objects

1996 ◽  
Vol 175 ◽  
pp. 55-56
Author(s):  
C. Stanghellini ◽  
P. Cassaro ◽  
M. Bondi ◽  
D. Dallacasa ◽  
R. Della Ceca ◽  
...  
Keyword(s):  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Radio Spectrum ◽  
Line Of Sight ◽  
Parent Population ◽  
Rapid Variability ◽  
Bl Lac Objects ◽  
Relativistic Jet ◽  
Bl Lac ◽  
Optical Continuum

BL Lac objects are an enigmatic class of active galactic nuclei. They are characterized by high luminosity, a flat radio spectrum that steepens at higher energies, relatively high optical and radio polarization, rapid variability and an optical continuum with weak or absent emission lines (see Urry and Padovani, 1995 for a recent review).These properties have been interpreted in terms of a relativistic jet closely aligned to the line of sight (Blandford and Rees, 1978, Ghisellini et al., 1993). This model, known as the beaming model, implies that there must be a so called “parent population” of radio sources intrinsically identical to BL Lac objects, but with the jets oriented at large angles to the line of sight. Browne (1983) was the first to propose the low luminosity FR I radio galaxies as the most likely candidates for the “parent population” of the core dominated BL Lac objects. An outcome of the beaming model is that all the properties not depending on orientation should be shared by the BL Lac objects and the FR I radio galaxies.

scholarly journals The Environments of Radio Galaxies

1996 ◽  
Vol 175 ◽  
pp. 323-324
Author(s):  
J.E. Pesce ◽  
R. Falomo ◽  
G. Fasano ◽  
R. Scarpa
Keyword(s):  
Radio Galaxies ◽  
Line Of Sight ◽  
Type I ◽  
Bl Lac Objects ◽  
Relativistic Jet ◽  
Bl Lac ◽  
The Galaxy ◽  
Galaxy Environment

In the unified schemes of AGNs BL Lac objects are believed to be Fanaroff-Riley (FR) type I radio galaxies with a relativistic jet aligned to the observer's line of sight (e.g. Urry & Padovani 1995). Kollgaard et al. (1992) and Owen et al. (1995) suggest some FR II sources can also be BL Lac parents. Clearly, isotropic properties such as the galaxy environment of both beamed and unbeamed objects should be identical.

scholarly journals GAMMA-RAY EMISSION FROM AGNS (SPECIAL FOCUS ON BL LAC OBJECTS)

2010 ◽  
Vol 19 (06) ◽  
pp. 841-848
Author(s):  
F. TAVECCHIO
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Line Of Sight ◽  
Special Focus ◽  
Bl Lac Objects ◽  
Relativistic Jet ◽  
Bl Lac ◽  
High Energy Emission

Blazars, radio-loud active galactic nuclei with the relativistic jet closely aligned with the line of sight, dominate the extragalactic sky observed at gamma-ray energies, above 100 MeV. We discuss some of the emission properties of these sources, focusing in particular on the "blazar sequence" and the interpretative models of the high-energy emission of BL Lac objects.

scholarly journals The Environment of OJ 287: Nearby Galaxies and a Long Optical Jet?

1996 ◽  
Vol 175 ◽  
pp. 47-48
Author(s):  
A. Sillanpää ◽  
L. Takalo ◽  
K. Nilsson ◽  
T. Pursimo ◽  
P. Teerikorpi ◽  
...  
Keyword(s):  
Large Scale ◽  
Radio Galaxies ◽  
Trigger Mechanism ◽  
Galaxy Clustering ◽  
Bl Lac Objects ◽  
Close Interaction ◽  
Relativistic Jet ◽  
Bl Lac ◽  
Nearby Galaxies ◽  
Bl Lacs

A widely accepted model for BL Lac objects is that they are radio galaxies with a relativistic jet pointing almost directly towards us. But we need a clear trigger mechanism for these jets. One possibility is the close interaction between the BL Lac host and the closeby galaxies (e.g. Heckman et al. 1986). This interaction has been seen many times in the case of quasars (Hutchings et al. 1989) but not so much is known about the close surroundings of the BL Lac objects although there has been some pioneer work like Stickel et al. (1993). The problem has usually been that the images are not deep enough and that the seeing has not been so good. To clarify the situation we have started an observing program to get very deep images in the sub-arcsecond seeing conditions from the whole 1 Jy sample (Stickel et al. 1991) of BL Lac objects. The aims of this study are: 1. to search for very close companions to the BL Lacs, 2. to study the large scale galaxy clustering around the BL Lacs and 3. to study the BL Lac hosts themselves.

