Main Colloquium
Dr. Lauren Rhodes	ORATED

McGill

The deaths of massive stars are sometimes accompanied by the launch of highly relativistic and collimated jets identified as gamma-ray bursts (GRBs). GRB 221009A has been dubbed the BOAT or brightest of all time for its record-breaking gamma-ray brightness. In this talk, I will present a summary of the observations conducted by my collaborators and I (Bright & Rhodes et al 2023, Fulton et al 2023, Rhodes et al 2024), resulting in comprehensive multi-wavelength coverage including the most detailed radio study of any GRB to date. At radio frequencies, it is also the brightest radio counterpart detected to date and our campaign spanned over three orders of magnitude in frequency space starting a few hours post burst and continuing to this day (over 900 days later). I will discuss the importance of such coverage for theoretical modelling and our understanding of jet geometry for all manner of jetted transients from tidal disruption events to x-ray binaries. Finally, I will present a brief overview of our plans to continue monitoring this fascinating object.

	Promotionskolloquium
Davit Alkhanishvili	ORATED

AIfA, Bonn

The Lambda-CDM model is the standard in cosmology, with large-scale structure clustering measurements playing a key role in parameter constraints. Next-generation galaxy surveys highlight the growing importance of higher-order statistics like the bispectrum, which offers improved constraints but introduces computational challenges. This thesis focuses on modeling the bispectrum using perturbation theory to enhance its role in extracting cosmological information. First, we test next-to-leading order perturbation theory expansions using N-body simulations, finding that effective field theory (EFT) provides the most accurate small-scale predictions. We also assess the impact of systematic and statistical errors. Next, we demonstrate how deep neural networks can be employed to model survey geometry effects on the power spectrum and bispectrum, achieving high accuracy with efficient computation. Lastly, we evaluate a third-order galaxy bias expansion against synthetic Eucilid-like survey catalogues, demonstrating that combining the power spectrum and bispectrum allows accurate cosmological parameter extraction up to mildly non-linear scales, improving constraints by a factor of 2-5 over the power spectrum alone.

	Main Colloquium
Patrick Reichherzer	ORATED

University of Oxford

Galaxy clusters host a zoo of radio morphologies—from compact bubbles and extended halos to sausages, bridges, and relics—all generated by cosmic rays (CRs) interacting with magnetic fields. The transport of these CRs across galaxy clusters reflects a reciprocal interaction across plasma scales. Large-scale processes (≳kpc) typically influence microscale behavior (~npc), but we show that microscale fluctuations—inherently patchy and intermittent in nature—shape large-scale radio morphologies in galaxy clusters by mediating CR propagation. This patchiness creates a heterogeneous medium where various plasma microinstabilities collectively affect CR transport. Our multi-scale simulations (kinetic to MHD) show a scale-dependent diffusion coefficient, with a transition at ~1–10 kpc: diffusion dominates below this scale, while advection takes over above it. This interplay shapes radio morphologies, revealing that microscale physics significantly affects macroscopic CR transport. We reveal that microscale physics isn't just driven—it actively sculpts the radio sky, offering testable predictions for next-generation observations.

	Special Colloquium
Dr. Yuh Tsunetoe	ORATED

Harvard University

Very long baseline interferometry (VLBI) observations reveal that relativistic jets like the one in M87 have a limb-brightened, double-edged structure. Meanwhile, analytic and numerical models struggle to reproduce this limb-brightening. We propose a model in which we invoke anisotropy in the distribution function of synchrotron-emitting nonthermal electrons such that electron velocities are preferentially directed parallel to magnetic field lines, as suggested by recent particle-in-cell simulations. We implement our emission model in both general relativistic magnetohydrodynamic (GRMHD) simulations and axisymmetric force-free electrodynamic (GRFFE) jet models and produce simulated jet images at multiple scales and frequencies using polarized general relativistic radiative transfer. We find that the synchrotron emission is concentrated parallel to the local helical magnetic field and that this feature produces limb-brightened jet images on scales ranging from tens of microarcseconds to hundreds of milliarcseconds in M87. We also present theoretical predictions for horizon-scale images that can be tested with next generationinstruments. Due to the scale-invariance of the GRMHD and GRFFE models, our emission prescription can be applied to other targets and serve as a foundation for a unified description of limb-brightened images of extragalactic jets.

