arXiv subjects

Giovanni Miniutti

Publications and source records attributed to Giovanni Miniutti.

At least 19 recordsLinked to original sources

arXiv2026

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

Quasi-periodic eruptions (QPEs) are recurring bursts of X-ray radiation originating from supermassive black holes (SMBHs). They are an unprecedented type of structured, high-amplitude SMBH variability, but the physical origins of their regularity, timescales, energetics, and emission are uncertain. We present new XMM-Newton observations of the QPEs in ZTF19acnskyy/``Ansky'', constituting the deepest observations of individual bursts in any source thus far. The X-ray spectra reveal time-evolving P Cygni profiles comprising blueshifted absorption and redshifted emission from L-shell transitions of Fe XIX-XXIV, with column densities $N_H\sim 10^{22-23}$ cm$^{-2}$ and bulk velocities of $|v_w/c|\sim 0.2$, indicating relativistic mass ejections during each eruption. We construct a time-dependent analytical model of a wind turning on to self-consistently compute its evolving luminosity and ionization properties, and find that the light curve and spectral lines can be simultaneously produced by a wide-angle outflow with $\dot{M}\sim 10^{-9}-10^{-8}\,M_\odot$ s$^{-1}$ kinetically powering the X-rays with an efficiency of $L_X/\dot{E}_K\sim 0.1$. Each eruption ejects $\sim 10^{-3}\,M_\odot$ and $\gtrsim 10^{49}$ erg of kinetic energy, setting an upper bound on the QPE lifetime of $\lesssim30$ years if the underlying mass reservoir is $\sim1 M_\odot$, and implying that the bursts may result in detectable multiwavelength signatures of reverberation and feedback. These measurements provide new quantitative constraints on QPE energetics, emission mechanisms, and the mass/energy they recycle into their circumnuclear environments, as well as an observational probe for direct comparison with physical models and hydrodynamical simulations of QPEs.

astro-ph.HE↗

arXiv2026

X-ray eclipse tomography: Resolving the extent of X-ray-emitting region(s) in the Seyfert galaxy ESO362-G18

X-ray spectral variability in active galactic nuclei (AGNs) can be either intrinsic or caused by external processes, such as variable absorption. Several transient occultation events from individual clouds or X-ray eclipses have been identified in a number of AGNs in the past two decades. We report results from the analysis of two Swift monitoring campaigns of the Seyfert galaxy ESO 362-G18, a changing-look AGN that showed transitions between optical spectral types 1.5 and 1.9 in the past, most likely induced by variable absorption. We identified two X-ray eclipses during the first Swift campaign, one of which we were able to follow almost entirely from ingress to egress. We used time-resolved spectroscopy to follow the evolution of the X-ray spectrum with time in order to derive the properties of the absorbing cloud and the size of the main X-ray-emitting region. The cloud is located towards the innermost dust sublimation zone, intermediate between the dust-free broad-line region and the dusty torus. The X-ray-emitting region is confined within 35 gravitational radii (Rg) from the centre. A deeper analysis indicated that the eclipsing cloud likely comprises a denser core and a more tenuous atmosphere. We were also able to estimate the size of the soft excess and hot corona X-ray-emitting regions separately. These are two of the most relevant continuum components in the X-ray spectra of unobscured AGNs. Our analysis suggests that the soft-excess-emitting region is 50% more extended than the hot corona one. However, it appears to co-exist with and is not replaced by the hot corona one in the innermost 30 Rg. Our results highlight the potential of X-ray eclipse tomography for providing a clearer view of the innermost accretion flow geometry and of the AGN surroundings out to the torus scale.

astro-ph.HE↗

arXiv2026

QPEs from Warped Disk Collisions with EMRIs: Brightness-Recurrence Diagram and Gravitational-Wave Follow-up

