Wisps in the Galactic center: NIR triggered observations of the radio source Sgr A* at 43 GHz

Abstract

Context. The compact radio and near-infrared (NIR) source Sagittarius A* (Sgr A*) associated with the supermassive black hole in the Galactic center was observed at 7 mm in the context of a NIR triggered global Very Long Baseline Array (VLBA) campaign. Aims. Sgr A* shows variable flux densities ranging from radio through X-rays. These variations sometimes appear in spontaneous outbursts that are referred to as flares. Multi-frequency observations of Sgr A* provide access to easily observable parameters that can test the currently accepted models that try to explain these intensity outbursts. Methods. On May 16-18, 2012 Sgr A* has been observed with the VLBA at 7 mm (43 GHz) for 6 hours each day during a global multi-wavelength campaign. These observations were triggered by a NIR flare observed at the Very Large Telescope (VLT). Accurate flux densities and source morphologies were acquired. Results. The total 7 mm flux of Sgr A* shows only minor variations during its quiescent states on a daily basis of 0.06 Jy. An observed NIR flare on May 17 was followed 4.5 hours later by an increase in flux density of 0.22 Jy at 43 GHz. This agrees well with the expected time delay of events that are casually connected by adiabatic expansion. Shortly before the peak of the radio flare, Sgr A* developed a secondary radio off-core feature at 1.5 mas toward the southeast. Even though the closure phases are too noisy to place actual constraints on this feature, a component at this scale together with a time delay of 4.5 +- 0.5 hours between the NIR and radio flare provide evidence for an adiabatically expanding jet feature.

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• Sgr A* and General Relativity
• The Milky Way's Supermassive Black Hole: How good a case is it? A Challenge for Astrophysics & Philosophy of Science
• The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA
• Variability Timescale and Spectral Index of Sgr A* in the Near Infrared: Approximate Bayesian Computation Analysis of the Variability of the Closest Supermassive Black Hole
• Unprecedented variability of Sgr A* in NIR
• Detection of intrinsic source structure at ~3 Schwarzschild radii with Millimeter-VLBI observations of SAGITTARIUS A*
• Radio observations of active galactic nuclei with mm-VLBI
• Rapid Variability of Sgr A* across the Electromagnetic Spectrum
• Silhouettes of invisible black holes
• Multiwavelength study of the flaring activity of Sgr A* in 2014 February-April
• Asymmetric structure in Sgr A* at 3mm from closure phase measurements with VLBA, GBT and LMT
• The intrinsic structure of Sagittarius A* at 1.3 cm and 7 mm
• Persistent Non-Gaussian Structure in the Image of Sagittarius A* at 86 GHz
• Simultaneous Monitoring of X-ray and Radio Variability in Sagittarius A*
• Formation of episodic jets and associated flares from black hole accretion systems
• Radiative shock oscillation model for the long-term flares of Sgr A*
• Micro-arcsecond structure of Sagittarius A* revealed by high-sensitivity 86 GHz VLBI observations
• Time delays between radio and X-ray and between narrow radio bands of Sgr A* flares in the shock oscillation model
• Monitoring the Size and Flux Density of Sgr A* during the Active State in 2019 with East Asian VLBI Network
• Visible shapes of black holes M87* and SgrA*