Radio and optical intra-day variability observations of five blazars

Abstract

We carried out a pilot campaign of radio and optical band intra-day variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287, B0925+504, and BL Lacertae) on December 18-21, 2015 by using the radio telescope in Effelsberg (Germany) and several optical telescopes in Asia, Europe, and America. After calibration, the light curves from both 5 GHz radio band and the optical R band were obtained, although the data were not smoothly sampled over the sampling period of about four days. We tentatively analyse the amplitudes and time scales of the variabilities, and any possible periodicity. The blazars vary significantly in the radio (except 3C66A and BL Lacertae with only marginal variations) and optical bands on intra-and inter-day time scales, and the source B0925+504 exhibits a strong quasi-periodic radio variability. No significant correlation between the radio-and optical-band variability appears in the five sources, which we attribute to the radio IDV being dominated by interstellar scintillation whereas the optical variability comes from the source itself. However, the radio-and optical-band variations appear to be weakly correlated in some sources and should be investigated based on well-sampled data from future observations.

Spica and the annual cycle of PKS B1322–110 scintillations

“…For sources at cosmological distances, the velocity of the pattern is essentially that of the screen (Cordes & Rickett 1998), and therefore the change in the velocity of the Earth as it orbits the Sun can strongly affect the variation timescales. This annual modulation has so far been reported in a handful of sources: J1819+3845 (Dennett- Thorpe & de Bruyn 2001, 2003; QSO B0917+624 (Jauncey & Macquart 2001;Rickett et al 2001;Fuhrmann et al 2002); PKS 1257−326 ; PKS B1519−273 (Jauncey et al 2003); PKS B1622−253 (Carter et al 2009); S5 0716+714 ); 0925+504 (Liu & Liu 2015;Liu et al 2017); S4 0954+65 ; 1156+295 (4C+29.45, Liu et al 2013; and J1128+5925 (Gabányi et al 2007b,a). Together with the two-station experiments (Dennett- Thorpe & de Bruyn 2002;Bignall et al 2006), which directly demonstrated the existence of a spatial flux pattern, the annual cycles provided the key evidence that proved IDV to be scintillation.…”

Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz

“…Its mean flux density is slightly increased from session 1 to session 2. The blazar has previously shown fast IDV with Urumqi 25 m and Efferlsberg 100 m telescope, its IDV timescales can be fitted with the annual modulated ISS model [36,37].…”

Multi-Wavelength Intra-Day Variability and Quasi-Periodic Oscillation in Blazars

“…Mostly, observations at centimeter and meter wavelengths have dominant extrinsic variability, which is due to interstellar scintillation of radio waves caused by the turbulent interstellar medium of the Milky Way, while IDV are in the millimeter wavelength of the intrinsic origin. Radio IDV studies of blazars were pioneered by the 100-m Effelsberg radio telescope in Germany, as well as other radio and mm wavelength telescopes (e.g., [17,25,102,[111][112][113][114][115][116][117][118][119][120][121]; and the references therein).…”

“…IDV was detected in all three radio frequencies, and it was also noticed that low and high frequency correlations do not peak at zero lag, which shows that low frequency radio observation is the combined effect of an intrinsic and an extrinsic mechanism. Optical and radio IDV observations were carried out by [121]. IDV observation along with VLBI analysis was carried out for the blazar S4 0917+624 [120].…”