Revisit the Circumnuclear X-ray Emission of NGC 2992 in a Historically Low State

TL;DR

This study uses Chandra X-ray observations of NGC 2992 during a low flux state to analyze circumnuclear soft X-ray emission, revealing outflows, a peculiar emission line, and extended Fe Kα emission, enhancing understanding of AGN-host interactions.

Contribution

It provides new high-resolution X-ray imaging spectroscopic data of NGC 2992 in a low flux state, clarifying the origin of soft excess and detecting a novel emission line.

Findings

Extended soft X-ray emission associated with outflows.

Detection of a narrow emission line at ~4.97 keV, possibly from highly ionized iron or spallation.

Asymmetric Fe Kα emission indicating reflection from cold gas.

Abstract

The inner-most region of the Seyfert galaxy NGC 2992 has long been suspected to be the location of intense AGN-host galaxy interaction, but photon pile-up in previous high-resolution observations hampered the study of soft X-ray excess and the interaction near its nucleus. We present an X-ray imaging spectroscopic analysis of the circumnuclear ($1^{\prime\prime}$--$3^{\prime\prime}$) region of NGC 2992 using the zeroth-order image of a 135 ks grating observation obtained with Chandra, which captured the nucleus in a historically low flux state. Extended soft X-ray emission is detected in the circumnuclear region with observed luminosity $L_{\rm X} \sim 7 \times 10^{39}\rm\ erg\ s^{-1}$. The majority of previously puzzling detection of soft excess could be associated with the outflow, indicated by the morphological correspondences between soft X-ray emission and figure-eight-shaped radio bubbles. An anomalous narrow emission line with the centroid energy $\sim4.97$ keV is found. If attributed to redshifted highly ionized iron emission (e.g., Fe xxv), the required outflow velocity is $\sim0.23\,c$. An alternative explanation is that this line emission could be produced by the nuclear spallation of iron. We also find asymmetric extended Fe K$\alpha$ emission along the galactic disk, which could originate from reflection by cold gas on $\sim 200$ pc scale.