	Master Colloquium
Kamalpreet Kaur	ORATED

MPIfR/Bonn

Recent radio observations of the Galactic Center (GC) have revealed a significant population of point sources, including potential pulsars and other compact objects. Detecting pulsars in the GC is challenging due to scattering effects that smear pulsed signals. However, image-based search techniques can overcome this limitation and identify potential pulsar candidates. Additionally, under certain conditions, the supermassive black hole Sagittarius A* (Sgr A*) can also be treated as a point source. It exhibits variability across the electromagnetic spectrum, with short-time variability at low radio frequencies (< 3 GHz) still largely unexplored. This work has two main objectives. Firstly, we identify potential pulsar candidates using the S4 band (2.62-3.50 GHz) of the MeerKAT Radio Telescope. We discovered 13 new unresolved sources by applying image-based techniques and proposed three potential pulsar candidates based on their spectral index. This highlights the importance of image-based search in identifying potential pulsar candidates in the scattering-dominated GC. Secondly, from the observation conducted on 21st March 2024, we report on the flux variability of Sgr A* with a modulation index of 5.38% at 2.79 GHz. This is done for the first time using the MeerKAT Radio Telescope, offering access to previously uncharted parameter space, which will help better understand variability and emission processes in Sgr A*.

	Main Colloquium
Prof. Naomi Ota	ORATED

Nara Women’s University

The XRISM satellite, launched in 2023, is the successor to Hitomi and marks a major step forward in high-resolution X-ray spectroscopy. Equipped with the microcalorimeter spectrometer Resolve, XRISM enables precise measurements of gas motions and turbulence in galaxy clusters. In this talk, I will present the initial results from XRISM observations of the A2029 galaxy cluster, highlighting gas dynamics in the cluster core and the role of non-thermal pressure in the outer regions. I will also discuss future prospects, including upcoming observational strategies and implications for galaxy cluster studies.

	SFB Colloquium
Dr. Nick Indriolo	ORATED

Johns Hopkins University, Baltimore

Chemical complexity in the molecular interstellar medium (ISM) is driven by fast ion-molecule reactions. This network of chemical reactions requires a source of ionization, and as molecular gas is generally well-shielded from ionizing UV photons, cosmic rays provide the dominant source of ionization in such environments. The impact of cosmic rays on atomic and molecular hydrogen is parameterized as the cosmic-ray ionization rate (CRIR; number of ionizations per atom/molecule per unit time), which serves as an important input variable in astrochemical modeling. Our understanding of cosmic rays in both diffuse and dense gas has vastly improved over the past decade as more detailed chemical models have been developed, and as more sensitive observations of molecules that respond to the CRIR have been made. The recent creation of 3D dust maps using Gaia differential extinction measurements allows, for the first time, ionization rates inferred from observations of molecular absorption lines to be assigned to a physical location in the nearby Galaxy. By combining this information we are beginning to build the first map of the CRIR in the solar neighborhood. I will discuss our ongoing work on this project, and how we can use such a map to better understand cosmic-ray acceleration and propagation.

	Special Colloquium
Julian Ruestig	ORATED

DZA

Strong gravitational lensing, a consequence of general relativity, magnifies distant background sources and transforms them into complex shapes when passing behind massive foreground objects. This powerful phenomenon offers a unique view into the distant cosmos by probing directly the distribution of dark matter and providing independent constraints on the Hubble constant. These research objectives call for the utmost precision in the estimation of the distributions of the lens mass and the source surface brightness. Fortunately, we stand at the threshold of a new era - recent and future strides in radio telescope technology, such as SKA and DSA 2000, promise to provide an abundance of observations of unprecedented quality. Realizing the full potential of these advancements hinges on achieving the highest reconstruction fidelity. In this talk, I will introduce LensCharm, a novel Bayesian approach for strong-lensing signal reconstruction that can be connected to Bayesian imaging algorithms such as resolve, allowing for non-parametric reconstruction of both source brightness and lens mass distribution along with their uncertainties.

