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 Frequency Dependence of the Parsec-scale Polarization Structures of BL Lac Objects

2001 ◽  
Vol 205 ◽  
pp. 140-141
Author(s):  
A.B. Pushkarev ◽  
D.C. Gabuzda ◽  
T.V. Cawthorne
Keyword(s):  
Line Emission ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Sky Survey ◽  
Radiation Sources ◽  
Wide Wavelength Range ◽  
Bl Lac ◽  
5 Ghz

BL Lacertae objects are active galactic nuclei with weak or undetectable line emission and strong variability in total intensity and linear polarization over a wide wavelength range from optical to radio. The radio emission and much of the optical emission is believed to be synchrotron radiation. Sources in the complete sample of BL Lac objects defined by Kühr and Schmidt (1990) have: 5 GHz fluxes of at least 1 Jy, radio spectral index α ≥ −0.5 (Sv ˜ v+α), rest frame equivalent width of the strongest emission lines less than 5 Å, and optical counterparts on the Sky Survey plates with brightness greater than 20m.

scholarly journals Discovery of diffuse optical emission lines from the inner Galaxy: Evidence for LI(N)ER-like gas

2020 ◽  
Vol 6 (27) ◽  
pp. eaay9711 ◽  
Author(s):  
D. Krishnarao ◽  
R. A. Benjamin ◽  
L. M. Haffner
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Center ◽  
Line Emission ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Hydrogen Gas ◽  
Emission Lines ◽  
Neutral Gas ◽  
Optical Line ◽  
Tilted Disk

Optical emission lines are used to categorize galaxies into three groups according to their dominant central radiation source: active galactic nuclei, star formation, or low-ionization (nuclear) emission regions [LI(N)ERs] that may trace ionizing radiation from older stellar populations. Using the Wisconsin H-Alpha Mapper, we detect optical line emission in low-extinction windows within eight degrees of Galactic Center. The emission is associated with the 1.5-kiloparsec-radius “Tilted Disk” of neutral gas. We modify a model of this disk and find that the hydrogen gas observed is at least 48% ionized. The ratio [NII] λ6584 angstroms/Hα λ6563 angstroms increases from 0.3 to 2.5 with Galactocentric radius; [OIII] λ5007 angstroms and Hβ λ4861 angstroms are also sometimes detected. The line ratios for most Tilted Disk sightlines are characteristic of LI(N)ER galaxies.

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.

scholarly journals Cm-Wavelength Flux Variability: Constraints on AGN Modeling

1994 ◽  
Vol 159 ◽  
pp. 497-497
Author(s):  
M.F. Aller ◽  
H.D. Aller ◽  
P.A. Hughes
Keyword(s):  
Flux Density ◽  
Linear Polarization ◽  
Total Flux ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Flux Variability ◽  
Bl Lac ◽  
Bl Lacs

To study whether the radio properties of BL Lacertae type objects and QSOs differ, we initiated a program in 1979 to monitor the total flux density and linear polarization at 14.5, 8.0 and 4.8 GHz of the strongest then known BL Lac objects which met the Hewitt-Burbidge criteria (Ledden, private communications) plus 3 subsequently identified high declination BL Lacs (Biermann et al. 1981). Results based on the behavior of the 45 brightest sample members are compared here with the properties of the QSOs in the flux-limited Pearson-Readhead sample (Pearson and Readhead 1988).

scholarly journals The Relationship of Hard X‐Ray and Optical Line Emission in Low‐Redshift Active Galactic Nuclei

2005 ◽  
Vol 634 (1) ◽  
pp. 161-168 ◽  
Author(s):  
T. M. Heckman ◽  
A. Ptak ◽  
A. Hornschemeier ◽  
G. Kauffmann
Keyword(s):  
Active Galactic Nuclei ◽  
Line Emission ◽  
Galactic Nuclei ◽  
X Ray ◽  
Optical Line ◽  
Relationship Of ◽  
The Relationship

scholarly journals X-Rays from Active Galactic Nuclei

1983 ◽  
Vol 6 ◽  
pp. 491-498 ◽  
Author(s):  
A.C. Fabian
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
X Rays ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac

Recent X-ray observations of active galactic nuclei and Seyfert galaxies in particular are briefly reviewed. The application of the efficiency limit to rapidly varying luminous sources such as NGC 6814 is discussed. It is argued that the variability and probable MeV spectral turnover imply that most of the electrons which radiate the observed flux are only mildly relativistic. A possible link between the steep soft X-ray spectra and featureless optical continua of BL Lac objects is considered.

scholarly journals Active Galactic Nuclei from the Extended Einstein Medium Survey

1987 ◽  
Vol 121 ◽  
pp. 329-335
Author(s):  
I.M. Gioia ◽  
T. Maccacaro ◽  
R.E. Schild ◽  
A. Wolter ◽  
J.T. Stocke ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Progress Report ◽  
Bl Lac Objects ◽  
Basic Properties ◽  
Bl Lac ◽  
Einstein Observatory

This paper presents a progress report on a major extension of the Einstein Observatory Medium Sensitivity Survey (MSS). The results obtained from the survey are briefly summarized, particular emphasis is given to the Active Galactic Nuclei (AGN) and BL Lac objects of the MSS. The basic properties of these classes of extragalactic objects are presented and discussed.

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 Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz

Universe ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 15
Author(s):  
Xiang Liu ◽  
Xin Wang ◽  
Ning Chang ◽  
Jun Liu ◽  
Lang Cui ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Forthcoming Paper ◽  
Galactic Latitude ◽  
Local Interstellar Medium ◽  
Bl Lac Objects ◽  
Spectrum Radio ◽  
First Results ◽  
First Time ◽  
Source Structure

Two dozens of radio loud active galactic nuclei (AGNs) have been observed with Urumqi 25 m radio telescope in order to search for intra-day variability (IDV). The target sources are blazars (namely flat spectrum radio quasars and BL Lac objects) which are mostly selected from the observing list of RadioAstron AGN monitoring campaigns. The observations were carried out at 4.8 GHz in two sessions of 8–12 February 2014 and 7–9 March respectively. We report the data reduction and the first results of observations. The results show that the majority of the blazars exhibit IDV in 99.9% confidence level, some of them show quite strong IDV. We find the strong IDV of blazar 1357 + 769 for the first time. The IDV at centimeter-wavelength is believed to be predominately caused by the scintillation of blazar emission through the local interstellar medium in a few hundreds parsecs away from Sun. No significant correlation between the IDV strength and either redshift or Galactic latitude is found in our sample. The IDV timescale along with source structure and brightness temperature analysis will be presented in a forthcoming paper.

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