X-ray Variability in the Nucleus of Cygnus A and the Radio Transient Cygnus A2

In 2015, a radio transient was discovered in Cygnus A with the VLA. This transient, named Cygnus A-2, is 0.42 arcsec removed from the AGN and can therefore not be resolved by most X-ray telescopes. We have looked for an X-ray counterpart to Cygnus A-2, using Chandra ACIS observations from 2015 to 2017. We simulated the source with Marx and compared it with the data, and find no evidence of an extension of the PSF in the direction of the transient. Based on this, we put an upper limit to the 2-10 keV X-ray luminosity of Cygnus A-2 of 2×1043 erg/s. Additionally, we present a spectral analysis of the AGN of Cygnus A using old and new Chandra observations. We compare the 2-10 keV X-ray luminosities with archival XMM-Newton, NuSTAR and Swift XRT data. The resulting light curve shows that the luminosity of Cygnus A was constant between 2000 and 2005, doubled in 2013 while observed by NuSTAR and Swift, and dropped back down in 2015. Previous analysis of the NuSTAR spectra has also indicated the presence of a fast, ionized wind, something not seen by Chandra and XMM-Newton. We discuss the possible connection between Cygnus A-2 and the X-ray light curve. The lack of X-rays from Cygnus A-2 in 2015 disfavors the interpretation of Cygnus A-2 as a steadily accreting black hole. Instead, we suggest that Cygnus A-2 is the radio afterglow of a tidal disruption event (TDE). This would explain the increase and subsequent fading of the X-ray luminosity between 2005 and 2015. A TDE could also have launched the short-lived, fast, ionized outflow seen by NuSTAR. If correct, it would provide further evidence that TDE rates in merging galaxies are much higher than previously thought.