	Master Colloquium
Lynn Hansen	ORATED

MPIfR/AIfA

The SKAMPI telescope is a new 15-m single-dish prototype telescope operated by the MPG as a stand-alone observatory and is currently undergoing system performance and science verification analyses. It is located on the South African SKA-mid site and equipped with an S-band and a Ku-band receiver. Utilizing SKAMPI, an S-band All Southern Sky Survey in total intensity covering 1.75-3.5GHz has been performed, which serves as a pathfinder to explore observation strategies for upcoming all sky surveys. This work presents an evaluation of SKAMPI's antenna pointing model, which accounts for systematic effects due to collimation errors, encoder offset, nonorthogonality of axes, axis plane tilt, and possible gravitational effects acting on the telescope dish. Additionally, a first version of the Ku-band pointing model has been estimated. The impact of the individual model parameters is tested and an optimised pointing model reducing the number of model parameters from 9 to 5 is proposed, thereby minimizing systematic pointing effects that would propagate into future surveys. A power spectrum analysis has been used to investigate the impact on the overall structure of the Galactic foreground and its scientific impact on CMB studies. We find that the change in the pointing model impacts various angular scales and can be associated with the primary beam properties of the telescope.

	Master Colloquium
Survi Kumari	ORATED

MPIfR/AIfA

Massive stars (≥8M⊙) are essential for the evolution of galaxies as they influence the surrounding medium and the subsequent star formation activity. They are much rarer than their lower-mass counterparts and are known to be formed in dense molecular clumps. Moreover, high-mass star forming clumps evolve on shorter timescales, within dynamic and complex environments and are still deeply embedded in their parent molecular cloud during the earliest phases, making it difficult to study the initial conditions involved. This makes the study of high-mass star forming regions extremely important and challenging. In these early stages, the gas temperature is low, allowing the environments to be probed by molecules whose rotational lines lie in the sub-millimeter wavelength range. Ammonia is a key tracer of dense gas and in dense, pre-stellar cores, reactions with deuterated ions (such as H2D+) convert it into its deuterated isotopologues NH2D, NHD2, and ND3. The abundance of deuterium bound in molecules (with respect to its parent species) is orders of magnitude higher in cold molecular clouds than the primordial [D]/[H] ratio (∼ 10e−5, Oliveira et al. 2003). The variation in deuterium fractionation has been used as a tracer of the evolutionary phases in low-mass star formation, therefore in my master’s thesis I investigate if the same can be done for the high-mass regime.

	Special Colloquium
Mr. Ezequiel Albentosa-Ruiz	ORATED

Universitat de València, Spain

The Galactic Center supermassive black hole, Sagittarius A* (Sgr A*), provides a unique laboratory for studying astrophysical variability across wavelengths. Using high-cadence, full-polarization light curves from ALMA observations during the 2018 Event Horizon Telescope (EHT) campaign (April 21–25), we analyze Sgr A*'s variability and polarization properties with standard time-series analysis tools. Comparing these results with the April 2017 light curves offers insights into the variability and consistency of Sgr A*'s behavior across both observational campaigns. We also take a closer look at April 24, 2018, when Chandra detected a notable X-ray flare, to investigate the time delay between high-energy and mm-wavelength peaks. Finally, we compare the observed variability in our light curves with predictions from GRMHD simulations, evaluating accretion models near Sgr A* under extreme conditions. The results presented in this talk provide new insights into Sgr A*'s accretion dynamics and multi-wavelength emission.

	Master Colloquium
Pranav Limaye	ORATED

AIfA/MPIfR

Fast Radio Bursts (FRBs) are extremely bright, coherent, short-duration flashes of radio light with an extragalactic origin. While some FRBs are known to repeat, a significant fraction have only been detected as one-off events. The underlying progenitor responsible for these intense, extragalactic radio bursts remains an open question. Although the coherent emission from these objects is observed over a very narrow bandwidth, different bursts from the same source can span a broad range of frequencies, making detection challenging for radio telescopes with limited bandwidth. This work presents an observational study of the active repeating FRB, FRB 20240114A, using the Effelsberg 100-m Radio Telescope. The newly installed Ultra BroadBand receiver on the telescope enables the study of FRBs over a wide frequency range of 1.3–6 GHz. Conducting FRB observations with this receiver allowed for the collection of a rich broadband sample of bursts from FRB 20240114A. Various statistical analyses were performed on this sample, comparing results with existing FRB studies and exploring potential connections to neutron stars, which are among the most widely favored FRB progenitor models.

