Intraday variability in compact extragalactic radio sources

Kraus, A.; Krichbaum, T. P.; Wegner, R.; Witzel, A.; Cimò, G.; Quirrenbach, A.; Britzen, S.; Fuhrmann, L.; Lobanov, A. P.; Naundorf, C. E.; Otterbein, K.; Peng, Bo; Risse, M.; Ros, E.; Zensus, J. A.

doi:10.1051/0004-6361:20030118

Cited by 119 publications

(172 citation statements)

References 37 publications

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“…The complete data calibration procedure guarantees a high level of accuracy, on the order of 0.5%, in normal weather conditions. Following the scheme by Kraus et al (2003), some quantities were used to evaluate significance and amplitude of the variability, namely the reduced chi-square-test, the rms flux density over mean flux density (the so-called modulation index, m), and the 3σ relative variability amplitude Y, which is corrected for noise-bias, defined as Y = 3 m 2 − m 2 0 , where m 0 is the mean modulation index of all calibrators, describing the statistical measurement accuracy during the observation. In Table 1, we list the observational information and the results of the observations, in which the time scales are obtained from a structure function analysis (SF) as introduced in the next section.…”

Section: Observation and Data Reductionmentioning

confidence: 99%

Intra-day variability observations of S5 0716+714 over 4.5 years at 4.8 GHz

Liu

Song

Marchili

et al. 2012

A&A

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Aims. We aim to search for evidence of annual modulation in the time scales of the BL Lac object S5 0716+714. Methods. The intra-day variability (IDV) observations were carried out monthly from 2005 to 2009, with the Urumqi 25 m radio telescope at 4.8 GHz.Results. The source has shown prominent IDV as well as long-term flux variations. The IDV time scale does show evidence in favor of an annual modulation, suggesting that the IDV of 0716+714 is dominated by interstellar scintillation. The source underwent a strong outburst phase between mid-2008 and mid-2009; a second intense flare was observed in late 2009, but no correlation between the total flux density and the IDV time scale is found, implying that the flaring state of the source does not have serious implications for the general characteristics of its intra-day variability. However, we find that the inner-jet position angle is changing throughout the years, which could result in an annual modulation noise in the anisotropic ISS model fit. There is also an indication that the lowest IDV amplitudes (rms in flux density) correspond to the slowest time scales of IDV, which would be consistent with an ISS origin of the IDV of 0716+714.

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Section: Observation and Data Reductionmentioning

confidence: 99%

Intra-day variability observations of S5 0716+714 over 4.5 years at 4.8 GHz

Liu

Song

Marchili

et al. 2012

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“…Radio flux-density observations of the BL Lac Object S5 1803+784 have been reported by Quirrenbach et al (1992Quirrenbach et al ( , 2000 and Kraus et al (2003). They show slow variability, i.e.…”

Section: Introductionmentioning

confidence: 76%

“…The blazar S5 1803+784 (z ≈ 0.68, Lawrence et al 1987;Stickel et al 1993) is an intraday variable source with rapid fluxdensity variations in the optical and radio regime (Wagner & Witzel 1995;Quirrenbach et al 1992Quirrenbach et al , 2000Kraus et al 2003) on timescales as short as 50 min in the optical (Wagner et al 1990). It has been observed and studied with different VLBI arrays at a range of different frequencies (e.g., Eckart et al 1986Eckart et al , 1987Witzel et al 1988;Charlot 1990;Strom & Biermann 1991;Fey et al 1996;Gabuzda 1999;Gabuzda & Cawthorne 2000;Gabuzda & Chernetskii 2003;Ros et al 2000Ros et al , 2001Britzen et al 2005aBritzen et al ,b, 2008).…”

Section: Application To 1803+784mentioning

confidence: 99%

The origin of intrinsic variability of intraday variable sources

Roland

Britzen

Witzel

et al. 2009

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Intraday variability (IDV) describes flux-density variations in the radio regime on timescales of a day and less. The origin of such variations has been attributed to both source intrinsic and extrinsic mechanisms. While there is growing evidence that faster fluxdensity variations (on the order of hours to minutes) are caused by refractive interstellar scattering, extrinsic mechanisms alone still fail to explain all the observations. In particular, in the blazar S5 0716+714, correlated variations at frequencies in the radio and the optical regimes indicate an intrinsic component to the variability. Using the characteristics of the relativistic ejection found for the blazar S5 1803+784, we find that the formation and the rotation of a warp in the inner part of the accretion disk produce a small perturbation of the relativistic beam and consequently a variation in the viewing angle and in the beamed synchrotron emission. We find that the relative flux variations become chaotic if the amplitude of the perturbation exceeds a critical value. We investigate the properties of the chaotic behavior of the solution to explain the observed properties of IDV sources, such as the flux variations, the polarized flux variations, and the observable frequency dependence. As a warp can form naturally in the inner part of the accretion disk, we conclude that both intrinsic and extrinsic mechanisms produce IDV sources.

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“…During normal weather conditions, we find m 0 values of between 0.5% and 0.7%. A more thorough description of the data calibration procedure can be found in Kraus (1997), Marchili (2009), and references therein.…”

Section: Observation and Data Calibrationmentioning

confidence: 99%

“…The flat-spectrum radio source AO 0235+164 (z = 0.94) was found to show variability on IDV timescales more than once in the past (see, e.g., Kraus et al 1999);Senkbeil et al (2008) reported a likely extreme-scattering-event in AO 0235+164 in July 2005. The source was observed with the Urumqi radio telescope in 21 epochs between December 2006 and November 2009.…”

Section: Variability Characteristics Of Ao 0235+164mentioning

confidence: 99%

On the influence of the Sun on the rapid variability of compact extragalactic sources

Marchili

Krichbaum

Liu

et al. 2011

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Since December 2004, we have performed a program to monitor intraday variable sources at a frequency of 5 GHz at the Urumqi Observatory. We present our analysis of the variability characteristics of the flat-spectrum radio source AO 0235+164, which detects an annual cycle in the variability amplitude. This appears to correlate with the solar elongation of the source. A thorough analysis of the results of the MASIV IDV survey -which provides the variability characteristics of a large sample of compact radio sourcesconfirms that there is a small but detectable component of the observed fractional modulation that increases with decreasing solar elongation. We discuss the hypothesis that the phenomenon is related to interplanetary scintillation.

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Intraday variability in compact extragalactic radio sources

Cited by 119 publications

References 37 publications

Intra-day variability observations of S5 0716+714 over 4.5 years at 4.8 GHz

Intra-day variability observations of S5 0716+714 over 4.5 years at 4.8 GHz

The origin of intrinsic variability of intraday variable sources

On the influence of the Sun on the rapid variability of compact extragalactic sources

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