Relativistic outflows power a quasi-periodic eruption: constraints on energetics, mass loss, and emission mechanisms

Quasi-periodic eruptions (QPEs) are recurring X-ray bursts from supermassive black holes and represent an extreme form of structured, high-amplitude SMBH variability, but the physical origin of their regularity, timescales, energetics, and emission remains uncertain.

The authors present new XMM-Newton observations of the QPEs in ZTF19acnskyy, also known as Ansky, which are the deepest observations of individual bursts in any QPE source so far. The X-ray spectra show time-evolving P Cygni profiles made of blueshifted absorption and redshifted emission from L-shell transitions of Fe XIX-XXIV, with column densities N_H ~ 10^22-23 cm^-2 and bulk velocities |v_w/c| ~ 0.2, indicating relativistic mass ejections during each eruption.

They build a time-dependent analytical model of a wind turning on to self-consistently compute its evolving luminosity and ionization properties. The model finds that both the light curve and the spectral lines can be produced simultaneously by a wide-angle outflow with mass-loss rate Mdot ~ 10^-9 to 10^-8 solar masses per second, kinetically powering the X-rays with an efficiency L_X/E_K ~ 0.1.

For a covering fraction f_Omega ~ 0.5, each eruption ejects about 10^-3 solar masses and at least 10^49 erg of kinetic energy. This sets an upper bound on the QPE lifetime of less than about 1000 bursts if the underlying mass reservoir is about 1 solar mass, and implies the bursts may yield detectable multiwavelength signatures of reverberation and feedback. The measurements provide new quantitative constraints on QPE energetics, emission mechanisms, and the mass and energy recycled into their circumnuclear environments, and offer an observational probe for direct comparison with physical models and hydrodynamical simulations of QPEs.