Promotionskolloquium
Timea Kovacs	ORATED

MPIfR

Magnetic fields play an important role in galaxy evolution, from processes such as gas dynamics and star formation to galactic outflows. However, the redshift evolution of galactic-scale magnetic fields is not well constrained, both observations and theoretical predictions are lacking, with only a handful of direct magnetic field strength measurements in distant galaxies. In my talk, I will present my results from both radio polarimetric observations and synthetic observations made with the IllustrisTNG50 simulation. First, I will present the analysis of broadband (1 - 8 GHz) spectro-polarimetric Very Large Array observations of two lensing systems (B1600+434 and B0218+357). Using these, we measured the halo magnetic field of a distant galaxy at z=0.414 (corresponding to 4.4 Gyr ago) for the first time with a strength of 1.2 - 1.8 uG, and found an axisymmetric disk field of 2 - 20 uG in a lensing galaxy at z=0.685 (6.3 Gyr ago), in agreement with the magnetic field strength and structure of nearby galaxies. Then, I will show how the observables of magnetic fields evolve over redshift using 16 500 galaxies at redshifts of 0 < z < 2 from the state-of-the-art cosmological magneto-hydrodynamic simulation IllustrisTNG50. I explore two methods used to obtain cosmic magnetic field strengths: deriving the magnetic field strength of intervening galaxies in front of polarized background quasars and deriving the magnetic field strength of the IGM by utilizing FRBs. In the near future, we expect the number of known lensing systems, quasars with intervening galaxies, and polarized FRBs to dramatically increase by tens of thousands of systems due to new radio surveys and telescopes. The results I am presenting demonstrate how the lensing method can be applied to different galaxies, and predict measuring the magnetic field strength of the IGM with a 2 rad m^-2 precision using FRBs will be possible in under 10 years.

	Main Colloquium
Prof. Dr. Julia Tjus	ORATED

RUB

Active galactic nuclei have long been discussed to be the sources of ultra-high-energy cosmic rays. The reason is simple: they are among the very few source classes that provide the right parameter range in terms of magnetic field strength and size that fulfill the necessary criterion for the acceleration to the highest observed cosmic-ray energy of 1e20eV. To prove this statement, or even to narrow down if the acceleration region sits in the inner jet, the termination show of the jet or the core is one of the major challenges in astro- and astroparticle physics. As cosmic-rays do not travel in straight lines, their directional information does not help for an anumbiguous identification. Iin this talk, it will be discussed how knowledge about the magnetic field structure and strength help to identify the origin of the acceleration zone and how we can use neutrinos to further pinpoint how active galaxies contribute to the cosmic ray spectrum.

	Informal Colloquium
Dr. Leonid Petrov	ORATED

NASA Goddard Space Flight Center, USA

Processing the output of assimilation numerical weather models, one can derive the state of the atmosphere on a 4D grid. When we know the state of the atmosphere, we can compute path delay in the neutral atmosphere, atmospheric opacity, and brightness temperature of the atmosphere to a given station, given azimuth and elevation, and given moment of time. NASA Goddard Space Flight Center runs a suite of operational assimilation numerical weather model. In addition, NASA runs an operational service for computation of slant path delays, atmospheric opacities, and brightness temperatures. An overview of these data products will be given, and their use in data analysis will be discussed.

	Special Colloquium
Dr Minghui Xu	ORATED

GFZ Potsdam

Effect of source structure is the (only) dominant factor that limits the accuracy of the celestial reference frame. The AGNs in absolute astrometric and geodetic observations are still assumed to be an ideally point on the sky although their structure and its evolution over both time and frequency are well understood in radio astronomy. I will report on my study about investigating these effects based on the observations from the new generation geodetic VLBI system, VLBI Global Observing System (VGOS). VGOS makes regular observations since 2019 with a network of 7 to 12 antennas simultaneously at the four bands in the range of 3 to 11 GHz. This network is expanding globally. I have imaged these VGOS observations on a routine basis via closure images because of the known issue of missing antenna calibrations for geodetic antennas. These VGOS images show that nearly all VGOS sources have “invisible” structure at the angular scales of 0.1 milli-arcsecond or higher. Another challenge of modeling source structure in VGOS observations is the image alignment over the four frequencies, where core shift will also play a role. According to my simulations, any misalignment among the highest three frequency bands is magnified in the source position estimates from VGOS. I will report on how to valid the image alignment by using phase delays. It is to be noted that not only for geodesy but also for astrometry modeling source structure is so important and is the necessary step forward.

