arXiv subjects

Andrew Mummery

Publications and source records attributed to Andrew Mummery.

At least 37 records · Page 2Linked to original sources

arXiv2025

AT 2018cow at ~5 years: additional evidence for a tidal disruption origin

The Luminous Fast Blue Optical Transient (LFBOT) AT 2018cow is the prototype of its class with an extensive set of multi-wavelength observations. Despite a rich data set there is, still, no consensus about the physical nature and origin of this event. AT 2018cow remained UV bright 2-4 years after the explosion, which points at an additional energy injection source, most likely from an accretion disk. We present additional late time UV data obtained with the Hubble Space Telescope, to show there is no significant fading in the optical since the last epoch and only marginal fading in the UV. The new UV data points match the predictions of previously published accretion disk models, where the disk is assumed to form from the tidal disruption of a low mass star by an intermediate mass black hole. This consistency provides evidence that AT 2018cow could indeed be a tidal disruption event. The marginal decay is in contrast with the predictions of light curves produced by interacting supernovae. The difference between expectations for disc emission and interacting supernovae will further increase with time, making data at even later times a route to robustly rule out interaction between supernova ejecta and circumstellar material.

astro-ph.HE↗

arXiv2025

Evidence for a steeper SMBH-Bulge mass relationship extended to low masses using TDE host galaxies

Tidal disruption events (TDEs) are excellent tools for probing low mass supermassive black holes (SMBHs) that may otherwise remain undetected. Here, we present an extended SMBH--Bulge mass scaling relationship using these lower mass TDE black holes and their host galaxies. Bulge masses are derived using Prospector fits to UV-MIR spectral energy distributions for the hosts of 40 TDEs that have a detected late-time UV/optical plateau emission, from which a SMBH mass is derived. Overall, we find that TDE plateaus are a successful method for probing BH scaling relations. We combine the observed TDE sample with a higher mass SMBH sample and extend the known relationship, recovering a steeper slope ($m = 1.34 \pm 0.03$) than current literature estimates, which focus on the high mass regime. For the TDE only sample, we measure an equally significant but shallower relationship with a power-law slope of $m = 1.17 \pm 0.10$ and significance $<0.001$. Forward modelling is used to determine whether known selection effects can explain both the comparatively flatter TDE only relation and the overall steepening across the full SMBH mass range. We find that the flattening at TDE masses can be accounted for, however the steepening can not. It appears that if a single slope extends for the whole BH mass range, it must be steeper to include the TDE population.

astro-ph.GA↗

arXiv2025

Black hole supercolliders

We show that collisions between particles free falling from infinity and a disk of material plunging off the retrograde innermost stable circular orbit of a near-extremal Kerr black hole is the unique astronomically natural way in which to create a gravitational particle accelerator with center of mass energies at the $10$'s to $100$'s of teraelectronvolt range, in other words a supercollider.

gr-qc↗

arXiv2025

The plunging region of a thin accretion disc around a Schwarzschild black hole

A set of analytic solutions for the plunging region thermodynamics have been developed recently under the assumption that the fluid undergoes a gravity-dominated geodesic plunge into the black hole. We test this model against a dedicated 3D global GRMHD simulation of a thin accretion disc around a Schwarzschild black hole using the code AthenaK. Provided that we account for non-adiabatic heating in the energetics, plausibly from grid-scale magnetic dissipation, we find an excellent agreement between the analytic model and the simulated quantities. These results are particularly important for existing and future electromagnetic black hole spin measurements, many of which do not to include the plunging fluid in their emission modelling. This exclusion typically stems from the assumption of a zero-stress boundary condition at the ISCO, forcing all thermodynamic quantities to vanish. Instead, we find a non-zero $δ_\mathcal{J}\approx 5.3 \%$ drop in the angular momentum over the plunging region, which is consistent with both prior simulations and observations. We demonstrate that this stress is small enough for the dynamics of the fluid in the plunging region to be well-described by geodesic trajectories, yet large enough to cause measurable dissipation near to the ISCO - keeping thermodynamic quantities from vanishing. In the plunging region, constant $α$-disc models are a physically inappropriate framework.

astro-ph.HE↗

arXiv2025

A rapid black hole spin or emission from the plunging region?

