VLBI imaging of M81* at 3.4 mm with source-frequency phase-referencing

Abstract

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 could be eventually 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 mm/sub-mm VLBI observations of weaker sources. From the analysis of the M81* visibilities, a core size of ~50 uas at 3.4 mm was estimated. This follows the power-law relationship with wavelength lambda^0.88, reported previously at lower frequencies. These results constrain the core size (at 3.4 mm) to a minimum of ~80 Schwarzschild radii of M81*.

arXiv comment10 pages, 5 figures,accepted by ApJ Letter

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Cited by in corpus (5)

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• Observational Evidence of a Centi-parsec Supermassive Black Hole Binary Existing in the Nearby Galaxy M81
• Multifrequency Very Long Baseline Interferometry Imaging of the Subparsec-scale Jet in the Sombrero Galaxy (M104)
• Millimeter-VLBI observations of low-luminosity active galactic nuclei with source-frequency phase-referencing