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 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 Multifrequency Polarization Variations in 0917+624

2001 ◽  
Vol 182 ◽  
pp. 119-122
Author(s):  
S.J. Qian ◽  
A. Kraus ◽  
T.P. Krichbaum ◽  
A. Witzel ◽  
J.A. Zensus
Keyword(s):  
Radio Sources ◽  
Apparent Brightness ◽  
Brightness Temperatures ◽  
Interstellar Scintillation ◽  
Spectrum Radio ◽  
Bl Lac ◽  
Show Evidence ◽  
Intraday Variability

AbstractIntraday variability in compact flat-spectrum radio sources has been intensively studied in recent years. For most IDV events the apparent brightness temperatures derived from the observed timescales are in the range of Tb,app ~ 1016−18 K. For extremely rapid variations, Tb,app can reach up to ~ 1021 K (e.g. Kedziora-Chudczer et al., 1997). Refractive interstellar scintillation may be the most likely extrinsic mechanism (Rickett et al., 1995; Qian, 1994a; Qian, 1994b). Especially for the case of extreme Tb,app (> 1018 K) RISS may be dominant (Dennet-Thorpe and de Bruyn, 2000). However, some IDV events with Tapp ~ 1017−18 K show evidence for an intrinsic origin e.g. the correlated radio-optical intraday variations observed in the BL Lac object 0716+714 (Wagner and Witzel, 1995, Qian et al, 1996). It seems important to distinguish between IDV which is a phenomenon intrinsic to the compact radio sources and IDV which is primarily due to RISS. Multifrequency polarization and VLB I observations would be most helpful (Gabuzda and Kochanev, 1997).

scholarly journals Intraday Variability and Microarcsecond Structure in Blazar Cores

2001 ◽  
Vol 205 ◽  
pp. 84-87 ◽  
Author(s):  
David L. Jauncey ◽  
Lucyna Kedziora-Chudczer ◽  
J. E. J. Lovell ◽  
Jean-Pierre Macquart ◽  
George D. Nicolson ◽  
...  
Keyword(s):  
William Shakespeare ◽  
Brightness Temperature ◽  
Circular Polarization ◽  
Julius Caesar ◽  
Principal Mechanism ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Interstellar Scintillation ◽  
Intraday Variability

The accumulation of evidence now strongly favours interstellar scintillation (ISS) as the principal mechanism causing intra-day variability (IDV) at cm wavelengths. While ISS reduces the implied brightness temperatures, they remain uncomfortably high. The distance to the scattering screen is an important parameter in determining the actual brightness temperature encountered. The high brightness temperatures, the presence of strong and variable circular polarization and the observed lifetimes of a decade or more for several IDV sources, pose significant problems for synchrotron theory. “The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.” William Shakespeare, Julius Caesar

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.

VERITAS OBSERVATIONS OF RELATIVISTIC OUTFLOWS IN LOW- AND INTERMEDIATE-FREQUENCY-PEAKED BL LAC OBJECTS

2014 ◽  
Vol 28 ◽  
pp. 1460178
Author(s):  
◽  
HEIKE PROKOPH
Keyword(s):  
Gamma Ray ◽  
Intermediate Frequency ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Bl Lac ◽  
Bl Lacs ◽  
Gamma Ray Telescopes ◽  
Very High

The majority of blazars detected at very high energies (VHE; E > 100 GeV) are high-frequency-peaked BL Lac objects (HBLs). Low- and intermediate-frequency-peaked BL Lacs (LBLs/IBLs with synchrotron-peak frequencies in the infrared and optical regime) are generally more powerful, more luminous, and have a richer jet environment than HBLs. However, only a handful of these IBL and LBLs have been detected by ground-based gamma-ray telescopes, typically during high-flux states. The VERITAS array has been monitoring five known VHE LBLs/IBLs since 2009: 3C 66A, W Comae, PKS 1424+240, S5 0716+714 and BL Lacertae, with typical exposures of 5-10 hours per year. The results of these long-term observations are presented, including a bright, subhour-scale VHE flare of BL Lacertae in June 2011, the first low-state detections of 3C 66A and W Comae, and the detection and characterization of the IBL B2 1215+30.

scholarly journals Interstellar Scintillation and Intraday Variability

1998 ◽  
Vol 164 ◽  
pp. 269-270
Author(s):  
Barney J. Rickett
Keyword(s):  
Intrinsic Variability ◽  
Brightness Temperatures ◽  
Interstellar Scintillation ◽  
Intraday Variability

AbstractSources that are compact enough to show intrinsic variability on times of a day or less (IDV) at cm wavelengths must also show interstellar scintillation (ISS) on similar timescales. However for many IDV sources, the variations could be entirely due to ISS, reducing the implied brightness temperatures to ~ 1013 K or less.

scholarly journals CM-Wavelength Fluxes and Polarizations of Compact Extra-Galactic X-Ray Sources

1982 ◽  
Vol 97 ◽  
pp. 335-336
Author(s):  
Margo F. Aller ◽  
Hugh D. Aller ◽  
Philip E. Hodge
Keyword(s):  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Radio Wavelength

Cm-wavelength observations of 15 BL Lac objects are presented. The degree of radio-wavelength variability is compared with the strength of the emission at optical and X-ray wavelengths.

scholarly journals Very high energy observations of the BL Lac objects 3C 66A and OJ 287

2007 ◽  
Vol 28 (3) ◽  
pp. 338-347 ◽  
Author(s):  
T. Lindner ◽  
D.S. Hanna ◽  
J. Kildea ◽  
J. Ball ◽  
D.A. Bramel ◽  
...  
Keyword(s):  
High Energy ◽  
Bl Lac Objects ◽  
Bl Lac ◽  
Very High Energy ◽  
Very High
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