scholarly journals The estimation of γ-ray Doppler factor for Fermi/LAT-detected blazars

2020 ◽  
Vol 37 ◽  
Author(s):  
Zhiyuan Pei ◽  
Junhui Fan ◽  
Jianghe Yang ◽  
Denis Bastieri
Keyword(s):  
Lower Limit ◽  
Galactic Nuclei ◽  
Relativistic Effects ◽  
Bl Lac Objects ◽  
Relativistic Jet ◽  
Spectrum Radio ◽  
Bl Lac ◽  
Doppler Factor ◽  
Bl Lacs ◽  
Extreme Observation

Abstract Blazars are a subclass of active galactic nuclei with extreme observation properties, which is caused by the beaming effect, expressed by a Doppler factor ( $\delta$ ), in a relativistic jet. Doppler factor is an important parameter in the blazars paradigm to indicate all of the observation properties, and many methods were proposed to estimate its value. In this paper, we present a method following Mattox et al. to calculate the lower limit on $\gamma$ -ray Doppler factor ( $\delta_{\gamma}$ ) for 809 selected Fermi/LAT-detected $\gamma$ -ray blazars by adopting the available $\gamma$ -ray and X-ray data. Our sample included 342 flat-spectrum radio quasars (FSRQs) and 467 BL Lac objects (BL Lacs), out of which 507 sources are compiled with available radio core-dominance parameter (R) from our previous study. Our calculation shows that the average values of the lower limit on $\delta_{\gamma}$ for FSRQs and BL Lacs are $\left\langle\delta_{\gamma}|_{\textrm{FSRQ}}\right\rangle = 6.87 \pm 4.07$ and $\left\langle\delta_{\gamma}|_{\textrm{BL\ Lac}}\right\rangle=4.31 \pm 2.97$ , respectively. We compare and discuss our results with those from the literature. We found that the derived lower limit on $\delta_{\gamma}$ for some sources is higher than that from the radio estimation, which could be possibly explained by the jet bending within those blazars. Our results also suggest that the $\gamma$ -ray and radio regions perhaps share the same relativistic effects. The $\gamma$ -ray Doppler factor has been found to be correlated with both the $\gamma$ -ray luminosity and core-dominance parameter, implying that the jet is possibly continuous in the $\gamma$ -ray bands, and R is perhaps an indicator for a beaming effect.

scholarly journals High Energy Phenomena in AGN Jets

1998 ◽  
Vol 188 ◽  
pp. 153-156
Author(s):  
F. Takahara
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Line Of Sight ◽  
Time Variability ◽  
Optical Polarization ◽  
Bl Lac Objects ◽  
Relativistic Jet ◽  
Bl Lac ◽  
Gamma Ray Emission ◽  
Superluminal Expansion

BL-Lac objects and optically violent variable quasars (OVVs), called together blazars, are characterized by rapid time variability, strong optical polarization, superluminal expansion and strong gamma-ray emission. Such properties are understood in the framework of a relativistic jet emanated from the central powerhouse. Blazars are considered to be objects for which the direction of the jet is very close to the line of sight.

scholarly journals A Comparison of the X-ray Spectra of Quasars and BL Lac Objects

1989 ◽  
Vol 134 ◽  
pp. 197-198
Author(s):  
D. M. Worrall ◽  
B. J. Wilkes
Keyword(s):  
Power Law ◽  
Radio Spectrum ◽  
Spectral Indices ◽  
Mean Power ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Infrared Frequencies

Quasars with similar core-compact radio properties can be classified by their differences at optical and infrared frequencies. Their X-ray properties might be expected to be similar if the synchrotron self-Compton mechanism relates their radio and X-ray emission. We have compared the 0.2–3.5 keV mean power-law energy spectral indices, , for 4 quasar classes: 12 Highly Polarized QSOs (HPQs), 19 Flat Radio Spectrum, core-compact, low-polarization, QSOs (FRS QSOs), 24 radio-selected BL Lac objects, and 7 X-ray-selected BL Lac objects.

