Late-Time X-ray Observations of the Transient Source Cygnus A-2

TL;DR

This study uses Chandra X-ray observations to investigate the transient source Cygnus A-2, setting flux limits and comparing data over several years to understand its nature and black hole activity.

Contribution

First detailed X-ray analysis of Cygnus A-2 with high-resolution imaging, providing flux limits and confirming the stability of the AGN morphology over time.

Findings

No X-ray detection of Cygnus A-2 within flux limits.

Black hole mass consistent with a flaring source.

Archival data confirms morphological stability.

Abstract

We examine Chandra observations of the powerful Fanaroff-Riley class II (FR II) radio galaxy Cygnus A for an X-ray counterpart to the radio transient Cygnus A-2 that was first detected in 2011. Observations are performed using the High-Resolution Camera (HRC) instrument in order to spatially resolve Cygnus A-2 and the central Active Galactic Nucleus (AGN) at a separation of 0.42 arcseconds. Simulated images are generated of the emission region, and radial profiles for the region of interest are extracted. A comparison between the simulations and observations reveals no X-ray detection of Cygnus A-2 to a 0.5-7.0 keV flux upper limit of $1.04 \times 10^{-12}\rm\,erg\,cm^{-2}\,s^{-1}$, or a rest-frame 2-10 keV luminosity of $8.6\times 10^{42}\rm\,erg\,s^{-1}$. We estimate the black hole mass of Cygnus A-2 based on our X-ray flux limit and find it to be consistent with a flaring black hole rather than a steadily accreting source. The HRC observations are additionally compared with archival ACIS data from 2016-2017, and both the overall morphology and the flux limits of the AGN complex agree between the two datasets. This consistency is despite the pile-up effect in ACIS which was previously considered to bias the observed morphology of the AGN. The agreement between the datasets demonstrates the viability of utilizing the archival Chandra data of Cygnus A to analyze its AGN at an unprecedented level of precision.