Transient Relativistic Iron Emission Line from an X-ray Flaring Supermassive Black Hole

TL;DR

This paper reports the first observation of a transient relativistic iron Kα emission line in an active galactic nucleus, triggered by an X-ray flare, providing new insights into SMBH and accretion disk physics.

Contribution

It presents the first detection of a transient relativistic iron line in an AGN, linking it to a coronal flare and offering a novel method to probe SMBH and disk properties.

Findings

Detected a broad iron Kα line 21.5 days after an X-ray flare.

Line width corresponds to a Keplerian velocity of 14,000 km/s.

Supports a model of reflection from a rapidly spinning black hole's accretion disk.

Abstract

We report the discovery of the first transient relativistic iron K{\alpha} line in an Active Galactic Nucleus (AGN) J1047+5907. The line was detected 21.5 days (rest-frame) after an X-ray coronal flare observed in 2008 and it exhibits significant broadening consistent with relativistic reflection from the accretion disk in the vicinity of the central supermassive black hole (SMBH). The line has a width of ~300 eV, corresponding to a Keplerian velocity of 14,000 km s-1, at a distance of 5-41 light-days from the SMBH, strongly implying that the observed coronal flare triggered the emergence of the line. This event provides rare direct evidence of the response of the accretion disk to impulsive coronal illumination and offers a new method to probe the SMBH and disk physics. The relativistic modeling favors a broadened line produced by distant reflection from an accretion disk around a rapidly spinning black hole viewed at an intermediate inclination, consistent with other observations. Systematic monitoring of type 1 AGN following strong X-ray flares may open a new observational window into the innermost regions of AGN, enabling constraints on the physics of SMBH and its accretion disk at different radii that are otherwise challenging to access.