scholarly journals Intraday Variability in Northern Hemisphere Radio Sources

2002 ◽  
Vol 19 (1) ◽  
pp. 14-18 ◽  
Author(s):  
T. P. Krichbaum ◽  
A. Kraus ◽  
L. Fuhrmann ◽  
G. Cimò ◽  
A. Witzel
Keyword(s):  
Flux Density ◽  
Radio Telescope ◽  
Physical Interpretation ◽  
Radio Sources ◽  
Intrinsic Variability ◽  
The Past ◽  
Interstellar Scintillation ◽  
Variability Pattern ◽  
Complex Source ◽  
Intraday Variability

AbstractWe summarise results from flux density monitoring campaigns performed with the 100 m radio telescope at Effelsberg and the VLA during the past 15 yrs. We briefly discuss some of the statistical properties from now more than 40 high declination sources (δ ≥ 30°), which show intraday variability (IDV). In general, IDV is more pronounced for sources with flat radio spectra and compact VLBI structures. For 0917+62, we present new VLBI images which suggest that the variability pattern is modified by the occurrence of new jet components. For 0716+71, we show the first detection of IDV at millimetre wavelengths (32 GHz). For the physical interpretation of the IDV phenomenon, a complex source and frequency dependent superposition of interstellar scintillation and source intrinsic variability should be considered.

scholarly journals Interstellar Scintillation and Intraday Variability

1998 ◽  
Vol 164 ◽  
pp. 269-270
Author(s):  
Barney J. Rickett
Keyword(s):  
Intrinsic Variability ◽  
Brightness Temperatures ◽  
Interstellar Scintillation ◽  
Intraday Variability

AbstractSources that are compact enough to show intrinsic variability on times of a day or less (IDV) at cm wavelengths must also show interstellar scintillation (ISS) on similar timescales. However for many IDV sources, the variations could be entirely due to ISS, reducing the implied brightness temperatures to ~ 1013 K or less.

The Over-estimation of the Flux Density of Weak Radio Sources

1969 ◽  
Vol 1 (5) ◽  
pp. 233-234
Author(s):  
H. S. Murdoch
Keyword(s):  
Monte Carlo ◽  
Flux Density ◽  
Lower Limit ◽  
Error Distribution ◽  
Radio Sources ◽  
Systematic Bias ◽  
Digital Recording ◽  
Analysis Techniques ◽  
Monte Carlo Techniques ◽  
The Past

The over-estimation of the flux density of radio sources near the lower limit of a survey has often been considered in the past. The use of digital recording and analysis techniques now enables a quantitative approach to the problem. Monte Carlo techniques may be used to determine the error distribution, including any systematic bias.

scholarly journals Measurements Of The Flux Density Of Discrete Radio Sources At 6 Cm Wavelength

1966 ◽  
Vol 19 (4) ◽  
pp. 577 ◽  
Keyword(s):  
Flux Density ◽  
Radio Telescope ◽  
Power Law ◽  
Radio Sources ◽  
Frequency Range ◽  
Thermal Radio ◽  
Discrete Radio Sources ◽  
Selection Of ◽  
Lower Frequencies

The flux densities of 67 non-thermal radio sources have been measured at a frequency of 5000 Mc/s with the CSIRO 210 ft radio telescope at Parkes. The sources were chosen from the stronger objects in the 3C catalogue (Edge et al. 1959), the CTA and CTD catalogues (Harris and Roberts 1960; Kellermann and Read 1965), and the Parkes catalogue (Bolton, Gardner, and Mackey 1964; Price and Milne 1965; Day et al. 1966). In the selection of sources observed in this program, special emphasis was placed on objects whose spectra at lower frequencies showed significant departures from the usual power law with an index near -0�8. Most of the sources reported here have not been previously measured at wavelengths shorter than 10 cm and thus the present observations extend the frequency range of their spectra by nearly a factor of two.

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 Compact Jets in 100 AGNs with the Strongest Broad-Band Variability of 1-22 GHz Spectra in 1997-2001

2002 ◽  
Vol 184 ◽  
pp. 297-298
Author(s):  
Yu. A. Kovalev ◽  
Y. Y. Kovalev ◽  
N. A. Nizhelsky ◽  
A. V. Bogdantsov
Keyword(s):  
Magnetic Field ◽  
Physical Model ◽  
Flux Density ◽  
Radio Telescope ◽  
Longitudinal Magnetic Field ◽  
Broad Band ◽  
Radio Sources ◽  
Spectral Evolution ◽  
Model Interpretation ◽  
Relativistic Jet

AbstractResults of monitoring observations at the radio telescope RATAN-600 and a model interpretation of instantaneous 1-22 GHz spectra at six frequencies for 100 selected AGNs are presented. The index of variability at these frequencies is shown for 550 sources monitored in 1997-2001 at 11 epochs. The spectra of the selected sources exhibit flux density variations of about 50% and up. The type of spectral evolution is similar for all the selected objects, favoring the same basic physical model. Model analysis shows that the nature of the radio sources and the observed variability behavior of the spectra can be explained by a model with a relativistic jet of parsec scale in a longitudinal magnetic field.

scholarly journals Examples of Extreme Intraday Variability

2001 ◽  
Vol 182 ◽  
pp. 113-117
Author(s):  
Lucyna Kedziora-Chudczer ◽  
David L. Jauncey ◽  
Mark A. Wieringa ◽  
Anastasios K. Tzioumis ◽  
Hayley E. Bignall
Keyword(s):  
Flux Density ◽  
Density Fluctuations ◽  
Total Flux ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Brightness Temperatures ◽  
Relativistic Beaming ◽  
Intraday Variability

