NewAthena Rising: SWG4

2 Jun 2026, 13:00 → 5 Jun 2026, 17:00 Europe/Madrid

ICE-CSIC Barcelona

Alessio Marino (Institute of Space Sciences, ICE/CSIC), Davide De Grandis (ICE-CSIC)

NewAthena Rising: SWG4 is a community conference intended for networking and collaboration within the Science Working Group 4 (Compact Objects) in the NewAthena Science community. While all the scientists in SWG4 are invited, the conference is specifically aimed at Early Career Researchers (<10 years from PhD). All talks will be delivered by ECRs.

To emphasise the community-driven nature of this conference, no talks were solicited; however, the SOC invited a number of keynote talks selected from the pool of submitted abstracts.

Keynote speakers:

• Alessio Anitra (Universita di Palermo, Italy)
• Maria Cristina Baglio (INAF-OAB, Italy)
• Francesco Barra (INAF-IASF Palermo, Italy)
• Camille Diez (ESA/ESAC)
• Hannah Fritze-Moon (NASA Goddard Space Flight Center, USA)
• Jaime Alonso Hernandez (Centro de Astrobiología CSIC-INTA, Spain)
• Christian Kirsh (Dr. Karl Remeis Observatory, Germany)
• Jan Kurpas (Leibniz-Institut für Astrophysik Potsdam, Germany)
• Amy Knight (Durham University, UK)
• Georgios Vasilopoulos (National and Kapodistrian University of Athens, Greece)

 

 

Tuesday 2 June

14:00 → 15:30 Welcome session: Chair: M. Kopsacheili

14:15 Welcome and LOC communications

Speaker: Davide De Grandis (ICE-CSIC)

Slides

14:45 SWG4 overview

Speaker: Matt Middleton (University of Southampton)

15:00 SIXTE simulations of compact objects (REMOTE)

The SIXTE (SImulation of X-ray TElescopes) software package is an end-to-end simulation framework which simulates the full observation process of an X-ray telescope, in which photons are generated from a source catalog, imaged by the telescope optics and detected by a sensor, generating events which may receive additional post-processing.
It is the official simulator for the NewAthena mission and implements both the WFI and X-IFU detectors, including their behavior at high count rates.

This talk will discuss SIXTE in the context of simulating compact objects, including how to specify both variable sources and large source catalogs for surveys. It will also describe the implementations of the NewAthena instruments, their high count rate effects, and strategies on how to mitigate them.

Speaker: Christian Kirsch

main.pdf

15:30 → 17:40 High-mass X-ray Binaries: Chair: M. Kospacheili, G. Sala

15:30 Stellar winds in high-mass X-ray binaries as seen by NewAthena

The spectral and timing behaviour of neutron star high-mass X-ray binaries (HMXBs) offers a unique opportunity to investigate accretion onto compact objects and the wind structures of massive stars. In particular, understanding the X-ray emission from neutron stars is a critical topic of research for current and future astrophysical studies. This is a prominent science case of the NewAthena mission and will be discussed in the upcoming NewAthena Special Issue. Recently, XRISM made it possible to resolve, for the first time in an HMXB, the Fe Kα doublet and to obtain precise measurements of wind velocities via Doppler shifts thanks to its microcalorimeter Resolve. These results demonstrated how high-resolution microcalorimeter spectroscopy can transform our view of (i) the wind geometry, (ii) the ionisation structure and chemical composition, and (iii) line-of-sight dynamics. With NewAthena, we will perform time-resolved spectroscopy for the first time on timescales down to hundreds of sec to track rapid absorption changes as the compact object orbits its donor star. In this talk, we will discuss our recent simulations and results in the context of the NewAthena Special Issue with reliable statistical approaches, using state-of-the-art frameworks for X-ray spectral analysis based on Bayesian inference (e.g. jaxspec).

Speaker: Camille Diez (ESA/ESAC)

2026_06_03_NewAthenaRisingWG4.pdf

15:55 Energy resolved pulse profiles of Vela X-1: Cross-calibrating XMM-Newton and NuSTAR to trace spectral features

Pulse profiles provide a powerful diagnostic of the emission geometry and radiative processes in accreting X-ray pulsars, but their observed shape is affected by instrumental properties. We demonstrate that the energy-dependent pulsed fraction can be used as a robust timing cross-calibration diagnostic to combine XMM-Newton/EPIC-pn and NuSTAR observations. Using a simultaneous observation of the accreting pulsar Vela X-1, we show that once instrumental effects such as deadtime, energy redistribution, and source and background region selection are accounted for, the pulsed fraction measured by the two instruments can be consistently superimposed in their common energy range. This enables a seamless combination of XMM-Newton and NuSTAR data covering the 0.5–70 keV band. Residual differences around the iron-line region are attributed to the different energy resolutions of the instruments. Modelling the pulsed fraction obtained from the combined dataset reveals localized broad dips likely associated with cyclotron scattering features and soft X-ray emission lines. We further show that during orbital phases of reduced absorption, timing signatures of emission lines become more pronounced when spectral features are weak. This demonstrates that timing analysis is sensitive to scattering processes not always evident in energy spectra, highlighting its role as a powerful complement to spectroscopy.

Speaker: Dimitrios Maniadakis (INAF)

NewAthena-2.pdf

16:10 Coffee break

16:40 A rare HMXB with a variable red supergiant running the show

X-ray binaries with red supergiant companions (RSGs) are extremely rare, and probe a very short-lived phase of binary evolution, just before the system is expected to undergo a second supernova. eRASS J085039.9-421151 (also Swift J0850.8-4219) was detected as a persistent source in the eROSITA survey at a relatively lower luminosity of 1e35 erg/s. The source was subsequently followed-up by NuSTAR, which showed a strong FeK-alpha line with an equivalent width of 0.7keV, and required a partial covering absorber with column density ~1e24 cm^-2 to yield a good fit. No pulsations were detected, but binary evolution scenarios lean towards a slowly rotating neutron star as the likely accretor. The system is one of only two RSG X-ray binaries in the Milky Way, with the other also showing similarly persistent behaviour and comparable X-ray luminosity, but markedly less obscuration. VLT/X-shooter data of the optical companion of eRASS J085039.9-421151, revealed its semi-variable nature as a red supergiant with multiple emission lines that vary in strength between the two available observations. In addition to emission lines attributed to the red supergiant's radial pulsations, there are also higher-ionisation lines that require the presence of hot plasma, likely indicating the accretion stream onto the neutron star. The obscuration was proposed to be due to the dusty environments that red supergiants are typically embedded in. However, recent XMM-Newton data do not show such strong levels of obscuration, making inferences on the absorber non-trivial, complicating the previous proposed picture. Multiwavelength study of such a system not only expands our current understanding of binary evolution, but also offers a window into the poorly understood stellar environment of red supergiants. The vastly improved spectral resolution and sensitivity offered by NewAthena makes the study of such a system an ideal science case, as it can pave the way for uncovering new such probes into late stage binary evolution.

Speaker: Aafia Zainab Ansar (Dr. Remeis Observatory Bamberg & ECAP, FAU)

NewAthena_COMeeting.pdf

16:55 The Missing Lines: Constraining Disk Parameters in Gamma-Ray Binaries with NewAthena

Gamma-ray binaries are high-mass systems characterized by spectral energy distributions that peak near 100 MeV. X-ray observations of these systems reveal no detected spectral lines; only upper limits on Fe Kα are reported. This line deficit may be intrinsic, originating from extreme plasma ionization, or pulsar-driven disruption of the circumstellar environment. From an instrumental perspective, however, current observatories may lack both the sensitivity to recover weak lines and the phase coverage to detect phase-dependent emission. NewAthena offers the opportunity to resolve this issue with its state-of-the-art high-resolution spectroscopy instrument.

The pulsar wind interaction with the disk near periastron is expected to increase plasma temperature, density, and ionization to levels potentially sufficient for line emission. Whether or not lines are detected, orbit-resolved simulations constrain the disk parameters, confirming physical conditions if lines are recovered, or placing upper limits on disk parameters if they are not.

To model this phase-dependent behaviour, we simulated orbit-resolved synthetic spectra via SIXTE in preparation for NewAthena observations. In this talk, we will present detection limits on weak spectral features, constraints on disk parameters under which line emission arises, and synthetic spectra across orbital phases.

