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High Energy Astrophysics and Cosmology in the era of all-sky surveys
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Asia/Yerevan
Marat Gilfanov,
Narek Sahakyan
(ICRANET-Armenia IO)
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08:30
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Registration 30m
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09:00
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Welcome
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10:40
Sky surveys
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09:10
From Deep to Wide: Mapping the Evolving Universe Through Extragalactic X-ray Surveys 30m
Extragalactic X-ray surveys have transformed our view of the high-energy universe, revealing the populations that produce the cosmic X-ray background (CXRB) and reshaping our understanding of black-hole growth and cosmic structure. I will review what X-ray surveys and their multiwavelength follow-up have uncovered about these populations over the past 27 years, drawing on results from missions including Chandra, Einstein Probe, INTEGRAL, MAXI, NuSTAR, Spektr-RG, Swift, and XMM-Newton. I will first discuss the identification, classification, and basic nature of the extragalactic sources detected in X-ray surveys, including active galactic nuclei (AGNs), galaxies, clusters and groups, and transients. Since AGNs dominate the CXRB, I will then highlight key insights into their demographics, physics, and ecology revealed by X-ray surveys. These include recent results on the drivers of AGN evolution, AGN-galaxy connections, highly obscured AGNs, high-redshift AGNs, dwarf-galaxy AGNs, as well as hypervariable AGNs and nuclear X-ray transients. I will conclude by outlining major unresolved questions and prospects for advancing the field through new observations, future missions, and complementarity with multiwavelength wide-field surveys.
Speaker: William Brandt (Penn State University) -
09:40
SRG/eROSITA all-sky survey results in the Eastern Galactic hemisphere 30m
After more than two years of scanning the sky during 2019--2022 the eROSITA X-ray telescope aboard SRG orbital observatory produced the best ever X-ray maps of the sky and discovered more than three million X-ray sources, of which about 20\% are stars with active coronas in the Milky Way, and most of the rest are galaxies with active nuclei, quasars and clusters of galaxies. eROSITA detected over ~10^3 sources that changed their luminosity by more than an order of magnitude, including about a hundred tidal disruption events. SRG/eROSITA samples of quasars and galaxy clusters will make it possible to study the large-scale structure of the Universe at z~1 and measure its cosmological parameters. I will review some of the SRG/eROSITA results in the Eastern Galactic hemisphere and future prospects.
Speaker: Prof. Marat Gilfanov -
10:10
SRG/eROSITA results on the Western Galactic hemisphere 30m
The eROSITA (extended ROentgen Survey with an Imaging Telescope Array) instrument aboard the Spektrum-Roentgen-Gamma (SRG) mission has significantly expanded the horizon of X-ray astronomy, delivering unprecedented legacy samples through its high sensitivity, wide field of view, and survey efficiency. These capabilities have enabled major advances in our understanding of growing supermassive black holes, active galactic nuclei (AGN), and rare nuclear transients.
eROSITA has also transformed studies of large-scale structure by providing the largest X-ray-selected sample of galaxy clusters and groups. By combining eROSITA data with optical surveys such as DESI Legacy Imaging Surveys, DES, HSC-SSP, and KiDS, the evolution of the cluster mass function now provides percent-level cosmological constraints, while also enabling the detection of diffuse baryons in cluster outskirts and cosmic filaments.
I will present an overview of some of the most significant results and discoveries from the western half of the sky, for which the German eROSITA consortium is responsible.Speaker: Dr Miriam E. Ramos-Ceja (Max Planck Institute for extraterrestrial Physics)
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Opening Remarks by H.E. Alessandro Ferranti, Ambassador of Italy to Armenia
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Coffee break 30m
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Sky surveys
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Galaxy and metagalaxy in hard X-rays with the ART-XC telescope onboard SRG 30m
The Mikhail Pavlinsky ART-XC onboard the Spektr-Roentgen-Gamma (SRG) Observatory has been successfully operating in orbit since 2019. During this time, it conducted eight all sky surveys, as well as a significant number of observations of the most interesting regions and objects of the Universe. In our the overview of the ART-XC results of all sky and Milke Way surveys, particular attention will be paid to the discovery and study of new and transient objects, performed through the multiwavelenght observations together with other space and ground instruments.
Speaker: Alexander Lutovinov -
11:50
The Hot Circumgalactic Medium in the eROSITA All-Sky Survey 20m
Studying the distribution and properties of hot gas around galaxies (hot CGM) helps constrain galaxy evolution models, but its observation is challenging. The first four SRG/eROSITA all-sky surveys (eRASS:4) allow us to detect the hot CGM by stacking a large sample of galaxies. In this talk, I will present the results we obtained: 1) X-ray surface brightness profiles and baryon budget of the hot CGM, 2) the relationship between the X-ray luminosity of the hot CGM and the stellar mass or halo mass of galaxies, 3) difference of the hot CGM around star-forming and quiescent galaxies.
Speaker: Yi Zhang (MPA)
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11:20
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Accreting millisecond pulsars
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Observations of millisecond X-ray pulsars by the SRG/ART-XC telescope 30m
We will present an overview of observations of rapidly rotating neutron stars
by the Pavlinsky ART-XC telescope on-board SRG mission. Despite the fact that
the telescope was designed for scanning large areas of the sky, its detectors
have a good time resolution (≈ 23 microseconds), and the onboard clock is
stable enough, which makes it possible to perform timing analysis of coherent
signals up to several hundreds Hz frequency. We will present the results of
observations of both isolated pulsars and accreting millisecond pulsars.Speaker: Sergey Molkov
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Lunch 1h 50m
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Sky surveys
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SRG/eROSITA and microwave observations of clusters of galaxies - synergy and competition 30m
SRG/eROSITA and microwave observations of clusters of galaxies
Speaker: Rashid Sunyaev -
15:00
Wide Field Survey Telescope (WFST): Overview and Recent Progress 30m
Wide Field Survey Telescope (WFST) is the largest time-domain survey facility in the northern hemisphere. The telescope is a dedicated photometric surveying facility being built jointly by the University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO). It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 giga-pixels on the primary focal plane for high-quality image capture over an FOV of 6.5 square degrees. WFST is located on the Tibetan Plateau, near Lenghu Town in Qinghai Province, at an altitude of 4200 meters. The WFST project began in 2018 and has already been completed and started astronomical observations in September 2023. In December 2024, after an ~1-year commissioning and pilot survey, WFST has begun formal time domain survey observations. In this talk, the performance and scientific progress of WFST will be presented.
Speaker: Prof. Yongquan Xue (University of Science and Technology of China)
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Little red dots, quasars and blazars
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Microquasars, Little Red Dots and AGN: Insights from Radio Sky Surveys 30m
The radio emission from Microquasars (MQs), Little Red Dots (LRDs) and Active Galactic Nuclei (AGN) is crucial to gain insight into the mass accretion, relativistic jets and feedback of black holes (BHs) in these astronomical objects. Based on archived radio monitoring data and the VLASS and FIRST sky surveys of the National Radio Observatory (NRAO), were obtain the following achievements:
1) An understanding of the General Relativity physics in the inner accretion disk to the BH in the microquasar GRS 1915+105, at the time of unusually large changes in the BH-jets during a deep X-ray obscured and high mid-infrared luminosity state observed with the JWST.
2) So far LRDs at z > 5 have been radio silent. However, using NRAO archive data was found radio emission associated to two LRD analogues at z = 0.1–0.2. More recently, using the VLASS and FIRST surveys was identified at z ≃ 0.4 a radio bright LRD analogue.
