Radio follow-up of the gamma-ray flaring gravitational lens JVAS B0218+357

TL;DR

This study used VLBA observations to monitor the gravitational lens JVAS B0218+357 following a gamma-ray flare, finding no significant radio flux or morphological changes, indicating the gamma-ray activity originates from the core region.

Contribution

First multi-epoch VLBA monitoring of JVAS B0218+357 post-gamma-ray flare, revealing no radio variability or morphological changes, constraining the gamma-ray emission region to the core.

Findings

No significant radio flux variability detected.

No morphological changes observed in the images.

Gamma-ray emission likely originates from the core region.

Abstract

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.