Speaker: Iuliia Shebalkova (Dublin City University)

HMXBs_Shebalkova.pptx

17:10 From Analysis to Insight: Tools and Applications in High-Mass X-ray Binaries

High Mass X-Ray binaries are fascinating systems. They consist of an O/B-type donor and a compact object (neutron star or black hole) embedded in the donor’s dense stellar wind, often in a close orbit, where orbital geometry and variability can be exploited to map the circumstellar environment.
During the years, we analysed interesting individual systems and, at the same time, developed some tools that we published to share with the community. In the eclipsing, wind and disc-fed system Cen X-3, the high inclination enables compact object eclipses and direct measurements of NS spin orbital Doppler modulations. During state transitions, from low-hard to high-soft, Doppler shifts of the Fe XXV emission line allow us to reconstruct the ballistic trajectory of emitting plasma as it is captured and accreted by the neutron star. These analyses motivated \texttt{xraybinaryorbit}, a Python package for modelling and fitting orbital modulations of different observables, including absorption and Doppler shifts.
We also explore rapid variability in the magnetar-candidate system 4U~0114+65, one of the slowest known X-ray pulsars ($P_{\rm spin}\sim 9000$ s). Its light-curves show peaks compatible to Rayleigh--Taylor instabilities at the magnetosphere. Short-lived dips and/or spikes in light-curves have the power to probe both accretion dynamics and wind structure (e.g. partial occultations by overdense clumps). To systematically characterise these features, we developed dipspeaks, an automatic dip and peak search based on autoencoders that returns a catalogue of events with noise probabilities. Finally, anticipating the diagnostic power of upcoming high-resolution spectroscopy with many time-binned, phase-resolved spectra, we introduce BLISS, a continuum independent blind line-search algorithm that streamlines the automatic detection and incorporation of emission lines in spectral modelling.

Speaker: Graciela Sanjurjo Ferrín (Universidad de Alicante)

new_athena_rising.pdf

19:30 → 21:30 Welcome cocktail: La Belter

Wednesday 3 June

10:00 → 12:50 Ultra-luminous X-ray sources: Chair: M. Middleton, A. Gurpide

10:00 Probing Extreme Accretion and Outflows in ULXs: The NewAthena Era

Ultraluminous X-ray sources (ULXs) represent the most extreme accreting X-ray binaries in the local Universe, with luminosities up to $ \sim10^{41}\ \rm erg/s$. They are now widely interpreted as stellar-mass compact objects accreting at super-Eddington rates in majority, as indicated by their soft X-ray spectral components, coherent pulsations in multiple systems, and the presence of powerful, mildly relativistic winds.
In this talk, I will outline the breakthrough science that will become possible with next-generation high-resolution X-ray spectrometers. Since accretion onto compact objects is broadly scale-invariant with mass, ULXs provide a unique laboratory for understanding disc structure, wind launching, and radiative feedback—processes that also shape stellar-mass X-ray binaries, tidal disruption events, and the supermassive black-holes in the early phases of the Universe.
NewAthena/X-IFU, with $\sim$ 4 eV resolution and $\gtrsim$ 6000 $\rm cm^{2}$ effective area, will make possible to detect and disentangle complex outflow geometries, separating ultrafast outflow from slower wind phases. Crucially, it will enable for the first time measurements on sub-hour timescales, allowing us to follow the coupled evolution of the disc and winds and to discriminate between radiative/thermal driving and magnetic acceleration.
This topic will be the core of the paper whose draft I submitted and has just been approved for the NewAthena special issue on JHEAP.

Speaker: Francesco Barra (INAF - IASF Palermo)

NewAthena_Barra.pdf

10:25 Super-orbital timing and phase-resolved spectroscopy of NGC 5907 ULX-1: probing geometric beaming in the most luminous ULX pulsar

NGC 5907 ULX-1, the most luminous ULX pulsar (peak luminosity 10⁴¹ erg/s), shows super-orbital modulation whose physical origin has implications for the magnetic field strength required to sustain super-Eddington accretion. From >10 years of Swift XRT monitoring (2014–2025), we characterise this modulation using Bayesian mixture models that properly marginalise over intermediate-flux states diluting the periodic signal in the recent high-flux epoch. We recover a tightly constrained ~78 d period with a fast-rise-exponential-decay profile that maintains phase-coherence across an extended quiescent interval (mid-2017–mid-2020; ~14 super-orbital cycles), favouring a precession mechanism anchored to the neutron star itself. We use this timing solution to assign super-orbital phases to the full archival set of XMM-Newton and NuSTAR observations, constructing phase-resolved broadband spectra that substantially extend the limited sampling available to earlier work (Fürst et al. 2017). Tracking the spectral continuum as a function of super-orbital phase offers a crucial diagnostic of the geometric beaming that is central to interpreting the extreme apparent luminosities of ULX pulsars: precession-driven changes in viewing angle modulate the degree of collimation visible to the observer, so phase-resolved spectroscopy can disentangle intrinsic luminosity variations from these viewing angle effects. For NGC 5907 ULX-1, where the apparent luminosity exceeds the neutron star Eddington limit by a factor of ~500, this approach provides a direct test of the beaming geometry invoked to reconcile the observed flux with physically plausible accretion rates.

Speaker: Nabil Brice (University of Hertfordshire)

slides_newathena.pdf

10:40 Four shalt thou (not?) count: new detections of mHz quasi-periodic oscillations in pulsating ULXs

Quasi-periodic oscillations in the mHz range (mHz QPOs) have been detected in different X-ray binaries, hosting either a neutron star or a black hole. Nonetheless, the presence of mHz QPOs in a few ULXs was initially interpreted as the footprint of accreting intermediate-mass black holes. The detection of mHz QPOs first in M82 X-2, and then in M51 ULX-7 (two known pulsating ULXs), however, has demonstrated that this feature is also present in neutron stars shining at super-Eddington luminosities. Additionally, the similar properties of the QPOs in these two pulsating ULXs (a stable centroid frequency and rms) suggest that they could represent a peculiar feature of this class of extreme neutron stars. In this talk, I’ll present the results of our analysis on two other pulsating ULXs, namely NGC 7793 P13 and NGC 5907 ULX-1. We significantly detect a mHz QPO in multiple observations of NGC 7793 P13. I will show how the properties of this QPO align with those of M82 X-2 and M51 ULX-7, supporting the hypothesis that they represent a common feature among pulsating ULXs. I will also show how NGC 5907 ULX-1 could be the fourth pulsating ULX with a mHz QPO, although, in this case, the feature is only marginally detected. NewAthena, with its superb spectral capabilities and time resolution, is expected to help us better understand the link between the mHz QPOs observed in PULXs, their spin signals and the extreme accretion regime of super-Eddington sources.

Speaker: Matteo Imbrogno (ICE-CSIC, IEEC)

Imbrogno_QPO_PULX.pdf

10:55 Spectral and Timing Variability Studies of PKS 2155-304 using Chandra and NuSTAR

Blazars exhibit strong variability across multiwavelength observations and multiple timescales. We present a systematic study of the X-ray spectral and timing variability of the TeV blazar PKS 2155-304 using Chandra and NuSTAR observations spanning 25 years (1999-2024). Timing analysis and flux distribution studies reveal moderate variability in most light curves and variable power spectral indices across the observational time. Hardness-ratio plots indicate that while many observations show limited spectral evolution with flux, some exhibit significant hardness changes correlated with brightness. We modeled the X-ray spectra with power-law, broken power-law, log-parabola, and bremsstrahlung plus power-law functions. The bremsstrahlung plus power-law model provides the best description for the majority of observations, suggesting the coexistence of thermal and non-thermal components in the X-ray emission. Additionally, we performed joint spectral fitting to Chandra and NuSTAR data during flares around MJD 56405-564056. These findings highlight the complex variability of PKS 2155-304 and provide new constraints on the relativistic jet’s non-thermal processes and possible thermal contributions to blazar emission.

