The long-term millimeter activity of active galactic nuclei

Abstract

We analyze the long-term evolution of the fluxes of six active galactic nuclei (AGN) -0923+392, 3C 111, 3C 273, 3C 345, 3C 454.3, and 3C 84 -in the frequency range 80−267 GHz using archival calibration data of the IRAM Plateau de Bure Interferometer. Our dataset spans a long timeline of ≈14 years with 974−3027 flux measurements per source. We find strong (factors ≈2−8) flux variability on timescales of years for all sources. The flux density distributions of five out of six sources show clear signatures of bi-or even multimodality. Our sources show mostly steep (α ≈ 0.5−1), variable spectral indices that indicate outflow dominated emission; the variability is most probably due to optical depth variations. The power spectra globally correspond to red-noise spectra with five sources being located between the cases of white and flicker noise and one source (3C 111) being closer to the case of random walk noise. For three sources the low-frequency ends of their power spectra appear to be upscaled in spectral power by factors ≈2−3 with respect to the overall powerlaws. In two sources, 3C 454.3 and 3C 84, the 1.3-mm emission preceeds the 3-mm emission by ≈55 and ≈300 days, respectively, probably due to (combinations of) optical depth and emission region geometry effects. We conclude that the source emission cannot be described by uniform stochastic emission processes; instead, a distinction of "quiescent" and (maybe multiple) "flare" states of the source emission appears to be necessary.

The Long-Term Centimeter Variability of Active Galactic Nuclei: A New Relation Between Variability Timescale and Accretion Rate*

“…Therefore, we may expect (1) smaller power spectral indices β and (2) observations of broken power-law periodograms at higher frequencies. Trippe et al (2011) showed that the power spectra of six radio bright AGNs at millimeter wavelengths have β ≈ 0.5, which is much smaller than the values we find in this work. However, windowing effects (especially red-noise leak and aliasing) were not taken into consideration then, making it hard to conclude on the general behavior of mm-radio periodograms.…”

Jet kinematics of the quasar 4C+21.35 from observations with the KaVA very long baseline interferometry array

“…According to the unified model of AGN (Urry & Padovani 1995), blazars are AGN whose jet axis is aligned with the line of sight within a few degrees. They are characterised by strong stochastic (red-noise type) variability across the whole electromagnetic spectrum, from γ-rays to the radio domain, on time scales from hours to years (e.g., Trippe et al 2011;Gupta et al 2012;Park & Trippe 2014;Aleksic et al 2011).…”

Origin of X-rays in the low state of the FSRQ 3C 273: evidence of inverse Compton emission

“…Considering these observations, we checked the literature for such connections to the 2007 X-ray flare in the source. The mm flux reached its minimum in 2004, and since about 2006 this flux has shown high variability (Trippe et al 2011). However, in this case no counterparts of this X-ray flare were noted in either radio or optical bands; moreover, we could find no report on the birth of any radio knot related to this 2007 "orphan" X-ray flare.…”