Evidence of a tidal disruption event in GSN 069 from the abnormal carbon and nitrogen abundance ratio

TL;DR

This paper presents evidence of a tidal disruption event in GSN 069, indicated by abnormal carbon and nitrogen abundances in its UV spectrum, suggesting a disrupted red giant star as the cause.

Contribution

It provides the first detailed UV spectral analysis of GSN 069 revealing abnormal C/N ratios and links this to a tidal disruption event involving a red giant star.

Findings

Detection of strong nitrogen lines and weak carbon lines in UV spectrum.

C/N abundance ratio constrained between -3.33 and -1.91.

Proposes a disrupted red giant star explains the observed abundance anomalies.

Abstract

GSN 069 is an ultra-soft X-ray active galactic nucleus that previously exhibited a huge X-ray outburst and a subsequent long-term decay. It has recently presented X-ray quasi-periodic eruptions (QPEs). We report the detection of strong nitrogen lines but weak or undetectable carbon lines in its far ultraviolet spectrum. With a detailed photoionization model, we use the C IV/N IV] ratio and other ratios between nitrogen lines to constrain the [C/N] abundance of GSN 069 to be from -3.33 to -1.91. We argue that a partially disrupted red giant star can naturally explain the abnormal C/N abundance in the UV spectrum, while the surviving core orbiting the black hole might produce the QPEs.