QPEs from EMRI Debris Streams Impacting Accretion Disks in Galactic Nuclei

Abstract

Quasi-periodic eruption (QPE) sources in galactic nuclei are often associated with a stellar object orbiting a supermassive black hole with hours-days period, brought in as an extreme mass-ratio inspiral (EMRI). In the presence of an accretion disk, repeated star-disk collisions lead to ablation of a small fraction of the stellar mass during each disk passage. We analytically follow the evolution of the stellar debris as it is tidally stretched outside the EMRI's Hill sphere, forming an elongated, dilute stream, that subsequently collides with the disk, half an orbit after the previous star-disk encounter. At sufficiently long orbital periods ($\gtrsim 12$ hr), the stream is too dilute to penetrate the disk, and is instead strongly shocked and deflected at its surface through a reverse shock. We obtain the resulting emission and explore implications for QPE observations. Due to their low optical depth and prolonged interaction time, radiation from the shocked streams typically dominates over that from shocked disk gas directly impacted by the star or by ejecta confined within its Hill sphere, as was first proposed by Yao et al. 2025. We find that: (1) QPE flare durations reflect the stream-disk collision timescale; (2) Flare luminosities of $10^{42-43}$ erg/s, consistent with observed QPEs, are robustly produced; (3) Soft X-ray flares with temperatures of $\sim$100 eV arise when the stream mass is sufficient to sustain a radiation mediated shock at the collision interface. Higher mass streams yield softer flares, typically outshone by the disk, while lower mass streams result in collisionless shocks, which likely produce fainter and harder flares. We discuss observational implications of the temporal evolution of the underlying disk, assuming it is the remnant of a prior tidal disruption event in the same galaxy.

27 pages, 8 figures. Updated to match published version

References in corpus (26)

• X-ray Quasi-Periodic Eruptions from two previously quiescent galaxies
• ASASSN-14ko is a Periodic Nuclear Transient in ESO 253-G003
• Quasi-periodic eruptions from impacts between the secondary and a rigidly precessing accretion disc in an extreme mass-ratio inspiral system
• GSN 069 -- A Tidal Disruption Near-Miss
• X-ray Quasi-periodic Eruptions driven by Star-Disc Collisions : Application to GSN069 and Probing the Spin of Massive Black Holes
• Interacting Stellar EMRIs as Sources of Quasi-Periodic Eruptions in Galactic Nuclei
• Repeating tidal disruptions in GSN 069: Long-term evolution and constraints on quasi-periodic eruptions' models
• Stellar transits across a magnetized accretion torus as a mechanism for plasmoid ejection
• Quasi-periodic eruptions from mildly eccentric unstable mass transfer in galactic nuclei
• Fundamental scaling relationships revealed in the optical light curves of tidal disruption events
• Host galaxy properties of quasi-periodically erupting X-ray sources
• Tormund's return: Hints of quasi-periodic eruption features from a recent optical tidal disruption event
• Quasi-Periodic Erupters: A Stellar Mass-Transfer Model for the Radiation
• Unstable Mass Transfer from a Main-Sequence Star to a Supermassive Black Hole and Quasi-Periodic Eruptions
• The complex time and energy evolution of quasi-periodic eruptions in eRO-QPE1
• X-ray eruptions every 22 days from the nucleus of a nearby galaxy
• Alive and kicking: A new QPE phase in GSN 069 revealing a quiescent luminosity threshold for QPEs
• Monthly quasi-periodic eruptions from repeated stellar disruption by a massive black hole
• Probing orbits of stellar mass objects deep in galactic nuclei with quasi-periodic eruptions
• Optical to X-ray Signatures of Dense Circumstellar Interaction in Core-Collapse Supernovae
• Period Evolution of Repeating Transients in Galactic Nuclei
• Ticking away: the long-term X-ray timing and spectral evolution of eRO-QPE2
• High-energy emission from tidal disruption events in active galactic nuclei
• SRG/eROSITA No. 5: Discovery of quasi-periodic eruptions every ~3.7 days from a galaxy at z>0.1
• Time-resolved Hubble Space Telescope UV observations of an X-ray quasi-periodic eruption source
• Review: Accretion Disk Evolution in Tidal Disruption Events

Cited by in corpus (7)

• Testing the Shock-cooling Emission Model from Star-Disk Collisions for Quasiperiodic Eruptions
• NICER observations reveal doubled timescales in Ansky's quasi-periodic eruptions (QPEs)
• Hubble constant measurement from QPEs as electromagnetic counterparts to extreme mass ratio inspirals
• Eccentric Disks from Gaseous Rings around Equal-Mass, Circular Binaries
• Polarization echoes from past nuclear activity in the quasi-periodic eruption source GSN 069
• A supermassive black hole under the radar: Repeating X-ray variability in a Seyfert galaxy
• Evolution of Quasi-Periodic Eruptions in the post-TDE Accretion Disk Perturbed by an Orbiting Star