Speaker: Rameshan Thimmappa (Villanova University)

PKS2155_NewAthena_Rising_03June2026_Rameshan.pptx

11:10 Ultraluminous and Hyperluminous X-ray Sources: Probing Extreme Accretion and Magnetism in Compact Objects (REMOTE)

Ultraluminous X-ray sources (ULXs) are among the most luminous non-nuclear X-ray emitters in nearby galaxies, with luminosities exceeding the Eddington limit expected for stellar-mass black holes. They were historically considered promising candidates for hosting intermediate-mass black holes (IMBHs). However, the discovery of coherent pulsations in several ULXs, together with detailed broadband X-ray observations, has demonstrated that many of these systems are powered by neutron stars undergoing super-Eddington accretion. These findings have significantly reshaped our understanding of extreme accretion and radiation processes around compact objects.

Hyperluminous X-ray sources (HLXs), characterized by luminosities above 1e41 erg/sec, have long been regarded as the strongest observational candidates for IMBHs. Nevertheless, the possibility that neutron stars may also power some HLXs challenges this interpretation and motivates renewed investigation into the physical mechanisms driving these sources.

Here, we examine the spectral properties of ULXs and HLXs using a physically motivated model that considers neutron stars as the central accretors. In this framework, the observed emission is described by a combination of soft thermal radiation and high-energy synchrotron emission originating within a strongly magnetized neutron-star magnetosphere. The resulting spectral features are consistent with an accreting neutron-star scenario, while the particle acceleration processes responsible for potential non-thermal emission remain an active area of research.

Future missions such as NewAthena will play a transformative role in this field. Its large collecting area and high-resolution spectroscopy will enable detailed studies of faint spectral features, improved characterization of outflows and accretion environments, and the detection of fainter ULX populations, providing crucial insights into the nature of these extreme sources.

Speaker: Tanuman Ghosh (Inter-University Centre for Astronomy and Astrophysics)

11:25 Coffee break

11:55 Feeding the Magnetized Whirlwind: Hunting Highly Magnetized Accreting Neutron Stars with NewAthena

X-ray pulsars (XRPs) provide a unique laboratory for studying accretion under extreme magnetic fields and strong-gravity conditions. Most are found in high-mass X-ray binaries, particularly systems with Be-star companions (BeXRBs), where episodic mass transfer can trigger bright X-ray outbursts reaching luminosities of ≳1E+38 erg/s. These systems probe the physics of magnetically channeled accretion and are closely connected to the study of the most luminous accreting binaries, including ultraluminous X-ray sources.
Despite decades of observations, key questions remain open. Major outbursts often have duty cycles of decades, meaning that each new X-ray observatory has the opportunity to catch events in systems that remained inactive during previous missions. With its large effective area and survey capabilities, Wide Field Imager (WFI) will significantly expand the accessible population of accreting pulsars, enabling studies of systems in nearby galaxies such as M31 that are currently too faint for detailed characterization with observatories like XMM-Newton.
At the same time, X-ray Integral Field Unit (X-IFU) will provide high-resolution spectroscopy of the accretion environment in magnetized neutron stars. The detection and characterization of narrow absorption and emission features associated with disk winds and magnetospheric outflows will offer new insights into the structure of the inner accretion flow and the physics of super-Eddington accretion.
In this talk, I will discuss how NewAthena can advance the study of accreting pulsars through three complementary avenues: catching rare outbursts in long-duty-cycle systems, extending studies to larger distances, and probing accretion-driven outflows with high-resolution X-ray spectroscopy.

Speaker: Georgios Vasilopoulos (National and Kapodistrian University of Athens)

Feeding the Magnetized Whirlwind

12:20 Ionizing feedback from super-Eddington compact objects in low-metallicity starbursts

Nebular He II λ4686 in low-metallicity star-forming galaxies requires a hard ionizing spectrum beyond that produced by stellar populations. I present new deep Chandra and XMM-Newton observations that quantify the relative contributions of ULXs and hot diffuse plasma to this ionizing field in nearby metal-poor starbursts. Chandra’s sub-arcsecond imaging resolves individual ULXs, deconfuses them from surrounding emission, and establishes their spatial association with young stellar clusters. XMM-Newton constrains the soft X-ray luminosity and temperature structure of the diffuse thermal plasma component. Combining spatially resolved X-ray spectroscopy with photoionization modeling, I derive the relative contributions of ULXs, hot gas, and young stellar populations to the photon budget required to power nebular He II and related high-ionization tracers. These observations provide empirical constraints on the emergent ionizing spectra of super-Eddington compact-object populations in metal-poor environments. These results define the observational framework within which NewAthena’s increased throughput and high-resolution spectroscopy will enable population-level constraints on super-Eddington accretion and its coupling to the surrounding medium in metal-poor galaxies.

Speaker: Margaritis Chatzis (University of Potsdam)

Ionizing feedback from super-Eddington compact objects in low-metallicity starbursts.pdf

12:35 Resolved extreme ionization around Holmberg II X-1: a new view on ULX radiative feedback

We present spatially resolved JWST NIRSpec and MIRI integral-field spectroscopy of the nebula surrounding the ultraluminous X-ray source Holmberg II X-1, providing the first direct view of high-ionization infrared emission on scales of only tens of parsecs in this system. By combining emission-line surface-brightness maps, diagnostic line ratios, and kinematic profiles, we detect intense [Ne V] and [Ne VI] emission that is strongly confined to a localized sector of the nebula, in contrast to the more extended hydrogen recombination and low-ionization emission. All detected transitions exhibit narrow velocity dispersions, with no evidence for broad wings or systematic velocity shifts, ruling out fast radiative shocks as the dominant excitation mechanism. The highest-ionization gas is aligned with previously identified radio structures, suggesting directional escape of hard photons from the accretion flow. Comparisons with other low-metallicity galaxies hosting ULXs show that similar high-ionization luminosities can arise in very different star-formation environments, pointing to the dominance of compact accretion as a source of hard ionizing radiation. These results demonstrate that anisotropic hard-photon feedback from compact objects can imprint observable signatures on the interstellar medium, providing a resolved laboratory for studying the coupling between accretion power and nebular ionization in extreme environments.

Speaker: Federico A. Fogantini (Space Telescope Science Institute)

Fogantini_HoIIX1_SWG4.pdf

12:50 → 14:35 Lunch

14:35 → 16:15 Low-mass X-ray binaries: Chair: B. De Marco

14:35 Highs, Lows, and Flares A Multi-band View of Shocks and Outflows in transitional millisecond pulsars

Transitional millisecond pulsars (tMSPs) bridge the gap between accreting neutron stars in low-mass X-ray binaries and rotation-powered millisecond radio pulsars, offering a unique laboratory to study the interplay between accretion and pulsar activity. These systems display a subluminous X-ray state characterized by rapid transitions between high, low, and flaring emission modes.

Multi-wavelength campaigns on the prototype tMSP PSR J1023+0038 have established a complex scenario in which a compact jet, discrete ejecta, inflowing matter, and the pulsar wind interact to regulate the source phenomenology. Recently, we carried out the first multi-wavelength polarimetric study of PSR J1023+0038 using data from IXPE, the VLT, and the VLA. We detect a linear polarization degree of (12±3)% in the 2–6 keV band during the high mode. The polarization angle is aligned with that measured in the optical band, strongly suggesting a common physical origin. In the low mode, the polarization is not significantly detected, yielding a 90% confidence upper limit of 26%.

These results indicate that both optical and X-ray polarization likely arise from synchrotron emission produced at the shock interface between the pulsar wind and the inner accretion flow. In addition, simultaneous radio, optical, and X-ray observations obtained during this campaign provide the first coordinated view of the flaring mode, highlighting the crucial role of outflows in shaping the system behaviour.

The capabilities of NewAthena will enable unprecedented studies of rapid mode switching and faint polarization-linked spectral components in tMSPs. Combined with coordinated optical and radio facilities, NewAthena will be key to disentangling the accretion–ejection physics of these systems, fully exploiting the multi-band synergies that define the next decade of high-energy astrophysics.