Quasi-Periodic Eruptions (QPEs) display correlated long/short and strong/weak patterns that remain unexplained by existing flat-disk collision models. We propose that these features arise from an extreme-mass-ratio inspiral (EMRI) colliding with a warped accretion disk, likely formed after a tidal disruption event. The warp modulates both recurrence time and burst energy, encoding the disk geometry -- and thus the spin of the central supermassive black hole (SMBH) -- into the X-ray light curve. We introduce the Brightness-Recurrence Diagram (BRD) to visualize this correlation, where QPE bursts trace an elliptical trajectory driven by the EMRI's apsidal precession; the tilt of this ellipse encodes whether the EMRI is prograde or retrograde relative to the SMBH spin. Applying this model to the prototypical QPE source GSN 069 successfully reproduces the observed patterns. The data are consistent with either a prograde stellar secondary or a retrograde stellar-mass black hole. In the stellar-mass black hole scenario, ongoing orbital decay could render the EMRI detectable by LISA within a few decades, facilitating gravitational-wave follow-up and independent multimessenger constraints on the system.

astro-ph.HE↗

arXiv2026

Persistence of the Millihertz X-ray Quasi-Periodic Oscillation in the Active Galactic Nucleus 1ES 1927+654

1ES 1927+654 is an extreme active galactic nucleus (AGN) that has defied our canonical expectations for how AGN appear across the electromagnetic spectrum and how they vary on short timescales. In 2022, this source began showing a X-ray quasi-periodic oscillation (QPO) at mHz frequencies, along with a newly launched radio jet. Unlike the handful of other known AGN QPOs, the QPO in 1ES 1927+654 showed a significant frequency evolution, spanning from 0.9-2.4 mHz from 2022-2024. In this work, we present the last 1.5 years of monitoring with XMM-Newton (250 ks) up to January 2026, which reveals that the QPO persists but has plateaued at a constant frequency of approximately 2.5 mHz. We perform detailed spectral-timing analyses on this exquisite dataset, consisting of over 900 QPO cycles, more than any AGN QPO to date. Our main findings are: (1) the stacked XMM-Newton power spectra shows no significant second harmonic, (2) a soft (reverberation-like) lag is observed at all frequencies and remains remarkably stable even as the QPO frequency evolved from 2022-2024, and (3) extreme X-ray jumps on the QPO period (up to ~80% baseline flux) persist to present day with a remarkably stable dip-rise-fall pattern. Finally, we also detect the first AGN QPO in NuSTAR observations, which is present from 2023 to 2026 at frequencies consistent with the XMM-Newton detections. While we explore models for eclipses and coupled disk-corona behavior to simultaneously explain the lags, dips, and QPO, these new observations strain such models.

astro-ph.HE↗

arXiv2026

A positive period derivative in the quasi-periodic eruptions of ZTF19acnskyy

We report the first direct measurement of the period derivative in a quasi-periodic eruption (QPE), finding a smoothly increasing period with $\dot{P}\approx (1.7\pm 0.02)\times10^{-2}$ d d$^{-1}$ in the source ZTF19acnskyy/"Ansky". Most models for QPEs invoke repeated interactions of a stellar-mass orbiting companion around the supermassive black hole (SMBH) in an extreme mass-ratio inspiral (EMRI). In these scenarios, a positive $\dot{P}$ is surprising, but not impossible to produce. We explore several possible explanations for the observed $\dot{P}$, including stable mass-transfer driven by impulsive mass loss events in an EMRI, velocity kicks at pericenter due to tidal interactions with the SMBH, apparent period changes due either to general relativistic precession effects in an EMRI or light travel-time delays in a hierarchical SMBH binary, and mass-transfer variations in a thermal/viscous disk instability model. We find that none of the considered models provides a complete explanation for the data, motivating further work on physical explanations for positive period derivatives in QPEs.

astro-ph.HE↗

arXiv2026

Discovery of crested quasi-periodic eruptions following the most luminous SRG/eROSITA tidal disruption event