	Main Colloquium
Dr. Michal Zajaček	ORATED

Department of Theoretical physics and Astrophysics, Faculty of Science, Masaryk University, Brno, Czech Republic

I will describe the detection of quasiperiodic ultrafast outflow in the system ASASSN-20qc at z=0.056 (Pasham et al., 2024). The outflow is revealed in the X-ray spectra as an absorption feature, which is periodically enhanced every ~8.5 days. The periodic nature of the ultrafast outflow is best explained by an orbiting perturber that is inclined with respect to the accretion flow. In this way, the orbiting body pushes the disc gas into the outflow funnel, where it is then accelerated by the ordered magnetic field (Sukova et al. 2021). The observed period of 8.5 days, in combination with the inferred SMBH mass of 10^7-10^8 Msun, indicates a semi-major axis of ~100 gravitational radii. The observed outflow rate to inflow rate ratio puts constraints on the influence radius of the perturber. For ASASSN-20qc, the influence radius of 3 gravitational radii suggests the presence of a massive perturber in the intermediate-mass black hole (IMBH) mass range. Quasiperiodic ultrafast outflows (QPOuts) are thus a novel phenomenon that can reveal new EMRI/IMRI candidates that otherwise do not exhibit significant periodic changes in the continuum flux density (or the accretion rate).

	Special Colloquium
Dr. Frederic Jaron	ORATED

TU Vienna

Long-term flux monitoring of astrophysical sources enables detailed analysis of the timing characteristics of their emission. This can be a powerful tool to investigate the physical processes at work in these systems. The TeV-emitting binary star LS I +61°303 has been observed in radio monitoring programs since 1977. It has also been the target for monitoring at higher energies and is included in the search for neutrinos. Periodic signals in the radio emission from this source have been observed to be present and remain stable over decades. Modulation patterns are systematically related across the electromagnetic spectrum. I will discuss these findings in a scenario of periodic accretion onto a compact object and different emission regions within a precessing jet.

	Special Colloquium
Dr. Paola Domínguez Fernández	CANCELED

Center for Astrophysics | Harvard & Smithsonian

TBD

	Special Colloquium
Dr. Martina Scialpi	ORATED

INAF

A large population of AGN pairs residing in the same galaxy—the so-called dual AGN—is predicted to exist at redshifts z > 0.5. These systems constitute the parent population of merging black holes (BHs), making their number and properties a key starting point for theoretical predictions on the level of the gravitational wave (GW) background and the event rate investigated in pulsar timing array (PTA) experiments and by the future LISA mission. Until recently, only a handful of dual AGN had been identified at sub-arcsec separations. In this talk, I will present the first statistically significant sample of these systems with separations ranging from 0.15" to 0.8" (~ kpc at z>0.5), selected using the innovative Gaia multi-peak (GMP) technique. However, follow-up observations are needed to confirm the nature of these objects and distinguish true dual AGN from gravitationally lensed systems. I will showcase spatially resolved optical and near-IR spectroscopy data of approximately 50 systems at cosmic noon, obtained with ground-based AO-assisted instruments including Keck, VLT, and LBT. Additionally, I will present how combining low-frequency and VLBI radio data with optical/IR observations enables us to confirm optically-selected objects and identify strong radio-selected dual AGN/lens candidates. Building on the classification of these systems, I will also present the first study of dual AGN properties, including the luminosity and the mass functions, their separation distributions, their fraction within the total AGN population, and how these characteristics evolve with redshift.

	Main Colloquium
Dr. Taro Shimizu	ORATED

MPE

Near-infrared interferometry is a unique tool to study the inner sub-parsec structure of AGN which is inaccessible with current single dish telescopes. With VLTI/GRAVITY, we can now spatially resolve not just the hot dust continuum on milliarcsecond scales through imaging but also the broad-line region on microarcsecond scales through spectro-astrometry. In this talk, I will review the latest results from our observations of local AGN with GRAVITY where we have mapped the kinematics of the BLR in seven nearby AGN, measured sizes of the hot dust for sixteen AGN, and reconstructed images for two AGN. BLR kinematics have allowed us to independently measure the BLR size and supermassive black hole mass where we begin to find a departure from the radius-luminosity relation at high luminosity. I will give an overview of the GRAVITY+ upgrades that will allow for direct black hole mass measurements out to high redshift and therefore a precise tracing of supermassive black hole-galaxy coevolution through cosmic time. With the addition of wide-angle off-axis fringe tracking and a state-of-the-art AO system, we have already pushed observations out to cosmic noon and beyond and I will show the first results and sample from this program.