	Special Colloquium
Lennart Heino	ORATED

University of Cape Town

This study explores the polarised emission of the faint extragalactic radio sources in the MIGHTEE (MeerKAT International Giga-Hertz Tiered Extragalactic Exploration, Jarvis et al., 2016) survey in order to systematically study cosmic magnetic fields in galaxies to high redshift. Tracing he presence and contribution of magnetic fields is an important aspect of understanding galaxy evolution. Reaching a sensitivity of 2 muJy/beam at a resolution of 6 arcseconds, MIGHTEE is providing an opportunity to chart the evolution of polarised emission from distant galaxies over cosmic time. The MIGHTEE survey detects polarised emission for a large number of radio sources down to total intensity flux densities of the order of 100 muJy. At these flux densities the source population is increasingly dominated by star-forming galaxies (SFGs) as opposed to active galactic nuclei (AGNs) which are dominant at high flux densities. Observations of the local universe show that both, AGN and SFG phenomena, are permeated by magnetic fields. Polarised emission of AGN can be traced to very distant galaxies. However, polarised emission of SFGs at moderate distance has been detected only once. I use multi-wavelength criteria to classify MIGHTEE radio objects as either SFG or AGN. I perform Rotation Measure Synthesis (RMSY) on the spectro-polarimetric data cubes and use the polarisation and RMSY spectra to search for polarised emission. A comparative analysis of the polarisation properties of SFGs and AGNs is performed. The analysis is extended to the lowest possible flux densities using stacking techniques. I will show results of the MeerKAT polarisation studies of radio sources down to a sensitivity at the micro-Jansky level.

	Special Colloquium
Dr. Nuria Jordana	ORATED

RUB

Gamma-ray bursts (GRBs) are bright extragalactic flashes of gamma-ray radiation and the most energetic explosions in the Universe. Their catastrophic origin —the merger of compact objects or the collapse of massive stars— drives the formation of a newborn compact remnant (black hole or magnetar) that powers two highly relativistic jets. As these jets continue to travel outwards, they collide with the external material surrounding the dying star, producing a long-lasting afterglow that can be seen across the entire electromagnetic spectrum, from the most energetic gamma-ray emission to radio wavelengths. But how can such material be accelerated and focused into narrow beams? To distinguish between jet models and ultimately determine the power source of GRBs, we study the polarization of the light during the first minutes after the explosion (using novel instruments on fully autonomous telescopes around the globe) and we directly probe the magnetic field properties in these extragalactic jets. In this talk, I will review the recent developments that have been made using this technology. Those include some insights on the progenitors and remnants of these energetic explosions, the first detection of highly polarized optical light from a GRB and confirmation of mildly magnetized jets, and the case of an exceptionally high-energy GRB produced by a highly magnetized jet.

	Main Colloquium
Dr. Elena Redaelli	ORATED

MPE

Research into star formation is a highly active area of modern astrophysics. Stars are born in dense and cold environments known as molecular clouds, which appear as dark patches in the night sky as optical radiation cannot penetrate them. Since these clouds are composed of molecules, molecular transitions at radio and microwave wavelengths represent the ideal diagnostic tool to probe these phases of the interstellar medium. I will show how through their analysis we can infer the physical and chemical structure of star-forming regions, to understand how they evolve. I will showcase examples of the power of this technique in both the low- and the high-mass regimes, each with its set of challenges.

