Correlated Multi–Wave Band Variability in the Blazar 3C 279 from 1996 to 2007

Abstract

We present the results of extensive multiYwave band monitoring of the blazar 3C 279 between 1996 and 2007 at X-ray energies (2Y10 keV), optical R band, and 14.5 GHz, as well as imaging with the Very Long Baseline Array ( VLBA) at 43 GHz. In all bands the power spectral density corresponds to ''red noise'' that can be fit by a single power law over the sampled timescales. Variations in flux at all three wave bands are significantly correlated. The time delay between high-and low-frequency bands changes substantially on timescales of years. A major multifrequency flare in 2001 coincided with a swing of the jet toward a more southerly direction, and in general the X-ray flux is modulated by changes in the position angle of the jet near the core. The flux density in the core at 43 GHz-increases in which indicate the appearance of new superluminal knots-are significantly correlated with the X-ray flux. We decompose the X-ray and optical light curves into individual flares, finding that X-ray leads optical variations (XO) in six flares, the reverse (OX ) occurs in three flares, and there is essentially zero lag in four flares. Upon comparing theoretical expectations with the data, we conclude that (1) XO flares can be explained by gradual acceleration of radiating electrons to the highest energies, (2) OX flares can result from either light-travel delays of the seed photons (synchrotron self-Compton scattering) or gradients in maximum electron energy behind shock fronts, and (3) events with similar X-ray and optical radiative energy output originate well upstream of the 43 GHz core, while those in which the optical radiative output dominates occur at or downstream of the core. Subject headingg s: galaxies: jets -quasars: individual (3C 279) -radiation mechanisms: nonthermalradio continuum: galaxies -X-rays: galaxies Online material: extended figure, machine-readable tables INTRODUCTIONBlazars form a subclass of active galactic nuclei (AGNs) characterized by violent variability on timescales from hours to years across the electromagnetic spectrum. It is commonly thought that at radio, infrared, and optical frequencies the variable emission of blazars originates in relativistic jets and is synchrotron in nature ( Impey & Neugenbauer 1988;Marscher 1998). The X-ray emission is consistent with inverse Compton ( IC) scattering of these synchrotron photons, although seed photons from outside the jet cannot be excluded ( Mause et al. 1996;Romanova & Lovelace 1997;Coppi & Aharonian 1999;Byażejowski et al. 2000;Sikora et al. 2001;Chiang & Böttcher 2002;Arbeiter et al. 2005). The models may be distinguished by measuring time lags between the seed-photon and Compton-scattered flux variations. Comparison of the amplitudes and times of peak flux of flares at different wave bands is another important diagnostic. For this reason, long-term multifrequency monitoring programs are crucially important for establishing a detailed model of blazar activity and for constraining the physics of relativistic jets. Here we report on such...

A Comparison of the X-Ray Emission from Tidal Disruption Events with those of Active Galactic Nuclei

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