Speaker: Maria Cristina Baglio (INAF-OAB)

NewAthena2026_pdf.pdf

15:00 Low-luminosity X-ray pulsations from an accreting millisecond pulsar: An ever-thinning thread between bright accretion and subluminous states

A never-ending competition takes place around rapidly spinning, weakly magnetized neutron stars in low-mass X-ray binaries. Inflowing matter spirals inward and, during outburst, is channeled along the neutron star’s magnetic field lines onto its magnetic poles, producing coherent X-ray pulsations. As the accretion rate declines, the rotating magnetosphere pushes back, halting accretion and switching off pulsations in the so-called “propeller” regime. In fast-spinning systems, this transition is particularly sensitive to small variations in the mass accretion rate. I will present an XMM-Newton Target of Opportunity observation of an accreting millisecond pulsar at the end of its 2025 outburst, complemented by radio and archival Chandra data. We detect X-ray pulsations with a remarkably high amplitude at a luminosity level where centrifugal inhibition of accretion is traditionally expected to dominate. This result challenges the standard accretion-propeller boundary and reveals an ever-thinning thread between bright accretion and subluminous disk states. Low-luminosity pulsations have been rarely observed, primarily due to instrumental sensitivity limits. NewAthena will be a game changer in this field: its combined high sensitivity, sub-millisecond timing resolution, and spectral capabilities will allow us to track these phenomena down to the faintest accretion states, probing the delicate balance between accretion flows and neutron star magnetospheres.

Speaker: Giulia Illiano (INAF-Astronomical Observatory of Brera (Merate))

Illiano_NewAthena.pdf

15:15 A New Era for Galactic Center Astrophysics: Revealing the X-ray Populations with NewAthena

The Galactic center (GC) is home to the largest known concentration of exotic X-ray sources ever identified in our Galaxy, including compact objects like cataclysmic variables (CVs) and low-mass X-ray binaries (LMXBs), as well as thousands of faint X-ray sources whose nature is unclear. Recent studies indicate that the X-ray populations in the innermost region of our Galaxy vary over different spatial scales. However, to unambiguously classify those sources and their distributions, we need sensitive X-ray instruments whose capabilities include a combination of high angular and spectral resolution. The former is crucial for resolving compact sources in the crowded GC region and disentangling contamination from overlapping diffuse emission; the latter can allow us to differentiate between different source classes based on their emission line properties. NewAthena surveys will be capable of revolutionizing the study of Galactic center X-ray populations, and – by classifying an unprecedented number of X-ray point sources – exponentially increasing our knowledge of the different types of X-ray sources populating our Galaxy.

Speaker: Shifra Mandel (Columbia University)

newathena_vf.pptx

15:30 Spectroscopic signatures of radiative winds in thermonuclear X-ray bursts

This study examines the observational signatures of optically thick winds in thermonuclear X-ray bursts (XRBs). By combining the wind models from Herrera et al. (2023) with the burst models from José et al. (2010), we reconstruct theoretical X-ray light-curves and effective temperature evolution. Using the HEASOFT package, we simulate observational counterparts of said theoretical predictions, as well as time-resolved spectra, for the NASA X-ray telescope on board the ISS, NICER (Nuclear star Interior Composition ExploreR) and for NewAthena. This research enhances understanding of radiative winds in XRBs and provides a framework for future observational assessments.

Speaker: Daniel Muñoz Vela (Universitat Politècnica de Catalunya)

The effect in the X-ray light-curves and spectra of Radiative Winds in thermonuclear X-ray bursts.pdf

15:45 Testing the Poynting-Robertson drag in thermonuclear X-ray bursts in 4U 1636-536: from archival data to NewAthena

We investigate the impact of thermonuclear X-ray bursts on the persistent emission of the low-mass X-ray binary 4U 1636–536. Archival observations from XMM-Newton and INTEGRAL were analyzed through time-resolved X-ray spectroscopy of a burst simultaneously detected by four instruments: EPIC-pn, RGS, JEM-X, and ISGRI. The persistent emission was modeled using a combination of accretion disk, Comptonization, and reflection components, while the burst emission was described by an additional blackbody component. We explore possible variations in the persistent emission adding a multiplicative scaling factor to the persistent emission model across all time intervals. Our results show a significant increase in the persistent emission during the burst. This behaviour is consistent with a temporary increase in the mass accretion rate, potentially driven by Poynting–Robertson drag induced by the burst radiation field. Additional spectral parameters, including luminosity, blackbody temperature, and flux, display coherent temporal evolution throughout the event. These findings support the scenario in which thermonuclear X-ray bursts can directly influence the accretion flow in neutron star low-mass X-ray binaries. We finally use our modelled evolution to simulate the time-resolved spectra during thermonuclear X-ray bursts of 4U 1636-536 as seen by NewAthena.

Speaker: Mireia Isern i Vizoso (Universitat Politècnica de Catalunya)

NewAthena_Workshop_Presentation.pdf

16:00 Detection of a 459 Hz X-ray Burst Oscillation in XTE J1810−189 using NICER (REMOTE)

We present a detailed temporal analysis of a Type I X-ray burst from the neutron star low-mass X-ray binary (NS-LMXB) XTE J1810−189, observed on 27 April 2023 with the Neutron Star Interior Composition Explorer (NICER). The burst displays a rapid rise time of 2.55 s, followed by an exponential decay with a timescale of 7.5 s, resulting in a total burst duration of ~13 s. Type I X-ray bursts are produced by unstable thermonuclear burning of accreted material on the surface of neutron stars in NS-LMXBs. Because these bursts originate at the stellar surface, they can display highly coherent brightness modulations, known as burst oscillations, which are commonly associated with the neutron star spin frequency. In this study, we report the detection of a burst oscillation signal at a frequency of ~459 Hz during the cooling tail of the burst. The signal exhibits a strong Leahy-normalized power of PL=35.95 at 458.92 Hz, corresponding to a single-trial significance of 5.53σ and a multiple-trial significance of 3.14σ. The folded pulse profile in the 0.2–12 keV energy band is well described by a constant plus sinusoidal model, yielding a fractional root-mean-squared amplitude of 14.63%. The detected oscillation frequency is consistent with the neutron star spin, implying a spin period of ∼2.18 ms and placing XTE J1810−189 among the rapidly rotating neutron stars in the NS-LMXB population. The detection of the oscillation during the cooling phase of the burst suggests that the observed modulation may be explained by surface mode oscillations or an asymmetric cooling wake. These results provide valuable constraints on the spin properties and burst oscillation mechanisms in XTE J1810−189 and contribute to a broader understanding of thermonuclear burst phenomena in accreting neutron stars.

Speaker: M. Varun (CHRIST University)

NewAthena Rising: SWG4_Varun

NewAthena Rising_ SWG4_Varun.pdf

NewAthena Rising_ SWG4_Varun.pptx

16:15 → 18:20 Accreting white dwarfs: Chair: S. Mereghetti

16:15 Coffee break

16:40 Expanding our view on symbiotic stars with NewAthena

In this contribution I will present recent results on the study of symbiotic stars, interacting systems in which a white dwarf accretes material from an evolved (typically a RGB or AGB) star. The very high luminosity and intrinsic variability of evolved stars complicates the identification and study of symbiotic stars. However, X-ray emission is a distinctive feature that opens a window to explore accretion on these systems. I will focus on three particular points:

(I) Current view of mass transfer in symbiotic stars, phenomenological description and characteristics of their X-ray emission.

(II) Recent results from high-angular resolution facilities (ALMA+VLTI) and synergies with X-ray observatories.

(III) Perspectives for research on symbiotic stars with NewAthena.

Speaker: Jaime Alonso Hernández (Centro de Astrobiología (CSIC-INTA))

Alonso-Hernandez_NewAthena_V2.pdf

Alonso-Hernandez_Newathena_V2.pdf

17:05 X-ray Periodicities in the Gamma Cas Analogues

The mechanism for X-ray generation in the Gamma Cas analogues, a small group of highly variable Oe/Be stars, has been a mystery for several decades. They are characterised by their hard X-ray spectra, often including strong Fe fluorescence lines, and X-ray luminosities in the gap between those seen in similar stars and the more luminous Be/X-ray Binaries. They have also been observed to be highly variable on a range of timescales, from seconds up to several years. Competing theories for the mechanism for X-ray production include magnetic interactions between the star and its decretion disk or accretion onto a white dwarf (WD) companion. Until now the missing evidence in favour of these sources being a new population of Be+WD binaries has been the absence of persistent significant periodicities associated with potential WD companions.