	Special Colloquium
Dr. Leonid Gurvits	ORATED

JIVE and TU Delft

In this impromptu presentation I will cover two VLBI topics pursued merely 240 km NW of Bonn. The first one deals with the initiative to build a next generation spaceborne VLBI system. I will start from a brief (and known to many in the audience) concept called TeraHertz Exploration and Zooming-in for Astrophysics (THEZA) as it stands now, five years after proposing it to ESA. I will then review a (much) scaled down version of THEZA called Black Hole Explorer (BHEX), also known to some people in the audience. BHEX is aiming to address a truly transformative science of the phenomenon of photon rings surrounding black holes. BHEX is led by a joint team of two major US establishments, Harvard CfA and NASA Goddard Space Flight Center, supported by other US research organisations, but has representatives from Europe and Japan too. Both initiatives, THEZA and BHEX can be seen as spaceborne extensions of global VLBI, EVN, VLBA, GMVA, EHT, ngEHT, ngVLA, etc. (cross out what you find irrelevant). My main take-home message from this part of the presentation is simple: spaceborne VLBI is inevitable. We better start thinking and working on this before too long. In the second part of this presentation, I will show results of the ongoing study of two newly suspected systems containing supermassive black hole binaries (SMBHBs). According to all reasonable scenarios of astrophysical evolution of galactic systems SMBHBs must exist and be abundant. They are expected to be major contributors to the gravitation wave background in the range of frequencies 0.1 mHz – 1 Hz which is to be covered by the Laser Interferometer Space Antenna (LISA) once it is up and running in the 2030s. Yet, as a class, SMBHBs remain rather elusive. There are several famous and rather likely suspects (e.g., OJ 287 – an object very well known in this audience, and several others). There is a number of much less known and sure cases, like those several I will present here. However, the overall statistics of more or less known suspected cases of SMBHB looks quite problematic from many astrophysical and cosmological standpoints. I will present our view on possible evolution of two new SMBHB suspects and present estimates of their inspiralling toward final coalescence accompanied by a gravitational wave outburst. Such outbursts are being assumed as potentially valuable cosmological probes called “standard sirens”. They will join the club of other standard objects (rods, candles), and together they will mark the birth of multimessenger observational cosmology.

	Master Colloquium
Mr. Abhinav Tyagi	ORATED

AIfA

The discovery and analysis of binary pulsars in compact orbits offer unique opportunities to test theories of gravity, particularly General Relativity, in the strong-field limit. Modern pulsar searches, often conducted in quasi-real-time using large GPU-based HPC clusters, underscore the critical need for speed in processing and analyzing this data. In this talk, I will introduce PulsarNet, a machine learning (ML) pipeline designed for the detection and parameter estimation of binary pulsars in time-series observations. PulsarNet (PN) represents the first fully ML-based search pipeline of its kind, marking a significant departure from conventional matched filtering techniques. It achieves comparable sensitivity for sinusoidal signals and pulsars with a high duty cycle (>15) and offers substantially faster processing speeds than traditional searches. PN employs a two-part ML model: comprising a classifier that pinpoints plausible pulsar signals in the Fourier domain, along with an innovative 'Attention'-based parameter predictor network for estimating the period and period derivative of a signal used to fold the data. While our early results are encouraging, I will also address some challenges of using a complete ML-based approach for pulsar searches, including recovering sensitivity for pulsars with a high number of harmonics in the Fourier domain. After training purely on simulated white noise data, we applied PN to search for pulsars in the Terzan 5 globular cluster and were able to recover 80% of the pulsars compared to traditional searches, while being 13 times faster. We anticipate that future models can bridge this sensitivity gap by implementing harmonic summing and retraining on real observations. PN stands as a proof-of-concept that purely ML-based searches are not only feasible but with some additional work can be effective for future pulsar processing, opening up a new parameter space for astrophysical discoveries.

	Special Colloquium
Dr. Christophe Risacher	ORATED

IRAM

I will present the current IRAM instrumentation at our two observatories (NOEMA and the 30m telescope) before detailing the current ongoing upgrade for NOEMA, preparing a dual-band observing mode capability (observing the 3 mm and 1.3 mm in parallel), which does require doubling the IF processing / transport and backends to allow using the full available instantaneous bandwidth. We will also show some of our development projects for the future generation receivers, aiming at increasing the IF bandwidth of the heterodyne receivers, to 4-20 GHz IF BW. Finally, we will show the plans and progress of our developments of large multibeam receivers for 3 mm and 1.3 mm for the IRAM 30m telescope.

	Main Colloquium
Prof. Dr. Tessa Baker	ORATED

University of Portsmouth

The first eight years of direct gravitational wave detection have had a huge impact not only on astrophysics, but also on cosmology and fundamental physics. Central to these developments have been Sirens, gravitational wave sources for which we can measure both distances and redshifts. The most spectacular kind of sirens are multimessenger events like the binary neutron star merger GW170817, with both gravitational wave and electromagnetic counterparts. However, these represent only a tiny fraction of all gravitational wave events. So are all the other gravitational wave events useless, from a cosmology perspective? In this talk I'll introduce the alternative Dark Sirens method, which enables us to extract cosmology from regular, non-counterpart gravitational wave events. I'll explain how this technique can be used to obtain an independent measurement of the Hubble constant, and also to test the laws of gravity operating on the largest scales. I'll describe some subtleties that require careful handling, (hopefully!) convince you that we can overcome them, and show the latest results obtained from gravitational wave detections to date.

