The Spectra of Opaque Radio Sources

Kellermann, K. I.; Pauliny-Toth, I. I. K.

doi:10.1086/180305

Cited by 546 publications

(414 citation statements)

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“…The brightness temperature is well below the inverse-Compton limit of 10 12 K (Kellermann & Pauliny-Toth 1969) and is consistent with the equipartition limit of ∼10 11 K (Readhead 1994). Additionally, we fitted a circular Gaussian distribution to the "hot spot" by only deleting the  components within this region and measured a brightness temperature of about 10 7 K.…”

Section: Tanami Vlbi Imagesupporting

confidence: 70%

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

Schulz

Kreikenbohm

Kadler

et al. 2016

A&A

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Context. Γ-ray-detected radio-loud narrow-line Seyfert 1 (γ-NLS1) galaxies constitute a small but interesting sample of the γ-ray-loud AGN. The radio-loudest γ-NLS1 known, PKS 2004−447, is located in the southern hemisphere and is monitored in the radio regime by the multiwavelength monitoring programme TANAMI. Aims. We aim for the first detailed study of the radio morphology and long-term radio spectral evolution of PKS 2004−447, which are essential for understanding the diversity of the radio properties of γ-NLS1s. Methods. The TANAMI VLBI monitoring program uses the Australian Long Baseline Array (LBA) and telescopes in Antarctica, Chile, New Zealand, and South Africa to monitor the jets of radio-loud active galaxies in the southern hemisphere. Lower resolution radio flux density measurements at multiple radio frequencies over four years of observations were obtained with the Australia Telescope Compact Array (ATCA). Results. The TANAMI VLBI image at 8.4 GHz shows an extended one-sided jet with a dominant compact VLBI core. Its brightness temperature is consistent with equipartition, but it is an order of magnitude below other γ-NLS1s with the sample value varying over two orders of magnitude. We find a compact morphology with a projected large-scale size <11 kpc and a persistent steep radio spectrum with moderate flux-density variability. Conclusions. PKS 2004−447 appears to be a unique member of the γ-NLS1 sample. It exhibits blazar-like features, such as a flat featureless X-ray spectrum and a core-dominated, one-sided parsec-scale jet with indications for relativistic beaming. However, the data also reveal properties atypical for blazars, such as a radio spectrum and large-scale size consistent with compact-steep-spectrum (CSS) objects, which are usually associated with young radio sources. These characteristics are unique among all γ-NLS1s and extremely rare among γ-ray-loud AGN.

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Section: Tanami Vlbi Imagesupporting

confidence: 70%

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

Schulz

Kreikenbohm

Kadler

et al. 2016

A&A

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“…In this model, the intrinsic brightness temperatures cannot exceed 10 11 -10 12 K (Kellermann & Pauliny-Toth 1969;Readhead 1994). Typical Doppler boosting is expected to be able to raise this temperature by a factor of ∼10 (see also Hovatta et al 2009;Lister et al 2013).…”

Section: Introductionmentioning

confidence: 94%

“…It is commonly considered that inverse Compton losses limit the intrinsic brightness temperature for incoherent synchrotron sources, such as AGNs, to about 10 12 K (Kellermann & Pauliny-Toth 1969). In the case of a strong flare, the "Compton catastrophe" is calculated to take about one day to drive the brightness temperature below 10 12 K. Moreover, Readhead (1994) has argued that, for sources near the equipartition of energy between the magnetic field and radiating particles, a more accurate upper value for the intrinsic brightness temperature is about 10 11 K (see also Lähteenmäki et al 1999;Hovatta et al 2009), which is often called the equipartition brightness temperature.…”

Section: Brightness Temperaturementioning

confidence: 99%

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

Gómez

Lobanov

Bruni

et al. 2016

ApJ

140

165

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We present the first polarimetric space very long baseline interferometry (VLBI) imaging observations at 22 GHz. BLLacertae was observed in 2013 November 10 with the RadioAstron space VLBI mission, including a ground array of 15 radio telescopes. The instrumental polarization of the space radio telescope is found to be less than 9%, demonstrating the polarimetric imaging capabilities of RadioAstron at 22 GHz. Ground-space fringes were obtained up to a projected baseline distance of 7.9Earth diameters in length, allowing us to image the jet in BLLacertae with a maximum angular resolution of 21 μas, the highest achieved to date. We find evidence for emission upstream of the radio core, which may correspond to a recollimation shock at about 40 μas from the jet apex, in a pattern that includes other recollimation shocks at approximately 100 and 250 μas from the jet apex. Polarized emission is detected in two components within the innermost 0.5 mas from the core, as well as in some knots 3 mas downstream. Faraday rotation analysis, obtained from combining RadioAstron 22 GHz and groundbased 15 and 43 GHz images, shows a gradient in rotation measure and Faraday-corrected polarization vector as a function of position angle with respect to the core, suggesting that the jet in BLLacertae is threaded by a helical magnetic field. The intrinsic de-boosted brightness temperature in the unresolved core exceeds 3 10 12 K, suggesting, at the very least, departure from equipartition of energy between the magnetic field and radiating particles.

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“…The synchrotron process encounters an absolute limit when the radiating electrons are cooled by inverse Compton scattering on their own emission. This 'inverse Compton catastrophe' sets in at about 10 12 K (Kellermann & Pauliny-Toth 1969). Assuming equipartition of the energy densities between the radiating particles and the magnetic field and using the magnetic field estimate from the spectral peak caused by synchrotron self-absorption, Readhead (1994) has derived an upper limit on the synchrotron brightness temperature of a few times 10 11 K (depending on the spectral index).…”

Section: Vlbi and Emission Processmentioning

confidence: 99%

Radio Emission from Flares in Single Late-type Stars

Benz

1995

International Astronomical Union Colloquium

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Radio observations provide the most direct information on nonthermal electrons in stellar flares and in the coronae of late-type stars. Radio emissions of single main-sequence F, G, and of many K stars have recently been discovered, in addition to the well-known dwarf M stars. Their long-duration radio flares with low circular polarization, slow variations and broad bandwidth can be attributed to gyrosynchrotron emission of mildly relativistic electrons. The same holds for the low-level ('quiescent') radio emission. On the other hand, highly polarized radio flares of M stars have been interpreted by coherent emissions from loss-cone instabilities of magnetically trapped electrons. These conjectures are consistent with recent VLBI observations. The identification of the radio emission process allows to estimate the high-energy component of the flare and compare it to the total flare energy. The weakly polarized radio emission may serve as a proxy for hard X-ray signatures of relativistic electrons. The fraction of primary energy released into energetic electrons then appears to be large and similar to solar flares.

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The Spectra of Opaque Radio Sources

Cited by 546 publications

References 0 publications

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

Radio Emission from Flares in Single Late-type Stars

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