We report the discovery of complex flaring activity from the galactic nucleus hosting the five-year-old tidal disruption event eRASSt J234402.9-352640 (J2344). With Einstein Probe and XMM-Newton observations, we detected highly structured soft X-ray variability. Through temporal decomposition of the XMM-Newton light curve and time-resolved spectral analysis, we identified broad, thermal flares recurring every $\sim$12 hours and lasting $\sim$2 hours, consistent with quasi-periodic eruptions (QPEs). Remarkably, these QPEs are accompanied by an unprecedented crest of hotter, shorter flares, each lasting between 5 and 30 minutes. These flares are predominantly found in the rising phases of the QPEs, although they also appear throughout the quiescence. These findings establish J2344 as a new member of the QPE emitter population and uncover a previously unobserved phenomenology that challenges current models of QPEs. In this letter, we present the phenomenological properties of this unique source and discuss possible interpretations within the framework of extreme-mass-ratio inspirals.

astro-ph.HE↗

arXiv2025

A supermassive black hole under the radar: Repeating X-ray variability in a Seyfert galaxy

In the last few years, a few supermassive black holes (SMBHs) have shown short-term (of the order of hours) X-ray variability. Given the limited size of the sample, every new addition to this class of SMBHs can bring invaluable information. Within the context of an automated search for X-ray sources showing flux variability in the \textit{Chandra} archive, we identified peculiar variability patterns in 2MASX J12571076+2724177 (J1257), a SMBH in the Coma cluster, during observations performed in 2020. We investigated the long-term evolution of the flux, together with the evolution of the spectral parameters throughout the \textit{Chandra} and \textit{XMM-Newton} observations, which cover a time span of approximately 20 years. We found that J1257 has repeatedly shown peculiar variability over the last 20 years, on typical timescales of $\simeq20-30$ ks. From our spectral analysis, we found hints of a softer-when-brighter behaviour and of two well-separated flux states. We suggest that J1257 might represent a new addition to the ever-growing size of relatively low mass SMBHs ($M\simeq10^6-10^7\mathrm{M}_\odot$) showing extreme, possibly quasi-periodic X-ray variability on short time scales. The available dataset does not allow for a definitive classification of the nature of the variability. However, given the observed properties, it could either represent a quasi-periodic oscillation at particularly low frequency or be associated with quasi-periodic eruptions in an AGN with peculiar spectral properties.

astro-ph.HE↗

arXiv2025

Prospects for EMRI/MBH parameter estimation using Quasi-Periodic Eruption timings: short-timescale analysis

Quasi-Periodic Eruptions (QPEs) are luminous, recurring X-ray outbursts from galactic nuclei, with timescales of hours to days. While their origin remains uncertain, leading models invoke accretion disk instabilities or the interaction of a massive black hole (MBH) with a lower-mass secondary in an extreme mass ratio inspiral (EMRI). EMRI scenarios offer a robust framework for interpreting QPEs by characterizing observational signatures associated with the secondary's orbital dynamics. This, in turn, enables extraction of the MBH/EMRI physical properties and provides a means to test the EMRI scenario, distinguishing models and addressing the question: what can QPE timings teach us about massive black holes and EMRIs? In this study, we employ analytic expressions for Kerr geodesics to efficiently resolve the trajectory of the secondary object and perform GPU-accelerated Bayesian inference to assess the information content of QPE timings. Using our inference framework, referred to as QPE-FIT (Fast Inference with Timing), we explore QPE timing constraints on astrophysical parameters, such as EMRI orbital parameters and MBH mass/spin. We find that mild-eccentricity EMRIs ($e\sim0.1-0.3$) can constrain MBH mass and EMRI semimajor axis/eccentricity to the 10% level within tens of orbital periods, while MBH spin is unconstrained for the explored semimajor axes $\geq 100R_g$ and monitoring baselines $\mathcal{O}(10-100\rm)$ orbits. Introducing a misaligned precessing disk generally degrades inference of EMRI orbital parameters, but can constrain disk precession properties within 10-50%. This work both highlights the prospect of QPE observations as dynamical probes of galactic nuclei and outlines the challenge of doing so in the multimodal parameter space of EMRI-disk collisions.

