Exploring the nature of the broadband variability in the flat spectrum radio quasar 3C 273

Abstract

The detailed investigation of the broadband flux variability in the blazar 3C 273 allowed us to probe the location and size of emission regions and their physical conditions. We conducted correlation studies of the flaring activity in 3C 273, which was observed for the period between 2008 and 2012. The observed broadband variations were investigated using the structure function and the discrete correlation function methods. Starting from the commonly used power spectral density (PSD) analysis at X-ray frequencies, we extended our investigation to characterise the nature of variability at radio, optical, and γ-ray frequencies. The PSD analysis showed that the optical and infrared light-curve slopes are consistent with the slope of white-noise processes, while the PSD slopes at radio, X-ray, and γ-ray energies are consistent with red-noise processes. We found that the estimated fractional variability amplitudes strongly depend on the observed frequency. The flux variations at γ-ray and mm-radio bands are found to be significantly correlated. Using the estimated time lag of (110 ± 27) days between γ-ray and radio light-curves, where γ-ray variations lead the radio bands, we constrained the location of the γ-ray emission region at a de-projected distance of 1.2 ± 0.9 pc from the jet apex. Flux variations at X-ray bands were found to have a significant correlation with variations at both radio and γ-ray energies. The correlation between X-ray and γ-ray light curves indicates two possible time lags, which suggests that two components are responsible for the X-ray emission. A negative time lag of −(50 ± 20) days, where the X-rays are leading the emission, suggests that X-rays are emitted closer to the jet apex from a compact region (0.02-0.05 pc in size), most likely from the corona at a distance of (0.5 ± 0.4) pc from the jet apex. A positive time lag of (110 ± 20) days (γ-rays are leading the emission) suggests a jet-base origin of the other X-ray component at ∼4 to 5 pc from the jet apex. The flux variations at radio frequencies were found to be well correlated with each other such that the variations at higher frequencies are leading the lower frequencies, which is expected from the standard shock-in-jet model.

Exploring the Variability of the Flat Spectrum Radio Source 1633+382. I. Phenomenology of the Light Curves

“…This approach is similar, although slightly less conservative, than taking the FWHM, followed by e.g. Rani et al (2013a) or Chidiac et al (2016). We note that, in any case, the results are not significantly affected by the errors on the time lag.…”

Multicolor Optical Monitoring of the Quasar 3C 273 from 2005 to 2016

“…Esposito et al (2015) studied the high energy spectrum of 3C 273 and suggested a two-component model to explain the complete high energy spectrum. Chidiac et al (2016) found that the variations at higher frequencies are leading the lower frequencies, which could be expected in the standard shock-in-jet model. Kalita et al (2015) found high flux variability over long time scales in optical, UV and X-ray bands, and that on intraday time scales 3C 273 shows small amplitude variability in X-ray bands.…”

“…Madsen et al (2015) investigated the spectral variability in the NuSTAR band and found an inverse correlation between flux and photon index. In the optical band, unlike other blazars which are highly polarised, 3C 273 is a low-polarization quasar (Valtaoja et al 1991;Xie et al 1999;Chidiac et al 2016). Generally, the properties of 3C 273 are very different from that of BL Lac objects and highly polarized quasars in the optical bands.…”

“…characteristics (Esposito et al 2015;Chidiac et al 2016). The flux and spectral variations of 3C 273 have been extensively studied over the entire electromagnetic spectrum (e.g.…”

“…The flux and spectral variations of 3C 273 have been extensively studied over the entire electromagnetic spectrum (e.g. Xie et al 1999Xie et al , 2004aGhosh et al 2000;Mantovani et al 2000;Collmar et al 2000;Sambruna et al 2001;Greve et al 2002;Kataoka et al 2002;Courvoisier et al 2003;Jester et al 2005;Attridge et al 2005;Savolainen et al 2006;McHardy et al 2007;Soldi et al 2008;Espaillat et al 2008;Pacciani et al 2009;Dai et al 2009;Fan et al 2009Fan et al , 2014Abdo et al 2010;Ikejiri et al 2011;Rani et al 2011;Vol'vach et al 2013;Beaklini & Abraham 2014;Kalita et al 2015;Esposito et al 2015;Madsen et al 2015;Chidiac et al 2016). Soldi et al (2008) studied the multiwavelength variability of 3C 273.…”