Alma C. Zook

Multiwavelength Observations of a Dramatic High-Energy Flare in the Blazar 3C 279

The blazar 3C 279, one of the brightest identified extragalactic objects in the γ-ray sky, underwent a large (factor of ~10 in amplitude) flare in γ-rays toward the end of a 3 week pointing by Compton Gamma Ray Observatory (CGRO), in 1996 January-February. The flare peak represents the highest γ-ray intensity ever recorded for this object. During the high state, extremely rapid γ-ray variability was seen, including an increase of a factor of 2.6 in ~8 hr, which strengthens the case for relativistic beaming. Coordinated multifrequency observations were carried out with Rossi X-Ray Timing Explorer (RXTE), Advanced Satellite for Cosmology and Astrophysics (ASCA; or, Astro-D), Roentgen Satellite (ROSAT), and International Ultraviolet Explorer (IUE) and from many ground-based observatories, covering most accessible wavelengths. The well-sampled, simultaneous RXTE light curve shows an outburst of lower amplitude (factor of 3) well correlated with the γ-ray flare without any lag larger than the temporal resolution of ~1 day. The optical-UV light curves, which are not well sampled during the high-energy flare, exhibit more modest variations (factor of ~2) and a lower degree of correlation. The flux at millimetric wavelengths was near a historical maximum during the γ-ray flare peak, and there is a suggestion of a correlated decay. We present simultaneous spectral energy distributions of 3C 279 prior to and near to the flare peak. The γ-rays vary by more than the square of the observed IR-optical flux change, which poses some problems for specific blazar emission models. The synchrotron self-Compton (SSC) model would require that the largest synchrotron variability occurred in the mostly unobserved submillimeter/far-infrared region. Alternatively, a large variation in the external photon field could occur over a timescale of a few days. This occurs naturally in the mirror model, wherein the flaring region in the jet photoionizes nearby broad emission line clouds, which, in turn, provide soft external photons that are Comptonized to γ-ray energies.

Kinematics of the Parsec-Scale Relativistic Jet in Quasar 3C 279: 1991-1997

We present results of long-term high-frequency VLBI monitoring of the relativistic jet in 3C 279, consisting of 18 epochs at 22 GHz from 1991 to 1997 and 10 epochs at 43 GHz from 1995 to 1997. Three major results of this study are apparent speeds measured for six superluminal components range from 4.8c to 7.5c (H0 = 70 km s-1 Mpc-1, q0 = 0.1), variations in the total radio flux are due primarily to changes in the VLBI core flux, and the uniform-sphere brightness temperature of the VLBI core is ~1 × 1013 K at 22 GHz after 1995, one of the highest direct estimates of a brightness temperature. If the variability brightness temperature measured for 3C 279 by Lahteenmaki & Valtaoja is an actual value and not a lower limit, then the rest-frame brightness temperature of 3C 279 is quite high and limited by inverse Compton effects rather than equipartition. The parsec-scale morphology of 3C 279 consists of a bright, compact VLBI core, a jet component (C4) that moved from ~2 to ~3.5 mas from the core during the course of our monitoring, and an inner jet that extends from the core to a stationary component, C5, at ~1 mas from the core. Component C4 followed a curved path, and we reconstruct its three-dimensional trajectory using polynomial fits to its position versus time. Component C5 faded with time, possibly due to a previous interaction with C4 similar to interactions seen in simulations by Gomez et al. Components in the inner jet are relatively short lived and fade by the time they reach ~1 mas from the core. The components have different speeds and position angles from each other, but these differences do not match the differences predicted by the precession model of Abraham & Carrara. Although VLBI components were born about six months prior to each of the two observed γ-ray high states, the sparseness of the γ-ray data prevents a statistical analysis of possible correlations.

THE SPEED AND ORIENTATION OF THE PARSEC-SCALE JET IN 3C 279

A high degree of relativistic beaming is inferred for the jets of blazars on the basis of several lines of evidence, but the intrinsic speed and angle of the jet to the line of sight for individual sources are difficult to measure. We have calculated inverse Compton Doppler factors for 3C 279 using the collection of VLBI data (including high-resolution space VLBI data at low frequencies) recently published by us (as Wehrle et al. and Piner et al.) and the collection of multiwavelength spectra recently published by Hartman et al. From the Doppler factor and superluminal apparent speed, we then calculate the Lorentz factor and angle to the line of sight of the parsec-scale relativistic jet. We follow the method previously used by Unwin et al. for 3C 345 to model the jet components as homogeneous spheres and the VLBI core as an unresolved inhomogeneous conical jet, using K?nigls formalism. The conical jet model can be made to match both the observed X-ray emission and the VLBI properties of the core with a suitable choice of Doppler factor, implying that the core makes a significant contribution to the X-ray emission, in contrast to the situation for 3C 345, where the jet components dominated the X-ray emission. The parameters of the K?nigl models indicate that the jet is particle dominated at the radii that produce significant emission (from ~5 to 20 pc from the apex of the jet for most models) and is not in equipartition. At the inner radius of the K?nigl jet the magnetic field is of order 0.1 G and the relativistic-particle number density is of order 10 cm-3. The kinetic energy flux in the jet is of order 1046(1 + k) ergs s-1, where k is the ratio of proton to electron energy, which implies a mass accretion rate of order 0.1(1 + k)/? M? yr-1, where ? is the efficiency of conversion of mass to kinetic energy. When all components are included in the calculation, then on average the core produces about half of the X-rays, with the other half being split between the long-lived component C4 and the brightest inner-jet component. We calculate an average speed and angle to the line of sight for the region of the jet interior to 1 mas of v = 0.992c (? = 8) and ? = 4? and an average speed and angle to the line of sight for C4 (at r ? 3 mas) of v = 0.997c (? = 13) and ? = 2?. These values imply average Doppler factors of ? = 12 for the inner jet and ? = 21 for C4.

Superluminal Motion in the Gamma-Ray Blazar 3C 279

The blazar 3C 279 is one of the strongest extragalactic sources of γ -rays, and is also one of the best studied superluminal radio sources. Definitive testing of models of the broad-band spectral energy distribution, especially in the X-ray and γ -ray regions requires knowledge of the evolution of the spectrum with time. Within the context of the relativistic jet model, multi-wavelength monitoring of the parsec-scale radio jet is also required. We present here the first steps toward such a test, using extensive VLBI monitoring over a 13 year interval at 22 GHz, and γ -ray observations between 1991 and 1996.

Multiwavelength observations of the February 1996 high-energy flare in the blazar 3C 279

We report CGRO, RXTE, ASCA, ROSAT, IUE, HST and ground-based observations of a large flare in 3C 279 in February 1996. X-rays and γ-rays peaked simultaneously (within one day). We show simultaneous spectral energy distributions prior to and near the flare peak. The γ-ray flare was the brightest ever observed in this source.