We will present the results of a comprehensive review of intra-observation variability in a large sample of 89 XMM-Newton and 45 Chandra observations, using both Fourier- and time-domain techniques to search for periodicities. We will identify those sources which appear to show periodicities across several observations, and outline how the periodicities in these sources might resolve the doubt over the nature of these exotic sources.

Speaker: Robbie Webbe (IRAP, Toulouse, France)

NA Rising - Gamma Cas.pdf

17:20 X-Ray Characterization of the Post-Nova Stage of V2487 Ophiuchi

V2487 Oph is a recurrent nova that underwent a fast and luminous eruption in 1998 (t₃ ≈ 8 days, peak magnitude 9.5). The host system hosts a massive white dwarf (~1.35 M☉) accreting from a donor star (~0.21 M☉) in a binary with an orbital period of 0.753 days (~18.1 hours). Previous X-ray observations conducted 2.7 and 3.2 years after the outburst suggested that accretion had resumed in the system. Here, we present the X-ray analysis of five observations of V2487 Oph obtained with XMM-Newton and Suzaku over 12 years following the 1998 eruption, characterising the long-term X-ray behaviour of the system and examining evidence for sustained or re-established accretion during the post-nova phase. We also include preliminary NewAthena simulations to evaluate how future high-resolution X-ray observations could improve the detection and characterisation of nova host systems.

Speaker: Elif ŞAFAK (Universitat Politècnica de Catalunya)

NewAthena Rising.pdf

17:35 Pole flip or precession: the enigmatic behaviour of intermediate polar DW Cancri

Accreting magnetic white dwarfs offer a unique window into accretion physics in binary systems. Like X-ray binaries, they harbour a standard Shakura-Sunyaev accretion disc whose inner edge can be magnetically truncated, yet their lower energies and longer dynamical timescales make the inner accretion geometry far more accessible. I will present results on DW Cnc, a well-studied intermediate polar that has recently revealed a remarkable suite of new phenomena. We report a new micronova burst detected by ASAS-SN reaching a peak optical luminosity of 6.6×10³³ erg s⁻¹ with a released energy consistent with a thermonuclear runaway in the magnetically confined accretion flow. Immediately preceding the burst, TESS and OPTICAM data reveal the reappearance of tilted disc precession as DW Cnc emerges from its low state. Strikingly, we also identify a new phenomenon in which the white dwarf spin signal switches on and off during the precession period, providing the first evidence for pole flipping in a disc-accreting system. These results place DW Cnc at the intersection of two poorly understood phenomena, micronovae and accretion column dynamics, and highlight the need for systematic monitoring of magnetic systems beyond serendipitous discovery. Here I will discuss how NewAthena will transform our ability to probe the inner accretion geometry of magnetic white dwarfs. In particular I will show how measurements of time-resolved velocity shifts in the Fe XXV/XXVI lines at eV precision will allow us to directly test competing models of disc–magnetosphere coupling and definitively distinguish pole switching from continuous accretion column precession.

Speaker: Martina Veresvarska (ICE-CSIC)

veresvarska_presentation

17:50 Probing the masses of White Dwarfs in Cataclysmic Variables with NewAthena

The mass of a white dwarf (WD) is a fundamental parameter for understanding its formation, evolution, and role in binary systems. A large fraction of WDs are found in interacting binaries known as Cataclysmic Variables (CVs), where the WD accretes material from a low-mass donor star, typically a late-type main-sequence star. The X-ray emission from a class of magnetic CVs called the Intermediate Polars (IPs), arises from an accreted matter shock heated up to high temperatures (kT ≈ 10–50 keV), which must cool before settling onto the WD surface. The post-shock gas is heated up to ~10⁸ K, resulting in highly ionized gas. While the post-shock gas cools and settles down onto the WD surface, it emits various X-ray emission lines of various medium Z elements. In addition to these lines, many CVs exhibit a prominent 6.4 keV Fe Kα fluorescence feature originating from reflection off the WD surface. We also see a strong 6.4 keV Fe K$\alpha$ fluorescence line in various CVs, which originates from the WD surface. The width of this line encodes information about the WD spin (modulated by inclination), which is especially relevant for non-magnetic CVs. The laboratory wavelengths of the Fe Kα doublet and Kβ transitions depend on the ionization state of Fe, and measuring their centroid positions provides access to the gravitational redshift. This enables direct WD mass measurements, while simultaneously constraining the surface temperature and, in turn, the secular-average accretion rate.

Speaker: Nazma Islam (NASA Goddard Space Flight Center and University of Maryland Baltimore County)

NIslam_NewAthena_talk.pdf

Thursday 4 June

10:00 → 11:45 Population studies: Chair: N. Rea

10:00 Timing studies with the NewAthena WFI: Compact object populations in external galaxies

The identification of compact object type as either black hole (BH) or neutron star (NS) is fundamental to understanding their formation and evolution, and provides critical constraints concerning the final stages of supernovae. At the population level, X-ray binaries are linked to a number of host galaxy parameters, inform the expected rate of gravitational wave detections, and may have contributed to heating of the IGM prior to the epoch of reionization. To date, time-domain determination of compact object type remains a relatively untapped tool outside of the Milky Way Galaxy, although it has shown great promise through, e.g., detection of Quasi Periodic Oscillations (QPOs) in extragalactic black holes and discovery of pulsations in Ultraluminous X-ray (ULX) sources. Timing studies of X-ray sources (such as pulsations and thermonuclear bursts) offer a reliable means of confirming the nature of compact objects like NSs, whereas spectral modeling often suffers from degeneracies. Measurements of QPOs, pulsations, and bursts in extragalactic populations (rather than individual bright sources) will lead to a revolution in the study of NS and BH population demographics, linking source phenomena to accretion and galaxy parameters (e.g., star formation, metallicity). NewAthena’s WFI features instrumental design characteristics that will make such timing studies of extragalactic X-ray binary (XRB) populations possible. Its wide field of view (40’ x 40’) can capture either significant fractions or the full extent of galaxies in single observations. The large collecting area collects sufficient photons to enable timing. The PSF is sufficient to spatially resolve populations down to scientifically interesting flux limits, and the WFI detector has good timing resolution for the determination of key XRB timing behaviors. In this talk, we discuss the WFI’s capabilities for performing such measurements in a variety of galaxy environments and to greater distances, showcasing its aptitude for timing studies of extragalactic XRB populations.

Speaker: Hannah Fritze Moon (NASA Goddard Space Flight Center)

Timing Studies With the NewAthena WFI: Compact Object Populations in External Galaxies

10:25 Highly Variable Sources in the XMM Slew Survey

The newest edition of the XMM Slew Survey catalogue incorporates more than eight years of new observations, adding nearly 70,000 new detections of sources to the previous version. With an extended baseline now covering more than 20 years of observations the Slew catalogue presents an opportunity to detect bright, long-period, variable sources.

By cross-matching the sources in the XMM Slew Catalogue v3 against ROSAT, eROSITA, XMM pointed observation and Swift source catalogues, and upper limits from some of these observatories, we have identified a large population of highly variable X-ray sources. In some cases these sources exhibit variability over several orders of magnitude, which is a strong indicator for astrophysical sources powered by compact objects. Many of these sources have not been identified as significantly variable before. We will present the population of significantly variable sources, and identify different kinds of X-ray sources such as tidal disruption events, strongly varying AGN and bursting X-ray binaries.

Speaker: Robbie Webbe (IRAP, Toulouse, France)

NA Rising - Slew Variability.pdf

10:40 A comprehensive census of X-ray periodic sources in dense clusters with NewAthena high-resolution timing

Accreting compact objects are the primary X-ray populations in globular clusters. Their periodic variations spanning rotational spins and orbital motions, provide essential diagnostics for identifying progenitor populations and tracing evolutionary pathways. While recent surveys of Milky Way globular clusters have established a preliminary census of these sources, offering insights into cataclysmic variable formation and exotic binaries, significant observational gaps remain in short-period systems. Unambiguously classifying these populations requires a simultaneous leap in angular resolution and timing precision, surpassing the constraints of current observatories. NewAthena deep surveys of globular and nuclear star clusters are poised to bridge this gap with its high timing resolution. By pushing detection sensitivity into the sub-second regime, NewAthena will uncover fast pulsators, including white dwarf pulsars, millisecond pulsars, and ultra-compact X-ray binaries, key potential sources of gravitational waves. This presentation demonstrates how NewAthena will transform our understanding of the most dynamic binaries in the densest stellar environments.

