scholarly journals Results from a monitoring program of low frequency variable sources

1986 ◽  
Vol 119 ◽  
pp. 149-155
Author(s):  
L. Padrielli ◽  
R. Fanti ◽  
A. Ficarra ◽  
L. Gregorini ◽  
F. Mantovani
Keyword(s):  
Monitoring Program ◽  
Low Frequency ◽  
Radio Sources ◽  
Main Question ◽  
Extragalactic Radio Sources ◽  
Low Frequency Variability ◽  
Flux Variability

The flux variability of extragalactic radio sources at decimetric wavelengths (Low Frequency Variability LFV) is mostly associated with the nuclei of compact radio sources. But is a not yet well understood phenomenon. The main question still is: where does this phenomenon take place?

scholarly journals The Low Frequency Variability of Extragalactic Radio Sources

1984 ◽  
Vol 110 ◽  
pp. 169-176 ◽  
Author(s):  
L. Padrielli
Keyword(s):  
Low Frequency ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Low Frequency Variability ◽  
Flux Variability

The flux variability of extragalactic radio sources at decimetric wavelengths (L.F.V.) is now considered a classical astrophysical subject connected with compact radio sources.

scholarly journals The Low Frequency Variability of Extragalactic Radio Sources

1987 ◽  
Vol 121 ◽  
pp. 211-214
Author(s):  
D.R. Altschuler ◽  
B.K. Dennison ◽  
K.J. Mitchell ◽  
S.L. O'Dell ◽  
J.J. Broderick ◽  
...  
Keyword(s):  
Low Frequency ◽  
Radio Sources ◽  
Frequency Range ◽  
Spectral Evolution ◽  
Entire Frequency Range ◽  
Extragalactic Radio Sources ◽  
Low Frequency Variability

The spectral evolution between 0.3 and 15 GHz of the extragalactic radio sources 0235+164 and 1611+343 (DA406) is presented. The data show two very different forms of behavior. For 0235+164 the variations over the entire frequency range are correlated and consistent with being intrinsic to the source, whereas for DA406 an extrinsic cause for the variability seems probable.

The Low Frequency Variability of Extragalactic Radio Sources

1987 ◽  
pp. 211-214
Author(s):  
D. R. Altschuler ◽  
B. K. Dennison ◽  
K. J. Mitchell ◽  
S. L. O’Dell ◽  
J. J. Broderick ◽  
...  
Keyword(s):  
Low Frequency ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Low Frequency Variability

scholarly journals PKS 1117+146: Gravitational Lens or Micro lobes

1996 ◽  
Vol 175 ◽  
pp. 118-119
Author(s):  
M. Bondi ◽  
M. Garrett ◽  
L. Gurvits
Keyword(s):  
Gravitational Lensing ◽  
Hot Spot ◽  
Low Frequency ◽  
Gravitational Lens ◽  
Central Component ◽  
Radio Sources ◽  
Double Structure ◽  
Global Arrays ◽  
Low Frequency Variability ◽  
First Time

PKS 1117+146 is a high power radio source (L327MHz=5.4 × 1026 W/Hz) identified with a galaxy of 20.1 red magnitude at z=0.362 (de Vries et al. 1995). At this redshift 1 mas ≃ 2.9 pc (H0 = 100 km/s–1Mpc–1). Based on the properties of the radio spectra, PKS 1117+146 is classified as a GigaHertz Peaked Spectrum source (GPS) (Stanghellini et al. 1990). The GPS are powerful but physically small (sub-galactic sizes) radio sources with turnovers in their radio spectra at v ≃ 1 GHz. They are supposed to be isotropically emitting radio sources confined by exceptional dense circumnuclear gas (O'Dea et al. 1991) or still relatively young (Fanti et al. 1990). PKS 1117+146 is also a low frequency variable (LFV) with no sign of variability at v > 1 GHz (Padrielli et al. 1987, Mitchell et al. 1994). The low frequency variability is caused by propagation effects in the interstellar medium of our Galaxy (Mantovani et al. 1990, Spangler et al. 1993). PKS 1117+146 was observed with VLBI global arrays at 608 MHz (Padrielli et al. 1991), at 327 MHz (Altschuler et al. 1995), and at 1667 MHz (Bondi et al. 1996). All the maps are in agreement showing a compact double structure with components separated by about 70 mas. Flux densities and separation of the two components derived from VLBI and MERLIN (see below) maps are listed in Table 1. The flux ratios of the two components from the VLBI observations are very similar, and the spectral index is relatively flat (α ≃ 0.3–0.4), even if the strong low frequency variability can introduce uncertainties. The similarity of the VLBI morphology and spectral properties of the two components suggested that 1117+146 could be a possible gravitational lens candidate prompting for higher frequency observations. We observed PKS 1117+146 with MERLIN at 22 GHz in March 1993. MERLIN observations reveal for the first time a weak central component with a total flux density of about 20 mJy (Fig.1). From Table 1 we can note that the P.A. between the components is constant at all the frequencies while the separation between the peak flux densities significantly increases at higher frequencies. This is the expected behaviour if the 2 components are 2 lobes with hot-spot at the outer edges. The MERLIN map at 22 GHz seems to rule out the possibility that the morphology of PKS 1117+146 is caused by gravitational lensing.

scholarly journals Spectral Index - Redshift Relation for Radio Galaxies and Quasars

1996 ◽  
Vol 175 ◽  
pp. 569-570
Author(s):  
R.D. Dagkesamanskii
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Cosmological Evolution ◽  
Radio Sources ◽  
Spectral Indices ◽  
Extragalactic Radio Sources

Cosmological evolution of synchrotron spectra of the powerful extragalactic radio sources was studied by many authors. Some indications of such an evolution had been found firstly by analysis of ‘spectral index - flux density’ (α – S) relation for the sample of relatively strong radio sources. Later Gopal-Krishna and Steppe extended the analysis to weaker sources and found that the slope of αmed(S) curve changes dramatically at intermediate flux densities. Gopal-Krishna and Steppe pointed out that the maxima of the αmed(S) curve and of differential source counts are at almost the same flux density ranges (see, Fig. 2). It has to be noticed that the all mentioned results were obtained using the low-frequency spectral indices and on the basis of low frequency samples.

scholarly journals Intensity Variations in Extragalactic Radio Sources at 13 cm

1972 ◽  
Vol 44 ◽  
pp. 224-224 ◽  
Author(s):  
G. D. Nicolson
Keyword(s):  
Low Frequency ◽  
Secular Change ◽  
Radio Sources ◽  
Complete Sample ◽  
Frequency Spectra ◽  
Extragalactic Radio Sources ◽  
The Relationship

Results of a three-year investigation into the variability of 55 Parkes sources at 13 cm are presented. Thirty-six of the sources comprise a complete sample of QSS with fluxes exceeding 2 flux units. The remaining sources include most other known or likely variables stronger than 2 flux units. The relationship between spectra and variability in QSS is investigated and it is confirmed that variables generally have flat low frequency spectra. A possible relationship between redshift and specific types of intensity variations is considered. Limits on the secular change in the intensity of non-variable QSS are set and are generally found to be ± 1.5% p.a. at 13 cm. Results for the remaining 19 sources are discussed and some preliminary findings of an extension patrol to include weaker sources in the range 1-2 flux units are given.

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