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

The blazar 3C 279, one of the brightest identied extragalactic objects in the c-ray sky, underwent a large (factor of D10 in amplitude) are in c-rays toward the end of a 3 week pointing by Compton Gamma Ray Observatory (CGRO), in 1996 JanuaryFebruary. The are peak represents the highest c-ray intensity ever recorded for this object. During the high state, extremely rapid c-ray variability was seen, including an increase of a factor of 2.6 in D8 hr, which strengthens the case for relativistic beaming. Coordinated multifrequency observations were carried out with Rossi X-Ray T iming Explorer (RXT E), 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 RXT E light curve shows an outburst of lower amplitude (factor of ^3) well correlated with the c-ray are without any lag larger than the temporal resolution of D1 day. The optical-UV light curves, which are not well sampled during the high-energy are, exhibit more modest variations (factor of D2) and a lower degree of correlation. The ux at millimetric wavelengths was near a historical maximum during the c-ray are 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 are peak. The c-rays vary by more than the square of the observed IRoptical ux change, which poses some problems for specic 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 eld could occur over a timescale of a few days. This occurs naturally in the "" mirror model, wherein the aring region in the jet photoionizes nearby broad emission line clouds, which, in turn, provide soft external photons that are Comptonized to c-ray energies.