3) The intriguing radio silence of the otherwise active BHs in LRDs and some types of AGN has been intensively debated and remains without an explanation with general consensus. In this talk it will be shown that the suppression of radio synchrotron emission from active BHs in LRDs and AGN may due to an Inverse Compton mechanism when the accreting BHs are embedded in nuclear bursts of massive stars.Speaker: Felix Mirabel
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Coffee break 30m
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Little red dots, quasars and blazars
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AstroGenesis: A Domain-Aware Multi-Agent Model for Data-Driven Astrophysics 30m
Astrophysics is entering a data-rich era driven by multi-wavelength observatories and multi-messenger experiments. These facilities produce vast, heterogeneous datasets that challenge traditional analysis pipelines. General-purpose AI systems, while powerful, often lack the contextual reasoning and scientific rigor required for astrophysical interpretation. AstroGenesis is an AI-powered, domain-aware multi-agent research assistant designed to revolutionize how astrophysicists access, analyze, and interpret astronomical data. Built upon a Retrieval-Augmented Generation (RAG) framework and a modular multi-agent architecture, AstroGenesis integrates literature retrieval, data access, theoretical modeling, and hypothesis generation into a unified ecosystem. Each specialized agent autonomously handles dedicated tasks-such as spectral fitting, time-series analysis, or model inference-under the coordination of a central supervisory agent that ensures transparency and reproducibility. Key innovations include a domain-aware RAG system that grounds responses in peer-reviewed literature; seamless integration with multi-wavelength and multi-messenger archives for both raw and processed data; and neural-network-based modeling agents trained on large-scale radiative simulations for real-time, physics-consistent inference. It is possible to inspect the machinery with a human-on-the-loop for validation, and feedback to further enhance reliability. Demonstrated through a prototype for blazar research, AstroGenesis can be generalized to diverse astrophysical phenomena. By unifying reasoning, data retrieval, and theoretical modeling within a scalable framework, it lowers the barrier to advanced analysis and fosters transparent, reproducible, cross-disciplinary discovery in modern astrophysics.
Speaker: Prof. Narek Sahakyan (ICRANET-Armenia IO) -
17:00
Little Red Dots as Sites for Cosmic Prebiotic Chemistry 20m
Both the Galactic Center and little red dots (LRDs) host million-solar-mass black holes within dense, cold reservoirs of molecules associated with dust grains, and are electromagnetically tranquil. These conditions enable complex molecular chemistry and may serve as natural laboratories for prebiotic genetic evolution by allowing the synthesis of organic molecules essential for life.
Speaker: Yu WANG (ICRA / ICRANet) -
17:20
Lighthouses in the Centres of Galaxies 20m
Geometric constraints on inner regions of active galactic nuclei (AGN) are crucial for uncovering the behaviour of matter in extreme gravitational environments and thus for providing tests of general relativity. A time lag between different energy bands occurs due to the different path lengths for photons which have travelled directly to us after being Compton up-scattered in the corona, and for those reflected by the surrounding accretion disc. The lag-energy spectrum therefore holds information on the geometry of the system and has been fit to provide constraints on geometric parameters. This technique is impacted by instrumental noise and stochastic variability, which is intrinsic to the accretion process and decreases the coherence between light curves. A reduced coherence results in larger uncertainties between the lag and therefore geometry. Quasi-periodic oscillations (QPOs) are extremely coherent, producing a peak in coherence observed at a certain frequency, and reduces the effects of the intrinsic stochastic variability on geometric uncertainties. In this work, we investigate the lags produced at the QPO frequency versus the entire broadband frequency range, showing that the increased coherence of this signal can be leveraged to provide better constraints in geometric properties surrounding AGN.
Speaker: Fiona Redmen (Universitat Autonoma de Barcelona) -
17:40
SRGA J2306 + 1556: an extremely X-ray luminous, heavily obscured, radio-loud quasar at z = 0.44 discovered by SRG/ART-XC 15m
We report on a detailed study of a luminous, heavily obscured ($N_{\rm H}\sim2\times 10^{23}$ cm$^{-2}$), radio-loud quasar SRGAJ230631.0+155633, discovered by the SRG/ART-XC telescope, which is located at $z=0.4389$ and is a type 2 AGN. We combine radio-to-X-ray data, including near-simultaneous ART-XC and Swift/XRT observations conducted in June 2023. During these follow-up observations, the source was found in a significantly fainter but still very luminous state ($L_{\rm X}=1.0^{+0.8}_{-0.3}\times 10^{45}$erg s$^{-1}$, absorption corrected, 2–10keV) compared to its discovery ($L_{\rm X}=6^{+6}_{-3}\times10^{45}$ erg s$^{-1}$), indicating intrinsic variability on a rest-frame time scale of $\sim 1$ year. The radio data reveal a giant FRII radio galaxy. From multi-wavelength photometry and the black hole--bulge relation we infer a bolometric luminosity of $\sim 6\times10^{46}$ erg s$^{-1}$ and a black hole mass of $\sim1.4\times10^{9}\,M_{\odot}$, implying accretion at $\sim30$% of the Eddington limit. SRGAJ230631.0+155633 proves to be one of the most luminous obscured quasars out to $z=0.5$.
The talk will also briefly highlight several new AGN being studied by the SRG/ART-XC team.Speaker: Grigorii Uskov (Space Research Institute of Russian Academy of Sciences (IKI))
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Welcome reception 2h 20m
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Transients and explosive phenomena
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The Universe in Real Time: Capturing Stellar Explosions as They Begin 30m
The study of transient phenomena in a multimessenger framework will remain a major driver of astrophysical discovery in the coming decades. Supernovae, Kilonovae, compact-object formation, Novae, Gamma-ray Bursts, and tidal disruption events connect electromagnetic emission with gravitational waves and neutrinos. The key physics unfolds within minutes to hours, yet most surveys return to the same region of the sky only after days. As a result, we learn what happened and how often, but rarely how these events begin or how they link to other messengers. We propose shifting from triggered follow-up to continuous high-cadence monitoring, allowing us to detect stellar explosions at, or even before, their electromagnetic onset. Real-time monitoring turns time-domain astronomy from retrospective interpretation to predictive exploration.
Speaker: Massimo Della Valle (INAF-Capodimnonte, Naples) -
09:30
Astrophysical transient search in Euclid fields 30m
The Euclid mission, though primarily designed for cosmology, offers wide-field, high-resolution, deep, multi-wavelength imaging that makes it a powerful asset for time-domain astronomy.
While its observing strategy is not optimized for transient searches, several fields are revisited multiple times over the mission lifetime.
In these regions, difference imaging enables the discovery of thousands of transients, creating valuable opportunities for studying time-variable phenomena and fostering strong synergies with upcoming surveys such as the Vera Rubin Observatory with LSST, and the Nancy Grace Roman Space Telescope.
In this talk, we will present preliminary results from a pilot key project in the Self-Calibration field, using both optical and NIR data obtained during the first three years of observations.
This project highlights Euclid’s capability to detect and characterize transients and serves as a stepping stone toward the transient program planned for the Euclid Deep Fields, in coordination with Rubin LSST and Roman.Speaker: Luca Izzo (INAF/OACN) -
10:00
Tidal disruption of a magnetized star 20m
Tidal disruptions of stars by supermassive black holes in galactic centers (TDEs) are now being actively studied both theoretically and observationally. They are observed throughout the electromagnetic spectrum, from radio to gamma-rays. It is still unclear how the emission is produced and, in particular, what is the role of the magnetic field of the disrupted star. There are many ways how magnetic fields might affect the dynamics of a TDE. They are likely responsible for the angular momentum transfer in the accretion disk formed at later stages and thus affect the radiation associated with the disk. Magnetic fields are also an important requirement for the formation of relativistic jets, that are seen in some TDEs. The goal of our study is to connect the field within the star to the fields that develop during the fallback and disk accretion. Using the fluid-dynamic code Athena++, we perform a large-scale three-dimensional adaptive-mesh magnetohydrodynamic simulation of a tidal disruption of a magnetized star. The fallback stream returning to the black-hole vicinity after the disruption contains smooth magnetic fields aligned with the stream lines. Formation of a nozzle shock near the pericenter of the initial orbit leads to a turbulent eccentric disk-like structure where the field is amplified and entangled on the local dynamic time scales up to approximate equipartition. The resulting field is mildly anisotropic and has a typical length several times smaller than the pericenter distance. The properties of the field are consistent with the early stages of turbulent dynamo.
Speaker: Pavel Abolmasov (Tel Aviv University)
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Future missions and instruments I
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MezzoCielo: a novel ultra-wide-field telescope for continuous all-sky monitoring 30m
Time-domain and multimessenger astronomy are entering a new observational regime in which rapid and continuous monitoring of large sky areas becomes essential for the detection and characterization of electromagnetic counterparts of gravitational waves, neutrinos, gamma-ray bursts, fast radio bursts, and other transient phenomena. Traditional wide-field surveys typically rely on sequential sky tiling, trading sky coverage against sensitivity and cadence. MezzoCielo explores a different observational paradigm: continuous monitoring of the entire accessible sky through a highly modular ultra-wide-field optical system.
