The extreme, intra-hour and >10% rms flux density scintillation observed in AGNs such as PKS 0405-385, J1819+3845 and PKS 1257-326 at cm wavelengths has been attributed to scattering in highly ...turbulent, nearby regions in the interstellar medium. Such behavior has been found to be rare. We searched for rapid scintillators among 128 flat spectrum AGNs and analyzed their properties to determine the origin of such rapid and large amplitude radio scintillation. The sources were observed at the VLA at 4.9 and 8.4 GHz simultaneously at two hour intervals over 11 days. We detected six rapid scintillators with characteristic time-scales of <2 h, none of which have rms variations >10%. We found strong lines of evidence linking rapid scintillation to the presence of nearby scattering regions, estimated to be <12 pc away for ~200 μas sources and <250 pc away for ~10 μas sources. We attribute the scarcity of rapid and large amplitude scintillators to the requirement of additional constraints, including large source compact fractions. J1819+3845 was found to display ~2% rms variations at ~6 h time-scales superposed on longer >11 day variations, suggesting that the highly turbulent cloud responsible for its extreme scintillation has moved away, with its scintillation now caused by a more distant screen ≈50 to 150 pc away.
Context.
Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the ...formation and collimation of these jets, but the details are much debated.
Aims.
We study the innermost jet morphology and magnetic field strength in the AGN 3C 345 with an unprecedented resolution using images obtained within the framework of the key science programme on AGN polarisation of the Space VLBI mission RadioAstron.
Methods.
We observed the flat spectrum radio quasar 3C 345 at 1.6 GHz on 2016 March 30 with RadioAstron and 18 ground-based radio telescopes in full polarisation mode.
Results.
Our images, in both total intensity and linear polarisation, reveal a complex jet structure at 300 μas angular resolution, corresponding to a projected linear scale of about 2 pc or a few thousand gravitational radii. We identify the synchrotron self-absorbed core at the jet base and find the brightest feature in the jet 1.5 mas downstream of the core. Several polarised components appear in the Space VLBI images that cannot be seen from ground array-only images. Except for the core, the electric vector position angles follow the local jet direction, suggesting a magnetic field perpendicular to the jet. This indicates the presence of plane perpendicular shocks in these regions. Additionally, we infer a minimum brightness temperature at the largest (
u
,
v
)-distances of 1.1 × 10
12
K in the source frame, which is above the inverse Compton limit and an order of magnitude larger than the equipartition value. This indicates locally efficient injection or re-acceleration of particles in the jet to counter the inverse Compton cooling or the geometry of the jet creates significant changes in the Doppler factor, which has to be > 11 to explain the high brightness temperatures.
High angular resolution images of extragalactic radio sources are being made with the Highly Advanced Laboratory for Communications and Astronomy (HALCA) satellite and ground-based radio telescopes ...as part of the Very Long Baseline Interferometry (VLBI) Space Observatory Programme (VSOP). VSOP observations at 1.6 and 5 gigahertz of the milli-arc-second-scale structure of radio quasars enable the quasar core size and the corresponding brightness temperature to be determined, and they enable the motions of jet components that are close to the core to be studied. Here, VSOP images of the gamma-ray source 1156+295, the quasar 1548+056, the ultraluminous quasar 0014+813, and the superluminal quasar 0212+735 are presented and discussed.
The TANAMI program has been observing parsec-scale radio jets of southern (declination south of − 30°) γ-ray bright AGN, simultaneously with Fermi/LAT monitoring of their γ-ray emission, via ...high-resolution radio imaging with Very Long Baseline Interferometry techniques. We present the radio and γ-rayproperties of the TANAMI sources based on one year of contemporaneous TANAMI and Fermi/LAT data. A large fraction (72%) of the TANAMI sample can be associated with bright γ-ray sources for this time range. Association rates differ for different optical classes with all BL Lacs, 76% of quasars, and just 17% of galaxies detected by the LAT. Upper limits were established on the γ-ray flux from TANAMI sources not detected by LAT. This analysis led to the identification of three new Fermi sources whose detection was later confirmed. The γ-ray and radio luminosities are related by Lγ ∝ Lr0.89±0.04. The brightness temperatures of the radio cores increase with the average γ-ray luminosity and the presence of brightness temperatures above the inverse Compton limit implies strong Doppler boosting in those sources. The undetected sources have lower γ/radio luminosity ratios and lower contemporaneous brightness temperatures. Unless the Fermi/LAT-undetected blazars are much γ-ray-fainter than the Fermi/LAT-detected sources, their γ-ray luminosity should not be significantly lower than the upper limits calculated here.
This Letter reports rich X-ray jet structures found in the Chandra observation of PKS 1055+201. In addition to an X-ray jet coincident with the radio jet, we detect a region of extended X-ray ...emission surrounding the jet as far from the core as the radio hot spot to the north, and a similar extended X-ray region along the presumed path of the unseen counterjet to the southern radio lobe. Both X-ray regions show a similar curvature to the west, relative to the quasar. We interpret this as the first example in which we separately detect the X-ray emission from a narrow jet and extended, residual jet plasma over the entire length of a powerful FR II jet.
This paper describes a radio astronomy programfor schools, the Goldstone-AppleValley Radio Telescope,GAVRT. The GAVRT program is designed to bring the inspiration and enthusiasm to a younger ...generation of teachers and children who learn about science by doing real science, just as Iosif Shklovsky brought to an older generation.
The Parkes half-jansky flat-spectrum sample Drinkwater, M. J.; Webster, R. L.; Francis, P. J. ...
Monthly notices of the Royal Astronomical Society,
01/1997, Letnik:
284, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present a new sample of Parkes half-jansky flat-spectrum radio sources, having made a particular effort to find any previously unidentified sources. The sample contains 323 sources selected ...according to a flux limit of 0.5 Jy at 2.7 GHz, a spectral index measured between 2.7 and 5.0 GHz of α2.7/5.0 > −0.5, where S(v) ∞vα, Galactic latitude ∣b∣ > 20° and −45°< declination (B1950) à< +10°. The sample was selected from a region 3.90 steradians in area. We have obtained accurate radio positions for all the unresolved sources in this sample, and combined these with accurate optical positions from digitized photographic sky survey data to check all the optical identifications. We report new identifications based on R- and Kn-band imaging and new spectroscopic measurements of many of the sources. We present a catalogue of the 323 sources, of which 321 now have identified optical counterparts and 277 have measured spectral redshifts.
PKS 0405–385: The Smallest Radio Quasar? Kedziora-Chudczer, L; Jauncey, D. L; Wieringa, M. H ...
The Astrophysical journal,
11/1997, Letnik:
490, Številka:
1
Journal Article
PDF