Speaker: Tong Bao (INAF-Osservatorio Astronomico di Brera)

TB_202606NewAthena.key

TB_202606NewAthena.pdf

10:55 Magnetar fraction in Core-Collapse Supernovae (REMOTE)

Understanding the birthrate of magnetars, highly magnetized neutron stars, is essential for constraining their role in high-energy astrophysical phenomena such as gamma-ray bursts (GRBs) and fast radio bursts (FRBs). In this talk, we aim to estimate the magnetar birthrate in the Milky Way by analyzing the Galactic population of observed young neutron stars. In this sample, magnetars appear to make up approximately 35% of this population, with the remainder classified as central compact objects (CCOs) or rotation-powered pulsars (RPPs). However, this percentage may be significantly affected by selection effects and observational biases. An important bias in defining a sample of young pulsars is the discrepancy between a neutron star’s characteristic age and its true age, particularly relevant for young neutron stars with low magnetic fields, which tend to appear much older than they actually are. Moreover the beamed nature of pulsar radio emission, causes many neutron stars to go undetected because their radio beams do not intersect our line of sight. These effects likely lead to an underrepresentation of pulsars in the observed young neutron star population. To investigate these biases, we collect a sample of nearby supernova remnants (SNRs) associated with neutron stars. We then model the spatial distribution and dynamical evolution of SNRs in the Galaxy to determine how many are required to reproduce the observed number in the Solar neighborhood. This enables us to estimate a lower limit for the Galactic core-collapse supernova rate. By combining this information with pulsar population synthesis models, we estimate the expected number of young pulsars, correcting for both age and beaming-related biases. This allows us to refine the inferred fraction of magnetars among the young neutron star population. The resulting magnetar birthrate provides an independent constraint that complements estimates based solely on population synthesis, offering new insights into the connection between strongly magnetized neutron stars and the high-energy and radio transient sky.

Speaker: Celsa Pardo Araujo (ICE-CSIC-IEEC)

11:10 Connecting radio pulsar, magnetars and XDINSs in a unified evolutionary framework with simulation-based inference

Understanding the Galactic population of isolated neutron stars within a unified framework provides key insights into their birth properties, evolutionary pathways, and the connections between different neutron star classes. In this work, we combine observational data from radio pulsars and isolated neutron stars exhibiting quiescent X-ray emission, employing a comprehensive population synthesis approach to investigate their origin and evolution. We develop a flexible population synthesis framework that models the dynamical, rotational, and magneto-thermal evolution of neutron stars, their radio and X-ray emission, and the selection effects of radio and X-ray surveys. Our models incorporate state-of-the-art 2D magneto-thermal simulations, allowing us to explore the impact of varying magnetic field configurations and envelope compositions. To simulate realistic X-ray spectra, we account for magnetospheric resonant cyclotron scattering and interstellar absorption. Additionally, we model the observational bias introduced by magnetar outbursts by linking the outburst rate to magnetic stresses in the stellar crust. We employ a simulation-based inference technique using artificial neural networks to reconstruct the birth properties, such as the initial magnetic field distribution and long-term magnetic field decay of the neutron star population. By combining radio and X-ray data we provide new constraints on the overall neutron star birth rate in the Galaxy and on the fraction of neutron stars exhibiting magnetar-like properties. This in turn can help quantify magnetar potential contribution to explain the rate of astrophysical transient phenomena, such as super-luminous supernovae, gamma-ray bursts and fast radio bursts.

Speaker: Michele Ronchi

newAthena_meeting.pdf

11:25 Coffee break

11:45 → 13:00 Isolated neutron stars: Chair: D. De Grandis

11:45 Growing and characterising the population of thermally emitting isolated neutron stars with NewAthena

The recently conducted eROSITA All-Sky Survey and the serendipitous source catalogues from pointed X-ray missions, like XMM-Newton, allow to significantly increase the population of thermally emitting isolated neutron stars (INSs). This promises exciting insights into the physics of ultra-dense matter, INS magnetic field evolution, and to study evolutionary pathways and links. However, with the current generation of X-ray instruments, long and time-expensive follow-up campaigns are required to weed out remaining contaminants and to establish the spectral and temporal state of the selected candidates, a necessary requirement before the new sources can be included in the aforementioned studies. In this talk, we will present how the the great positional accuracy, unparalleled spectral resolution, and large collecting area of the instruments aboard NewAthena not only allow for serendipitous INS discoveries, but will likewise revolutionise the identification and characterisation of thermally emitting INSs at unprecedented flux limits.

Speaker: Jan Kurpas (Leibniz-Institut für Astrophysik Potsdam (AIP))

talk_newathena_jkurpas.pdf

12:10 Origin of Magnetar Magnetic Fields: Insights from 3D Magneto-Thermal Simulations

Magnetars, the most strongly magnetized class of the isolated neutron star population, are characterized by large-scale dipolar magnetic fields of order $10^{14}$ G, which are responsible for their rapid spin-down. The origin of such intense dipolar fields remains an open problem. In this talk, I will discuss the role of the chiral magnetic effect, arising from the chiral anomaly, which enables mutual conversion between magnetic helicity and electron chiral asymmetry. We present results for scenarios with both nonzero and vanishing net magnetic helicity, the latter being more representative of realistic birth conditions in proto–neutron stars. Using three-dimensional magneto-thermal simulations, we demonstrate that the chiral magnetic effect transfers magnetic energy from small-scale fields—expected at birth—to large-scale dipolar structures without requiring any external energy input. This mechanism provides a physical explanation for the formation of the large-scale dipolar structure observed in magnetars.

Speaker: Clara Dehman (University of Alicante)

ClaraDehman_NewAthena2026.pdf

12:25 Polarised signatures from highly magnetised isolated neutron stars

Highly magnetised isolated neutron stars are amongst the most interesting and exotic objects observable in our sky. X-ray polarisation carries information about the physics occurring in the extreme environments surrounding these sources that is otherwise inaccessible to us. In particular, magnetars and X-ray Dim Isolated Neutron Stars (XDINSs) may be key to finally probing vacuum birefringence, a quantum electro-dynamics (QED) effect that has long been predicted but never tested. Mode conversion at the QED vacuum resonance in a magnetised atmosphere, alongside additional effects such as particle bombardment and partial ionisation, can leave significant imprints on the polarisation signature of thermal emission, while remaining otherwise unidentifiable in the overall spectrum. With the continued success of Imaging X-ray Polarimetry Explorer (IXPE) and the ongoing development of new polarimetric telescopes (e.g. REDSoX / GOSoX, eXTP), a new age of X-ray exploration has begun. Future facilities such as eXTP, GOSoX and NewAthena will provide invaluable information. Combining the polarimetric capabilities of the former with the effective area and energy resolution of the latter will allow us to accurately reconstruct emission maps and the complex magnetic field topology of these sources, opening new avenues for scientific discovery.

Speaker: Ruth Kelly

NewAthena_Jun2026_RuthKelly.pdf

12:40 The Lighthouse pulsar-wind nebula: Ultimate Laboratory for Relativistic Particle Astrophysics

The spectacular Lighthouse nebula offers a rare opportunity to study how the most energetic pulsar wind particles escape into the ambient ISM near the apex of the bowshock of the highly supersonic pulsar. The >7-arcmin-long pulsar filament is by far the brightest among its peers and the only one allowing for informative spatially-resolved spectroscopy constraining the SED of the injected particles, the physics of the particle beam/magnetic field interaction, and leptonic cosmic ray propagation in ISM. We use deep CXO observations to demonstrate how NewAthena will be able to constrain spectral evolution of particle SED along the pulsar filament.