Emission from within the plunging region of black hole accretion flows has recently been detected in two X-ray binary systems. There is, furthermore, a possible discrepancy between the inferred spins of gravitational wave and electromagnetically detected black holes. Motivated by these two results we demonstrate, using theoretical calculations, numerical simulations and observational data, that the inclusion of emission from within the innermost stable circular orbit (ISCO) results in a black hole with a low spin producing a thermal continuum X-ray spectrum that mimics that produced by a much more rapidly rotating black hole surrounded by a disk with no emission from within the ISCO. We demonstrate this explicitly using the observed X-ray spectrum of a canonical soft-state high mass X-ray binary system M33 X-7. A vanishing ISCO temperature model requires a high spin $a_\bullet = 0.84\pm0.05$, as has been found previously in the literature. However, a disk around a Schwarzschild black hole can equally well (in fact slightly better) describe the data, provided that photons emitted from within the plunging region are included, and the ISCO stress is in line with that seen in numerical simulations of the accretion process. We then present an analysis of two further soft-state X-ray binaries (MAXI J1820+070 and MAXI J0637$-$430) which require the presence of intra-ISCO emission at high statistical significance. These two sources sit on the low-spin moderate-stress part of the degeneracy exhibited by M33 X-7, suggesting that when high quality data are available the high-spin low-stress region of parameter space is ruled out. We discuss how future advances in numerical simulations and data modelling will be essential to determining the spin of X-ray binary black holes which may well be systematically lower than current continuum fitting methods suggest.

astro-ph.HE↗

arXiv2025

The X-ray variability of tidal disruption events

When a star is torn apart by the tidal forces of a supermassive black hole (a so-called TDE) a transient accretion episode is initiated and a hot, often X-ray bright, accretion disk is formed. Like any accretion flow this disk is turbulent, and therefore the emission from its surface will vary stochastically. As the disk has a finite mass supply (i.e., at most the initial mass of the disrupted star) the disk will also undergo long-timescale evolution, as this material is lost into the black hole. In this paper we combine theoretical models for this long time evolution of the disk with models for the stochastic variability of turbulent accretion flows which are correlated on short (orbital) timescales. This new framework allows us to demonstrate that (i) dimming events should be more prevalent than brightening events in long term TDE X-ray light curves (i.e., their log-luminosity distribution should be asymmetric), (ii) TDE X-ray light curves should follow a near- (but formally sub-)linear correlation between their root mean square variability and the mean flux, (iii) the fractional variability observed on short timescales across an X-ray observing band should increase with observing energy, and (iv) TDEs offer a unique probe of the physics of disk turbulence, owing to their clean spectra and natural evolutionary timescales. We confirm predictions (i) and (ii) with an analysis of the long timescale variability of two observed TDEs, and show strong support for prediction (iii) using the intra-observation variability of the same two sources.

astro-ph.HE↗

arXiv2025

Collisions with tidal disruption event disks: implications for quasi-periodic X-ray eruptions

A popular class of models for interpreting quasi-periodic X-ray eruptions from galactic nuclei (QPEs) invoke collisions between an object on an extreme mass ratio inspiral (EMRI) and an accretion disk around a supermassive black hole. There are strong links between QPE systems and those disks which formed following a tidal disruption event (TDE), and at least two events (AT2019qiz and AT2022upj) are known to have occurred following an otherwise typical TDE. We show that the fact that these disks were formed following a TDE strongly constrains their properties, more so than previous models have assumed. Models based on steady-state AGN-like disks have mass contents which grow strongly with size $M_{\rm disk}\propto R_{\rm out}^{7/2}$ and do not conserve the mass or angular momentum of the disrupted star. A very different scaling must be satisfied by a TDE disk in order to conserve the disrupted stars angular momentum, $M_{\rm disk} \propto R_{\rm out}^{-1/2}$. These constraints substantially change the predicted scaling relationships between QPE observables (luminosity, duration, energy, temperature) and the QPE period. They also allow QPE observables to be written in terms of the properties of the two stars assumed to be involved (the one tidally disrupted and the one on an EMRI), making plausibility tests of these models possible. We show that these modifications to the disk structure imply that (i) QPEs cannot be powered by collisions between an orbiting black hole and a TDE disk, (ii) QPEs also cannot be powered by collisions between the surface of a stellar EMRI and a TDE disk. A framework in which the collisions are between a TDE disk and a star which has puffed up to fill its Hills sphere with a trailing debris stream (as seen in recent simulations) cannot be ruled out from the data, and should be the focus of further study.