astro-ph.HE↗

arXiv2025

Rapidly varying ionization features in a Quasi-periodic Eruption: a homologous expansion model for the spectroscopic evolution

Quasi-Periodic Eruptions (QPEs) are recurring bursts of soft X-ray emission from supermassive black holes (SMBHs), which a growing class of models explains via extreme mass-ratio inspirals (EMRIs). QPEs exhibit blackbody-like emission with significant temperature evolution, but the minimal information content of their almost pure-thermal spectra has limited physical constraints. Here we study the recently discovered QPEs in ZTF19acnskyy (``Ansky''), which show absorption-like features evolving dramatically within eruptions and correlating strongly with continuum temperature and luminosity, further probing the conditions underlying the emission surface. The absorption features are well-described by dense ionized plasma of column density $N_{\rm H}\gtrsim 10^{21}$ cm$^{-2}$, blueshift $0.06\lesssim v/c \lesssim 0.4$, and either collisional or photoionization equilibrium. With high-resolution spectra, we also detect ionized blueshifted emission lines suggesting a nitrogen over-abundance of $21.7^{+18.5}_{-11.0}\times$ solar. We interpret our results with orbiter-disk collisions in an EMRI system, in which each impact drives a shock that locally heats the disk and expels X-ray emitting debris undergoing radiation pressure-driven homologous expansion. We explore an analytical toy model that links the rapid change in absorption lines to the evolution of the ionization parameter and the photosphere radius, and suggest that $\sim 10^{-3}M_\odot$ ejected per eruption with expansion velocities up to $v_{\rm max}\sim 0.15c$, can reproduce the absorption features. With these assumptions, we show a P Cygni profile in a spherical expansion geometry qualitatively matches the observed line profiles. Our work takes a first step towards extending existing physical models for QPEs to address their implications for spectral line formation.

astro-ph.HE↗

arXiv2025

Discovery of Quasi-periodic Eruptions in the Tidal Disruption Event and Extreme Coronal Line Emitter AT2022upj: implications for the QPE/TDE fraction and a connection to ECLEs

Quasi-periodic eruptions (QPEs) are recurring soft X-ray transients emerging from the vicinity of supermassive black holes (SMBHs) in nearby, low-mass galaxy nuclei; about ten QPE hosts have been identified thus far. Here we report the \textit{NICER} discovery of QPEs in the optically-selected Tidal Disruption Event (TDE) and Extreme Coronal Line Emitter (ECLE) AT2022upj, exhibiting a large spread in recurrence times from 0.5-3.5 days, durations from 0.3-1 days, peak luminosities from $10^{42.5-43.0}$ erg s$^{-1}$, and erratic flare profiles. A wealth of evidence now links at least some QPEs to the newly-formed accretion flows emerging from TDEs; AT2022upj is the third QPE reported in an optically discovered TDE. Marginalizing over the uncertain distributions of QPE peak luminosity, recurrence time, delay after TDE peak, and lifetime, we use the burgeoning sample to make a Bayesian estimate that the fraction of optical TDEs resulting in QPEs within 5 years post-disruption is $9^{+9}_{-5}$\%. Along with AT2019qiz, AT2022upj also marks the second of the three optical TDE+X-ray QPEs showing coronal line emission, suggesting ECLEs may represent a subset of TDEs particularly efficient at forming QPEs and/or that sustained QPE X-ray emission contributes to coronal line emission in some galaxy nuclei.