	Special Colloquium
Dr. Nienke van der Marel	ORATED

Leiden University

Structures such as gaps and rings in ALMA observations of protoplanetary disks have long been hailed as signposts of planet formation. However, a direct link between exoplanets and protoplanetary disks remained hard to identify. Recent work has shown that gapped disks retain high millimeter-dust masses up to at least 10 Myr, whereas the majority of disks is compact and decreases its dust mass rapidly. This can be understood when considering dust evolution, where dust traps prevent radial drift in the gapped disks. The fraction of gapped disks shows a stellar mass dependence, and I propose a scenario linking this dependence with that of giant exoplanet occurrence rates. It is shown that there are enough exoplanets to account for the observed disk structures if gapped disks are caused by exoplanets more massive than Neptune, under the assumption that most of those planets eventually migrate inwards. On the other hand, the known anti-correlation between transiting super-Earths and stellar mass implies those planets must form in the compact disks, consistent with those exoplanets forming through pebble accretion in drift-dominated disks. I will demonstrate some of the latest insights on rocky planet formation in compact disks, as well as new insights on gas giant planet formation in larger gapped disks. Finally, I will show that dust traps and radial drift may play a crucial role in regulating the chemical composition of disks, which sets the C/O ratio of exoplanet atmospheres as traced in the coming years with the James Webb Space Telescope.

	Special Colloquium
Dr. Sasha Plavin	ORATED

Black Hole Initiative, Harvard University

Increasing numbers of high-energy neutrinos coming from blazars are being detected, but data sparsity makes it challenging to quantitatively describe each source individually. In this talk, we present the results of modeling the distribution of a bright blazars sample, taking their geometry and observed radio and neutrino properties into account. This lets us constrain the contribution of all blazars to high-energy neutrino flux, to evaluate the effects of relativistic beaming, and to estimate hadrons contribution to the total jet power.

	Main Colloquium
Dr Julia Stadler	ORATED

MPA

A new generation of galaxy surveys is soon to release their first data. While holding the potential to transform our understanding of the origin and evolution of the Universe, the analysis of these datasets poses considerable challenges. The state-of-the-art approach compares theory and data in terms of summary statistics, such as the galaxy power spectrum. However, information is lost in this compression. Another major concern is theoretical uncertainties in the small-scale processes of galaxy formation and consequently in the galaxy bias relation. Forward modeling the three-dimensional large-scale galaxy density enables the comparison between model and data at the level of density fields, and thereby it foregoes the loss of information in the data compression step. By basing the forward model on perturbative methods, namely the Effective Field Theory of Large Scale Structure (EFT of LSS), one can robustly marginalize over theoretical uncertainties in the galaxy bias relation. Such an analysis not only provides tight cosmological parameter constraints but also offers insights into the initial conditions and structure formation history over the survey volume. I will discuss the status of field-level analysis for galaxy clustering and show results and developments with the LEFTfield code. Forward modeling allows for the self-consistent incorporation of many observational effects, and I discuss redshift-space distortions as an important step on the way to realizing the potential of this technique for observational data.

	Special Colloquium
Dr. Etienne Bonnassieux	ORATED

University of Wuerzburg

In the last few years, the international LOFAR baselines have become accessible to a broad public at 144 MHz. This is due to a better understanding of the instrument itself, the development of new techniques, and the availability of a dedicated pipeline. In this talk, I will give a brief introduction to the general problem of interferometry, the specific case of VLBI, and the hybrid case of LOFAR-VLBI, with an eye on future SKA-VLBI and ngVLA. I will then give specific examples, and conclude with concrete scientific returns made possible with the investment of time and energy in technical interferometric work.