The proposed concept is based on a spherical refractive assembly coupled to a hemispherical focal surface populated by a large number of identical optical cameras. The system exhibits strong spherical and chromatic aberrations, but with high uniformity across the full field of view, enabling local correction by replicated optical channels. In its final configuration, MezzoCielo is expected to monitor approximately 10000 square degrees with about 900 optical cameras, delivering seeing-limited imaging with arcsecond level sampling and a total focal plane of about 80 gigapixels. The project combines large instantaneous sky coverage, substantial collecting area, scalability, and high observational cadence within a sustainable and modular architecture. Current activities include optical and mechanical prototyping, development of an on-sky demonstrator, and definition of science-driven technical requirements and data-handling strategies.
MezzoCielo is proposed as a scalable platform for continuous all-sky multimessenger astronomy.Speaker: Demetrio Magrin (INAF - Osservatorio Astronomico di Padova)
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Coffe break 30m
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Future missions and instruments I
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Sharpening the TeV sky with the ASTRI Mini-Array 30m
The most energetic gamma-ray sky, spanning the TeV to PeV domain, has recently revealed a complex landscape of galactic sources, including Pevatrons, microquasars, dark accelerators, and extragalactic transients, offering new insights while posing significant challenges for understanding the non-thermal Universe. These challenges require new instruments capable of resolving complex morphologies, rapid variability and providing precise spectroscopy.
The ASTRI Mini-Array, an international project led by INAF and in partnership with the University of São Paulo (IAG-USP), IAC, and North West University, is designed to meet these goals through an array of nine dual-mirror Schwarzschild-Couder Cherenkov telescopes, currently being deployed at the Observatorio del Teide. With an angular resolution of approximately 3 arcminutes and an energy resolution down to 10% across a 1–200 TeV range, the array enables precise morphological and spectral characterization of complex sources. Furthermore, its exceptionally wide field of view (~10°) facilitates deep surveys of crowded Galactic regions and selected extragalactic fields, the study of large extended sources, and tiling of large uncertainty regions (e.g. from gravitational-wave events). Currently in its commissioning phase, the first telescopes are providing an initial glimpse on the array's capabilities, while fostering collaborations with multifrequency facilities and complementary instruments such as LHAASO, MAGIC and CTAO.Speaker: Antonio Stamerra (INAF-OAR) -
11:50
Reaching a resolution of 10 microarcsec in the optical to resolve accretion disks and more 30m
The quantum properties of a gas of bosons were predicted by Einstein 100 years ago. The first experimental evidence of its consequences were obtained by Hanbury-Brown & Twiss in 1954, correlating the arrival times of photons detected by two optical telescopes. Extremely large telescopes and 10ps resolution single photon detectors bring the key improvements to reach, in the optical, angular resolutions better than these achieved in the radio by the Event Horizon Telescope and to obtain, for instance, the first images of accretion disks around galactic compact objects, active galactic nuclei and quasars.
Speaker: Roland Walter (University of Geneva) -
12:20
Very-High-Energy Gamma-Ray Astronomy with CTAO: Status and Science at the Dawn of Operations 30m
The Cherenkov Telescope Array Observatory (CTAO) will be the next-generation facility for very-high-energy gamma-ray astronomy, covering the energy range from ~20 GeV to 300 TeV with sensitivity at least an order of magnitude beyond current instruments. As the first open, proposal-driven gamma-ray observatory, with stations in La Palma (North) and near Paranal (South), CTAO will deliver full-sky coverage and novel capabilities for the study of cosmic accelerators, transient phenomena, and extreme astrophysical environments.
In this talk, I will present an overview of CTAO's key scientific goals, expected performance, and the current status of construction — at a particularly exciting moment, as the observatory is now on the threshold of early science operations. With first light imminent and initial observations set to begin within the next couple of years, CTAO is transitioning from a future facility to a present reality. Its energy range and sensitivity make it ideally positioned to address open questions across several of the conference's core themes: the origin and acceleration of cosmic rays, the physics of relativistic jets in blazars and gamma-ray bursts, and the high-energy counterparts of gravitational wave and neutrino events. As early science gets underway, CTAO will become an essential new window onto the most extreme and energetic phenomena in the Universe.
Speaker: Prof. Michele Doro (University of Padova)
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Lunch 2h
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Future missions and instruments II
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The NewAthena X-ray Observatory 30m
NewAthena will be the European Space Agency’s next large X-ray observatory. It will have revolutionary capabilities enabled by the combination of a large collecting-area mirror, a high-resolution spatially resolved X-ray integral-field spectrometer, and a wide-field X-ray imager. This next-generation observatory will thus enable transformational progress across all areas of astrophysics. NewAthena is the second L-class mission in ESA’s Cosmic Vision programme, expected to undergo formal adoption by ESA in 2027 and then enter the implementation phase, with launch planned for ~2039.
This talk will provide an update on the status of the NewAthena study phase. I will highlight plans for the next generation of large-area X-ray sky surveys using NewAthena's Wide-Field Imager, and I will discuss the broad range of science that NewAthena will enable – including tracing the growth of supermassive black holes across cosmic time and their impact on galaxy evolution, the assembly of the large-scale structure of the Universe, the stellar lifecycle (and its endpoints), the equation of dense matter in neutron stars, and the astrophysical nature of neutrino and gravitational wave sources.
Speaker: Prof. James Aird (University of Edinburgh) -
15:20
Exploring the Extremes with eXTP 30m
The enhanced X-ray Timing and Polarimetry (eXTP) mission is a flagship X-ray observatory designed to probe fundamental physics and astrophysics under extreme conditions. Combining high-throughput spectroscopy, high-resolution timing, and sensitive polarimetry, eXTP aims to constrain the equation of state of matter at supra-nuclear densities, detect quantum electrodynamics (QED) effects, and map matter dynamics in strong gravitational fields. Additionally, it will serve as a powerful facility for time-domain and multi-messenger astronomy. Formally selected in 2025 with a scheduled launch in 2030, eXTP represents a major international collaboration led by China. In this talk, I will present the mission profile, payload specifications, and an overview of its expected performance and key science cases.
Speaker: Hua Feng (Institute of High Energy Physics) -
15:50
The NUSES space mission 20m
NUSES is a satellite mission composed by two scientific payloads: Terzina and Zirè.
Zirè is conceived to perform measurements of electrons, protons and light nuclei up to hundreds of MeV as well as gamma-rays in the energy range between 0.1-30 MeV. Its Low-Energy Module can detect charged particles with energy as low as hundreds of keV. Scientific goals for this payload feature low-energy cosmic rays, transient gamma-rays events, and study of Sun-Earth environment for space weather and the Magnetosphere-Ionosphere-Lithosphere Coupling.
Terzina is meant for observation of the Cherenkov light produced by the Extended Atmospheric Showers generated by High-Energy Cosmic Rays with energy higher than 100 PeV, and NUV light emission from the Earth limb that could be produced by Earth skimming neutrinos above PeV energy.
The detailed scientific goals and the status of the mission development will be presented.Speaker: Leandro Silveri (New York University Abu Dhabi)
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Coffee break 30m
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The Galactic Center
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X-ray emission from the Galactic Center 30m
In my talk I will review our recent results related to the X-ray emission from the Galactic Center region, especially, the non-thermal emission of the Arches stellar cluster as observed with XMM-Newton and Chandra.
Speaker: Roman Krivonos (Space Research Institute (IKI), Moscow, Russia) -
17:10
Faint X-ray sources in the Nuclear Stellar Disk using deep Chandra observations 20m
Recent studies based on XMM-Newton and SRG/ART-XC observations have reported an excess of X-ray emission per unit stellar mass in the Nuclear Stellar Disk (NSD) compared to regions farther from the Galactic Center. These results are based on hard X-ray measurements (4-12 keV) and studies of the Fe XXV emission line at 6.7 keV. In this work, we investigate the population of faint X-ray sources in the NSD using deep Chandra observations (peak exposure $\sim$800 ks) in the 4-8 keV band. In the region of highest sensitivity, 546 sources are detected within an area of 25 arcmin$^2$. We construct the source number-flux distribution (dN/dS) and compare it with model predictions based on the luminosity function of the Solar neighborhood, as well as with previous logN-logS measurements in the Norma region. We find good agreement between our data, the model, and the Norma region results across the entire flux range probed by the observations, down to the sensitivity limit of $\sim 2.2 \times 10^{-15}$ erg $s^{-1}$ $cm^{-2}$. Our results indicate that the detected source population in the NSD remains consistent with the expected stellar population, dominated by Cataclysmic Variables (CVs) and Active Binaries (ABs) down to the observation's sensitivity limit. This suggests that the reported emissivity excess in the NSD either arises from a population of even fainter sources below our detection threshold or requires a different physical interpretation, such as a contribution from a truly diffuse component.