Speaker: Seth Gagnon (The George Washington University)

Gagnon_NewAthena_2026.pdf

13:00 → 14:55 Lunch

14:55 → 17:35 Low-mass X-ray binaries: Chair: M. Del Santo, A. Marino

14:55 Probing the Link Between kHz QPOs and Relativistic Iron Lines in Neutron Star LMXBs with New Athena

The simultaneous presence of kilohertz quasi-periodic oscillations (kHz QPOs) and relativistic Fe K emission lines in neutron star Low-Mass X-ray Binaries offers a unique opportunity to probe the innermost accretion flow. The frequency of a kHz QPO is thought to trace the orbital motion of matter in the inner accretion disk, while the Fe K line profile, shaped by relativistic broadening, provides a geometric probe of the same region. If both signals originate from the same radius, timing and spectroscopy provide independent diagnostics that can be directly translated into a neutron star mass measurement through the definition of the gravitational radius.
However, current observatories lack the effective area required to measure the Fe line and track kHz QPOs on comparable timescales. Long integrations are needed to model the relativistic line with sufficient precision, during which the QPO frequency may drift and the continuum and illumination conditions may evolve, washing out any intrinsic correlation.
NewAthena will overcome these limitations by combining a large collecting area with high energy resolution. This will enable simultaneous timing and spectroscopic constraints on kilosecond timescales and allow a direct comparison between inner disk radii inferred from Fe K line modeling and from kHz QPO frequencies across different spectral states.
We present dedicated NewAthena simulations of bright neutron star LMXBs in which both relativistic disk reflection and kHz QPOs have been robustly detected, such as 4U 1636–53, 4U 1608–52, and 4U 1820–30. Our results demonstrate that the inner disk radius can be constrained in a few kiloseconds, avoiding the long integrations currently required and enabling a self-consistent test of whether dynamical and spectroscopic radii track each other in the inner accretion flow.
This work has been accepted for publication as part of the JHEAP Special Issue dedicated to the NewAthena science case.

Speaker: Alessio Anitra (Universita di Palermo)

Anitra_presentation_newAthena.pdf

15:20 Flip-Flops and QPO switching in GX 339–4 during the 2021 and 2024 NICER outbursts

GX 339–4 is a low-mass X-ray binary often used as an archetype, showing typical outburst behaviour. The source undergoes a full outburst every 2–3 years, passing through all known accretion states. We used NICER data to study the spectral-timing properties of the 2024 outburst of GX 339–4 and to compare them with the 2021 outburst. In particular we focused on rapid “flip-flop” transitions, i.e. step-like changes in X-ray flux that often come with changes in the timing properties. Through Monte Carlo simulations we assessed the statistical significance of candidate QPO peaks in the power spectra, testing for the short-timescale appearance and disappearance of Type-B QPO signatures. We used this statistically defined classification to compare variability across flip-flop levels, to extract energy spectra for intervals with and without QPO signatures, and to study relations between QPO peak frequency and other variability properties. This analysis highlights the importance of high-throughput, high-time-resolution observations to capture rapid accretion regime changes and transient variability components. We will discuss how NewAthena, with its large effective area and spectral capabilities, will enable deeper investigation of the physical mechanisms driving rapid state switching and QPO phenomenology in black hole X-ray binaries.

Speaker: Federico Ferretti (università degli studi roma tre)

Ferretti_NewAthena.pdf

15:35 XMM-Newton spectroscopy and spectral analysis of Swift J1727.8-1613 across the soft-to-hard transition.

The black hole candidate low-mass X-ray binary Swift J1727.8-1613 experienced one of the brightest outbursts ever observed in an X-ray binary in August 2023. Since then, this unique source has been observed across the entire electromagnetic spectrum. XMM-Newton monitored the low-mass X-ray binary for 3 days as it transitioned from the soft state – dominated by the multi-blackbody emission from the accretion disk – to the hard state – dominated by the comptonized emission from the hot corona. While disk winds are usually detected in the hard-to-soft transition, very few sources have been studied in the soft-to-hard transition, when the X-ray flux drops by several orders of magnitude. Here, we present the rare case of X-ray spectroscopy and spectral analysis in the decaying phase of the outburst using high-resolution XMM-Newton spectra. These results can give us valuable insight into the presence of outflows in the soft-to-hard transition of low-mass X-ray binaries.

Speaker: Maïmouna Brigitte (Astronomical Institute of the Czech Academy of Sciences)

BRIGITTE_NewAthena_WG4 meeting.pdf

15:50 You snooze, you lose: triggering NewAthena on the early rise of LMXB outbursts with XB-NEWS

NewAthena will advance our understanding of accretion onto stellar‑mass compact objects by enabling high‑throughput pointed X‑ray observations of low‑mass X‑ray binaries (LMXBs), including the elusive early stages of outbursts, through the combination of WFI wide‑field imaging/fast timing and X‑IFU high‑resolution spectroscopy. However, it is very difficult to predict when an LMXB will undergo a new outburst, and they are usually only detected with X-ray all-sky monitors once they brighten above their sensitivity limits (a few mCrab on day timescales), when the outburst is already well underway. This causes a gap in the coverage of the rise of the outbursts, limiting our understanding of their initial evolution. We address this gap with the X‑ray Binary New Early Warning System (XB‑NEWS), an automated pipeline that processes Las Cumbres Observatory (LCO) optical observations in real time to detect the onset of LMXB outbursts. From our long‑term monitoring of ~50 LMXBs (2005-2023) with the Faulkes Telescopes and LCO, we are detecting the optical brightening of XRBs typically ~12 days before the outbursts are detected in X-rays with all-sky monitors like MAXI. In addition, we show that outbursts rise at shorter optical wavelengths before rising at longer wavelengths, consistent with an ionising heating wave propagating through the disk at the onset of the outburst. XB‑NEWS therefore provides days‑to‑weeks advance warning that can be used to prioritise time‑critical NewAthena follow‑up and organise simultaneous multi-wavelength campaigns, enabling WFI/X‑IFU observations at the very onset of LMXB outbursts, revealing the initial physical processes and conditions that trigger the subsequent accretion state transitions, and outflows such as winds and jets.

Speaker: Kevin Alabarta Jativa (INAF-Osservatorio Astronomico di Brera)

You snooze, you lose: Triggering NewAthena on the early rise of LMXB outbursts with XB-NEWS

16:05 Coffee break

16:35 Accretion geometry of neutron star low-mass X-ray binaries: the IXPE view and the road to NewAthena (REMOTE)

This talk discusses IXPE X-ray polarimetric measurements of low-mass X-ray binaries hosting weakly magnetized neutron stars. IXPE observations reveal that most of these sources are significantly polarized in the X-rays, providing unprecedented insight into the geometry of their accretion flow. These results challenge scenarios based on a standard accretion disk plus boundary layer, suggesting more complex geometries and a significant contribution from scattering. Possible physical interpretations and implications for NewAthena will be discussed.

Speaker: Francesco Ursini

16:50 Pitfalls and solutions to model miss-specification in X-ray spectral modelling (REMOTE)

The wealth and complexity of X-ray data provided by modern observatories has seen a dramatic improvement in recent years, in part due to new facilities like NICER and IXPE. This trend will accelerate further with new techniques like polarimetric timing, as well as future missions like NewAthena. On the other hand, the software modelling tools utilized by the community to model X-ray data are mostly legacy stand-alone packages which are tailored to one-dimensional spectral analysis, and have relatively limited tools for advanced statistical analysis. In my talk, I will discuss how the limits of the existing software infrastructure can bias the retrieval of physical parameters from spectral models, using the measurement of black hole spin as an example. I will also discuss potential short and long term solutions to this problem, from more advanced Bayesian sampling techniques to surrogate models based on machine learning methods. Finally, I will discuss the current implementation of some of these methods in the newly released nDspec analysis package, which I hope to contribute to the NewAthena software suite.

Speaker: Matteo Lucchini (University of Amsterdam)

NewAthena.pdf

17:05 Table models in X-ray spectroscopy: a look towards the future

We are beginning to encounter computational and inference problems where complex models of atomic physics such as xillver must account for more and more parameters to properly model the absorption and emission lines present within our data. Coupled with the advent of XRISM, spectra tables must become unwieldingly large to compensate for the increase in energy resolution which makes it difficult to load into computers and interpolate between expected spectra. The launch of newAthena in 2037 will make these problems worse as new datasets will require appropriately sophisticated models, which are also becoming more complex as well.