	Special Colloquium
Prof. Dr. Peter L. Biermann	ORATED

MPI für Radioastronomie

The WAT (wide angle tail) radio galaxies ESO 137-006 and 3C338 show radio filaments including some extending between the two radio tails. If, in analogy to the Parker Solar wind, jets carry a powerful relativistic electric current, driven by gradient drift currents of particles in a $p^{-2}$ spectrum, Maxwell's continuity equation shows that a temporal variation in jet power would inevitably lead to a localized short-lived charging-up, i.e. a temporary patch of electric field. Progenitors of the observed radio filaments are the relic jets left by repeated episodes of nuclear activity and pushed sideways by the ram pressure, though remaining connected to the broad radio lobes. The Debye shielding distance using the same $p^{-2}$ spectrum approaches the radio galaxy scale, with a huge total energy content. Here we propose that discharges dissipating the transient patches of electric fields through the filaments illuminate them. The same process will illuminate jets emanating from rapidly rotating young stellar mass black holes (BHs), and lead to lightning. Lightning allows particle spectra of $p^{-3}$ to $p^{-5}$ for electrons, as visible in radio data of Galactic filaments, and extragalactic filaments; correspondingly protons and other nuclei have spectra of $p^{-2}$ to $p^{-4}$. The steep spectrum allows a steep dependence of residence time on energy/momentum with $p^{-5/3}$, that is suggested by fits to the AMS spectra for transport in the OB-Super-bubble: Based on earlier ideas here a model is proposed that focusses on the cosmic ray interaction first in the wind shock shell of super giant stars, when the supernova driven shock races through, and second in the OB-Superbubble full of lightning: The two key aspects are i) a much larger column of interaction, allowed because of heavy element enrichment of the interaction zone, and ii) even He, C, and O may have a small secondary contribution, as the difference to the Fe spectrum suggests; this small secondary component is visible in the $^3$He data. In this model OB-Superbubbles are thunderstorms.

	Master Colloquium
Sachin Pradeep	ORATED

MPIfR

Fast Radio Bursts are subject to scattering and scintillation due to interactions with one or more plasma screens within the interstellar medium or the halos of the host galaxy and the Milky Way. These screens contain structures of AU scales, which lead to the multipath propagation of the single pulses. A common argument is that when two screens appear "pointlike" to each other, they scintillate on the scale of both screens. This condition is commonly invoked to constrain scattering to FRB host galaxies. In this study, we use simulations to explore the resolving phase space where the screens appear extended to each other and its effect on observables. The main result is the quenching of broad-scale Milky Way scintillations when the screens resolve each other. Additionally, we demonstrate through simulations that the quenching phenomenon can be used to locate the host galaxy screen, thereby probing the host galaxy ISM at AU scales. The work also introduces a new theoretical model and a novel simulation tool to study multi-screen scattering, which can be easily adapted to study images arising from gravitational lensing and microlensing from CGM clouds.

	Main Colloquium
Prof. Dr. Tom Ray	ORATED

Dublin Institute for Advanced Studies

+++ Note the unusual time to accommodate the speaker +++ One of the primary goals of the James Webb Space Telescope (JWST) is to investigate the very earliest stages of star formation. This is a task well suited to JWST as it is capable of observing through dust-enshrouded molecular clouds with unprecedented spatial resolution and sensitivity. After reviewing JWST’s capabilities, I will explore what we have learned in the first 18 months of operation about the outflows that the youngest stars launch, the chemistry of their associated accretion disks, and the relationship between the two.

	Main Colloquium
Dr. Alexandra Veledina	ORATED

Turku University

Imaging X-ray Polarimetry Explorer (IXPE) is the first satellite fully dedicated to X-ray polarimetry measurements. It is sensitive to the direction of the electric field in the X-ray photons and examines the polarization of the incoming signal - the excess of photons with a given direction of electromagnetic wave oscillations. Polarization arises from the broken spherical symmetry of the system and is a fine tool to probe the source geometry. IXPE operations have revealed pivotal insights into various astrophysical phenomena, including accreting black holes and neutron stars, pulsars and their nebulae, magnetars, blazars, and the center of our Galaxy. In this presentation, I will give an overview of the novel findings in the field of accreting black holes, as illuminated by IXPE data.

	Special Colloquium
Dr. Nicola Marchili	ORATED

Istituto di Radioastronomia - INAF, Bologna, Italy

Compact radio sources can show remarkable flux density variations at GHz frequencies on a wide range of timescales. The origin of the variability is a mix of source-intrinsic mechanisms and propagation effects, the latter being generally identified with scattering from the interstellar medium. Some of the most extreme episodes of variability, however, show characteristics that are not consistent with any of the explanations commonly proposed. I will present the results of an in-depth variability analysis carried out on light curves from the impressive database of the US Navy's extragalactic source monitoring program at the Green Bank Interferometer (GBI), a long-term project mainly aimed at the investigation of extreme scattering events. I will show that the Sun heavily contributes to the variability observed in compact radio sources.