Speaker: Valentin Nezabudkin (Space Research Institute, MIPT)
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Little red dots, quasars and blazars
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Increasing the X-ray source search sensitivity in Chandra's Deep Field South using likelihood-based detection 20m
Likelihood function-based methods are a theoretically optimal way of detecting sources. They maximize the use of all available information about the telescope and expected spectral information about the source.
In this talk, we describe how this new method was set up and applied to the Chandra's Deep Field South, a unique X-ray dataset with its record 7 Ms exposure and sub-arcsec spatial resolution of the telescope. Our preliminary results show that the gain in detection sensitivity is approximately equivalent to doubling the existing exposure. The increase in number of detected sources is partially due to the largely increased number of detected obscured Active galactic nuclei, that begin to appear at the detection threshold of our method. Thus, with this approach we begin to probe the little-studied population of objects, that make a major contribution to the Cosmic X-ray background emission above 10 keV.
Speaker: Andrey Mukhin (IKI RAS)
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Flash talks
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X-ray Flare Activity in the Pleiades with eROSITA 5m
The Pleiades open cluster was observed in multiple eROSITA all-sky survey passes, each separated by roughly six months, providing a sample of young low-mass stars with X-ray light curves. Starting from the catalogue of 850 SRG/eROSITA sources associated with Pleiades stars from Khamitov et al. (2024), we developed a flare-detection pipeline that estimates a per-survey persistent rate by iteratively excluding flare-like bins and then applies a per-bin Poisson significance test. We validated the pipeline with simulations to quantify the false-detection rate under null variability and the recovery efficiency under injected flares, and used the simulation-derived efficiency to correct the observed flare distributions. I will present the resulting flare catalogue, the population-level trends and the next analysis steps, including an extension to a wider candidate-member sample.
Speaker: Yasmin Nehme (Max Planck for astrophysics) -
17:55
The Origin of super-Eddington Flares in the high-mass X-ray binary LMC X-4 5m
Some accreting neutron stars in massive and low-mass X-ray binaries exhibit flaring activity. The flares are accompanied by changes in spectra, pulsation profiles, and the long-term luminosity of the system. The flares themselves vary in duration and peak luminosity. Different flares have different origins; however, in many cases, the nature of the flares is unknown. In this work, we describe the behavior of the massive X-ray binary LMC X-4 during flaring activity. We demonstrate that the variability properties and the pulsar’s behavior during the flares are incompatible with most of the previously proposed mechanisms for flare production. Our analysis is based on the study of the neutron star spin dynamics and the regularity of changes in the pulse profile shape, performed using a long RXTE observation that shows four flares. In particular, our analysis demonstrate that the changes in the pulse profile shape during flares occur regularly, which contradicts models of material capture onto the neutron star magnetic field lines or the Rayleigh–Taylor instability.
Speaker: Iuliia Kliain (Space Research Institute (IKI) RAS, Higher School of Economics)
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Gamma-ray bursts
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Cosmological Distributions and Evolution of Gamma-ray and Fast Radio Bursts and their relation to Star Formation Rate and Gravitational Waves 30m
Formation rate (FR) history of extragalactic sources provide crucial information on how the universe emerged from the dark ages to its current stage. Best observed FR is that of stars (SFR) that rises from high redshifts to redshift of ~3 and declines to today. Active galactic nuclei (AGNs) show a similar trend but with different parameters. Transient sources like gamma-ray bursts (GRBs), and to some degree fast radio bursts (FRBs), by virtue of their large redshifts are good candidates for determining this history and its relation to SFR.
Methods: Achievement of this task requires determination of
the "Luminosity Function" (LF) and the cosmological
evolution of luminosity and FRs. This is often done by a
forward fitting of the data to some assumed parametric
forms for the LF and evolution, with many parameters, and
often ignoring luminosity evolution. However, recent works
use the non-parametric methods developed by Lynden-Bell and
Efron and Petrosian (EP), which determines the luminosity
evolution directly from "truncated" data. In this talk I
will review past and more recent estimates of LFs and FR
evolution of GRBs (and if time permits FRBs), using these
nonparametric methods.
Data: A critical issue here is to have samples with
measured "fluxes" and redshifts (z) with well defined
truncation determined by observational selection effects,
which we call "complete samples". The main source for GRBs
has been the Neil Gehrels Swift Observatory with some data
from Konus-Wind and Fermi-GBM. The main source for FRBs has
been the CHIME radio telescope. An important uncertainty is
the selection effects of securing redshifts. As I will
discuss use of Machine Learning (ML) to estimates redshifts
can help in this regard.
Theory: An important issue for the transient sources, which are often poorly localized is their progenitors. GRBs are divided into two groups; Long-soft and Short-hard. So- called collapsars are assumed to be the progenitors of GRBs, while SGRBs progenitors are believed to be neutron star (NS)-NS or NS-black hole mergers, which are also
sources of gravitational waves (GWs) and Kilonovae. FRBs
also come in two variety “repeaters” and “non-repeaters”
with magnetars as likely progenitors.
Results: GRBs consistently shown (1) presence of strong
luminosity evolution,a broken power-law LF and varied
formation rate evolution. Collapsars, being short lived
stars are expected to follow the SFR. We find that LGRBs
seem to follow the SFR at high-z’s but deviate
significantly from it, as a low low-z component that
increase with decreasing-z. SGRBs FR increases with
decreasing z’s, similar to the low redshift component of
LGRBs, often modeled by a delayed SFR expected from compact
object mergers. These finding raise doubt about the
standard separation by duration of GRBs and affects the
expected frequency of GWs and Kilonovae.
FRBs also show luminosity evolution and a delayed FR
supporting the magnetar origin.
This work is carried out with extensive collaboration with
Maria Dainotti and several graduate and undergraduate
students.Speaker: Vahe' Petrosian (Stanford University) -
09:30
The case of GRB 220101A: the first example of a GRB triggered by two Supernovae 14.7 s apart 30m
We investigate GRB 220101A provides , the first of a new family of long GRBs exceeding a total energy of 10^54 erg, within a newly modified BdHN model. Its exceptional luminosity is explained by a pair-supernova triggering the event, followed after ∼ 7 minutes by an induced core-collapse supernova. What makes GRB 220101A so exceptional is: (1) its redshift z = 4.61, and (2) the high-quality multiwavelength observations obtained from a large number of space-based telescopes and (3) an equally large number of ground-based telescopes. Three afterglow components are observed: (1) a GeV emission originating from the black hole, (2) an X-ray emission originating from the supernova ejecta, and (3) an optical afterglow due to the millisecond pulsar. Most exceptional is the newly formed neutron star originating 14.7 s after the pair-supernova trigger.
Speaker: Remo Ruffini -
10:00
Physics of GRB afterglows: new insights from TeV observations 30m
Recent observations of several Gamma-Ray Burst (GRB) afterglows in the TeV domain have profoundly impacted the theory of particle acceleration and radiation in relativistic shocks. We can now confidently state that the Synchrotron-Self-Compton (SSC) model for afterglow emission has successfully passed experimental verification. Furthermore, simultaneous multi-wavelength observations -- spanning from soft X-rays to TeV gamma-rays -- place strict constraints on the emission zone parameters and their temporal evolution. These constraints align with the predictions of the pair-balance model (based on the converter acceleration mechanism) while disfavoring conventional diffusive shock acceleration. Finally, unique observations of the very early TeV afterglow of GRB 221009A provide new insights into the dynamics of the external shock powering the emission. We highlight a hydrodynamic model of a blast wave with intermittent energy supply -- an extension of the standard Blandford-McKee model -- which shows good agreement with the observed light curve.
Speaker: Evgeny Derishev (Institute of Applied Physics RAS)
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09:00
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10:30
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11:00
Coffee break 30m
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11:00
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12:00
AGN, blazars and jets
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11:00
Relativistic jets: new insights on the jet physics from formation to energy dissipation 30m
Over the past decade, major advances in both observations and numerical simulations have transformed our understanding of relativistic jets in astrophysical systems. In this talk I will review the recent progress in jet physics, focusing on the launching process, jet propagation and energy dissipation. I will discuss the role of magnetic fields in the jet evolution from field amplification and ordering near the central engine to the development of current-driven instabilities leading to turbulence that can dissipate magnetic energy. I will compare this to magnetic dissipation via large scale current sheets in striped jets. Last, I will briefly discuss the implications of these processes for the production of the observed high-energy emission.
