Variable Radio Sources at 843 MHz

1994 ◽  
Vol 11 (1) ◽  
pp. 33-38 ◽  
Author(s):  
D. Campbell-Wilson ◽  
R. W. Hunstead
Keyword(s):  
Interstellar Medium ◽  
Flux Density ◽  
Large Amplitude ◽  
Preliminary Report ◽  
Radio Sources ◽  
Amplitude Variability ◽  
Variable Radio

AbstractThis paper is a preliminary report on the flux density monitoring of calibration sources used at the Molonglo Observatory Synthesis Telescope. We show two examples of large amplitude variability at 843 MHz which we attribute to refractive scintillation in the Galactic interstellar medium.

Four Southern Intraday Variable Radio Sources

1998 ◽  
Vol 164 ◽  
pp. 271-272 ◽  
Author(s):  
L. L. Kedziora-Chudczer ◽  
D. L. Jauncey ◽  
M. H. Wieringa ◽  
J. E. Reynolds ◽  
A. K. Tzioumis
Keyword(s):  
Flux Density ◽  
Progress Report ◽  
Radio Sources ◽  
High Flux ◽  
Inverted Spectrum ◽  
Spectrum Radio ◽  
Variable Radio

AbstractThis is a progress report on the ATCA IDV survey of compact, flat or inverted spectrum radio sources. We found that four sources: PKS 0405–385, PKS 1034–293, PKS 1144–397, and PKS 1519–273 out of the sample of 125 show high flux density variability on the daily timescale. The characteristics of observed IDV are discussed and we reflect on its possible origin.

7.8-GHz Flux Density Measurements of Variable Radio Sources

1972 ◽  
Vol 77 ◽  
pp. 819 ◽  
Author(s):  
William A. Dent ◽  
Gabriel Kojoian
Keyword(s):  
Flux Density ◽  
Radio Sources ◽  
Density Measurements ◽  
Variable Radio

15.5-GHz flux-density measurements of variable radio sources

1974 ◽  
Vol 79 ◽  
pp. 1232 ◽  
Author(s):  
W. A. Dent ◽  
J. E. Kapitzky ◽  
G. Kojoian
Keyword(s):  
Flux Density ◽  
Radio Sources ◽  
Density Measurements ◽  
Variable Radio

scholarly journals Correlated Flux Density Outbursts and Structural Variations in a Sample of Low Frequency Variable Radio Sources

1994 ◽  
Vol 159 ◽  
pp. 420-420
Author(s):  
M. Bondi ◽  
L. Padrielli ◽  
R. Fanti ◽  
L. Gregorini ◽  
F. Mantovani ◽  
...  
Keyword(s):  
Flux Density ◽  
Low Frequency ◽  
Radio Sources ◽  
Structural Variations ◽  
Vlbi Observations ◽  
Variable Radio

Snapshot VLBI observations at 18 cm have been obtained with a global array at three epochs (1980.1, 1981.8, 1987.9) in order to investigate flux density and/or structural variations for a sample of 21 low frequency variable sources (Padrielli et al. 1987 Astron Astrophys. Suppl. Ser., 67, 63; Bondi et al. 1993 in preparation).

scholarly journals High-Precision NBPP Timing Measurements at Nançay

2000 ◽  
Vol 177 ◽  
pp. 55-56
Author(s):  
I. Cognard ◽  
J.-F. Lestrade ◽  
D.C. Backer ◽  
P.S. Ray ◽  
R.S. Foster ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Real Time ◽  
Flux Density ◽  
Electron Density ◽  
San Francisco ◽  
High Precision ◽  
Line Of Sight ◽  
Radio Sources ◽  
Search Data ◽  
Scattering Events

The Nançay radiotelescope in France is a large collecting area (7000m2) with receivers around 1.4, 1.7 and 3.5GHz. At this observatory, we are conducting frequent high-precision timing observations of 5 millisecond pulsars (PSR B1937+21, B1821-24 since 1988; J1643-1224, J1713+0747 and B1620-26 since 1996) with a swept frequency oscilllator based on a DDS as a dedisperser.The most interesting result from these dense series of observations is the detection of several Extreme Scattering Events in direction of B1937+21 and possibly in direction of B1821-24 (Cognard, 1993,Nature,366, 320; Cognard & Lestrade, 1996, in ASP Conf. Ser. Vol 105, Pulsars: Problems and Progress (San Francisco: ASP), 469; Lestrade, Rickett & Cognard 1998, A&A,334, 1068). The flux density variations and TOA fluctuations observed have been used to estimate the size (several AU) and electron density (a few hundreds electrons cm−3) of the discrete ionised clouds localized in the interstellar medium that are thought to be responsible for this phenomena. The number of events recorded at Nançay in direction of B1937+21 yields the space density 105– 106pc−3for these clouds. This density is very large and is about 100 times higher than the density estimated from Extreme Scattering Events observed in direction of extragalactic radio sources (Fiedler et al., 1994,ApJ,430, 581). This might mean that the line of sight to B1937+21 is peculiar. This is being investigated with additional observations of a larger array of pulsars at Nançay with the Navy-Berkeley-Pulsar Processor (Figure 1) This processor NBPP (Foster et al., in ASP Conf. Ser. Vol 105, Pulsars: Problems and Progress (San Francisco: ASP), 25) has been used to acquire pulsar search data for 2 years at Nancay and we are now using its real-time folding capability.

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 Rotating Structures in Extragalactic Variable Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 337-338
Author(s):  
Hugh D. Aller ◽  
Philip E. Hodge ◽  
Margo F. Aller
Keyword(s):  
Large Amplitude ◽  
Position Angle ◽  
Radio Sources ◽  
Variable Radio

Four sources have now been found by the Michigan variability program which exhibit large amplitude rotations in polarization position angle with time. The most straightforward explanation for the phenomenon is a physical rotation in the radio emitting region.

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