scholarly journals Serendipitous VLBI Observations of Intraday Variability in the BL Lac Objects 1334–127, 2131–021, and 2155–152

1998 ◽  
Vol 164 ◽  
pp. 273-274
Author(s):  
P. Yu. Kochanev ◽  
D. C. Gabuzda
Keyword(s):  
Rapid Variability ◽  
Bl Lac Objects ◽  
Polarization Structure ◽  
Vlbi Observations ◽  
Bl Lac ◽  
Vlbi Data ◽  
Intraday Variability

AbstractGlobal λ = 6 cm VLBI polarization observations of intraday variability in the three BLLacertae objects 1334–127, 2131–021, and 2155–152 are analyzed. Integrated VLA measurements during the VLBI observations show that although there were no substantial total intensity variations, the polarizations for these three sources varied significantly during the VLBI experiment. The VLBI data were divided into 2-3 hour segments in order to search for corresponding rapid variability in the VLBI polarization structure. Our analysis shows that the VLA polarization variability in 2155–152 and 2131–021 is present in the VLBI data (i.e., it occurred on mas scales), but this is not the case for 1334–127.

scholarly journals Statistical Effects of Doppler Beaming and Malmquist Bias on Flux-Limited Samples of Compact Radio Sources

1998 ◽  
Vol 164 ◽  
pp. 137-138
Author(s):  
Matthew L. Lister ◽  
Alan P. Marscher
Keyword(s):  
Active Galactic Nuclei ◽  
Luminosity Function ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Radio Sources ◽  
Apparent Velocity ◽  
Parent Population ◽  
Relativistic Jet ◽  
Spectrum Radio ◽  
Statistical Effects

AbstractWe examine the effects of Doppler beaming on flux-limited samples of compact extragalactic radio sources using Monte Carlo simulations. We incorporate a luminosity function and z-distribution for the parent population, and investigate models in which the unbeamed synchrotron luminosity L of a relativistic jet is related to its bulk Lorentz factor Γ. The predicted flux density, redshift, monochromatic luminosity, and apparent velocity distributions of our simulated flux-limited samples are compared to the Caltech-Jodrell Bank (CJF) sample of flat-spectrum, radio core-dominated active galactic nuclei (AGNs).We find that a relation between L and Γ is not needed to reproduce the characteristics of the CJF sample. Introducing a positive correlation between these quantities results in an underabundance of objects with high viewing angles, while a negative correlation gives generally poor fits to the data.

scholarly journals The Compact Magnetic Field Structures of AGN from Space VLBI Polarization Observations

2001 ◽  
Vol 205 ◽  
pp. 134-135
Author(s):  
D.C. Gabuzda ◽  
J.L. Gómez
Keyword(s):  
Magnetic Field ◽  
Active Galactic Nuclei ◽  
Linear Polarization ◽  
Line Emission ◽  
Galactic Nuclei ◽  
Emission Mechanism ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Bl Lac ◽  
Optical Line

BL Lacertae objects are active galactic nuclei with weak, sometimes undetectable, optical line emission and strong variability in total intensity and linear polarization over a broad range of wavelengths from ultraviolet to radio. It is believed that synchrotron radiation is the dominant emission mechanism virtually throughout the spectrum. Their strong linear polarization makes BL Lac objects prime targets for space VLBI polarization observations.

scholarly journals X-Ray Surveys as Tools to Investigate the Cosmological Evolution of Quasars, BL Lac Objects and Clusters of Galaxies

1987 ◽  
Vol 124 ◽  
pp. 593-595
Author(s):  
Isabella M. Gioia ◽  
Tommaso Maccacaro ◽  
Anna Wolter
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Progress Report ◽  
Cosmological Evolution ◽  
Clusters Of Galaxies ◽  
Bl Lac Objects ◽  
X Ray ◽  
Basic Properties ◽  
Bl Lac ◽  
Einstein Observatory

We present a progress report on a major extension of the Einstein Observatory Medium Sensitivity Survey (MSS). The basic properties of the extragalactic sources identified with Active Galactic Nuclei (AGN) and clusters of galaxies are discussed. Results from previous work are briefly summarized.

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