VLTI/AMBER differential interferometry of the broad-line region of the quasar 3C273

摘要

Unveiling the structure of the Broad Line Region (BLR) of AGNs is critical to understand the quasar phenomenon.Resolving a few BLRs by optical interferometry will bring decisive information to confront, complement and calibratethe reverberation mapping technique, seed of the mass-luminosity relation in quasars. BLRs are much smaller than theangular resolution of the VLT and Keck interferometers and they can be resolved only by differential interferometryvery accurate measurements of differential visibility and phase. The latest yields the photocenter variation with λ, and constrains the size, position and velocity law of various regions of the BLR. AGNs are below the magnitude limit forspectrally resolved interferometry set by currently available fringe trackers. A new “blind” observation method and adata processing based on the accumulation of 2D Fourier power and cross spectra permitted us the first spectrallyresolved interferometric observation of a BLR, on the K=10 quasar 3C273. A careful bias analysis is still in progress, butwe report strong evidence that, as the baseline increases, the differential visibility decreases in the iP/iasubα/sub line. Combinedwith a differential phase certainly smaller than 3°, this yields an angular radius of the BLR larger than 0.4milliarcseconds, or 1000 light days at the distance of 3C273, much larger than the reverberation mapping radius of 300light days. Explaining the coexistence of these two different scales, and possibly structures and mechanisms, impliesvery new insights about the BLR of 3C273.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.