Description
Organisers: Noel Castro Segura, Melissa Ewing, Scott Hagen, Amy Knight, Martina Veresvarska, Federico Vincentelli
Accretion processes are ubiquitous throughout the universe and play a crucial role in the evolution of astrophysical systems across all size scales. Accretion often occurs in binary systems like white dwarfs and X-ray binaries, which can host neutron stars or stellar mass black holes. Here, the gravitational pull of a compact object draws material from its companion star, resulting in bright emission across the electromagnetic spectrum. The consequences of accretion in binaries are widespread and vital when investigating supernovae progenitors, energetic transients and gravitational regimes. Despite the diversity among accreting systems, accretion itself is scale-invariant. Therefore, gathering the accretion community at NAM is essential to foster discussions of the connections and analogies between different classes of accreting systems and the advancements from forthcoming missions like NewAthena.
In this session, we will discuss the inward and outward flow of mass, energy and angular momentum in white dwarf, neutron star and black hole binaries and their consequences, covering topics from accretion disc radiation and outflows to thermonuclear bursts and quasi-periodic oscillations. Historically, high-energy astrophysics sessions at NAM have combined discussions of accreting binaries with supermassive black holes.
Disc winds are ubiquitous in accreting binaries and have an intimate connection to the accretion disc; however, the driving mechanism of the winds and their impact on the observed spectrum remain poorly understood. In this talk, I will first review the physics behind accretion disc winds and their observational signatures. I will then discuss how numerical simulations (specifically,...
Disk winds are prevalent in a variety of accreting systems, such as young stellar objects, accreting white dwarfs (AWDs), X-ray binaries, and active galactic nuclei (AGN). In the context of AWDs and AGN, radiation pressure acting on spectral lines has been proposed as a key mechanism for driving these outflows. Although previous hydrodynamical simulations have largely supported this idea, they...
Cataclysmic variables (CVs) can exhibit rapid increases in optical flux. These bursts are broadly classified into categories based on properties such as total energy, peak luminosity and duration. A subset of CVs, referred to as Intermediate Polars (IPs) possess strong magnetic fields that can disrupt the inner disk regions, and which are thought to rarely exhibit bursts. Previous studies...
Fundamental questions remain about the accretion and outflow physics of cataclysmic variable stars, and their counterparts, AM CVn systems. In an AM CVn system, both the accretor and donor are white dwarf stars. To date, only one AM CVn system has been detected in the radio spectrum and the mechanism for this is yet to be determined. Using observations from the Karl J. Jansky Very Large Array...
Cataclysmic Variables (CVs) are close binaries in which a white dwarf is accreting from a donor star that fills its Roche lobe. Whilst the evolution of CVs is an important subject they are also the natural laboratory for studying accretion in other less accessible objects.
The number of confirmed CVs continues to grow thanks particularly to large-scale photometric, spectroscopic and x-ray ...
Hard X-ray emission from white dwarfs (WD) is generated by the presence of a stellar companion either by their coronal emission or by an accretion disk formed by the material stripped from the companion. Recent studies have proven that Jupiter-like planets can be the donors of material to create an accretion disk and generate hard X-ray emission. Under this light, here we discuss our X-ray...
Transitional millisecond pulsars (tMSPs) are a unique class of neutron star binaries that switch between an accretion-powered low-mass X-ray binary (LMXB) state and a rotation-powered radio millisecond pulsar (MSP) state. The first confirmed tMSP system, PSR J1023+0038, is currently in an LMXB state, exhibiting rapid mode switching between distinct high, low, and flaring states at X-ray,...
The discovery of coherent X-ray pulsations from ultraluminous X-ray sources (ULXs) provided the firstย concrete evidence that some ULXs host neutron stars (NSs) accreting at super-Eddington rates.ย This raises many new questions regarding the physics of super-Eddington accretion in the presence of strong magnetic fields and the fraction of the ULX population hosting NS accretors. One way to...
Ultraluminous X-ray sources challenge our understanding of extreme accretion regimes, particularly ULX pulsars like NGC5907 ULX1. This remarkable system exceeds the neutron star Eddington limit by a factor of ~500 (L_X,peak ~10^41 erg/s) and exhibits a ~78-day super-orbital periodicity, providing a test case - as the most luminous ULX pulsar - to differentiate between competing descriptions of...
