Radio follow-up of the gamma-ray flaring gravitational lens JVAS   B0218+357
  We present results on multifrequency Very Long Baseline Array (VLBA) monitoring observations of the double-image gravitationally lensed blazar JVAS B0218+357. Multi-epoch observations started less than one month after the gamma-ray flare detected in 2012 by the Large Area Telescope on board Fermi, and spanned a 2-month interval. The radio light curves did not reveal any significant flux density variability, suggesting that no clear correlation between the high energy and low-energy emission is present. This behaviour was confirmed also by the long-term Owens Valley Radio Observatory monitoring data at 15 GHz. The milliarcsecond-scale resolution provided by the VLBA observations allowed us to resolve the two images of the lensed blazar, which have a core-jet structure. No significant morphological variation is found by the analysis of the multi-epoch data, suggesting that the region responsible for the gamma-ray variability is located in the core of the AGN, which is opaque up to the highest observing frequency of 22 GHz. 
Cristiana Spingola, D. Dallacasa, M. Orienti, M. Giroletti, J. P.   McKean, C. C. Cheung, T. Hovatta, S. Ciprini, F. D'Amman...
astro-ph.GA astro-ph.HE