Speaker: Prof. Omer bromberg (Tel Aviv university) -
11:30
Optical-ɣ-Ray Correlations in Blazars from Time-Domain Surveys 15m
Blazars are among the most variable non-thermal sources in the Universe, exhibiting broadband emission from radio to $\gamma$-rays. With the new era of large-scale surveys such as the Vera C. Rubin Observatory, their optical variability can now be regularly monitored with unprecedented depth, paving the way to probe their emission mechanisms in a time-domain, multi-wavelength context.
In this work, we investigate the connection between optical and $\gamma$-ray emissions in a large sample of blazars using multi-year light curves from Fermi-LAT and Rubin’s predecessor, ZTF. We introduce a robust similarity metric to quantify cross-band correlations and implement a flare-detection pipeline based on the rise and fall structure of extreme-amplitude emission events. Building on this, we develop a real-time algorithm designed to identify extreme optical states and trigger follow-up observations.
We find a zero time lag between the optical and $\gamma$-ray band for most of the sources, and optical-$\gamma$-ray correlations beyond $>3\sigma$ for about 20% of them, which supports co-spatial emission regions.
Our real-time triggering strategy achieves a purity of over 70% for $\gamma$-ray flares and nearly 100% for optical low states, demonstrating that optical surveys can efficiently anticipate high-energy activity and confidently trigger spectroscopic observations of the host galaxy. These results highlight the growing potential of all-sky optical surveys as drivers of multi-wavelength follow-up, providing a powerful complement to current high-energy facilities such as $\textit{Fermi}$-LAT.
Speaker: Julian HAMO (IJCLab - Université Paris-Saclay) -
11:45
Quasi-Periodic Signatures of a High-Redshift Intermediate Mass Black Hole 15m
High-frequency quasi-periodic oscillations (QPOs) in black hole X-ray binaries, typically in the 60–450 Hz range, are associated with processes near the innermost stable circular orbit and scale directly with black hole mass. For supermassive black holes, analogous oscillations are expected in the sub-millihertz regime and were first detected in the narrow-line Seyfert 1 galaxy RE J1034+396. These detections extend the mass–frequency scaling relation from stellar mass to supermassive accreting systems. However, the intermediate-mass range (10⁴–10⁶ M⊙), where QPOs are expected in the millihertz regime, remains underrepresented. Here we present observations of the lensed active galactic nucleus ULAS J081621.49+213442.65 at z ≈ 7.46, an intermediate mass black hole candidate magnified by a foreground galaxy by a factor exceeding 1000, making this intrinsically faint source observable. We detect a stable quasi-periodic signal in the rest-frame UV light curves of the object, at millihertz frequencies, persisting across multiple epochs. The frequency of the QPO implies a black hole mass of a few ×10⁴ M⊙, providing the first compelling evidence for long-sought intermediate-mass black hole progenitors of supermassive black holes at high redshift.
Speaker: Ekaterina Koptelova (Graduate Institute of Astronomy, NCU)
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11:00
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12:00
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13:45
Lunch 1h 45m
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13:45
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21:45
Social Program: Excursion and Conference Dinner 8h
For details please see
https://indico.global/event/16224/page/5866-social-events
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09:00
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10:30
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09:00
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10:45
Multi-messenger approaches in astrophysics
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09:00
Multi-messenger constraints on core-collapse supernovae in the Local Universe (Part I) 30m
Identifying the central engine of core-collapse supernovae (CC-SNe) is key objective in observational astronomy. This may be unveiled by gravitational wave emission, complementary to EM and neutrinos, that may break the degeneracy between neutron stars and black holes. Through illustrative case studies, we demonstrate the discovery potential of this approach with current-generation GW detectors, promising a new window into the physics of stellar death and compact object formation. (Based on van Putten, Abchouyeh & Della Valle, ApJL 972, L23, 2024.)
Speaker: maurice van putten (Sejong University) -
09:30
Multi-messenger constraints on core-collapse supernovae in the local Universe (part II) 25m
The progenitor mass and central engine of a core-collapse supernova (CC-SNe) continue to be a mystery despite the modern surveys of the transient universe. A multi-messenger approach including both EM and gravitational-waves, however, provides a unique window to break the degeneracy between a newly born neutron star and black hole central engines of CC-SNe. Considering the 160Mpc horizon distance to BH central engines, here we apply such approach to the nearby event SN 2023ixf. Over the observation window proceeding the first discovery of SN 2023ixf, our results show no joint H1-L1 signal associated with the birth of rotating BH central engine. Together with photometric-spectroscopic data, we interpret this null result to indicate the absence of BH formation. This outcome, instead, supports the birth of a NS central engine, therefore progenitor mass less than $20M_\odot$.
Speaker: Maryam Aghaei Abchouyeh -
09:55
Multi-messenger signatures of turbulent black hole coronae 30m
The annoucement by the IceCube collaboration of a 4.2σ excess of high-energy neutrinos (1–10 TeV) spatially associated with the Seyfert 2 galaxy NGC 1068 marked a breakthrough in multi-messenger astrophysics. Recent evidence also suggests correlations with other Seyfert galaxies (e.g., NGC 4151, NGC 7469), indicating non-jetted active galactic nuclei (AGN) as significant contributors to the extragalactic neutrino flux. The striking mismatch between neutrino and γ-ray emissions in NGC 1068 points to neutrino production in a compact, photon-opaque region, most plausibly the turbulent corona of its supermassive black hole (Murase et al. 2020). Proton acceleration up to 10–100 TeV in such magnetized, highly turbulent environments thus emerges as a key mechanism to explain these observations.
We discuss here our efforts to understand this signal, from the microphysical picture of stochastic particle acceleration in turbulence to its implementation in a sophisticated numerical framework modeling the relevant non-linear kinetic processes. This includes the interplay between turbulent dissipation and acceleration, radiative and hadronic losses and transport processes in the corona. This framework makes use of the AM3 radiative solver (Klinger et al. 2024).
Our models reproduce the IceCube neutrino signal for NGC 1068 and predict spectral shapes that can constrain coronal properties and acceleration mechanisms. This work provides a powerful tool to explore multi-messenger emission across diverse astrophysical environments, bridging gaps between particle-in-cell simulations and macroscopic source modeling.
Speaker: Dr Martin LEMOINE (APC (CNRS - U. Paris Cite)) -
10:25
Accretion and dynamics of compact objects in AGN disks: multi-messenger implications 20m
Compact objects or stars in nuclear clusters can interact with AGN disks during their motion, exchanging energy and angular momentum, and eventually settling into disk-plane motion. Additionally, the outer regions of AGN disks may undergo gravitational collapse, forming stars that evolve into compact objects and migrate inward. By studying the accretion and dynamics of various compact objects (white dwarfs, neutron stars, and black holes) in AGN disks, their respective fates and the resulting multi-wavelength and multi-messenger signals are investigated.
Speaker: SHURUI ZHANG (ICRANet)
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09:00
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10:45
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11:15
Coffee break 30m
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11:15
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13:10
Cosmic rays and ultra-high energy gamma-rays, neutrinos
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11:15
Full-sky searches for very-high-energy neutrinos 30m
The detection by the KM3NeT experiment of a neutrino with a record-breaking energy of 220 PeV represents a major milestone in neutrino astrophysics. I will review the broader implications of this observation in a full-sky context, including its combination with data from other experiments, searches for the potential source of this event and population studies of similar astrophysical objects, as well as its possible multimessenger connection to ultra-high-energy cosmic rays.
Speaker: Sergey Troitsky (Institute for Nuclear Research, Russian Academy of Sciences (RU)) -
11:45
Selected Results from Ground-based Gamma-Ray Astrophysics and Near-Future Prospects 30m
In this report, we would like to present some interesting recent results and developments in ground-based gamma-ray and cosmic-ray astrophysics, using the MAGIC IACT and some other well-known detectors as examples. Measuring Cherenkov light from air showers has become a standard, highly sensitive method for investigating sources in the energy range from a few tens of GeV to 100 TeV. The strength of this technique lies not only in its high sensitivity but also in its superior angular resolution. However, ground-based detectors that measure charged particles from air showers instead of light demonstrate very high sensitivity over a very wide field of view and deliver novel, impressive results. This situation is made even more fascinating by the ongoing discussions, construction and/or improvement plans for detectors as well as by the application of novel artificial intelligence methods, which can strongly impact the scientific prospects.