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

Stepping Up Superradiance Constraints on Axions

Light feebly-coupled bosonic particles can efficiently extract the rotational energy of rapidly spinning black holes on sub-astrophysical timescales via a phenomenon known as black hole superradiance. In the case of light axions, the feeble self-interactions of these particles can lead to a non-linear coupled evolution of many superradiant quasi-bound states, dramatically altering the rate at which the black hole is spun down. In this work, we extend the study of axion superradiance to higher order states, solving for the first time the coupled evolution of all states with $n \leq 5$ in the fully relativistic limit (with $n$ being the principle quantum number). Using a Bayesian framework, we re-derive constraints on axions using the inferred spins of solar mass black holes, demonstrating that previously adopted limit-setting procedures have underestimated current sensitivity to the axion decay constant $f_a$ by around one order of magnitude, and that the inclusion to higher order states allows one to reasonably capture the evolution of typical high-spin black holes across a much wider range of parameter space, thereby allowing constraints to be extended to more massive axions. We conclude with an extensive discussion on the systematics associated with spin inference from x-ray observations.

hep-ph↗

arXiv2025

Galaxy scale consequences of tidal disruption events: extended emission line regions, extreme coronal lines and infrared-to-optical light echoes

Stars in galactic centers are occasionally scattered so close to the central supermassive black hole that they are completely disrupted by tidal forces, initiating a transient accretion event. The aftermath of such a tidal disruption event (TDE) produces a bright-and-blue accretion flow which is known to persist for at least a decade (observationally) and can in principle produce ionizing radiation for hundreds of years. Tidal disruption events are known (observationally) to be overrepresented in galaxies which show extended emission line regions (EELRs), with no pre-TDE classical AGN activity, and to produce transient ``coronal lines'', such as [FeX] and [FeXIV]. Using coupled CLOUDY-TDE disk simulations we show that tidal disruption event disks produce a sufficient ionizing radiation flux over their lifetimes to power both EELR of radial extents of $r \sim 10^4$ light years, and coronal lines. EELRs are produced when the ionizing radiation interacts with low density $n_H \sim 10^1 - 10^3 \, {\rm cm}^{-3}$ clouds on galactic scales, while coronal lines are produced by high density $n_H \sim 10^6 - 10^8 \, {\rm cm}^{-3}$ clouds near the galactic center. High density gas in galactic centers will also result in the rapid switching on of narrow line features in post-TDE galaxies, and also various high-ionization lines which may be observed throughout the infrared with JWST. Galaxies with a higher intrinsic rate of tidal disruption events will be more likely to show macroscopic EELRs, which can be traced to originate from the previous tidal disruption event in that galaxy, which naturally explains why TDEs are more likely to be discovered in galaxies with EELRs. We further argue that a non-negligible fraction of so-called optically selected ``AGN'' are tidal disruption events.

astro-ph.HE↗

arXiv2025

Time-resolved Hubble Space Telescope UV observations of an X-ray quasi-periodic eruption source

X-ray quasi-periodic eruptions (QPEs) are a novel mode of variability in nearby galactic nuclei whose origin remains unknown. Their multi-wavelength properties are poorly constrained, as studies have focused almost entirely on the X-ray band. Here we report on time-resolved, coordinated Hubble Space Telescope far ultraviolet and XMM-Newton X-ray observations of the shortest period X-ray QPE source currently known, eRO-QPE2. We detect a bright UV point source ($L_{\rm FUV} \approx {\rm few} \times 10^{41}$ erg s$^{-1}$) that does not show statistically significant variability between the X-ray eruption and quiescent phases. This emission is unlikely to be powered by a young stellar population in a nuclear stellar cluster. The X-ray-to-UV spectral energy distribution can be described by a compact accretion disk ($R_{\rm out} = 343^{+202}_{-138} \ R_{\rm g}$). Such compact disks are incompatible with typical disks in active galactic nuclei, but form naturally following the tidal disruption of a star. Our results rule out models (for eRO-QPE2) invoking i) a classic AGN accretion disk and ii) no accretion disk at all. For orbiter models, the expected radius derived from the timing properties would naturally lead to disk-orbiter interactions for both quasi-spherical and eccentric trajectories. We infer a black hole mass of log$_{10}(M_{\rm BH}) = 5.9 \pm 0.3$ M$_{\odot}$ and Eddington ratio of 0.13$^{+0.18}_{-0.07}$; in combination with the compact outer radius this is inconsistent with existing disk instability models. After accounting for the quiescent disk emission, we constrain the ratio of X-ray to FUV luminosity of the eruption component to be $L_{\rm X} / L_{\rm FUV} > 16-85$ (depending on the intrinsic extinction).

