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Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron II. Observations of 3C 273 at minimum activity
Astrophysics of Galaxies · Submitted 5 Jul 2017
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Thus, the availability of interferometric baselines capable of providing {\mu}as angular resolution does not systematically imply measured brightness temperatures over the known physical limits for astrophysical sources.
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The abstract, sentence by sentence
RadioAstron is a 10 m orbiting radio telescope mounted on the Spektr-R satellite, launched in 2011, performing Space Very Long Baseline Interferometry (SVLBI) observations supported by a global ground array of radio telescopes. With an apogee of about 350 000 km, it is offering for the first time the possibility to perform {\mu}as-resolution imaging in the cm-band. We present observations at 22 GHz of 3C 273, performed in 2014, designed to reach a maximum baseline of approximately nine Earth diameters. Reaching an angular resolution of 0.3 mas, we study a particularly low-activity state of the source, and estimate the nuclear region brightness temperature, comparing with the extreme one detected one year before during the RadioAstron early science period. We also make use of the VLBA-BU-BLAZAR survey data, at 43 GHz, to study the kinematics of the jet in a 1.5-year time window. We find that the nuclear brightness temperature is two orders of magnitude lower than the exceptionally high value detected in 2013 with RadioAstron at the same frequency (1.4x10^13 K, source-frame), and even one order of magnitude lower than the equipartition value. The kinematics analysis at 43 GHz shows that a new component was ejected 2 months after the 2013 epoch, visible also in our 22 GHz map presented here. Consequently this was located upstream of the core during the brightness temperature peak. These observations confirm that the previously detected extreme brightness temperature in 3C 273, exceeding the inverse Compton limit, is a short-lived phenomenon caused by a temporary departure from equipartition. Thus, the availability of interferometric baselines capable of providing {\mu}as angular resolution does not systematically imply measured brightness temperatures over the known physical limits for astrophysical sources.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | RadioAstron is a 10 m orbiting radio telescope mounted on the Spektr-R satellite, launched in 2011, performing Space Very Long Baseline Interferometry (SVLBI) observations supported by a global ground array of radio telescopes. | background 0.85 | 0.06 | 0.01 | asserted 1.00 |
| s1 | With an apogee of about 350 000 km, it is offering for the first time the possibility to perform {\mu}as-resolution imaging in the cm-band. | background 0.91 | 0.08 | 0.02 | asserted 0.75 |
| s2 | We present observations at 22 GHz of 3C 273, performed in 2014, designed to reach a maximum baseline of approximately nine Earth diameters. | method 0.80 | 0.89 | 0.02 | asserted 0.98 |
| s3 | Reaching an angular resolution of 0.3 mas, we study a particularly low-activity state of the source, and estimate the nuclear region brightness temperature, comparing with the extreme one detected one year before during the RadioAstron early science period. | contribution 0.77 | 0.96 | 0.05 | asserted 0.99 |
| s4 | We also make use of the VLBA-BU-BLAZAR survey data, at 43 GHz, to study the kinematics of the jet in a 1.5-year time window. | method 0.94 | 0.73 | 0.02 | asserted 0.97 |
| s5 | We find that the nuclear brightness temperature is two orders of magnitude lower than the exceptionally high value detected in 2013 with RadioAstron at the same frequency (1.4x10^13 K, source-frame), and even one order of magnitude lower than the equipartition value. | result 1.00 | 0.96 | 0.24 | asserted 1.00 |
| s6 | The kinematics analysis at 43 GHz shows that a new component was ejected 2 months after the 2013 epoch, visible also in our 22 GHz map presented here. | result 1.00 | 0.92 | 0.05 | asserted 1.00 |
| s7 | Consequently this was located upstream of the core during the brightness temperature peak. | interpretation 0.60 | 0.73 | 0.05 | asserted 1.00 |
| s8 | These observations confirm that the previously detected extreme brightness temperature in 3C 273, exceeding the inverse Compton limit, is a short-lived phenomenon caused by a temporary departure from equipartition. | interpretation 0.98 | 0.77 | 0.75 | asserted 1.00 |
| s9 | Thus, the availability of interferometric baselines capable of providing {\mu}as angular resolution does not systematically imply measured brightness temperatures over the known physical limits for astrophysical sources. | interpretation 1.00 | 0.54 | 0.74 | asserted 0.98 |
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Original abstract
RadioAstron is a 10 m orbiting radio telescope mounted on the Spektr-R satellite, launched in 2011, performing Space Very Long Baseline Interferometry (SVLBI) observations supported by a global ground array of radio telescopes. With an apogee of about 350 000 km, it is offering for the first time the possibility to perform {\mu}as-resolution imaging in the cm-band. We present observations at 22 GHz of 3C 273, performed in 2014, designed to reach a maximum baseline of approximately nine Earth diameters. Reaching an angular resolution of 0.3 mas, we study a particularly low-activity state of the source, and estimate the nuclear region brightness temperature, comparing with the extreme one detected one year before during the RadioAstron early science period. We also make use of the VLBA-BU-BLAZAR survey data, at 43 GHz, to study the kinematics of the jet in a 1.5-year time window. We find that the nuclear brightness temperature is two orders of magnitude lower than the exceptionally high value detected in 2013 with RadioAstron at the same frequency (1.4x10^13 K, source-frame), and even one order of magnitude lower than the equipartition value. The kinematics analysis at 43 GHz shows that a new component was ejected 2 months after the 2013 epoch, visible also in our 22 GHz map presented here. Consequently this was located upstream of the core during the brightness temperature peak. These observations confirm that the previously detected extreme brightness temperature in 3C 273, exceeding the inverse Compton limit, is a short-lived phenomenon caused by a temporary departure from equipartition. Thus, the availability of interferometric baselines capable of providing {\mu}as angular resolution does not systematically imply measured brightness temperatures over the known physical limits for astrophysical sources.
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Cites as background 1 paper
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Since the launch of the Fermi mission, carrying the Large Area Telescope (LAT), and the subsequent improvement of the $γ$-ray source census, several authors have found hints of correlation between the radio emission and $γ$-ray flares in Fanaroff-Riley I (FRI) and II (FRII) sources - sometimes linked to the ejection of a new superluminal component detected at mm-band ( [ref] ) -as well as in blazars (e.g., [ref] ).
Exploring the FRI/FRII radio dichotomy with the Fermi satellite · $γ$-ray emission detected by Fermi-LAT · 0.99
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