	Special Colloquium
Dr. Jakob Knollmueller	ORATED

TU Munich

Sagittarius A* (Sgr A*), the supermassive black hole at the heart of our galaxy, provides unique opportunities to study black hole accretion, jet formation, and gravitational physics. The rapid structural changes in Sgr A*’s emission pose a significant challenge for traditional imaging techniques. We present dynamic reconstructions of Sgr A* using Event Horizon Telescope (EHT) data from April 6th and 7th, 2017, analyzed with a one-minute temporal resolution with the resolve framework. This Bayesian approach employs adaptive Gaussian Processes and Variational Inference for data-driven self-regularization. Our results not only fully confirm the initial findings by the EHT Collaboration for a time-averaged source but also reveal intricate details about the temporal dynamics within the black hole environment. We find an intriguing dynamic feature on April 6th that propagates in a clock-wise direction.

	Main Colloquium
Dr. Sara Ellison	ORATED

University of Victoria

Astronomy's current model of galaxy evolution is built on a foundation of hierarchical growth, in which small galaxies merge together to form larger ones. In addition to the simple accrual of mass, this merging process is predicted to fundamentally change the galaxies properties, such as dramatic morphological transformations, the triggering of bursts of star formation and high rates of accretion onto the central supermassive black hole. In this talk I will explain the physical processes behind these predictions, and present the observations that we are performing in order to test the theory. Although many of the predictions are indeed borne out by experiment, there have been some surprising conflicts as well, that demand revisions to our models of how mergers shape galaxy evolution. +++ Note the unusual time & that this is an online-only colloquium +++

	Special Colloquium
Dr. Etienne Bonnassieux	CANCELED

University of Wuerzburg

TBD

	Main Colloquium
Dr. Enrique Lopez-Rodriguez	ORATED

Stanford University

Galaxy evolution strongly depends on the physics of the interstellar medium (ISM). The ISM is permeated by B-fields, in which magnetic energy is in close equipartition with the thermal energy. This physical condition makes the B-fields dynamically important at several stages of galaxy evolution affecting gas flows in the ISM and driving gas inwards toward the galaxy's centers, and outwards toward the intergalactic medium via galactic outflows. Thus, B-fields remain an important, but still highly ignored, ingredient to understanding the evolution of galaxies across cosmic time. Far-infrared and sub-mm wavelengths have recently been key to providing a complete picture of extragalactic magnetism by doing what only HAWC+/SOFIA, JCMT/POL-2, and ALMA can do: measuring magnetic fields in the densest areas of the universe. Using FIR/Sub-mm and radio polarimetric observations, in combination with the kinematics of the neutral and molecular gas, a topographic study of B-field in galaxies is characterized for the first time. In this talk, I will present the results of SALSA (Survey for extragALactic magnetiSm with SOFIA Legacy Program): the magnetic properties in the multi-phase ISM of nearby galaxies observed in the wavelength range of 50-890 um. These results have opened a new window of exploration on galaxy evolution and provide the building blocks for scientific cases of future IR polarimetric missions. +++ The speaker will be staying at the institute from 29.01 to 02.02+++

	Special Colloquium
Sang-Hyun Kim	ORATED

Korea Astronomy and Space Science Institute and the University of Science and Technology, Korea

Blazars are a subclass of active galactic nuclei (AGNs) and are among the most powerful objects in the universe. Their relativistic jets are pointing towards Earth, resulting in relativistically boosted emission, rapid variability, and superluminal jet motions. The variable emissions extending from radio to gamma-ray energies indicate that blazar jets are efficient and energetic particle accelerators. However, despite many discoveries and detailed studies, there are still some long-standing puzzles of blazar jet physics that remain unsolved. For instance, what are the particle contents of jets? What physical mechanisms drive the particle acceleration in jets? Where and how do jets generate high-energy emissions? This study aims to address these questions by exploring the multiwavelength light curves of a blazar CTA 102. This source exhibits flaring activity from radio to gamma-rays in 2012–2018 observations. Very long baseline interferometry (VLBI) observations of the source show a compact bright region at the upper end of the parsec-scale jet referred to as the VLBI core. Strong correlations between the core flux variability and the single-dish flux variability suggest that the variability of radio emissions may come from the very compact core region. In this talk, I will present the results from this work, including spectral properties and magnetic field strengths of the synchrotron self-absorption region, multiwavelength correlations with respect to the gamma-ray light curve, and VLBI kinematics of the radio jet related to gamma-ray flares. I will also introduce a study on the association of a blazar PKS 0735+178 with high-energy neutrinos, in collaboration with the TeV Effelsberg Long-term AGN Monitoring (TELAMON) program.