The Imaging X-ray Polarimetry Explorer (IXPE) provides, for the first time, sensitivity to X-ray polarisation in the 2โ8 keV band, offering two powerful diagnostics to probe the extreme physics of accreting matter around compact objects: polarisation degree (PD) and polarisation angle (PA). I will present results from the first IXPE observation of the black hole X-ray binary (BH-XRB) IGR...
Jets from stellar mass black holes in X-ray binaries (XRBs) and supermassive black holes in blazars provide distinct opportunities to study the jets of black holes across two different mass regimes. They also represent samples with very different selection effects. Historically, the apparent speeds of XRB jets have been observed to be lower than those of blazars, leading to the assumption that...
We present a comprehensive spectral and timing analysis of the newly discovered black hole transient Swift J1727.8-1613, based on broadband (1-150 keV) observations from Insight-HXMT during its 2023 outburst. Using the flexible, energy-conserving SSsed model, we identify the presence of both thermal and non-thermal Comptonization components in the hard component dominated state. We track the...
In this talk, I will present Hubble Space Telescope (HST) and AstroSat ultraviolet (UV) spectroscopy of the black hole X-ray binary MAXI J1820+070 during its 2018 outburst. Our observations span three accretion statesโluminous hard, hard-intermediate, and soft stateโproviding a rare multi-state UV view of this system. The source exhibits remarkably low extinction, E(B-V) = 0.2 ยฑ 0.05, making...
Current estimates suggest that the Milky Way contains approximately 100 million stellar-mass black holes; however, only about 100 have been detected, mainly due to the bright X-ray signal resulting from rapid accretion events from a close binary partner. The population of black holes in wide, non-accreting binaries with a companion star, predicted to be around 10 million, remains elusive, with...
Pre-main-sequence binary systems provide a unique laboratory for studying dynamical truncation in discs. We studied the inner region of a nearby Herbig Ae/Be binary system using the VLTI/GRAVITY and VLTI/PIONIER instrument. Spectrally-dispersed interferometry with GRAVITY allowed us to determine the origin of the Br ฮณ line emission and to study how the accretion rates on the primary and...
While many ULXs are now known to host neutron star accretors, distinguishing between different accretor types remains challenging without the direct detection of pulsations. Here we present the first broadband (0.3-25 keV) spectroscopic analysis of IC5052 ULX using simultaneous XMM-Newton and NuSTAR observations. Our analysis reveals a remarkably hard spectrum compared to other ULXs studied in...
Explosive accreting transients like Cataclysmic Variables and Low-Mass X-ray Binaries can leap several magnitudes in brightness during their frequent outbursts. Many sources are well-studied both at their explosive ~15th magnitude heights and their quiescent flickering as faint as 20th mag. But what if we went fainter?
There are a hidden population of transients that are too far away to be...
Binary hardening is more efficient in gas-rich environments, leading to an enhanced number of close-separation binaries.
While the exact criteria for common envelope (CE) formation are still uncertain, it is generally suggested that the binary pericenter should be small to initiate an unstable mass transfer. Hence, CE formation is expected to be more prevalent in gas-rich environments,...
Dwarf novae serve as crucial laboratories for studying accretion physics, binary mass transfer, and the endpoints of stellar evolution - with early discovery and intensive follow-up being crucial to capitalise on the opportunity they provide.
In this talk I will present GOTO065054+593624, a dwarf nova first discovered in real-time by the [Kilonova Seekers citizen science project][1], which...
GK Persei, an intermediate polar cataclysmic variable, is surrounded by a supernova remnant. Its most recent period of activity was reported in December 2022, during which it was suggested to be undergoing an outburst similar to that of a dwarf nova. GK Persei was observed in February 2023 from the San Pedro Mรกrtir Observatory in Mexico using OPTICAM, a triple-channel fast optical system...
The source of strong hard X-ray emission in accreting black holes is controversial. The truncated thin disc/hot inner flow models have multiple strengths but other geometries are also suggested including a disc corona, and/or jet base. I will show how new data from X-ray polarisation as well as advances in reflection modelling can give new insight into the fundamental structures producing hard...
Quasi-periodic oscillations (QPOs) are a common feature observed in accreting compact objects, including black holes, neutron stars, and, as recently discovered, accreting white dwarfs (AWDs). In X-ray binaries (XRBs), these QPOs are often attributed to mechanisms such as relativistic frame-dragging (Lense-Thirring precession, but their true origin remains debated. Here, I will present recent...
