Intraday Variability of Flat-Spectrum Radio Sources

1998 ◽  
Vol 164 ◽  
pp. 257-264
Author(s):  
S. J. Wagner
Keyword(s):  
High Frequency ◽  
Large Fraction ◽  
Small Scale ◽  
Electromagnetic Spectrum ◽  
Radio Sources ◽  
Rapid Variability ◽  
Spectrum Radio ◽  
Interstellar Scattering ◽  
Polarization Characteristics ◽  
Intraday Variability

AbstractThe characteristics of rapid variability of flat-spectrum radio sources are reviewed. A large fraction of the blazar population is found to show variability on timescales shorter than one day throughout the entire electromagnetic spectrum. The spectral indices and polarization characteristics change equally fast.Structure functions of the well-monitored sources show pronounced breaks on scales of about 10 to 50 hours, with flatter slopes towards the fast end. This illustrates that Intraday Variability (IDV), i.e. the high frequency end of the power spectrum is qualitatively different and requires different mechanisms than slower variations.While intrinsic IDV provides direct clues on small-scale structure over fifteen decades in frequency, extrinsic contributions from interstellar scattering contributes at the lowest frequencies, and remains difficult to disentangle from the intrinsic effects.

scholarly journals CSS versus Large Size Sources

1996 ◽  
Vol 175 ◽  
pp. 63-66 ◽  
Author(s):  
R. Fanti ◽  
R. E. Spencer
Keyword(s):  
Flux Density ◽  
High Power ◽  
High Frequency ◽  
Large Fraction ◽  
Radio Sources ◽  
Frequency Spectra ◽  
Large Size ◽  
Spectrum Radio

A large fraction of the sources in flux density limited radio samples have angular sizes < 2 arcsec (and hence projected linear sizes ≤ 10–15 kpc for H0 = 100 Km/(sec Mpc), and steep (α > 0.5, S∝ v–α) high frequency spectra (Kapahi, 1981; Peacock and Wall 1982). The proportion of these Compact Steep–spectrum Sources (CSSs) is high (15–30% depending on the selection frequency) amongst distant (z > 0.2) radio sources of high power, both galaxies and quasars. We include in this class the GHz Peaked Spectrum Radio Sources (GPS), sub–kpc objects whose radio spectra are peaked at GHz frequencies (see, e.g., O'Dea et al, 1991).

scholarly journals Magnetic Field Strengths of GPS Radio Sources

1999 ◽  
Vol 194 ◽  
pp. 324-326
Author(s):  
V. G. Panajyan
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
Radio Sources ◽  
Spectral Indices ◽  
The Past ◽  
Spectrum Radio ◽  
Field Strengths

GHz peaked spectrum radio sources (GPS) are believed to be a subclass of compact steep spectrum radio sources (CSS) with high frequency spectral indices α < −0.5 (5 ˜ vα), linear sizes of pc to kpc scale and turnover spectra near 1GHz. Due to the work of many radioastronomers during the past two decades many properties of CSS and GPS radio sources at present are known (O'Dea,C.P. et al.1998, and references therein).

scholarly journals Evolution of low-frequency contribution in emission of steep-spectrum radio sources

2014 ◽  
Vol 11 (S308) ◽  
pp. 631-635
Author(s):  
Alla P. Miroshnichenko
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Radio Spectrum ◽  
Unified Model ◽  
Linear Size ◽  
Radio Sources ◽  
Mean Values ◽  
Spectrum Radio ◽  
Size Characteristic ◽  
The Mean

AbstractWe consider evolution properties of galaxies and quasars with steep radio spectrum at the decametre band from the UTR-2 catalogue. The ratios of source's monochromatic luminosities at the decametre and high-frequency bands display the dependence on the redshift, linear size, characteristic age of examined objects. At that, the mean values of corresponding ratios for considered galaxies and quasars have enough close quantities,testifying on the unified model of sources. We analyse obtained relations for two types of steep-spectrum sources (with linear steep spectrum (S) and low-frequency steepness after a break (C+)) from the UTR-2 catalogue.

scholarly journals Multifrequency Polarization Variations in 0917+624

2001 ◽  
Vol 182 ◽  
pp. 119-122
Author(s):  
S.J. Qian ◽  
A. Kraus ◽  
T.P. Krichbaum ◽  
A. Witzel ◽  
J.A. Zensus
Keyword(s):  
Radio Sources ◽  
Apparent Brightness ◽  
Brightness Temperatures ◽  
Interstellar Scintillation ◽  
Spectrum Radio ◽  
Bl Lac ◽  
Show Evidence ◽  
Intraday Variability

AbstractIntraday variability in compact flat-spectrum radio sources has been intensively studied in recent years. For most IDV events the apparent brightness temperatures derived from the observed timescales are in the range of Tb,app ~ 1016−18 K. For extremely rapid variations, Tb,app can reach up to ~ 1021 K (e.g. Kedziora-Chudczer et al., 1997). Refractive interstellar scintillation may be the most likely extrinsic mechanism (Rickett et al., 1995; Qian, 1994a; Qian, 1994b). Especially for the case of extreme Tb,app (> 1018 K) RISS may be dominant (Dennet-Thorpe and de Bruyn, 2000). However, some IDV events with Tapp ~ 1017−18 K show evidence for an intrinsic origin e.g. the correlated radio-optical intraday variations observed in the BL Lac object 0716+714 (Wagner and Witzel, 1995, Qian et al, 1996). It seems important to distinguish between IDV which is a phenomenon intrinsic to the compact radio sources and IDV which is primarily due to RISS. Multifrequency polarization and VLB I observations would be most helpful (Gabuzda and Kochanev, 1997).