astro-ph.HE↗

arXiv2025

The X-ray Integral Field Unit at the end of the Athena reformulation phase

The Athena mission entered a redefinition phase in July 2022, driven by the imperative to reduce the mission cost at completion for the European Space Agency below an acceptable target, while maintaining the flagship nature of its science return. This notably called for a complete redesign of the X-ray Integral Field Unit (X-IFU) cryogenic architecture towards a simpler active cooling chain. Passive cooling via successive radiative panels at spacecraft level is now used to provide a 50 K thermal environment to an X-IFU owned cryostat. 4.5 K cooling is achieved via a single remote active cryocooler unit, while a multi-stage Adiabatic Demagnetization Refrigerator ensures heat lift down to the 50 mK required by the detectors. Amidst these changes, the core concept of the readout chain remains robust, employing Transition Edge Sensor microcalorimeters and a SQUID-based Time-Division Multiplexing scheme. Noteworthy is the introduction of a slower pixel. This enables an increase in the multiplexing factor (from 34 to 48) without compromising the instrument energy resolution, hence keeping significant system margins to the new 4 eV resolution requirement. This allows reducing the number of channels by more than a factor two, and thus the resource demands on the system, while keeping a 4' field of view (compared to 5' before). In this article, we will give an overview of this new architecture, before detailing its anticipated performances. Finally, we will present the new X-IFU schedule, with its short term focus on demonstration activities towards a mission adoption in early 2027.

astro-ph.IM↗

arXiv2025

Millihertz Oscillations Near the Innermost Orbit of a Supermassive Black Hole

Recent discoveries from time-domain surveys are defying our expectations for how matter accretes onto supermassive black holes (SMBHs). The increased rate of short-timescale, repetitive events around SMBHs, including the newly-discovered quasi-periodic eruptions (QPEs), are garnering further interest in stellar-mass companions around SMBHs and the progenitors to mHz frequency gravitational wave events. Here we report the discovery of a highly significant mHz Quasi-Periodic Oscillation (QPO) in an actively accreting SMBH, 1ES 1927+654, which underwent a major optical, UV, and X-ray outburst beginning in 2018. The QPO was first detected in 2022 with a roughly 18-minute period, corresponding to coherent motion on scales of less than 10 gravitational radii, much closer to the SMBH than typical QPEs. The period decreased to 7.1 minutes over two years with a decelerating period evolution ($\ddot{P} > 0$). This evolution has never been seen in SMBH QPOs or high-frequency QPOs in stellar mass black holes. Models invoking orbital decay of a stellar-mass companion struggle to explain the period evolution without stable mass transfer to offset angular momentum losses, while the lack of a direct analog to stellar mass black hole QPOs means that many instability models cannot explain all of the observed properties of the QPO in 1ES 1927+654. Future X-ray monitoring will test these models, and if it is a stellar-mass orbiter, the Laser Interferometer Space Antenna (LISA) should detect its low-frequency gravitational wave emission.

astro-ph.HE↗

arXiv2024

Eppur si muove: Evidence of disc precession or a sub-milliparsec SMBH binary in the QPE-emitting galaxy GSN 069

X-ray quasi-periodic eruptions (QPEs) are intense soft X-ray bursts from the nuclei of nearby low-mass galaxies typically lasting about one hour and repeating every few. Their physical origin remains debated, although so-called impacts models in which a secondary orbiting body pierces through the accretion disc around the primary supermassive black hole (SMBH) in an extreme mass-ratio inspiral (EMRI) system are considered promising. In this work, we study the QPE timing properties of GSN 069, the first galactic nucleus in which QPEs were identified, primarily focusing on Observed minus Calculated (O-C) diagrams. The O-C data in GSN 069 are consistent with a super-orbital modulation on tens of days whose properties do not comply with the impacts model. We suggest that rigid precession of a misaligned accretion disc or, alternatively, the presence of a second SMBH forming a sub-milliparsec binary with the inner EMRI is needed to reconcile the model with the data. In both cases, the quiescent accretion disc emission should also be modulated on similar timescales. Current X-ray monitoring indicates that this might be the case, although a longer baseline of higher-cadence observations is needed to confirm the tentative X-ray flux periodicity on firm statistical grounds. Future dedicated monitoring campaigns will be crucial to test the overall impacts plus modulation model in GSN 069, and to distinguish between the two proposed modulating scenarios. If our interpretation is correct, QPEs in GSN 069 represent the first electromagnetic detection of a short-period EMRI system in an external galaxy, opening the way to future multi-messenger astronomical observations. [abridged]