This, along with the fact that our underlying models of this types of data are non-linear, introduce bias in inference of key physical parameters even with lower resolution data and causes parameter spaces to be overly complex and hard to map compared to if you were to use the true analytical model. In this talk, I discuss how surrogate models can serve as alternatives to table models and can help to reduce these problems by interpolating in high dimensional space in a non-linear fashion. I will also discuss the practicalities of actually implementing these techniques and what approaches people should take when first exploring these methods.

Speaker: Benjamin Ricketts (SRON/University of Amsterdam)

Table models in X-ray spectroscopy: a look towards the future

17:20 Optical Polarization Across Outburst and Quiescence in the black hole X-ray binary V4641 Sgr

Polarimetric observations provide valuable insight into the geometry and physical mechanisms responsible for
optical emission in compact binary systems. In this work, we present multiwavelength (BVRI) optical
polarimetric measurements of the X-ray binary V4641 Sgr obtained during both outburst and quiescent phases,
as part of a broader multi-band campaign linking the optical behavior of the system to its Radio and X-ray
properties.
We characterize the polarization properties of the source across different epochs and wavelengths, including a
careful assessment of the contribution from interstellar polarization. The resulting intrinsic polarization
estimates are compared with previous polarimetric measurements of V4641 Sgr. Although the degree of
polarization is low, it exhibits notable band-dependent variations between outburst and quiescence. These
results allow us to explore several possible origins for the observed polarization, including contributions from
the jet, the hot inner accretion flow, and the accretion disc. In the era of NewAthena, the development of multiwavelength synergies will be essential, as demonstrated in this work.

Speaker: Anita Maria Vena

V4641Sgr_NewAthena.pdf

17:35 → 17:50 Neutron star equation of state: Chair: A. Marino

17:35 Dense Matter Equation of State from Astrophysical Observations

Neutron stars are excellent laboratories to study the physics of matter at extreme conditions, which are beyond the scope of any terrestrial experiments. Recent multimessenger observations of neutron stars such as the measurements of the tidal deformability from the gravitational wave observation, the simulataneous mass and radius measurements of several pulsars in X-rays by the \textit{Neutron Star Interior Composition Explorer} (NICER) instrument aborad the International Space Station along with the discoveries of massive radio pulsars with $\sim 2 M_\odot$ in the last decade have significant implications towards the understanding the equation of state of dense nuclear matter. In this talk, I will discuss how this information is combined with the nuclear experimental data to constrain the properties and the composition of the interior of the neutron stars. I will also review the correlation between certain nuclear empirical parameters, such as the symmetry energy, and incompressibility with the macroscopic structure parameters, such as the radius and tidal deformability of the star.

Speaker: Prasanta Char (Universidad de Salamanca, Spain)

Char_NewAthena.pdf

20:00 → 23:00 Social dinner: Restaurante Salamanca

Friday 5 June

10:00 → 11:10 Neutron star equation of state: Chair: S. Guillot

10:00 Measuring Compact Object Masses and Constraining the Neutron Star Equation of State with X-ray Eclipse Mapping

X-ray eclipse mapping is a valuable modelling technique capable of constraining the mass and radius of compact objects in eclipsing binaries and probing the outflow from the companion star. In this talk, I will demonstrate the capabilities and recent developments of the X-ray Transit and EClipse software, X-TREC, through the modelling of the X-ray eclipses observed in three systems: the neutron star (NS) low mass X-ray binaries (LMXBs) EXO 0748--676 and Swift J1858.6--0814 and the black hole (BH) high mass X-ray binary (HMXB) M33 X-7. In all cases, we obtain tight constraints on the mass ratio and binary inclination. These measurements, when combined with radial velocity amplitudes from stellar absorption/emission lines, can place constraints on the masses of the binary components. For example, we combine our measured binary mass ratio, q ~ 0.2, and inclination, ~ 76.5 degrees, from mapping the XMM-Newton eclipses of EXO 0748--676, with the previously measured radial velocity of 410 km/s, derived from Doppler mapping analysis of H-alpha emission during quiescence by Bassa et al. (2009). This returns an NS mass of ~ 2 solar masses, thus favouring a hard equation of state. We further uncover evidence for irradiation-driven ablation in Swift J1858.6--0814 and EXO 0748--676, revealing their relation to spider pulsars.

Speaker: Amy Knight (Durham University)

Knight_NARising_Jun2026.pptx

10:25 Future dense matter constraints from millisecond pulsars with NewAthena

The Equation of State (EoS) of ultra-dense matter inside Neutron Stars (NS) is one of the long-standing questions of modern astrophysics and a key science goal of NewAthena. To constrain the composition of this dense matter, we measure the macroscopic observables of NSs, such as their masses and radii. The most precise method to measure the radius of NSs is Pulse Profile Modeling (PPM), where we model the X-ray surface emission of millisecond pulsars (MSPs). These models are fitted to phase-resolved X-ray observations of MSPs, which allows us to constrain their radius.
As MSPs are faint sources, this method requires a low background and a large collecting area, along with timing capabilities. To achieve this, we currently exploit megasecond long phase-resolved Neutron Star Interior Composition ExploreR (NICER) spectra associated with phase-averaged XMM-Newton spectra. This results in four exploitable radius measurements with $\pm 1\,$km (~10%) uncertainties.
In this talk, I will present the future performances of NewAthena to constrain the EoS of dense matter with PPM. NewAthena meets all of the requirements to perform PPM without the need for NICER or XMM-Newton data. We expect the individual radius measurement uncertainties to decrease down to $\pm 300\,$m, with an exposure of ~200 ks per source, which will put tight constraints on the EoS. I will also present the capabilities of NewAthena to differentiate between NS surface emission models, such as the atmosphere composition, or between different geometric configurations of the emission regions.

Speaker: Lucien Mauviard (IRAP - Institut de Recherche en Astrophysique et Planétologie - CNRS)

MAUVIARD_NewAthena_SWG4_2.pdf

10:40 Lifting systematic biases in neutron star quiescent LMXBs with NewAthena to constrain the dense matter equation of state

Neutron stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs) have been used in the past two decades for mass and radius measurements to better constrain the equation-of-state of dense matter. However, various sources of systematic uncertainties were put forward, possibly biasing the radius values by as much as 50%. They include the unknown NS spin and atmospheric composition, as well as possible surface anisotropies.
A new method, inspired from pulse-profile modeling (PPM) of millisecond pulsars (MSPs), has recently been developed to constrain masses and radii of qLMXBs by including rotation and hot spots in the spectral modeling.

We will show that NewAthena will significantly improve these measurements thanks to its effective area, yielding an excellent signal-to-noise ratio (SNR). This will put more stringent constraints on the possibility of hot spots or on the spectral broadening due to the NS rotation. NewAthena’s time resolution will also allow to search for pulsations from these systems. Finally, the atmosphere composition can be determined thanks to observations of the NS binary companion with JWST, or with the ELT in the near-future.
All in all, this new method free of systematic biases combined to NewAthena’s excellent SNR will provide EOS constraints from qLMXBs on a par with PPM of MSPs.

Speaker: Christine Kazantsev (IRAP, Toulouse, France)

Kazantsev_qLMXBs.pdf

10:55 Equation of State at finite temperature in the era of new nuclear physics and multimessenger constraints

In this contribution, I will start with an overview of different types of equation of state modelling in the Bayesian formalism, to demonstrate the িmpact of different experimental and observational constraints. Further, I will present equations of state at finite temperature obtained with Brussels-Skyrme-on-a-Grid (BSkG) energy density functionals developed at Brussels, which are unified across the crust and core of the neutron star environment. These models have demonstrated remarkable accuracy over the whole nuclear chart on the masses, and fission barriers of nuclei, but at the same time they also satisfy recent astrophysical constraints. I will also outline the impact of our calculations at finite temperatures on the composition of the crust in the neutron stars. Our next goal is to apply these equations of state in the end-to-end simulation of binary neutron star mergers.

Speaker: Chiranjib Mondal (Universite Libre de Bruxelles)

NewAthena_Mondal_2026.pdf

11:10 → 11:30 Concluding remarks

11:10 Concluding remarks

Speaker: Alessio Marino (Institute of Space Sciences, ICE/CSIC)

11:30 → 12:00 Coffee break

12:00 → 13:00 NewAthena: Science, Status and Prospects

Special colloquium

12:00 Special Talk

Speaker: Prof. Matteo Guainazzi