scholarly journals Morphology of Steep Spectrum Radio Sources Showing Variability at Low Frequency

1988 ◽  
Vol 129 ◽  
pp. 125-126
Author(s):  
Franco Mantovani ◽  
Tom Muxlow ◽  
Lucia Padrielli
Keyword(s):  
Interstellar Medium ◽  
Flux Density ◽  
Large Fraction ◽  
Low Frequency ◽  
Line Of Sight ◽  
Radio Sources ◽  
Relativistic Motion ◽  
High Brightness ◽  
Spectrum Radio ◽  
Low Frequency Variability

The observed variability at low frequency of the radio sources can be explained within the framework of the generally accepted models either extrinsic (refractive scintillation in the interstellar medium) or intrinsic (bulk relativistic motion along direction near the line of sight) for variability. Both explanations require a large fraction of the source flux density to be contained in a small high brightness component, of tens of m.a.s. in size. Radio sources with steep straight spectral index are usually tens of Kpc sized, with weak central components and they do not generally show low frequency variability.

scholarly journals Sub-mas Jets in Gamma-Active Blazars: Results from High Frequency VLBI

1998 ◽  
Vol 164 ◽  
pp. 37-38 ◽  
Author(s):  
T.P. Krichbaum ◽  
A. Kraus ◽  
K. Otterbein ◽  
S. Britzen ◽  
A. Witzel ◽  
...  
Keyword(s):  
Flux Density ◽  
High Frequency ◽  
Gamma Ray ◽  
Angular Resolution ◽  
High Angular Resolution ◽  
Electromagnetic Spectrum ◽  
Spectrum Radio ◽  
Tight Correlation

AbstractWe report new results from high frequency (22-86 GHz) VLBI monitoring observations of selected blazars. These Gamma-bright sources show pronounced correlated flux density variations over the full electromagnetic spectrum (radio to Gamma-ray bands). From our high-angular resolution images (0.1-0.2 mas), we find increasing evidence for a tight correlation between this activity and the production of new jet components. Here we present results for the 3 sources PKS 0528+134, 3C 273, & 0836+710.

Intraday variability of three flat-spectrum radio sources

2009 ◽  
Vol 53 (5) ◽  
pp. 389-400 ◽  
Author(s):  
A. G. Gorshkov ◽  
A. V. Ipatov ◽  
I. A. Ipatova ◽  
V. K. Konnikova ◽  
V. V. Mardyshkin ◽  
...  
Keyword(s):  
Radio Sources ◽  
Spectrum Radio ◽  
Intraday Variability

scholarly journals Searching for signs of jet-driven negative feedback in the nearby radio galaxy UGC 05771

2019 ◽  
Vol 489 (4) ◽  
pp. 4944-4961 ◽  
Author(s):  
Henry R M Zovaro ◽  
Nicole P H Nesvadba ◽  
Robert Sharp ◽  
Geoffrey V Bicknell ◽  
Brent Groves ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Source ◽  
Large Fraction ◽  
Host Galaxy ◽  
Radio Sources ◽  
Host Galaxies ◽  
Ionized Gas ◽  
Spectrum Radio ◽  
Hydrodynamical Simulations ◽  
Jet Plasma

ABSTRACT Hydrodynamical simulations predict that the jets of young radio sources can inhibit star formation in their host galaxies by injecting heat and turbulence into the interstellar medium (ISM). To investigate jet–ISM interactions in a galaxy with a young radio source, we have carried out a multiwavelength study of the z = 0.025 Compact Steep Spectrum radio source hosted by the early-type galaxy UGC 05771. Using Keck/OSIRIS observations, we detected H2 1–0 S(1) and [Fe ii] emission at radii of 100s of parsecs, which traces shocked molecular and ionized gas being accelerated outwards by the jets to low velocities, creating a ‘stalling wind’. At kpc radii, we detected shocked ionized gas using observations from the CALIFA survey, covering an area much larger than the pc-scale radio source. We found that existing interferometric radio observations fail to recover a large fraction of the source’s total flux, indicating the likely existence of jet plasma on kpc scales, which is consistent with the extent of shocked gas in the host galaxy. To investigate the star formation efficiency in UGC 05771, we obtained IRAM CO observations to analyse the molecular gas properties. We found that UGC 05771 sits below the Kennicutt–Schmidt relation, although we were unable to definitively conclude if direct interactions from the jets are inhibiting star formation. This result shows that jets may be important in regulating star formation in the host galaxies of compact radio sources.

CTD 93 and the Nature of Gigahertz Peaked Spectrum Radio Sources

1999 ◽  
Vol 515 (2) ◽  
pp. 558-566 ◽  
Author(s):  
David B. Shaffer ◽  
K. I. Kellermann ◽  
T. J. Cornwell
Keyword(s):  
Radio Sources ◽  
Spectrum Radio

scholarly journals Bulk Relativistic Motion in a Complete Sample of Radio Selected AGN

1987 ◽  
Vol 121 ◽  
pp. 287-293
Author(s):  
C.J. Schalinski ◽  
P. Biermann ◽  
A. Eckart ◽  
K.J. Johnston ◽  
T.Ph. Krichbaum ◽  
...  
Keyword(s):  
Dynamic Range ◽  
Radio Sources ◽  
Relativistic Motion ◽  
Complete Sample ◽  
Superluminal Motion ◽  
Spectrum Radio ◽  
Wide Range ◽  
Show Evidence

A complete sample of 13 flat spectrum radio sources is investigated over a wide range of frequencies and spatial resolutions. SSC-calculations lead to the prediction of bulk relativistic motion in all sources. So far 6 out of 7 sources observed with sufficient dynamic range by means of VLBI show evidence for apparent superluminal motion.

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