AbstractWe present results of the ATCA IDV Survey of southern extragalactic radio sources. We discuss briefly the properties of the 22 new intraday variable sources discovered in the Survey. The follow-up observations of a few extreme examples of strong intraday variability are presented. We find that the characteristics of the total flux density fluctuations at different wavelengths are consistent with intersteller scintillations (ISS) of the microarcsecondsize soorten components. However, the scintillating components of a few extreme IDVs are characterized by the brightness temperatures far exceeding the TB = 1012 K limit. The relativistic beaming invoked in such sources would require Doppler factors up to as high as δ ~ 103.

scholarly journals Radio Observations at 1.4 GHz of Abell Clusters

1982 ◽  
Vol 97 ◽  
pp. 91-92
Author(s):  
C. Fanti ◽  
R. Fanti ◽  
L. Feretti ◽  
A. Ficarra ◽  
I.M. Gioia ◽  
...  
Keyword(s):  
Flux Density ◽  
Radio Telescope ◽  
Angular Resolution ◽  
Radio Sources ◽  
Distance Class ◽  
Cluster Galaxies ◽  
Abell Clusters ◽  
Peak Flux ◽  
Complete Discussion ◽  
Statistical Studies

We have observed with the Westerbork Synthesis Radio Telescope (WSRT) at 1.4 GHz the Abell clusters included in the HEAO-2 satellite observing program, for which radio information was not available. In practice we excluded the clusters south of 15°, in order to ensure an adequate angular resolution in declination; moreover we did not observe distance class (d.c.) 6 clusters for which better resolution and sensitivity would be necessary. The final list includes 61 clusters. These have been observed to a limiting peak flux density of about 5 mJy, corresponding to average minimum radio powers ranging from ∼5×1021 to ∼2×1023 W/Hz for d.c. 1 to 5. By adding the present data to those already available in the literature, we have radio information about all the clusters of d.c. 1 and 2, north of 15°, except A1185. The sample of d.c. 3 clusters contains 60% of the clusters of this class, but seems unbiased both for richness criteria and for radio characteristics; therefore it is useful for statistical studies. The observed clusters of d.c. 4 and 5, instead, are richer than average. The list of the observed clusters is presented in table 1: the Abell name is given in column 1, the d.c. in column 2, the richness class in column 3, the number of radio detected cluster galaxies in column 4 (in parentheses the number of galaxies for which the membership of the cluster is doubtful or the radio identification is not certain is given). The identification of the radio sources with the cluster galaxies of d.c. 5 is still in progress. While a more complete discussion of the properties of radio sources in clusters will be performed later, using the data about all the clusters of the sample, here we summarize the results of the discussion on d.c. 1 and 2 clusters.

scholarly journals Effelsberg Monitoring of a Sample of RadioAstron Blazars

2017 ◽  
Author(s):  
Jun Liu ◽  
Thomas P. Krichbaum ◽  
Xiang Liu ◽  
Alex Kraus ◽  
Hayley Bignall ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Flux Density ◽  
Radio Telescope ◽  
Galactic Nuclei ◽  
High Brightness ◽  
Space Radio Telescope ◽  
Long Baseline ◽  
Interstellar Scintillation ◽  
Flux Monitoring ◽  
Long Baselines

The launch of the RadioAstron space radio telescope provides a unique opportunity to study the extreme high brightness temperature of Active Galactic Nuclei (AGNs) with unprecedented long baselines of up to 28 Earth diameters. A coordinated ground-based flux density monitoring of RadioAstron targets is essential to determine the effect of interstellar scintillation (ISS) on the Space Very Long Baseline Interferometry (SVLBI) visibilities. Moreover, a combination/comparison of scintillation with SVLBI observations is expected to reveal the relative influence of source brightness temperature, compactness, and properties of the interstellar medium on the observed variability at centimeter wavelengths. In 2014 we started a RadioAstron target triggered flux monitoring with the Effelsberg 100-m radio telescope in support of this SVLBI mission. A total of 112 targets were observed during the five-session monitoring performed so far. In this paper we present a statistical study on the short-term flux density variability of the sample, which is focused on the variability characteristics and derived physical properties of the observed sources.

The MASIV survey: spectroscopic identifications of compact radio sources

2013 ◽  
Vol 9 (S304) ◽  
pp. 110-111
Author(s):  
T. Pursimo ◽  
R. Ojha ◽  
D. Jauncey ◽  
J. Lovell ◽  
M. Dutka ◽  
...  
Keyword(s):  
Black Hole ◽  
Fresnel Zone ◽  
Angular Size ◽  
Radio Sources ◽  
Central Black Hole ◽  
Short Term ◽  
Interstellar Scintillation ◽  
Intraday Variability

AbstractInterstellar scintillation (ISS) has been shown to be primarily responsible for the short term intraday variability (IDV) exhibited by extragalactic sources at centimeter wavelengths (e.g. Bignall et al. 2006 and references therein). For a source to scintillate its angular size must be comparable to that of the first Fresnel zone (Narayan 1992) which implies microarcsecond angular sizes for screen distances of tens to hundreds of parsecs. This has the potential to probe within a few light months of the central black hole (Bignall et al. 2006). The aim of the Microarcsecond Scintillation-Induced Variability (MASIV) survey was to provide a catalogue of at least a hundred AGNs that vary on timescales of hours to days to provide the basis of detailed studies of the IDV population drawn from a well-defined sample.

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