	Main Colloquium
Dr. Elena Redaelli	CANCELED

MPE

Research into star formation is a highly active area of modern astrophysics. Stars are born in dense and cold environments known as molecular clouds, which appear as dark patches in the night sky as optical radiation cannot penetrate them. Since these clouds are composed of molecules, molecular transitions at radio and microwave wavelengths represent the ideal diagnostic tool to probe these phases of the interstellar medium. I will show how through their analysis we can infer the physical and chemical structure of star-forming regions, to understand how they evolve. I will showcase examples of the power of this technique in both the low- and the high-mass regimes, each with its set of challenges.

	Special Colloquium
Dr. Juliusz Doboszewski	ORATED

University of Bonn

Assessment of scientific theories is an important part of modern science. But how to go about it in the (rather unique) epistemic situation we find ourselves in cosmology? After all, we only have access to a limited portion of a single universe. In this context, attention to conceptual and philosophical issues can be particularly useful for cosmologists. I will introduce some philosophical notions, including elements of confirmation theory, approaches to eliminative reasoning, non-empirical theory assessment, and problems of underdetermination and unconceived alternatives. For illustration I will discuss three episodes: 1950s debates about steady state theory, 2010s debates about inflation, and the current search for primordial black holes. About the speaker: Juliusz is postdoctoral researcher in the Lichtenberg Group for History and Philosophy of Physics at Uni Bonn, also affiliated with the Harvard University's Black Hole Initiative and involved in the next generation Event Horizon Telescope. He focuses on philosophy of astrophysics, especially global spacetime structure in general relativity and QFT in curved spacetime & quantum gravity.

	Promotionskolloquium
Jompoj Wongphecauxson	ORATED

MPIfR

Pulsars are rotating neutron stars that emit pulsating signals. They serve as valuable tools for studying a wide range of topics, from general relativity to the interstellar medium. The discovery of a pulsar in the Galactic centre (GC) would be particularly fascinating due to its proximity to the Sgr A\*, the black hole at the centre of our Galaxy. Such a discovery could provide insights into the local environment and the nature of the black hole itself. In the GC, up to 1000 pulsars were predicted, but thus far only six have been found, including a magnetar. One of the explanations is that the dense environment in the GC causes extreme interstellar scattering, reducing the sensitivity of pulsar surveys, particularly for short-period pulsars. To improve our sensitivity to long-period pulsars, a Fast Folding Algorithm (FFA) was used rather than the traditional Fast Fourier Transform (FFT). During my study, an FFA pipeline for accelerated pulsars was implemented for the first time to search for pulsars within 1 deg around GC using the data from the High Time Resolution Universe Pulsar Survey-South Low latitude. In this work, a new slow pulsar (PSR J1746-2829) was discovered with an angular distance of ~0.5 deg from the GC. Follow-up observations revealed that this pulsar has properties that are usually associated with radio magnetars. Interestingly, there is another object in the GC that shows magnetar-like properties, in addition to the known magnetar. This may suggest that the GC has an anomalously large fraction of magnetars to non-recycled pulsars compared to the rest of the Galaxy. Extreme interstellar scattering can significantly reduce the sensitivity of pulsar surveys. Fortunately, the scattering time is decreasing with the fourth power of the observing frequency. As a result, the FFA pipeline for accelerated pulsars was modified to search for a high observational frequency (230 GHz) dataset from the three most sensitive stations from the Event Horizon Telescope observations of Sgr A* in 2017. This survey is the highest frequency pulsar survey to date, leading to negligible interstellar effects. However, pulsars have a steep spectrum, making them dimmer at higher frequencies, and harder to detect. We used the FFA and FFT with acceleration search pipelines to search for pulsars in this dataset, but no new pulsars were detected. The further empirical sensitivity analysis shows that we are only sensitive to less than 2\% of the known pulsar population in this search, with less sensitivity on the slow pulsars, highlighting the need for FFA searches.