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 Intraday Variability Statistics in Radio-Selected and X-Ray Selected BL Lac Objects Implications for Unified schemes

1996 ◽  
Vol 175 ◽  
pp. 246-247
Author(s):  
J. Heidt
Keyword(s):  
High Variability ◽  
Electromagnetic Spectrum ◽  
Spectral Indices ◽  
Single Model ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Optical Domain ◽  
Intraday Variability

BL Lac objects, characterized by their high variability across the electromagnetic spectrum, strong and variable polarization in the radio and optical domain and a (nearly) featureless continuum can in general be divided into the radio-selected (RBL) and X-ray selected BL Lac objects (XBL) according to their αro – αox spectral indices (Stocke et al., 1985). Attempts to unify both classes within a single model have been suggested e.g. by Ghisellini et al. (1993) or Giommi et al. (1994).

scholarly journals Multi-Frequency Studies of Intrinsic Intraday Variability

2001 ◽  
Vol 182 ◽  
pp. 105-111
Author(s):  
Stefan J. Wagner
Keyword(s):  
Electromagnetic Spectrum ◽  
Potential Contribution ◽  
Bl Lac Objects ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Interstellar Scintillation ◽  
Bl Lac ◽  
Radio Wavelength ◽  
Very High ◽  
Intraday Variability

AbstractIntraday variability is detected in Blazars throughout the electromagnetic spectrum. Only radio emission is affected by interstellar scintillation. The characteristics of variability observed at different frequencies are often similar and suggest that intrinsic variations also contribute to the changes detected in the radio wavelength regime. This in turn implies very high brightness temperatures.Unambiguous signatures of scintillation and of intrinsic changes have been identified. The properties of intrinsic variations are reviewed to illustrate their potential contribution to variability in the radio domain. Such intrinsic changes need to be discriminated against when studying scintillation in quasars and BL Lac objects. Observations of scintillating sources and of sources with significant intrinsic IDV suggest interesting modifications to the standard paradigm of AGN.

scholarly journals Spectral Variability of Six Bright Bl Lac Objects in the Near IR

1994 ◽  
Vol 159 ◽  
pp. 400-400
Author(s):  
E. Massaro ◽  
R. Nesci ◽  
G.C. Perola ◽  
D. Lorenzetti ◽  
L. Spinoglio
Keyword(s):  
Time Scales ◽  
Spectral Slope ◽  
Spectral Variability ◽  
Rapid Variability ◽  
Bl Lac Objects ◽  
Near Ir ◽  
Solid Nitrogen ◽  
Bl Lac ◽  
Typical Time ◽  
Flux Level

The results of several photometric campaigns (1986–1993) in the near IR of the six bright BL Lac objects 3C 66A, PKS 0422+004, PKS 0735+178, PKS 0754+100, PKS 0829+046 and OQ 530 are presented. The observations were carried out at the 1.5 m Italian IR Telescope at Gornergrat (TIRGO − 3150 m a.s.l.) equipped with a IR photometer using a InSb detector cooled at the solid nitrogen temperature and the standard J, H, K filters. The principal aims of our program are the search of rapid variability (typical time scales of 1 day or less) and of correlations between the flux level (typically in the J band, where the largest variation amplitude is found) and the spectral slope. In the following we summarize some relevant results.

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 High Dynamic Range VLBI Observations of the 3C120 Radio Jet

1988 ◽  
Vol 129 ◽  
pp. 31-32
Author(s):  
J. M. Benson ◽  
R. C. Walker ◽  
T.W.B. Muxlow ◽  
P. N. Wilkinson ◽  
R. Booth ◽  
...  
Keyword(s):  
Radio Galaxy ◽  
Dynamic Range ◽  
High Dynamic Range ◽  
Radio Sources ◽  
Bl Lac Objects ◽  
Vlbi Observations ◽  
Close Proximity ◽  
Bl Lac ◽  
High Dynamic ◽  
3C 120

3C 120 is a nearby radio galaxy (z = 0.033) that shows superluminal motions in its radio jet within one parsec of the nucleus. The apparent velocities of the moving features are approximately 1.5 mas/yr. This object is of particular interest because it is clearly identified with an N-type galaxy, unlike all other superluminal radio sources which are only seen in quasars and BL Lac objects. Because of the close proximity of 3C 120, we have been able to make a series of VLBI and VLA images at stepped resolutions, and thereby map the radio jet continuously from the radio nucleus (0.5 h−1 parsec) into the diffuse 400 h−1 kpc structure.

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.

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