Time-resolved XRISM spectroscopy reveals the evolution and structure of the corona in MCG-6-30-15

TL;DR

This study uses time-resolved XRISM, NuSTAR, and XMM-Newton spectra to analyze the corona's evolution and structure in the AGN MCG-6-30-15, revealing dynamic changes during variability events.

Contribution

First detailed time-resolved spectral analysis of MCG-6-30-15 combining multiple observatories to study coronal evolution during variability.

Findings

Coronal emission is from a rapidly spinning black hole with a > 0.93.

Corona is mostly within 10rg but expands to 15rg during flares.

Coronal size and motion changes explain spectral variability and black hole spin measurements.

Abstract

We present a time-resolved analysis of high-resolution spectra of the AGN MCG-6-30-15 obtained by XRISM alongside broadband spectra from NuSTAR and XMM-Newton during a coordinated observing campaign in February 2024. These observations provide some of the most detailed measurements of X-ray reflection from the innermost regions of the accretion disc around a supermassive black hole, and its evolution during periods of significant variability. We find that both the X-ray spectrum and its variability can be described by a self-consistent model of the reflection of the coronal X-ray emission from the accretion disc around a rapidly-spinning (a > 0.93) black hole, in which the observed variability arises from underlying changes in the luminosity, spatial extent and motion of the corona. While the corona is compact, residing within 10rg of the black hole for the majority of the observations, finite spatial extent is required to fully explain the shape of the reflection spectrum. A flare was observed in the X-ray emission during which the corona expanded to around 15rg and was accelerated away from the black hole reaching a velocity of 0.27c. Around the flare were short dips in the observed flux, during which the corona was found to have collapsed to a confined region, within 2.5rg of the black hole, enhancing the relativistic effects observed from the inner accretion disc. We find it is necessary to account for such significant spectral variation in order to obtain accurate measurements of the spin of the black hole via X-ray reflection spectroscopy.