astro-ph.HE↗

arXiv2024

Fragments of harmony amid apparent chaos: a closer look at the X-ray quasi-periodic eruptions of the galaxy RX J1301.9+2747

Quasi-periodic eruptions (QPEs) are an extreme X-ray variability phenomenon associated with low-mass supermassive black holes. First discovered in the nucleus of the galaxy GSN 069, they have been so far securely detected in five other galaxies, including RX J1301.9+2747. When detected, the out-of-QPE emission (quiescence) is consistent with the high-energy tail of thermal emission from an accretion disk. We present the X-ray and radio properties of RX J1301.9+2747, both in quiescence and during QPEs. We analyse X-ray data taken during five XMM-Newton observations between 2000 and 2022. The last three observations were taken in coordination with radio observations with the Karl G. Jansky Very Large Array. We also make use of EXOSAT, ROSAT, and Chandra archival observations taken between 1983 and 2009. XMM-Newton detected 34 QPEs of which 8 have significantly lower amplitudes than the others. No correlated radio/X-ray variability was observed during QPEs. In terms of timing properties, the QPEs in RX J1301.9+2747 do not exhibit the striking regularity observed in the discovery source GSN 069. In fact there is no clear repetition pattern between QPEs: the average time separation between their peaks is about four hours, but it can be as short as one, and as long as six hours. The QPE spectral properties of RX J1301.9+2747 as a function of energy are however very similar to those of GSN 069 and of other QPE sources. The quiescent emission of RX J1301.9+2747 is more complex than that of GSN 069, as it requires a soft X-ray excess-like component in addition to the thermal emission from the accretion disk. Its long-term X-ray quiescent flux variations are of low-amplitude and not strictly monotonic, with a general decay over $\sim 22$ years. We discuss our observational results in terms of some of the ideas and models that have been proposed so far for the physical origin of QPEs.

astro-ph.HE↗

arXiv2024

The Lunar Gravitational-wave Antenna: Mission Studies and Science Case

The Lunar Gravitational-wave Antenna (LGWA) is a proposed array of next-generation inertial sensors to monitor the response of the Moon to gravitational waves (GWs). Given the size of the Moon and the expected noise produced by the lunar seismic background, the LGWA would be able to observe GWs from about 1 mHz to 1 Hz. This would make the LGWA the missing link between space-borne detectors like LISA with peak sensitivities around a few millihertz and proposed future terrestrial detectors like Einstein Telescope or Cosmic Explorer. In this article, we provide a first comprehensive analysis of the LGWA science case including its multi-messenger aspects and lunar science with LGWA data. We also describe the scientific analyses of the Moon required to plan the LGWA mission.

gr-qc↗

arXiv2024

Testing EMRI models for Quasi-Periodic Eruptions with 3.5 years of monitoring eRO-QPE1

