Interstellar Scintillation Observations of 146 Extragalactic Radio Sources

Rickett, B. J.; Lazio, T. Joseph W.; Ghigo, F. D.

doi:10.1086/504897

Cited by 46 publications

(68 citation statements)

References 53 publications

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“…Further, ISS on longer time scales (days to weeks) is present in a large number of radio sources (e.g. Rickett et al 2006). Here, we investigate a possible contribution of ISS to the observed cm-up to mm-variability of 0716+714.…”

Section: Variability Versus Frequency: Comparison With Weak Interstelmentioning

confidence: 99%

Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71

Fuhrmann

Krichbaum²,

Witzel³

et al. 2008

A&A

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Aims. The BL Lac object S5 0716+71 was observed in a global multi-frequency campaign to search for rapid and correlated flux density variability and signatures of an inverse-Compton (IC) catastrophe during the states of extreme apparent brightness temperatures. Methods. The observing campaign involved simultaneous ground-based monitoring at radio to IR/optical wavelengths and was centered around a 500-ks pointing with the INTEGRAL satellite (November 10−17, 2003). Here, we present the combined analysis and results of the radio observations, covering the cm-to sub-mm bands. This facilitates a detailed study of the variability characteristics of an inter-to intra-day variable IDV source from cm-to the short mm-bands. We further aim to constrain the variability brightness temperatures (T B ) and Doppler factors (δ) comparing the radio-bands with the hard X-ray emission, as seen by INTEGRAL at 3−200 keV. Results. 0716+714 was in an exceptionally high state and different (slower) phase of short-term variability, when compared to the past, most likely due to a pronounced outburst shortly before the campaign. The flux density variability in the cm-to mm-bands is dominated by a ∼4 day time scale amplitude increase of up to ∼35%, systematically more pronounced towards shorter wavelengths. The cross-correlation analysis reveals systematic time-lags with the higher frequencies varying earlier, similar to canonical variability on longer time-scales. The increase of the variability amplitudes with frequency contradicts expectations from standard interstellar scintillation (ISS) and suggests a source-intrinsic origin for the observed inter-day variability. We find an inverted synchrotron spectrum peaking near 90 GHz, with the peak flux increasing during the first 4 days. The lower limits to T B derived from the inter-day variations exceed the 10 12 K IC-limit by up to 3−4 orders of magnitude. Assuming relativistic boosting, our different estimates of δ yield robust and self-consistent lower limits of δ ≥ 5−33 -in good agreement with δ VLBI obtained from VLBI studies and the IC-Doppler factors δ IC > 14−16 obtained from the INTEGRAL data. Conclusions. The non-detection of S5 0716+714 with INTEGRAL in this campaign excludes an excessively high X-ray flux associated with a simultaneous IC catastrophe. Since a strong contribution from ISS can be excluded, we conclude that relativistic Doppler boosting naturally explains the apparent violation of the theoretical limits. All derived Doppler factors are internally consistent, agree with the results from different observations and can be explained within the framework of standard synchrotron-self-Compton (SSC) jet models of AGN.

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Section: Variability Versus Frequency: Comparison With Weak Interstelmentioning

confidence: 99%

Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71

Fuhrmann

Krichbaum²,

Witzel³

et al. 2008

A&A

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“…Rickett et al [38] completed their analysis of the 146 sources in the 2 and 8 GHz Green Bank Interferometer variability survey. The sources were chosen on the basis of their known variability and/or compact VLBI structure.…”

Section: -Present: Statistical Studies and The Role Of Interstellmentioning

confidence: 99%

“…A clearer evaluation of the spectral index dependence is shown in Figure 5 of Rickett et al (2006) [38], as they sampled a wider selection of the steeper spectral index population.…”

Section: -Present: Statistical Studies and The Role Of Interstellmentioning

confidence: 99%

Interstellar Scintillation and Scattering of Micro-arc-second AGN

et al. 2016

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Abstract:The discovery of the first quasar 3C 273 led directly to the discovery of their variability at optical and radio wavelengths. We review the radio variability observations, in particular the variability found at frequencies below 1 GHz, as well as those exhibiting intra-day variability (IDV) at cm wavelengths. Observations have shown that IDV arises principally from scintillation caused by scattering in the ionized interstellar medium of our Galaxy. The sensitivity of interstellar scintillation towards source angular sizes has provided a powerful tool for studying the most compact components of radio-loud AGN at microarcsecond and milliarcsecond scale resolution.Keywords: quasars; variability; interstellar scattering 1965-1980s: Low Frequency VariabilityFollowing the identification of the first quasar 3C 273 [1,2], quasar variability was observed at optical wavelengths [3], and then at the radio wavelengths of 3.75 cm [4] and 32.5 cm [5]. At 3.75 cm, the variability was interpreted as intrinsic to the sources, as the observations displayed a timescale of a year or more. However, at lower frequencies the observed variability of CTA102 did not fit this pattern. Sholomitskii's published 1964-65 Soviet telescope data is shown in Figure 1, for which he claimed detection of variability at 32.5 cm wavelength on a time-scale of months or less.

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“…The origin of the variability in the radio bands has not yet been solved. For the most extreme sources -the so-called fast-scintillators (see Dennett-Thorpe & de Bruyn 2002;Bignall et al 2003), which have total flux variations of the order of 100% on timescales of hours -the variability is most likely caused by InterStellar Scintillation (ISS), caused by nearby scattering screens located at a distance of several parsecs (see Dennett-Thorpe & de Bruyn 2002;Rickett et al 2006). However, only a very small fraction of IDV sources can be labelled as fast scintillators.…”

Section: Introductionmentioning

confidence: 99%

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

Marchili

Krichbaum

Liu

et al. 2011

A&A

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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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Interstellar Scintillation Observations of 146 Extragalactic Radio Sources

Cited by 46 publications

References 53 publications

Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71

Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71

Interstellar Scintillation and Scattering of Micro-arc-second AGN

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

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