astro-ph.HE↗

arXiv2025

The size of accretion disks from self-consistent X-ray spectra and UV/optical/NIR photometry fitting: applications to ASASSN-14li and HLX-1

We implement a standard thin disk model with the outer disk radius ($R_{\rm out}$) as a free parameter, integrating it into standard X-ray fitting package to enable self-consistent and simultaneous fitting of X-ray spectra and UV/optical/NIR photometry. We apply the model to the late-time data ($Δt \approx 350-1300$ days) of the tidal disruption event (TDE) ASASSN-14li. We show that at these late-times the multi-wavelength emission of the source can be fully described by a bare compact accretion disk. We obtain a black hole mass ($M_{\rm BH}$) of $7^{+3}_{-2}\times10^{6} M_{\odot}$, consistent with host-galaxy scaling relations; and an $R_{\rm out}$ of $45 \pm 13 \, R_{\rm g}$, consistent with the circularization radius, with possible expansion at the latest epoch. We discuss how simplistic models, such as a single-temperature blackbody fitted to either X-ray spectra or UV/optical photometry, lead to erroneous interpretations on the scale/energetics of TDE emission. We also apply the model to the soft/high state of the intermediate-mass black hole (IMBH) candidate HLX-1. The model fits the full spectral energy distribution (from X-rays to NIR) without needing an additional stellar population component. We investigate how relativistic effects improve our results by implementing a version of the model with full ray tracing calculations in the Kerr metric. For HLX-1, we find $M_{\rm BH} = 4^{+3}_{-1} \times 10^{4} M_{\odot}$ and $R_{\rm out} \approx {\rm few} \times 10^{3} \, R_{\rm g}$, in agreement with previous findings. The relativistic model can constrain the inclination ($i$) of HLX-1 to be $10^o \leq i \leq 70^o$.

astro-ph.HE↗

arXiv2025

Black hole-disc coevolution in the presence of magnetic fields: refining the Thorne limit with emission from within the plunging region

The accretion of material onto a black hole modifies the properties of that hole owing to the capture of both matter and radiation. Adding matter to the hole through an accretion disc generally acts to increase the hole's spin parameter, while the capture of radiation generally provides a retarding torque. The balance between the torques provided by adding matter and radiation leads to a maximum spin parameter that can be obtained by a black hole which grows by accretion, known as the Thorne limit. In the simplest theory of thin disc accretion this Thorne limit has the value $a_{\bullet, {\rm lim}} \simeq 0.998$. The purpose of this paper is to highlight that any modification to theories of accretion flows also modify this limiting value, and to compute precisely the modification arising from a particular extension of accretion theory: the inclusion of bright emission from within the plunging region which is sourced from the magnetohydrodynamic stresses ubiquitously observed in simulations. This extra emission further suppresses black hole spin-up and results in new, lower, limits on the final black hole spin. These limits depend on the details of the magnetic stresses acting within the plunging region, but typical values seen in simulations and observations would lower the limit to $a_{\bullet, {\rm lim}} \simeq 0.99$, a subtle but not negligible deviation.

astro-ph.HE↗

arXiv2024

The optical, UV-plateau and X-ray tidal disruption event luminosity functions reproduced from first principles

We reproduce the luminosity functions of the early-time peak optical luminosity, the late-time UV plateau luminosity, and the peak X-ray luminosity of tidal disruption events, using an entirely first-principles theoretical approach. We do this by first fitting three free parameters of the tidal disruption event black hole mass distribution using the observed distribution of late time UV plateau luminosities, using a time-dependent relativistic accretion model. Using this black hole mass distribution we are then, with no further free parameters of the theory, able to reproduce exactly the peak X-ray luminosity distribution of the tidal disruption event population. This proves that the X-ray luminosity of tidal disruption events are sourced from the same accretion flows which produce the late time UV plateau. Using an empirical scaling relationship between peak optical luminosities and black hole masses, itself calibrated using the same relativistic accretion theory, we are able to reproduce the observed peak optical luminosity function, again with no additional free parameters. Implications of these results include that there is no tidal disruption event "missing energy problem", that the optical and X-ray selected tidal disruption event populations are drawn from the same black hole mass distribution, that the early time optical luminosity in tidal disruption events is somewhat simple, at least on the population level, and that future LSST observations will be able to constrain the black hole mass function at low masses.