Speaker: Dr Razmik Mirzoyan -
12:15
Exploring Active Galactic Nuclei with LST-1 30m
Very-high-energy (VHE) gamma rays provide a unique window on the most extreme astrophysical environments and are a key probe of potential multi‑messenger sources. To fully exploit this potential, the Cherenkov Telescope Array Observatory (CTAO) is being built as the next‑generation facility for VHE gamma‑ray astronomy, offering an order‑of‑magnitude improvement in sensitivity, a wide energy coverage from 20 GeV to 300 TeV, and rapid response to transient phenomena.
The Large-Sized Telescope prototype LST‑1 marks a major milestone toward the realization of CTAO. In this contribution, I will present the first results on Active Galactic Nuclei (AGN) obtained with LST‑1 during its early science phase, highlighting its performance and scientific potential at the lowest energies accessible to imaging atmospheric Cherenkov telescopes. Discoveries such as OP 313, the most distant VHE blazar detected to date, or minute‑scale variability from BL Lacertae demonstrate LST‑1’s ability to detect and characterize rapidly variable extragalactic sources. These early AGN results show that LST‑1 is already delivering high‑quality scientific data and provide a preview of the transformative impact CTAO will have on extragalactic high‑energy astrophysics in the coming decade.Speaker: Lea Heckmann (APC, CNRS/IN2P3 - Université de Paris Cité) -
12:45
UHECR anisotropy and search for their sources 25m
Ultra-high energy cosmic rays (UHECR) are charged particles, with energies greater than 1 EeV that are reaching the Earth from space. The origin of UHECR and their nature remain unknown. In this talk I will discuss the studies of distribution of UHECR arrival directions over the sky in search for their sources, that are expected to be extragalactic. I will also discuss the method of estimation of UHECR charge from their anisotropy and its application to the data of UHECR experiments.
Speaker: Mikhail Kuznetsov (INR RAS)
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11:15
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13:10
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15:00
Lunch 1h 50m
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15:00
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15:15
AGN, blazars and jets
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15:00
Blazar jet dynamics and neutrino production 15m
Recent studies indicate the connection between the detection of high-energy neutrinos from blazars and beaming of their relativistic jets, suggesting that the jets are the sites of the neutrino production. Detailed studies of the jet structure and dynamics, made possible by means of very-long-baseline radio interferometry (VLBI), shed light on the localization of the neutrino-emitting zone and on the mechanism of acceleration and interactions of relativistic protons. Observational evidence for spine–sheath jet stratification, in particular, may resolve the long-standing discrepancy between the high Doppler factors required by neutrino models and the slow speeds measured from VLBI component tracking. We present the results of new multi-epoch VLBI observations of prominent neutrino-candidate blazars and discuss their theoretical implications.
Speaker: Polina Kivokurtseva (INR RAS)
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15:00
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15:15
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16:05
Spectral formation near compact objects
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15:15
X- and gamma-ray radiation from the high-temperature plasma and spectra of accreting black holes 25m
We present our numerical computations of broadband radiation spectra formed in a layer of high-temperature ($kT_{e}\sim 50$ keV) semitransparent plasma (with a Thomson optical depth of $\tau_{T}\sim 1-3$) with an electron number density of $N_{e}\sim 10^{17}-10^{19}\ \mbox{cm}^{-3}$, characteristic of the accretion disk regions surrounding a black hole in X-ray binaries. The computations take into account the bremsstrahlung processes of photon production and absorption and their subsequent Comptonization. We show that the intrinsic radiation of such a high-temperature plasma is sufficient to explain the X-ray spectra observed in the low (hard) state of galactic black hole candidates and X-ray novae. None of the generally assumed additional soft photons (with energies of $h\nu\leq 1$ keV) are required to maintain Comptonization; moreover, their presence would lead to strong distortions of the spectrum compared to the observed one or would require very fine-tuning of the plasma parameters. In the hard X-ray range, the resulting power-law radiation spectrum with a photon index of $\alpha\sim 1.4-1.7$, exponentially decaying at $\geq 50$ keV, significantly exceeds the bremsstrahlung flux that would be expected from a similar plasma layer in the limit of its very small depth. This is the result of multiple inverse Compton scattering of bremsstrahlung photons. Importantly, the power-law spectrum of the radiation of such a high-temperature plasma should, according to computations, extend unchanged down the energy axis all the way to the infrared, optical, and ultraviolet bands ($h\nu\sim 1-3$ eV). At energies of $h\nu\leq 1$ eV, the depth for bremsstrahlung absorption rapidly increases, and the radiation spectrum becomes Rayleigh-Jeans. To explain the steeper ($\alpha\sim 2.1-2.5$) X-ray spectra observed in accreting black holes in the high (soft or two-component) state, it is indeed necessary for a large number of soft external photons to enter the hot cloud, in addition to the photons of the plasma's own bremsstrahlung. Such photons could be emitted by the surface of the outer, dense, cold accretion disk, the inner edge of which, during these states, characterized by a strong soft component in the X-ray spectrum, approaches the black hole as closely as possible. The optical and infrared radiation of systems in these states is associated specifically with the emission from the outer disk, whereas during their low states, it can be generated directly in the hot, inflated central region of the disk. Under favorable circumstances (disk size and inclination), the low-frequency radiation from this region can significantly exceed in flux and luminosity the emission from the outer, cool regions of the accretion disk.
Speaker: Sergei Grebenev (Space Research Institute) -
15:40
Frontiers of Extreme Plasma Astrophysics 25m
Relativistic plasma astrophysics has undergone rapid development in recent years, driven by increasingly sophisticated observations and large-scale, high-fidelity numerical simulations. These advances have shed new light on a range of phenomena, including the broadband emission mechanisms of neutron star magnetospheres and the accretion flows and relativistic jets in both stellar-mass and supermassive black holes. In this talk, I will present recent progress in these areas, with particular emphasis on state-of-the-art numerical methods. I will demonstrate how simulations not only test existing theoretical models but often lead to the development of new paradigms. I will also highlight some of our group's current work on ambitious simulation campaigns aimed at addressing open questions in high-energy astrophysics.
Speaker: Hayk Hakobyan (Flatiron Institute)
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15:15
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16:05
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16:35
Coffee break 30m
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16:35
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17:05
Sky surveys
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16:35
The soft X-ray all-sky map observed with EP/WXT 30m
The Einstein Probe Wide-Field X-ray Telescope (WXT), leveraging lobster-eye optics, rejuvenates the soft X-ray imaging all-sky survey. We present the first EP-WXT narrow-band maps and hardness ratio maps, where a global anti-correlation between soft X-ray and HI emission is evident. We highlight intriguing diffuse soft X-ray emission features shaping the formation and evolution of the Milky Way, including potential hot debris associated with the last major merger of the Milky Way, a complex region with new Galactic supernova remnant candidate(s), a coherent soft shell enveloping the northern X-ray bipolar bubble, contrasting with a highly asymmetric southern counterpart, and other enigmatic features. By design, this inaugural paper serves not as a definitive discovery but as an exploration portfolio, charting intriguing features to catalyze dedicated follow-up studies. The EP-WXT all-sky maps showcase the unique potential of lobster-eye optics, promising a legacy survey of the X-ray emitting hot Universe.
Speaker: Junjie Mao
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16:35
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17:05
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18:05
Cosmology and large scale structure
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17:05
Tracing the large-scale structure of the Universe back in time: why and how? 30m
Upcoming and ongoing cosmological surveys, such as Euclid and DESI, are mapping the distribution of tens of millions of galaxies across cosmic time. These data sets will provide unprecedented opportunities to constrain the fundamental physical theory governing the Universe, including the nature of gravity, dark matter and dark energy. To fully exploit this potential, however, one must reconstruct the past matter distribution, before nonlinear gravitational evolution transformed the early density field into the complex large-scale structure observed in the late-time Universe. This talk will review key results and discuss several of the methods developed to achieve this goal.
