VLTI-GRAVITY observations of blazars
Abstract
Parsec-scale jets of blazars have so far been spatially resolved only in millimeter and submillimeter wavelengths, where very long baseline interferometry can be used to obtain milliarcsecond-scale images of the jets. We have attempted to spatially resolve the near-infrared emission in jet-dominated blazars for the first time. We used the VLTI-GRAVITY instrument to obtain milliarcsecond-scale near-infrared interferometric observations of a flaring blazar Ton 599. Additionally, we observed four non-flaring blazars using the GRAVITY-wide mode, where a nearby bright star is used as a fringe tracker. We modeled the squared visibilities of Ton 599 and found that they are incompatible with a single unresolved point source unless there is a significant amount of additional unknown coherence loss in the instrument. With the present data, we cannot distinguish between a model with an unresolved point source and extended emission or coherence loss and a model with a single Gaussian component. This suggests that we are seeing the unresolved or only partially resolved jet-base in near-infrared wavelengths. The wide-field mode of GRAVITY was challenging for the additional relatively faint targets, resulting in either non-detections or poor-quality data that could not be modeled. Our observations demonstrate that it is possible to detect the compact jet emission in blazars with near-infrared interferometry, suggesting that with the improved GRAVITY+ instrument it will be possible to spatially resolve and image the near-infrared emission of blazar jets.
Cite
@article{arxiv.2604.19210,
title = {VLTI-GRAVITY observations of blazars},
author = {Talvikki Hovatta and Elina Lindfors and Heidi Korhonen and Preeti Kharb and Markus Wittkowski and Aaron Labdon and Tapio Pursimo and Kaj Wiik},
journal= {arXiv preprint arXiv:2604.19210},
year = {2026}
}
Comments
Accepted for publication in A&A. 6 pages of main text with 4 figures. V2 includes minor language edits and updated references