Evidence of a Massive Stellar Disruption in the X-ray Spectrum of ASASSN-14li

TL;DR

This study analyzes high-resolution X-ray spectra of the tidal disruption event ASASSN-14li, revealing evidence of a massive stellar disruption through absorption lines and abundance patterns, suggesting a disrupted star with CNO processing.

Contribution

The paper provides the first detailed high-resolution X-ray spectral analysis of ASASSN-14li, identifying specific abundance patterns indicative of a massive star disruption, which was not previously established.

Findings

Detection of narrow, blue-shifted absorption lines in X-ray spectra.

Abundance pattern consistent with a star having undergone CNO processing.

Evidence supporting a massive star disruption over typical AGN activity.

Abstract

The proximity and duration of the tidal disruption event (TDE) ASASSN-14li led to the discovery of narrow, blue-shifted absorption lines in X-rays and UV. The gas seen in X-ray absorption is consistent with bound material close to the apocenter of elliptical orbital paths, or with a disk wind similar to those seen in Seyfert-1 active galactic nuclei. We present a new analysis of the deepest high-resolution XMM-Newton and Chandra spectra of ASASSN-14li. Driven by the relative strengths of He-like and H-like charge states, the data require [N/C] > 2.4, in qualitative agreement with UV spectral results. Flows of the kind seen in the X-ray spectrum of ASASSN-14li were not clearly predicted in simulations of TDEs; this left open the possibility that the observed absorption might be tied to gas released in prior AGN activity. However, the abundance pattern revealed in this analysis points to a single star rather than a standard AGN accretion flow comprised of myriad gas contributions. The simplest explanation of the data is likely that a moderately massive star (M ~ 3 Msun) with significant CNO processing was disrupted. An alternative explanation is that a lower mass star was disrupted that had previously been stripped of its envelope. We discuss the strengths and limitations of our analysis and these interpretations.