Radioastron Observations of the Quasar 3c273: A Challenge to the Brightness Temperature Limit

Kovalev, Y. Y.; Kardashëv, N. S.; Kellermann, K. I.; Lobanov, A. P.; Johnson, Michael D.; Gurvits, L. I.; Voitsik, P. A.; Zensus, J. A.; Anderson, J. M.; Bach, U.; Jauncey, D. L.; Ghigo, F. D.; Ghosh, T.; Kraus, A.; Lisakov, M. M.; Petrov, Leonid; Romney, J. D.; Salter, C. J.; Sokolovsky, K. V.

doi:10.3847/2041-8205/820/1/l9

Cited by 92 publications

(82 citation statements)

References 41 publications

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“…Our observations of PSR B0329+54 are the first to detect the signatures of diffractive substructure on baselines that entirely resolve the ensemble-average scattered image. And while refractive substructure has been detected in the galactic center radio source Sgr A * (Gwinn et al 2014) and in the quasar 3C 273 (Kovalev et al 2016;Johnson et al 2016), our results are the first detections of either class of substructure that are not sensitive to properties of the intrinsic source. If the visibilities could be coherently integrated indefinitely, then as the integration time Tint increases the diffractive power in the delay-rate spectrum (e.g., Figure 2) should decrease as 1/ √ Tint.…”

Section: Comparison With Theory and Other Observationsmentioning

confidence: 45%

PSR B0329+54: substructure in the scatter-broadened image discovered with RadioAstron on baselines up to 330 000 km

Попов

Bartel

Gwinn

et al. 2016

Mon. Not. R. Astron. Soc.

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We have resolved the scatter-broadened image of PSR B0329+54 and detected substructure within it. These results are not influenced by any extended structure of a source but instead are directly attributed to the interstellar medium. We obtained these results at 324 MHz with the ground-space interferometer RadioAstron which included the space radio telescope (SRT), ground-based Westerbork Synthesis Radio Telescope and 64-m Kalyazin Radio Telescope on baseline projections up to 330,000 km in 2013 November 22 and 2014 January 1 to 2. At short 15,000 to 35,000 km groundspace baseline projections the visibility amplitude decreases with baseline length providing a direct measurement of the size of the scattering disk of 4.8 ± 0.8 mas. At longer baselines no visibility detections from the scattering disk would be expected. However, significant detections were obtained with visibility amplitudes of 3 to 5% of the maximum scattered around a mean and approximately constant up to 330,000 km. These visibilities reflect substructure from scattering in the interstellar medium and offer a new probe of ionized interstellar material. The size of the diffraction spot near Earth is 17, 000 ± 3, 000 km. With the assumption of turbulent irregularities in the plasma of the interstellar medium, we estimate that the effective scattering screen is located 0.6 ± 0.1 of the distance from Earth toward the pulsar.

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Section: Comparison With Theory and Other Observationsmentioning

confidence: 45%

PSR B0329+54: substructure in the scatter-broadened image discovered with RadioAstron on baselines up to 330 000 km

Попов

Bartel

Gwinn

et al. 2016

Mon. Not. R. Astron. Soc.

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“…13 K was recently detected in the quasar 3C273 with a VLBI array including the space-based RadioAstron antenna (Kovalev et al 2016). However, later observations of the quasar with a similar high angular resolution when 3C273 was in a low-activity state found the value of T b,obs to be an order of magnitude lower than the equipartition value (Bruni et al 2017).…”

Section: -5×10mentioning

confidence: 99%

Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program

Jorstad

Marscher

Morozova

et al. 2017

ApJ

331

499

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We analyze the parsec-scale jet kinematics from 2007 June to 2013 January of a sample of γ-ray bright blazars monitored roughly monthly with the Very Long Baseline Array at 43GHz. In a total of 1929 images, we measure apparent speeds of 252 emission knots in 21 quasars, 12 BLLacertae objects (BLLacs), and 3 radio galaxies, ranging from 0.02c to 78c; 21% of the knots are quasi-stationary. Approximately one-third of the moving knots execute non-ballistic motions, with the quasars exhibiting acceleration along the jet within 5pc (projected) of the core, and knots in BLLacs tending to decelerate near the core. Using the apparent speeds of the components and the timescales of variability from their light curves, we derive the physical parameters of 120 superluminal knots, including variability Doppler factors, Lorentz factors, and viewing angles. We estimate the half-opening angle of each jet based on the projected opening angle and scatter of intrinsic viewing angles of knots. We determine characteristic values of the physical parameters for each jet and active galactic nucleus class based on the range of values obtained for individual features. We calculate the intrinsic brightness temperatures of the cores, T b,int core , at all epochs, finding that the radio galaxies usually maintain equipartition conditions in the cores, while ∼30% of T b,int core measurements in the quasars and BLLacs deviate from equipartition values by a factor >10. This probably occurs during transient events connected with active states. In the Appendix, we briefly describe the behavior of each blazar during the period analyzed.

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“…The outstanding problems of blazars have been with us for decades: Extreme variability on time-scales shorter than we can understand, intraday flares occurring parsecs downstream of the black hole, brightness temperatures beyond the~10 12 K inverse Compton limit [83] (measured with VLBI including the space-based RadioAstron antenna [84]), the absence of an obvious source of seed photons for producing γ-ray on parsec scales, and acceleration of particles to energies >30 GeV on time-scales of minutes, then cooling them just as rapidly. One way to solve the time-scale problem is with Doppler factors~100, which once would have been considered beyond belief, but now seems rather conservative compared to γ-ray burst models.…”

Section: Potential Solutions To Blazar Conundrumsmentioning

confidence: 99%

Variability of Blazars and Blazar Models over 38 Years

Marscher

2016

Galaxies

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Abstract:Since 1978, when BL Lac objects and violently variable quasars were married to become "blazars", physical interpretations of the phenomenon have evolved. Remarkably, though, the general picture of relativistic jets beaming their radiation in our direction, proposed that year by Blandford and Rees, remains intact. The main stress on theoretical models has come from observations that reveal ever more extreme variability requiring rampant particle acceleration on time-scales of minutes, often parsecs away from the central black hole. Here the author reviews many of the observations and theoretical ideas that have shaped his studies of blazars over about 40 years. This leads to his preferred scenario that blazar jets contain a helical magnetic field close to the black hole, turbulent plasma on parsecs scales, and both standing and moving shock waves. Particle acceleration can then occur in multiple stages involving the second-order Fermi process, magnetic reconnections, and modest jumps in energy at shock fronts. The most extreme variability, as well as brightness temperatures 100 times the inverse Compton limit, probably require occasional exceptionally high bulk Lorentz factors. These can result, for example, from supersonic, relativistic turbulence, or ultra-relativistic flows propelled from sites of magnetic reconnection. Future efforts in these and other areas can determine whether these potential solutions are valid.

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Radioastron Observations of the Quasar 3c273: A Challenge to the Brightness Temperature Limit

Cited by 92 publications

References 41 publications

PSR B0329+54: substructure in the scatter-broadened image discovered with RadioAstron on baselines up to 330 000 km

PSR B0329+54: substructure in the scatter-broadened image discovered with RadioAstron on baselines up to 330 000 km

Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program

Variability of Blazars and Blazar Models over 38 Years

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