J/MNRAS/235/1313 J/MNRAS/235/1313 Metric wave Extragalactic Variability O B Slee B C Siegman Mon. Not. R. Astron. Soc. 235 1313 1988 1988MNRAS.235.1313S VIII/35 : Radio Sources observed with Culgoora Circular Array Slee O.B. 1995, Aust. J. Phys., 48, 143 =1995AuJPh..48..143S Slee O.B. 1994, Einstein On-line Service, 'rad_cul80_160' Slee O.B. et al. 1982, Proc. Astron. Soc. Aust. 4, 278 Slee O.B. et al. 1983, Proc. Astron. Soc. Aust., 5, 114 =1983PASAu...5..114S Slee O.B. and Siegman, B.C. 1988, MNRAS, 235, 1313 =1988MNRAS.235.1313S Radio sources We report a detailed statistical study of the intensity variations in 412 extragalactic radio sources randomly selected from the ~2000 sources which have been observed with the Culgoora circular array at 80 and 160 MHz during the interval 1970-84. Our results are: (i) About 47 per cent of the sample displays significant variability on time scales of months or years. (ii) A similar degree of variability is shown by QSOs, radio galaxies and sources in blank optical fields. (iii) Sources with flatter radio spectra are more variable. (iv) There is a weak increase in variability for the lower-galactic-latitude sources. (v) There is a correlation between month-to-month variability and year-to year variability in the same sources. (vi) The degree of variability at 80MHz is related to that at 160MHz. (vii) Most of the sources in both the variable and non-variable categories have a component with angular diameter <1arcsec. Our results are partly consistent with an origin in refractive scintillation by large-scale electron density turbulence in the intervening medium. There are, however, serious difficulties in explaining, from the existing theory of slow galactic scintillation, the short time-scale of the scintillation. Our results are probably more in accord with the focusing and occulting effects of compact interstellar ionized structures recently identified at microwave frequencies.

Name Source name --- RAh Right ascension (B1950) h RAm Right ascension (B1950) min RAs Right ascension (B1950) s DE- Declination sign --- DEd Declination (B1950) deg DEm Declination (B1950) arcmin DEs Declination (B1950) arcsec OptID Optical Identification --- z Redshift of optical identification --- alpha Radio spectral index --- GLON Galactic longitude deg GLAT Galactic latitude deg F80MHz Average flux density at 80 MHz Jy o_F80MHz Number of observations at F80MHz --- M1a 1-monthly 80 MHz modulation index number=1 Variability modulation indices as defined by Slee and Siegman (1988MNRAS.235.1313S). A value of '-1.00' means that no variability (95% confidence level) was detected. A blank indicates that the data were not available to test for variability. --- M12a 12-month 80 MHz modulation index number=1 Variability modulation indices as defined by Slee and Siegman (1988MNRAS.235.1313S). A value of '-1.00' means that no variability (95% confidence level) was detected. A blank indicates that the data were not available to test for variability. --- F160MHz Average flux density at 160 MHz Jy o_F160MHz Number of observations at F160MHz --- M1b 1-month 160 MHz modulation index number=1 Variability modulation indices as defined by Slee and Siegman (1988MNRAS.235.1313S). A value of '-1.00' means that no variability (95% confidence level) was detected. A blank indicates that the data were not available to test for variability. --- M12b 12-month 160 MHz modulation index number=1 Variability modulation indices as defined by Slee and Siegman (1988MNRAS.235.1313S). A value of '-1.00' means that no variability (95% confidence level) was detected. A blank indicates that the data were not available to test for variability. --- Patricia Bauer CDS 1996Aug21We thank Heinz Andernach <hja@vilspa.esa.es> for providing an access to his set of radio catalogues (R190), and to Bruce Slee <BSLEE@rp.CSIRO.au> for his assistance. J_MNRAS_235_1313.xml