A deep X-ray view of the bare AGN Ark 120. II. Evidence for Fe K emission transients

Abstract

We report on the results from a large observational campaign on the bare Seyfert galaxy Ark 120, jointly carried out in 2014 with XMM-Newton, Chandra, and NuSTAR. The fortunate line of sight to this source, devoid of any significant absorbing material, provides an incomparably clean view to the nuclear regions of an active galaxy. Here we focus on the analysis of the iron fluorescence features, which form a composite emission pattern in the 6$-$7 keV band. The prominent K$\alpha$ line from neutral iron at 6.4 keV is resolved in the Chandra High-Energy Transmission Grating spectrum to a full-width at half maximum of 4700${}_{-1500}^{+2700}$ km s${}^{-1}$, consistent with an origin from the optical broad-line region. Excess components are detected on both sides of the narrow K$\alpha$ line: the red one (6.0$-$6.3 keV) clearly varies in strength in about one year, and hints at the presence of a broad, mildly asymmetric line from the accretion disk; the blue one (6.5$-$7.0 keV), instead, is likely a blend of different contributions, and appears to be constant when integrated over long enough exposures. However, the Fe K excess emission map computed over the 7.5 days of the XMM-Newton monitoring shows that both the red and the blue features are actually highly variable on timescales of $\sim$10$-$15 hours, suggesting that they might arise from short-lived hotspots on the disk surface, located within a few tens of gravitational radii from the central supermassive black hole and possibly illuminated by magnetic reconnection events. Any alternative explanation would still require a highly dynamic, inhomogeneous disk/coronal system, involving clumpiness and/or instability.

25 pages, 10+2 figures, 5 tables. Accepted for publication in The Astrophysical Journal

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Cited by in corpus (15)

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• The Nature of Soft Excess in ESO 362-G18 Revealed by XMM-Newton and NuSTAR Spectroscopy
• The first broadband X-ray view of the narrow line Seyfert 1 Ton S180
• A deep X-ray view of the bare AGN Ark 120. III. X-ray timing analysis and multiwavelength variability
• The lively accretion disk in NGC 2992. I. Transient iron K emission lines in the high flux state
• Long term X-Ray Observations of Seyfert 1 Galaxy Ark 120: On the origin of soft-excess
• Correlation between relativistic reflection fraction and photon index in NuSTAR sample of Seyfert 1 AGN
• Direct observation of the Broad Line Region in X-rays during the low state of NGC4051
• Origins of the UV/X-ray Relation in Arakelian 120
• Short time-scale X-ray spectral variability in the Seyfert 1 galaxy NGC 3783
• The Low Temperature Corona in ESO 511$-$G030 Revealed by NuSTAR and XMM-Newton
• Hard X-Ray broadband spectroscopy of Mrk 876: characterizing its spectrum
• Poynting-Robertson effect on black-hole-driven winds