VLBI Imaging of M81∗ at λ = 3.4 mm with Source-frequency Phase-referencing
Journal article, 2018

We report on the first VLBI image of the M81 nucleus (M81∗) at a wavelength of 3.4 mm, obtained with the source-frequency phase-referencing (SFPR) technique. Thanks to the SFPR calibration, the coherent integration time eventually could be increased by more than an order of magnitude, which enabled the detection of fringes at the level of 45 mJy beam -1 with a dynamic range higher than 130:1. This paves the way toward future millimeter/submillimeter VLBI observations of weaker sources. From the analysis of the M81∗ visibilities, a core size of ∼50 μas at 3.4 mm was estimated. This follows the power-law relationship with wavelength, , reported previously at lower frequencies. These results constrain the core size (at 3.4 mm) to a minimum of ∼80 Schwarzschild radii of M81∗.

methods: data analysis

techniques: interferometric

galaxies: individual (M81)


Wu Jiang

Shanghai Astronomical Observatory

Chinese Academy of Sciences

Zhiqiang Shen

Chinese Academy of Sciences

Shanghai Astronomical Observatory

Dongrong Jiang

Shanghai Astronomical Observatory

Chinese Academy of Sciences

Ivan Marti-Vidal

Chalmers, Space, Earth and Environment, Onsala Space Observatory

Noriyuki Kawaguchi

Shanghai Astronomical Observatory

Astrophysical Journal Letters

2041-8205 (ISSN) 2041-8213 (eISSN)

Vol. 853 1 L14

Subject Categories

Accelerator Physics and Instrumentation

Medical Laboratory and Measurements Technologies

Atom and Molecular Physics and Optics



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