Speaker: Prof. Adi Nusser -
17:35
Gamma-ray cosmology: axion-like particles and Hubble constant measurements from the extragalactic background light 15m
The extragalactic background light (EBL) encodes the signature of galaxy evolution and photon production history since the epoch of reionization. The optical and infrared photons that dominate the EBL can interact with 𝛾-rays above a certain energy threshold to create e+/e- pairs, leading to absorption imprints seen in the very-high energy (VHE; E > 100 GeV) spectra of extragalactic sources. The past decades of 𝛾-ray astronomy have recently enabled the first purely parametric 𝛾-ray measurement of the EBL spectrum at $z = 0$. In this work, we show how this 𝛾-ray cosmology result can be extended to explore both particle physics and cosmology, when combined with EBL estimates from deep field surveys. Assuming axion-like particles (ALPs) make up the entirety of dark matter, we derive new constraints on the coupling constant between ALPs and photons, over an energy range broader than typically observed by the Hubble space telescope. Furthermore, we measure the local Hubble constant independently from both cosmic microwave background observations and cosmic distance ladder estimates, with precision greater than the current gravitational waves constraints. These results highlight the potential of 𝛾-ray cosmology with the current generation of instruments, setting the stage for the next generation instruments, the Cherenkov Telescope Array Observatory (CTAO).
Speaker: Lucas Gréaux (Ruhr Universität Bochum) -
17:50
Quantum Droplets in Space: Electromagnetic- and Graviational-Wave Signatures of White Dwarf-Black Hole Tidal Stripping 15m
We investigate the tidal stripping of a cold helium white dwarf (WD) by a stellar-mass black hole (BH). Owing to the degenerate nature of the WD, quantum effects are expected to play a significant role in the dynamics. To capture these effects, we employ a full quantum hydrodynamic framework to simulate the formation of the accretion disk. The WD is modelled as a Bose–Fermi droplet composed of attractively interacting degenerate atomic bosons and fermions. The droplet is placed in the field of a non-rotating BH. We use the pseudo-Newtonian potential by Paczynski and Wiita.
Our numerical simulations show that the infalling material undergoes fragmentation during disc formation as a result of nonlinear effects. The quantum matter captured by the BH after periastron passage acts as a source of intense electromagnetic emission, producing bursts that resemble the recurrent flaring observed in X-ray sources. We also identify quantised vortices in the bosonic component of the accretion disc that may produce distinct electromagnetic signatures. Their formation naturally explains the occurrence of flicker noise. After tidal stripping, the remnant WD recedes from the BH while quantum vortices propagate along its surface. We also investigate the gravitational radiation generated during this process.
Speaker: Dr Marek Nikołajuk (University of Bialystok, Faculty of Physics)
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17:05
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09:00
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10:45
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09:00
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10:30
X-ray polarimetry
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09:00
New insights on cosmic sources from X-ray polarimetry 30m
The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on December 2021 (re)opened the window of X-ray polarimetry. In its first 4.5 years of operation IXPE observed objects belonging to almost all classes of X-ray sources, with a wealth of interesting and often surprising results. In this talk I will provide a (inevitably biased) review of IXPE results, and briefly discuss possible future X-ray polarimetric missions.
Speaker: Giorgio Matt (Roma Tre University) -
09:30
The IXPE View of NS-LMXBs: New Insights from X-ray Polarimetry into Emission Geometry and Accretion Physics 30m
X-ray timing and broadband spectroscopy have been the main methods for studying the rich and complex phenomenology of neutron stars with weak magnetic fields for a long time. Nowadays, X-ray polarimetry offers the missing, independent set of observables that are directly relevant to comprehending the geometry and nature of the emission regions: polarization degree and angle. This allows for breaking the degeneracies due to the fact that different geometries and physical conditions might yield equivalent spectral and timing signatures. Some of the main results obtained in this frame by using the Imaging X-ray Polarimetry Explorer (IXPE) will be reported in this talk. X-ray polarization seems to vary in response to the intensity and spectral hardness associated with possible variations in the accretion rate and possibly to the geometry of the emitting regions. The possible contribution from an extended accretion-disk corona or a disk-wind component, the spreading layer, and the boundary layer is also discussed.
Speaker: Alessandro Di Marco (INAF - IAPS) -
10:00
IXPE observations of black hole binaries: new constraints on accretion geometry 30m
The advent of X-ray polarimetry has opened a new observational window into the accretion physics of compact objects. Observations with the Imaging X-ray Polarimetry Explorer (IXPE) provide unique constraints on the geometry and physical conditions of emission regions in black hole X-ray binaries. However, the first polarimetric results have raised new challenges for existing accretion models. In particular, the detection of unexpectedly high polarization fractions in both the hard and soft spectral states places strong constraints on the mechanisms responsible for X-ray emission and the structure of the accretion flow. In this talk, I will describe possible solutions to these emerging puzzles and discuss implications of IXPE observations for our understanding of black hole accretion models.
Speaker: Alexandra Veledina (University of Turku)
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09:00
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10:30
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11:00
Coffee break 30m
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11:00
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12:00
X-ray polarimetry
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11:00
X-ray polarisation of accreting pulsars: current results and future prospects 30m
X-ray polarimetry has recently opened a new observational window on accreting neutron stars, enabling direct measurements of the polarization properties of radiation formed in ultra-strong magnetic fields. The first systematic observations of X-ray pulsars with IXPE have provided phase-resolved measurements of polarization degree and angle, allowing direct constraints on the geometric configuration of these systems.
These measurements have also uncovered several unexpected results, including systematically lower polarization degrees than predicted by standard models and complex phase-dependent polarization behaviour. In addition, evidence for multi-component polarized emission has emerged. While these findings demonstrate the diagnostic power of X-ray polarimetry, current observations remain limited by photon statistics and relatively narrow energy coverage.
In this talk, I will review the present observational status of X-ray polarimetry of accreting pulsars and discuss how future missions will significantly advance the field. The combination of large effective area and broad energy coverage will enable high-precision phase- and energy-resolved polarimetric studies across different luminosity states. This will allow quantitative investigation of polarization evolution with accretion rate, detailed studies of depolarization processes, and much stronger constraints on system geometry.
Speaker: Dr Sergey Tsygankov (University of Turku) -
11:30
X-ray spectropolarimetric insights into the inner regions of accretion flows 30m
I will discuss the current paradigm for the innermost regions of black hole accretion flows in light of constraints from X-ray spectroscopy. The main spectral components observed in luminous accretion states will be outlined, highlighting how their modeling has led to a broad picture of the radiative and dynamical processes operating in the vicinity of the black hole horizon. Despite this progress, some fundamental properties remain uncertain, reflecting the intrinsic complexity of spectral decomposition. I will critically address the ongoing discussion on the estimation of black hole spin, as well as the geometry and spatial extent of the primary emitting and reprocessing regions within the accretion flow. Finally, I will address how polarimetric measurements provide additional constraints, opening new possibilities for refining theoretical models.
Speaker: Andrzej Niedzwiecki (University of Lodz)
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11:00
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12:00
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12:30
Insight-HMXT
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12:00
Overview on the research progresses of Insight-HXMT 30m
Insight-HXMT is the first Chinese X-ray astronomy satellite and was launched to a 550 km orbit on 15th June 2017. The Insight-HXMT consists of three collimated telescopes HE (20-250keV), ME (5-30 keV) and LE (1-15 keV), and is characterized by a broadband energy coverage, where at above 20 keV it has a large detection area and, at below 3 keV it has good energy/time resolution and is free from pile-up problem in observation of the bright source. The core sciences of the Insight-HXMT are Galactic survey for the discovery of X-ray source and monitoring of the source variability, pointed observations for observing the BH and NS XRB systems in their bright or outburst phases, all-sky monitoring GRBs and observation of the GW EM counterpart. Here I will briefly introduce on behalf of the Insight-HXMT team the research progresses, including observation of the extreme event of GRB/FRB and exploration of the outburst from compact object system of BHXRB/NSXRB.
Speaker: SHU ZHANG (INSTITUTE OF HIGH ENERGY PHYSICS,BEIJING,CHINA)
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12:00
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12:30
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14:30
Lunch 2h
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14:30
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15:35
AGN
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14:30
Reflection-dominated CT AGN candidates — first SRG/eROSITA results from the Eastern Galactic hemisphere 20m
We describe a population of AGNs with extremely hard spectra found among the sources registered by SRG/eROSITA on the Eastern Galactic hemisphere. Such spectra cannot be explained by inverse Compton scattering typical of “normal” AGNs, but can be produced by the X-ray emission reflected from a dusty torus, indicating significant obscuration (up to the Compton-thick regime). We developed a method for selecting CT AGN candidates using SRG/eROSITA data from the Lockman Hole deep survey. Using the ~1 Ms XMM-Newton observations, we studied one of these candidates, SRGe J105149.5+573244, and showed that it has a relativistically broadened Fe K𝛂 line. We applied a similar selection procedure to the catalog of SRG/eROSITA sources registered on the Eastern Galactic hemisphere. The talk will cover preliminary results of this study.
