We present new Nuclear Spectroscopic Telescope Array (NuSTAR ) and Chandra observations of NGC 3393, a galaxy reported to host the smallest separation dual active galactic nuclei (AGN) resolved in the X-rays. While past results suggested a 150 pc separation dual AGN, three times deeper Chandra imaging, combined with adaptive optics and radio imaging suggest a single, heavily obscured, radio-bright AGN. Using Very Large Array and Very Long Baseline Array data, we find an AGN with a two-sided jet rather than a dual AGN and that the hard X-ray, UV, optical, near-infrared, and radio emission are all from a single point source with a radius <0.″2. We find that the previously reported dual AGN is most likely a spurious detection resulting from the low number of X-ray counts (<160) at 6-7 keV and Gaussian smoothing of the data on scales much smaller than the point-spread function (PSF) (0.″25 versus 0.″80 FWHM). We show that statistical noise in a single Chandra PSF generates spurious dual peaks of the same separation (0.″55±0.″07 versus 0.″6) and flux ratio (39% ± 9% versus 32% counts) as the purported dual AGN. With NuSTAR, we measure a Compton-thick source (NH 2.2 ± 0.4 × 1024 cm-2) with a large torus half-opening angle, θtor = 79-19+1° which we postulate results from feedback from strong radio jets. This AGN shows a 2-10 keV intrinsic-to-observed flux ratio of ≈150 (L2-10 keV int = 2.6 ± 0.3 × 1043 erg s-1 versus L2-10 keV observed = 1.7 ± 0.2 × 1041 erg s-1). Using simulations, we find that even the deepest Chandra observations would severely underestimate the intrinsic luminosity of NGC 3393 above z > 0.2, but would detect an unobscured AGN of this luminosity out to high redshift (z ≈ 5).
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science