A Dramatic Millimeter Wavelength Flare in the Gamma-Ray Blazar NRAO 530

We present 3 mm wavelength VLBI observations and up to 30 yr of monitoring at radio through submillimeter wavelengths of the gamma-ray blazar NRAO 530. We discuss the dramatic flare that tripled the millimeter wavelength flux in 1994 and 1995 following three decades of increasing activity. VLBI observations during the flare show the creation of new components in a bent jet on subparsec scales. The components move at an apparent velocity of 7c. The observations also imply expansion in a separate component with a speed greater than 26c. We apply synchrotron self-Compton models to the core and jet to determine magnetic field strengths, particle densities, and Doppler boosting factors. We are unable to provide a satisfactory physical explanation for the high apparent velocity component.

The increase in millimeter and radio wavelength fluxes is correlated with a rise in the gamma-ray flux detected by EGRET. We show that gamma-ray detections do not always occur during or immediately prior to a millimeter wavelength flare, contrary to assertions in the literature. We associate the VLBI component creation with the gamma-ray activity, although not with a specific flare.

We consider what may distinguish gamma-ray blazars from other variable, flat-spectrum radio objects. Our data strengthen the correlation between superluminal motion and gamma-ray emission in blazars. The distribution of jet misalignment angle for 28 EGRET sources, determined from a survey of the literature, does not differ significantly from that of other blazars. This suggests that the geometries of gamma-ray blazars do not differ from those of gamma-ray-quiet blazars on the scales sampled by VLBI.