astro-ph.HE↗

arXiv2024

Fitting transients with discs (FitTeD): a public light curve and spectral fitting package based on evolving relativistic discs

We present FitTeD, a public light curve and spectral fitting Python-package based on evolving relativistic discs. At its heart this package uses the solutions of the time dependent general relativistic disc equations to compute multi-band light curves and spectra. All relevant relativistic optics effects (Doppler and gravitational energy shifting, and gravitational lensing) are included. Additional, non-disc light curve and spectral components can be included to (for example) model the early time rise and decay of tidal disruption event light curves in optical-to-UV bands. Monte Carlo Markov Chain fitting procedures are included which return posterior distributions of black hole and disc parameters, allowing for the future automated processing of the large populations of transient sources discovered by (e.g.,) the Vera Rubin Observatory. As an explicit example, in this paper we model the multi-wavelength light curves of the tidal disruption event AT2019dsg, finding a good fit to the data, a black hole mass consistent with galactic scaling relationships, and a late-time disc Eddington ratio consistent with the observed launching of an outflow observed in radio bands.

astro-ph.HE↗

arXiv2024

The three-dimensional structure of black hole accretion flows within the plunging region

We analyse, using new analytical models and numerical general relativistic magnetohydrodynamic simulations, the three-dimensional properties of accretion flows inside the plunging region of black hole spacetimes (i.e., at radii smaller than the innermost stable circular orbit). These simulations are of thick discs, with aspect ratios of order unity $h/r \sim 1$, and with a magnetic field geometry given by the standard low-magnetization "SANE" configuration. This work represents the first step in a wider analysis of this highly relativistic region. We show that analytical expressions derived in the "thin disc" limit describe the numerical results remarkably well, despite the large aspect ratio of the flow. We further demonstrate that accretion within this region is typically mediated via spiral arms, and that the geometric properties of these spiral structures can be understood with a simple analytical model. These results highlight how accretion within the plunging region is fundamentally two dimensional in character, which may have a number of observational implications. We derive a modified theoretical description of the pressure within the plunging region which accounts for turbulent heating and may be of use to black hole image modelling.

astro-ph.HE↗

arXiv2024

Plunging region emission in the X-ray binary MAXI J0637$-$430

On the second of November 2019 the black hole X-ray binary MAXI J0637$-$430 went into outburst, at the start of which it was observed in a thermal ``disc-dominated'' state. High photon energy (extending above 10 keV) observations taken by the NuSTAR telescope reveal that this thermal spectrum can not be fit by conventional two-component (disc plus corona) approaches which ignore disc emission sourced from within the plunging region of the black hole's spacetime. Instead, these models require a third ``additional'' thermal component to reproduce the data. Using new disc solutions which extend classical models into the plunging region we show that this ``additional'' thermal emission can be explained self-consistently with photons emitted from the accretion flow at radii within the innermost stable circular orbit of the black hole. This represents the second low mass X-ray binary, after MAXI J1820+070, with a detection of plunging region emission, suggesting that signatures of this highly relativistic region may well be widespread but not previously widely appreciated. To allow for a detection of the plunging region, the black hole in MAXI J0637$-$430 must be at most moderately spinning, and we constrain the spin to be $a_\bullet < 0.86$ at 99.9$\%$ confidence. We finish by discussing the observational requirements for the robust detection of this region.

astro-ph.HE↗

arXiv2024

Continuum emission from within the plunging region of black hole discs

The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a powerful probe of the mass and spin of the central black hole. The vast majority of existing ``continuum fitting'' models neglect emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however, find non-zero emission sourced from these regions. In this work we extend existing techniques by including the emission sourced from within the plunging region, utilising new analytical models which reproduce the properties of numerical accretion simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component, but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component has been added in by hand in an ad-hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional models which neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820+070 black hole spin which must be low $a_\bullet < 0.5$ to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission component in the MAXI J1820+070 spectrum between $6$ and $10$ keV, highlighting the necessity of including this region. Our continuum fitting model is made publicly available.

astro-ph.HE↗