	Master Colloquium
Jannick Schulze	ORATED

MPIfR

The SKAMPI telescope is a new single-dish prototype telescope, located on the South African SKA-mid site, which is currently undergoing science commissioning. The telescope stores metadata on the state of the telescope and environmental conditions for each observation. This metadata can be used to investigate potential systematic errors by studying telescope behaviour under changing conditions over time. A workflow has been developed to validate and characterise sensor data, using two different types of Machine Learning approaches that generate models fully describing SKAMPI. These models have been evaluated and learned relations have been extracted from the trained models to validate results and investigate dependencies. A difference in azimuth- and elevation-dependency of exceeding ADC-input saturation of the receiver system is shown. Overall the developed workflow provides first insights into the systematics of SKAMPI and, over a longer time span of operation, could be used to investigate time-dependencies of said relations. In addition it is shown that an ISS downlink emitter, or similar satellite-based emitters, can be successfully used to image SKAMPIs antenna pattern up to the 4th sidelobe.

	Main Colloquium
Dr. Javier R. Goicoechea	ORATED

IFF-CSIC

The earliest stages of (exo)planet formation takes place in protoplanetary disks of gas and dust around young stars. It has become evident that the majority of these disks originate within a cluster of stars, subjecting them to intense ultraviolet (UV) radiation. Despite its relevance to planet formation theories (our proto-Solar System disk formed in a cluster) little is known about the role of this external UV radiation in the formation, evolution, and chemical composition of embryonic planetary systems. The unprecedented capabilities of JWST combined to ground based observatories such as ALMA now enables us to characterize protoplanetary disks irradiated by UV from the cluster.

	Main Colloquium
Dr. Hannah Uebler	ORATED

MPE

One of the most surprising results coming out of the first two years of science operations with JWST is the unexpectedly high abundance of actively accreting black holes in the early Universe. Compared to the local population, many of these early black holes appear to differ in various aspects, such as their relation to their host galaxies or their multi-wavelength properties. These observational findings challenge our understanding of the past evolution of present-day supermassive black holes, and provide new ways to constrain theoretical models of black hole formation and growth. I will give an overview of recent observational results on massive black holes in the first few billion years and how they fit into current models, largely driven by the unprecedented capabilities of JWST to explore cosmic dawn, and with a focus on results from the NIRSpec GTO surveys JADES and GA-NIFS.

	Special Colloquium
Prof. Dr. Jongho Park	ORATED

KyungHee University

Very Long Baseline Interferometry (VLBI) achieves ultrahigh angular resolution by utilizing widely separated radio telescopes. The quality of VLBI images improves with more participating telescopes, a principle realized by the Global VLBI Alliance (GVA). In this talk, I will present recent advances in AGN jet studies enabled by the GVA. 1. We identified a dense, cold ambient medium near the core of the 3C 84 jet, which guides its propagation on parsec scales and significantly influences its overall shape. 2. Our observations of NGC 315 reveal that its jet, previously known for a center-brightened morphology at parsec scales, is actually edge-brightened—a feature unresolved in earlier VLBI studies. I will discuss the physical implications of these findings and explore future research opportunities with the GVA and the Global Millimeter VLBI Array (GMVA).

	Special Colloquium
Dr. Guang-Xing Li	ORATED

SWIFAR, Kunming

Modern Astronomical Observations provide high-fidelity images that might contain complex structures. The effective approaches to analyzing these structures remain missing. Here, I present a method, which can extract information from these maps by analyzing the relationship between measurement values from adjacent pixels. The method can reveal regularities in the parameter space, which is hard to obtain otherwise, and can provide optimal ways to divide a region into patches of heterogeneous properties. I provide examples where the method has been used to analyze astronomical, medical, agricultural, and climate images.

	Main Colloquium
Dr. Frank Rieger	ORATED

IPP

Accreting supermassive black holes are believed to drive the energy output in the form of radiation and relativistic plasma outflows (jets) seen in active galactic nuclei (AGN). As the most powerful, persistent sources in the Universe, AGN provide a unique possibility to explore the realm of extreme physics. I will highlight some recent advances in the high-energy plasma diagnostics of these objects, ranging from magnetospheric processes in the vicinity of supermassive black holes to the physical characteristics of their large-scale jets. On black-hole horizon scales, for example, gap-type particle acceleration is a likely mechanism behind the rapidly variable gamma-ray emission observed in sources such as M87, and may supply the plasma necessary for continuous jet formation. On larger scales, a combination of first and second-order Fermi-type acceleration processes presumably plays a key role in shaping the non-thermal emission properties of AGN jets. I will give an introduction to these scenarios, comment on their potential role for ultra-high energy cosmic-ray production, and address some of the key challenges currently facing this field.