Search

We present Chandra ACIS imaging spectroscopy results for the extended (1.5"-8") hard X-ray emission of the Compton thick (CT) Seyfert NGC 5728. We find spectrally and spatially-resolved features in the Fe K$\alpha$ complex (5.0-7.5 keV), redward and blueward of the neutral 6.4 keV line in the extended bicone. The [red, blue] features have [6.5$\sigma$, 5.3$\sigma$] significance, with an equivalent width = [2.0 keV, 2.5 keV], much higher than in the nuclear spectrum. These energies imply line-of-sight velocities of ~19,000-42,000 km s$^{-1}$ for the red wing, and ~ -28,000 km s$^{-1}$ for the blue wing, if the emission is due to neutral Fe K$\alpha$. These red and blue wings are radially extended ~6"(1.2 kpc), and ~5"(1 kpc), respectively, as confirmed by narrow-band X-ray imaging. Our models discard the possibility that the red wing could arise from a Compton shoulder, and show that the flux in the blue wing is unlikely to arise (at ~3$\sigma$ significance) from a blend of Fe K$\beta$ and highly ionized Fe lines.

Recent deep Chandra observations of nearby Compton thick (CT) AGN have produced surprising results, uncovering extended emission not only in the soft X-rays but in the hard emission (>3 keV), challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe Ka lines are associated with the torus in the standard picture of AGN. In this work, we present the analysis of our deep (~261 ks) X-ray Chandra ACIS-S observations of NGC 5728, a nearby (z=0.00932) CT AGN. We find that the diffuse emission is more extended at lower energies, in the bicone direction out to ~2 kpc radially, but also significantly extended in the direction of the cross-cone, out to ~1.4 kpc. Our results suggest that the ratio of detected photons in the cross-cone to the bicone region is ~16%, below 3 keV, decreasing to 5% for energies 3-6 keV. The nuclear spectrum suggests a low photoionization phase mixed with a more ionized gas component, while the bicone and cross-cone spectra are dominated by a mix of photoionization and shocked gas emission. A mixture of thermal and photoionization models to fit the spectra indicates the presence of complex gas interactions, consistent with previous observations of other CT AGN (e.g., ESO 428-G014).

We present Chandra ACIS imaging spectroscopy results for the extended (1.5"-8") hard X-ray emission of the Compton thick (CT) Seyfert NGC 5728. We find spectrally and spatially-resolved features in the Fe K$α$ complex (5.0-7.5 keV), redward and blueward of the neutral 6.4 keV line in the extended bicone. The [red, blue] features have [6.5$σ$, 5.3$σ$] significance, with an equivalent width = [2.0 keV, 2.5 keV], much higher than in the nuclear spectrum. These energies imply line-of-sight velocities of ~19,000-42,000 km s$^{-1}$ for the red wing, and ~ -28,000 km s$^{-1}$ for the blue wing, if the emission is due to neutral Fe K$α$. These red and blue wings are radially extended ~6"(1.2 kpc), and ~5"(1 kpc), respectively, as confirmed by narrow-band X-ray imaging. Our models discard the possibility that the red wing could arise from a Compton shoulder, and show that the flux in the blue wing is unlikely to arise (at ~3$σ$ significance) from a blend of Fe K$β$ and highly ionized Fe lines.

We write in response to the call from the 2020 Decadal Survey to submit white papers illustrating the most pressing scientific questions in astrophysics for the coming decade. We propose exploration as the central question for the Decadal Committee's discussions.The history of astronomy shows that paradigm changing discoveries are not driven by well formulated scientific questions, based on the knowledge of the time. They were instead the result of the increase in discovery space fostered by new telescopes and instruments. An additional tool for increasing the discovery space is provided by the analysis and mining of the increasingly larger amount of archival data available to astronomers. Revolutionary observing facilities, and the state of the art astronomy archives needed to support these facilities, will open up the universe to new discovery. Here we focus on exploration for compact objects and multi messenger science. This white paper includes science examples of the power of the discovery approach, encompassing all the areas of astrophysics covered by the 2020 Decadal Survey.

We report the results of high-resolution subpixel imaging of the hard continuum and Fe K�� line of the Compton Thick (CT) Active Galactic Nucleus (AGN) ESO 428-G014, observed with Chandra ACIS. While the 3-4 keV emission is dominated by an extended component, a single nuclear point source is prominent in the 4-6 keV range. Instead, two peaks of similar intensity, separated by ~36 pc in projection on the plane of the sky are detected in the Fe K�� emission. The SE knot could be marginally associated with the heavily obscured hard continuum source. We discuss four possible interpretations of the nuclear morphology. (1) Given the bolometric luminosity and likely black hole (BH) mass of ESO 428-G014, we may be imaging two clumps of the CT obscuring torus in the Fe K�� line. (2) The Fe K�� knots may be connected with the fluorescent emission from the dusty bicone, or (3) with the light echo of a nuclear outburst. (4) We also explore the less likely possibility that we may be detecting the rare signature of merging nuclei. Considering the large-scale kpc-size extent of the hard continuum and Fe K�� emission (Papers I and II), we conclude that the AGN in ESO 428-G014 has been active for at least 104 yrs. Comparison with the models of Czerny et al (2009) suggests high accretion rates during this activity., ApJ in press