Intraday Variability in Quasars and BL LAC Objects

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.

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900080670 ◽

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).

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Multi-Frequency Studies of Intrinsic Intraday Variability

International Astronomical Union Colloquium ◽

10.1017/s0252921100000798 ◽

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.

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Intraday Variability Statistics in Radio-Selected and X-Ray Selected BL Lac Objects

Extragalactic Radio Sources ◽

10.1007/978-94-009-0295-4_88 ◽

1996 ◽

pp. 246-247

Author(s):

J. Heidt

Keyword(s):

Bl Lac Objects ◽

X Ray ◽

Bl Lac ◽

Intraday Variability

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900140811 ◽

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900079961 ◽

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.

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Characterizing the γ-ray long-term variability of PKS 2155−304 with H.E.S.S. and Fermi-LAT

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629419 ◽

2017 ◽

Vol 598 ◽

pp. A39 ◽

Cited By ~ 20

Author(s):

◽

H. Abdalla ◽

A. Abramowski ◽

F. Aharonian ◽

F. Ait Benkhali ◽

...

Keyword(s):

Flicker Noise ◽

High Energy ◽

Long Term Results ◽

Noise Power ◽

Quiescent State ◽

Physical Processes ◽

Bl Lac Objects ◽

Power Spectral ◽

Bl Lac

Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term variability of the BL Lac object PKS 2155−304 is analyzed in the high (HE, 100 MeV < E < 300 GeV) and very high energy (VHE, E > 200 GeV) γ-ray domain. Over the course of ~9 yr of H.E.S.S. observations the VHE light curve in the quiescent state is consistent with a log-normal behavior. The VHE variability in this state is well described by flicker noise (power-spectral-density index βVHE = 1.10+0.10-0.13) on timescales larger than one day. An analysis of ~5.5 yr of HE Fermi-LAT data gives consistent results (βHE = 1.20+0.21-0.23, on timescales larger than 10 days) compatible with the VHE findings. The HE and VHE power spectral densities show a scale invariance across the probed time ranges. A direct linear correlation between the VHE and HE fluxes could neither be excluded nor firmly established. These long-term-variability properties are discussed and compared to the red noise behavior (β ~ 2) seen on shorter timescales during VHE-flaring states. The difference in power spectral noise behavior at VHE energies during quiescent and flaring states provides evidence that these states are influenced by different physical processes, while the compatibility of the HE and VHE long-term results is suggestive of a common physical link as it might be introduced by an underlying jet-disk connection.

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