Speaker: Mikhail Belvedersky (IKI RAS) -
14:50
From spectral energy distribution to line suppression: probing the physics of the X-ray-weak WLQ SDSS J101353.45+492758.1 20m
Weak-emission-line quasars (WLQs) represent an extreme subclass of active galactic nuclei (AGNs), displaying unusually faint or absent emission lines despite luminous quasar-like continua. The source SDSS J101353.45+492758.1 is a particularly striking example, characterized by a nearly lineless UV–optical spectrum and a pronounced X-ray weakness.
We first analyze its broadband spectral energy distribution (SED) using relativistic thin-disk (kerrbb) and multicomponent AGN (relagn) models. Both approaches consistently indicate a black hole mass of ∼ 2 × 10^9 M_sun and a moderate accretion rate (m_dot ≈ 0.1). However, the fits require a strongly suppressed or absent hot corona, while the inclusion of a warm, optically thick Comptonizing region significantly improves the agreement with the data. These results support an intrinsically X-ray weak nature.
To further investigate the origin of the extreme emission-line weakness, we are conducting dedicated photoionization simulations with Cloudy. Using SEDs motivated by our observational modeling, we explore how variations in coronal strength, warm Comptonization, and possible geometrical configurations affect the predicted equivalent widths of key emission lines (e.g., C IV, Mg II).
This combined SED and photoionization approach provides new insight into the coupling between the accretion flow, coronal structure, and line-emitting gas in X-ray-weak quasars, and highlights SDSS J101353.45+492758.1 as a valuable laboratory for understanding the physical diversity of WLQs.
Speaker: Laetitia Gibaud (Faculty of Physics, University of Bialystok) -
15:10
A novel approach to the relation between X-ray and ultraviolet luminosities of quasars using SRG/eROSITA and SDSS data 20m
The statistical analysis of the relationship between ultraviolet (UV) and X-ray emission from active galactic nuclei (AGN) allows for a better understanding of the processes occurring during accretion of matter onto a supermassive black hole in the center of AGN, and also tests the possibility of using quasars as "standard candles" for measuring distances on cosmological scales in the Universe. We have developed a new method for finding the parameters of this relation, which consistently takes into account (i) X-ray and UV flux limited object selection, (ii) X-ray and UV variability of quasars, and (iii) the decreasing space density of quasars with increasing luminosity. We examine the relation between X-ray (at 2 keV, $L_{\rm X}$) and UV (at 2500Å, $L_{\rm UV}$) monochromatic luminosities of quasars using a sample of 2414 sources from the SRG/eROSITA all-sky survey and the Sloan Digital Sky Survey data release 16 quasar catalogue (SDSS DR16Q), which are sufficiently bright in X-ray and the optical to have well defined X-ray fluxes and nearly 100% statistical completeness. Assuming the relation of the form $l_{\rm X}=\gamma l_{\rm UV}+\beta$, where $l_{\rm X}≡\log(L_{\rm X}/[\rm erg\,s^{-1}\,Hz^{-1}])$ and $l_{\rm UV}\equiv \log(L_{\rm UV}/[\rm erg\,s^{-1}\,Hz^{-1}])$, we find $\gamma=0.69\pm0.02$, and normalization, $l_{\rm X}=26.47\pm0.02$ at $l_{\rm UV}=30.5$. A novel aspect of our work is allowance for intrinsic scatter (which adds to the dispersion induced by quasar variability and flux measurement uncertainties) of the $L_{\rm X} - L_{\rm UV}$ relation in both variables, i.e. in X-ray and UV luminosity. The intrinsic X-ray scatter ($\sigma^2_{\rm intX}=0.063\pm0.005$) strongly dominates over the UV one ($\sigma^2_{\rm intUV}=0.002^{+0.003}_{-0.002}$).
Speaker: Sergey Prokhorenko (Space Research Institute of the Russian Academy of Sciences (IKI)) -
15:30
Study of X-ray and optical spectral properties of AGN from the SRG/ART-XC All-Sky Survey using Swift/XRT and SDSS archival data 5m
We present the results of our analysis of the X-ray spectra of a large subsample of active galactic nuclei (AGN) from the catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope aboard the SRG orbital observatory during its all-sky survey (ARTSS1-5). The analysis is based on archival observations with the Swift/XRT telescope in the 1–10 keV energy range. For all sources, we derive, for the first time, estimates of the power-law continuum photon index, intrinsic absorption column density, and absorption-corrected X-ray flux. In addition, we present preliminary results of our analysis of optical spectra of AGN from the ARTSS1-5 catalog, obtained from the SDSS archive. Specifically, we report measurements of key parameters of broad and narrow emission lines. The study was carried out as part of a broader effort aimed at constructing a statistically complete multi-wavelength database of AGN from the ARTSS1–5 catalog.
Speaker: Aleksei Sokolov (IKI RAS)
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14:30
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15:35
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Coffee break 30m
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16:05
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17:15
Radio pulsars and their nebulae
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16:05
Double-torus pulsar wind nebulae as sources of high energy particles and radiation 25m
Galactic pulsar wind nebulae are suitable targets for studying relativistic plasmas because they radiate in all energy ranges, and a number of PWNe are close enough that their spectra, dynamics and morphology can be resolved in great detail. Pulsar wind nebulae often exhibit a jet-torus morphology in X-rays, unless distorted by very strong external flow. Typically, nebulae form a single torus, but some develop double X-ray tori. Numerical PWNe models struggle to explain this dichotomy, and a suitable MHD model has been recently proposed and tested against observations. The model reproduces virtually all X-ray features in Vela PWN, a prototype double-torus nebula resolved in detail by the Chandra X-ray observatory. The model also indicates some additional X-ray features that should be characteristic of double-torus objects.
We prove the existence of these features in Vela by reprocessing its archival Chandra observations. The model naturally explains the high degree of polarization detected in Vela by the IXPE observatory and the precession of the Vela's double-torus. By direct numerical modeling of high energy particle propagation within the double-torus nebulae we demonstrated that the Vela-like PWNe can accelerate protons and leptons well above hundred TeV.Speaker: Georgii Ponomarev -
16:30
On the statistical properties of the widths of the mean radio pulsar profiles 20m
Using the data from FAST and MeerKAT radio telescope surveys, we carried out a detailed statistical analysis of the distributions of the observed widths of mean radio pulsar profiles. The availability of the high-quality polarization data made it possible to separately consider mean profiles formed by the ordinary (O) and extraordinary (X) orthogonal polarization modes. We performed an analysis of the dependency of the profile widths on pulsar periods, which revealed statistically significant differences between the O and X mode profiles subsamples. It was shown that the pulsar profiles, formed by the O mode are on average wider than the profiles, formed by the X mode, which can be explained by the O mode refraction in pulsar magnetosphere. Thus, we have statistically confirmed the main theoretical predictions regarding orthogonal modes propagation, using large and homogeneous data sample.
Speaker: Arsenii Istomin (Moscow Institute of Physics and Technology, Lebedev Physical Institute) -
16:50
Statistics of orthogonal radio pulsars 20m
New surveys by the FAST and MeerKAT observatories have enabled, for the first time, a robust statistical study of orthogonal pulsars using large homogeneous samples. These objects, with magnetic axis nearly perpendicular to the rotation axis, are particularly sensitive to magnetospheric physics and serve as a key test for neutron star evolution models. We show that the statistical properties of orthogonal interpulse pulsars—specifically their period distribution and relative abundance are inconsistent with modern numerical models. To improve our understanding of orthogonal pulsars, we develop a novel method for determining the three-dimensional structure of the accelerating potential above the polar caps. Unlike previous approaches, our method is applicable to any inclination angle, including exact orthogonal rotators. Obtained results allowed us to calculate corresponding secondary plasma transverse density profiles, which are necessary for studying pulsars mean intensity profiles and their statistics in general.
Speaker: Fedor Kniazev (Moscow Institute of Physics and Technology, Lebedev Physical Institute)
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16:05
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17:15
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Concluding remarks 15m
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09:00
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