Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A

Abstract

We report the appearance of a new radio source at a projected offset of 460 pc from the nucleus of Cygnus A. The flux density of the source (which we designate Cygnus A-2) rose from an upper limit of <0.5 mJy in 1989 to 4 mJy in 2016 (nu=8.5 GHz), but is currently not varying by more than a few percent per year. The radio luminosity of the source is comparable to the most luminous known supernovae, it is compact in VLBA observations down to a scale of 4 pc, and it is coincident with a near-infrared point source seen in pre-existing adaptive optics and HST observations. The most likely interpretation of this source is that it represents a secondary supermassive black hole in a close orbit around the Cygnus A primary, although an exotic supernova model cannot be ruled out. The gravitational influence of a secondary SMBH at this location may have played an important role in triggering the rapid accretion that has powered the Cygnus A radio jet over the past 10^7 years.

10 pages, 4 figures, accepted to ApJ. Includes some minor corrections, added references, and higher-resolution Figure 1

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Cited by in corpus (9)

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• Imaging the AGN Torus in Cygnus
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• Chandra Observations of Abell 2261 Brightest Cluster Galaxy, a Candidate Host to a Recoiling Black Hole
• A 4~Kpc Molecular Gas Lane in Cygnus A
• Evidence for a TDE origin of the radio transient Cygnus A-2
• Archival VLBA observations of the Cygnus A Nuclear Radio Transient (Cyg A-2) Strengthen the Tidal Disruption Event Interpretation
• Late-Time X-ray Observations of the Transient Source Cygnus A-2