Quasi-Periodic Eruptions (QPEs) are luminous X-ray outbursts recurring on hour timescales, observed from the nuclei of a growing handful of nearby low-mass galaxies. Their physical origin is still debated, and usually modeled as (a) accretion disk instabilities or (b) interaction of a supermassive black hole (SMBH) with a lower mass companion in an extreme mass-ratio inspiral (EMRI). EMRI models can be tested with several predictions related to the short- and long-term behavior of QPEs. In this study, we report on the ongoing 3.5-year NICER and XMM-Newton monitoring campaign of eRO-QPE1, which is known to exhibit erratic QPEs that have been challenging for the simplest EMRI models to explain. We report 1) complex, non-monotonic evolution in the long-term trends of QPE energy output and inferred emitting area; 2) the disappearance of the QPEs (within NICER detectability) in October 2023, then reappearance by January 2024 at a luminosity $\sim$100x fainter (and temperature $\sim$3x cooler) than initial discovery; 3) radio non-detections with MeerKAT and VLA observations partly contemporaneous with our NICER campaign (though not during outbursts); and 4) the presence of a possible $\sim$6-day modulation of the QPE timing residuals, which aligns with the expected nodal precession timescale of the underlying accretion disk. Our results tentatively support EMRI-disk collision models powering the QPEs, and we demonstrate that the timing modulation of QPEs may be used to jointly constrain the SMBH spin and disk density profile.

astro-ph.HE↗

arXiv2023

Constraints on the narrow-line region of the X-ray quasi-periodic eruption source GSN 069

The origins of quasi-periodic eruptions (QPEs) are poorly understood, although most theoretical explanations invoke an accretion disk around a supermassive black hole. The gas and stellar environments in the galactic nuclei of these sources are also poorly constrained. In this paper, we present an analysis of archival Hubble Space Telescope (HST) images to study the narrow-line [O III] emission in the QPE source GSN 069. We find strong evidence for a compact nuclear [O III] emission region of size $\lesssim 35$ pc, overlaid on top of extended [O III] emission up to 2 kpc away from the nucleus. The age of the accretion system is estimated to be between 10 and 100 yr. The [O III] luminosity of the compact region was measured to be $(2.1 \pm 0.3) \times 10^{40}\,\rm erg\,s^{-1}$. Based on CLOUDY simulations, we constrain that the [O III] emitting gas has a hydrogen number density in the range $5 \times 10^{3} < n_{\rm H} \lesssim 10^{8}\,\rm cm^{-3}$ and volume filling factor $f_{\rm V} < 2 \times 10^{-3}$. We suggest that the dense gas in the nuclear region of GSN 069 originates from molecular clouds (with total mass $\gtrsim 3 \times 10^{3}\,M_{\odot}$), which are freshly ionised by the soft X-ray photons from the accretion disk. We predict possible evolution of the compact narrow-line region on emission-line diagnostic diagrams, and hence future HST or integral-field unit observations can be used to further pin down the age of this puzzling system.

astro-ph.HE↗

arXiv2023

Quasi-periodic eruptions from impacts between the secondary and a rigidly precessing accretion disc in an extreme mass-ratio inspiral system

X-ray quasi-periodic eruptions (QPEs) represent a recently discovered example of extreme X-ray variability associated with supermassive black holes. These are high-amplitude bursts recurring every few hours that are detected in the soft X-ray band from the nuclei of nearby galaxies whose optical spectra lack the broad emission lines typically observed in unobscured active galaxies. The physical origin of this new X-ray variability phenomenon is still unknown and several theoretical models have been presented. However, no attempt has been made so far to account for the varying QPE recurrence time and luminosity in individual sources, nor for the diversity of the QPE phenomenology in the different known erupters. We present a semi-analytical model based on an extreme mass-ratio inspiral (EMRI) system where the secondary intersects, along its orbit, a rigidly precessing accretion disc surrounding the primary. We assume that QPEs result from emission from an adiabatically expanding, initially optically thick gas cloud expelled from the disc plane at each impact. We produced synthetic X-ray light curves, which we then compared with X-ray data from four QPE sources: GSN 069, eRO-QPE1, eRO-QPE2, and RX J1301.9+2747. Our model aptly reproduces the diversity of QPE properties between the considered objects and it is also able to naturally account for the varying QPE amplitudes and recurrence times in individual sources. Future implementations will enable us to refine the match with the data and to estimate the system parameters precisely, making additional use of multi-epoch QPE data. We briefly discuss the nature of the secondary object, as well as the possible implications of our findings for the EMRI population at large.

astro-ph.HE↗