Conveners
Repeating transients in galactic nuclei: confronting observations with theory: Tuesday block 1
- Petra Suková (Astronomical Institute of the CAS)
- Francesco Tombesi (Tor Vergata University of Rome)
Repeating transients in galactic nuclei: confronting observations with theory: Tuesday block 2
- Francesco Tombesi (Tor Vergata University of Rome)
- Petra Suková (Astronomical Institute of the CAS)
Description
In the last few years, a mysterious new class of astrophysical objects have been uncovered. These are spatially coincident with centers of external galaxies and show X-ray variations that repeat on timescales of minutes to a month. They manifest in three different ways in the data: stable quasi-periodic oscillation (QPOs), quasi-periodic eruptions (QPEs) and quasi-periodic outflows (QPOuts). QPOs are systems that show smooth recurrent X-ray brightness variations while QPEs are sudden changes that appear like eruptions. QPOuts represent systems that exhibit repeating outflows moving at mildly-relativistic velocities of (0.1-0.3)c, here c is the speed of light. Their underlying physical mechanism is a topic of heated debate, with most models proposing that they originate either from instabilities within the inner accretion flow or from orbiting objects. There is a huge excitement especially from the latter class of models as it has been argued that some repeating systems could host extreme mass ratio inspirals potentially detectable with upcoming space-based gravitational wave interferometers. Consequently, paving the path for an era of “persistent” multi-messenger astronomy.
The deployment of large sky surveys are enabling the characterization of the transient night sky in unprecedented detail. Among other things, such surveys are revealing novel modes of variability around supermassive black holes which are incompatible with the behaviour of active galactic nuclei.
This includes quasi-periodic X-ray eruptions, or QPEs, which repeat on timescales of hours-days...
Tidal disruption events (TDEs) are one of the most dramatic nuclear transients in which a star is destroyed by the intense tidal force of supermassive black holes in a few hours, generating a flare luminous enough to outshine the entire host galaxy. Since its first detection in the 1990s, the number of detected events have been steadily growing thanks to ongoing surveys and telescopes, such as...
Quasi-periodic eruptions (QPEs) are an emerging class of high amplitude bursts of X-ray radiation, repeating on a hours-day timescale, recently discovered near the central supermassive black holes (SMBHs) of a few low-mass galaxies. I will briefly review our current theoretical understanding of QPEs, and will focus on a scenario involving a main-sequence star repeatedly colliding with an...
Quasi Periodic Eruptions (QPEs) are a puzzling X-ray phenomena
recently discovered in a number of sources with similar properties.
In this talk, I am going to present a theoretical model that is able
to reproduce their phenomenology in at least 4 sources. The QPEs
arise from impacts between an Extreme Mass Ratio Inspiral (EMRI)
object and a rigidly precessing TDE-like accretion...
This preliminary study aims to explore the contrasting X-ray signatures of accretion and ejection processes in supermassive black holes, focusing on both persistent active galactic nuclei (AGN) and transient sources, such as tidal disruption events (TDEs), quasi-periodic eruptions (QPEs), and quasi-periodic outflows (QPOuts). We will examine the continuum emission characteristics, comparing...
Recently, a previously quiescent nearby galactic nucleus, ASASSN-20qc, went to an outburst during which it has shown quasioperiodic ultra-fast outflows (qUFOs) with changing column density every cca 8 days. Different physical mechanisms have been proposed to explain such behaviour, with the most promising scenario being the smaller, probably intermediate-mass black hole, orbiting the primary...
The recently reported transient event ASASSN-20qc (Pasham et al., 2024), which was revealed first by the optical outburst and then the delayed soft X-ray emission, was shown to exhibit a quasiperiodic ultrafast outflow. I will show using analytical as well as numerical calculations (see also the contribution by Petra Sukova) that such a behaviour is consistent with the intermediate-mass black...
Detecting and interpreting electromagnetic counterparts to binary black hole mergers will require a detailed understanding of the complex plasma dynamics governing the surrounding accretion flow, particularly for binaries including at least one supermassive black hole. Quasi-periodicities observed in active galactic nuclei (AGN) may already provide a clue as to how a secondary black hole in...
