Detection of a Highly Ionized Outflow in the Quasi-periodically Erupting Source GSN 069

TL;DR

This study reveals a highly ionized, fast outflow in the QPE source GSN 069 through high-resolution X-ray spectroscopy, providing new insights into the nature of quasi-periodic eruptions and their connection to transient black hole activity.

Contribution

First high-resolution spectral analysis of a QPE source identifying a blueshifted outflow with detailed ionization and velocity properties, linking it to recent transient activity.

Findings

Detected a blueshifted outflow with velocity 1700-2900 km/s.

Identified emission and absorption lines consistent with a highly ionized outflow.

Connected the outflow to the recent activity of GSN 069 since 2010.

Abstract

Quasi-periodic eruptions (QPEs) are high-amplitude, soft X-ray bursts recurring every few hours, associated with supermassive black holes. Many interpretations for QPEs were proposed since their recent discovery in 2019, including extreme mass ratio inspirals and accretion disk instabilities. But, as of today, their nature still remains debated. We perform the first high-resolution X-ray spectral study of a QPE source using the RGS gratings onboard XMM-Newton, leveraging nearly 2 Ms of exposure on GSN 069, the first discovered source of this class. We resolve several absorption and emission lines including a strong line pair near the N VII rest-frame energy, resembling the P-Cygni profile. We apply photoionization spectral models and identify the absorption lines as an outflow blueshifted by $1700-2900$ km/s, with a column density of about $10^{22}$ cm$^{-2}$ and an ionization parameter $\log (\xi$/erg cm s$^{-1})$ of $3.9-4.6$. The emission lines are instead redshifted by up to 2900 km/s, and likely originate from the same outflow that imprints the absorption features, and covers the full $4\pi$ sky from the point of view of GSN 069. The column density and ionization are comparable to the outflows detected in some tidal disruption events, but this outflow is significantly faster and has a strong emission component. The outflow is more highly ionized when the system is in the phase during which QPEs are present, and from the limits we derive on its location, we conclude that the outflow is connected to the recent complex, transient activity of GSN 069 which began around 2010.