Alumni 2026
Marten Scheuck (12.1.) - Christian Sorgenfrei (29.1.) - Clara Escanuela Nieves (27.4.)
Clara Escanuela Nieves (Spain) - 27.04.2026
Improvements in Shower Reconstruction and Data Analysis Techniques for IACTs, and a Study of RX J1713.7–3946 ( thesis pdf, 45 MB )
Very-high-energy gamma rays (> 100 GeV) reveal fundamental insights into the particle composition, acceleration mechanisms, and particle escape from cosmic sources. Unlike charged cosmic rays deflected by magnetic fields, gamma rays travel in straight lines, tracing their origin directly. Ground-based telescope arrays study these gamma rays by collecting Cherenkov light from secondary particles produced when they interact with the atmosphere. Current instruments such as the High Energy Stereoscopic System (H.E.S.S.) have made significant advances in this field. The Cherenkov Telescope Array Observatory (CTAO) will achieve unprecedented sensitivity through two large arrays of telescopes equipped with high-performance Cherenkov cameras and advanced data analysis techniques.
The first part of this thesis presents and validates new methods for the CTAO data processing chain that improve the observatory’s sensitivity and precision, with particular emphasis on reliability under suboptimal observation conditions. The study encompasses photoelectron extraction, image cleaning, and an alternative image parameterisation method. An online data volume reduction algorithm considerably reduces stored data while maintaining the observatory’s performance. Simultaneously, a rapid online muon-tagging method identifies muon candidates for calibration. Together, these methods enhance the CTAO performance and reconstruction robustness.
Supernova remnants are theorised to be the primary sources of Galactic cosmic rays. RX J1713.7-3946 is among the brightest and most studied remnants at high energies. In the second part of this thesis, a new joint analysis of H.E.S.S. in conjunction with data from the Fermi Large Area Telescope (LAT) reveals significant gamma-ray emission outside the remnant. This provides strong evidence for protons escaping the acceleration site. Spectral differences within the remnant further indicate the acceleration of multiple particle types.
Supervisor: James Hinton (MPIK)
Christian Sorgenfrei (Germany) - 29.01.2026
Determining the innermost structure of quasars by microlensing: Measuring, simulating and interpreting light curves of multiple quasars ( thesis pdf, 45 MB )
This thesis aims at measuring quasar microlensing light curves and applying them to constrain the structure of quasar accretion disks. Thus, data was taken in two photometric filters at the Las Cumbres Observatory, using their global network of 1m telescopes since 2014. In the first part, applying difference imaging analysis together with point spread function photometry aided with Gaia data, we measure the light curves of the multiple images of eight gravitationally lensed quasars in the R and V band, covering almost ten years with in total 1872 epochs. For each quasar, we determine difference curves of the time delay corrected light curves. This removes the intrinsic quasar brightness variations present in all images with only uncorrelated microlensing variability of the individual images remaining. We find these additional variations, attributed to the source size depended microlensing of the individual images by compact objects in the lens galaxy, throughout our whole data set.
For the second part of this thesis, we focus on the prominent microlensing signal in image B of the quadruple quasar HE0435-1223, revealed through our difference curves. The variations appear to be chromatic, i.e. depend on the filter, with higher amplitude fluctuations in the V band. This is expected, since the hotter central region of the accretion disk experiences more microlensing variation due to its smaller size. To quantify this observation, by means of microlensing simulations, we are able to infer that the accretion disk of HE0435-1223 is indeed larger in radius by factors of 1.24^{+0.08}_{−0.20}, 1.42^{+0.11}_{−0.22} and 1.43^{+0.10}_{−0.23} in the R with respect to the V band, depending on the disk model, in agreement with the expectation from thin accretion disk theory, though with a tendency towards a shallower temperature profile. Additionally, we find disk half-light radii of 0.7 to 1.0 Einstein radii, corresponding to average inclined disk scale radii of around log 〈R2500/cm〉 ≃ 16.4^{+0.5}_{−0.7} at 2500Å in the quasar rest-frame.
Supervisor: Jocahim Wambsganss (ARI)
Marten Scheuck (Germany) - 12.01.2026
The structure of the innermost regions of circumstellar discs with VLTI/MATISSE ( thesis pdf, 15 MB )
Circumstellar discs serve as the progenitors of planetary systems. Their inner regions (from <1 au to a few astronomical units) are where terrestrial (i.e. Earth-like) planets form. Structures closely connected to planet formation, such as spirals, rings, or gaps, have been observed in the outer disc regions (∼20– 400 au). These outer regions are being intensively studied with instruments like SPHERE at near-infrared wavelengths or ALMA in the (sub-)millimetre. The innermost regions, on the other hand, have only been made accessible recently by interferometers with high spatial resolutions in the near- and mid-infrared (e.g. AMBER, MIDI, PIONIER, and GRAVITY on the VLTI). In this thesis, I use spectro-interferometric observations with the VLTI/MATISSE instrument, covering a broad wavelength range in the mid-infrared from the L/M (2.8–4.2 µm/4.5–5 µm) up to the N band (8– 13 µm), to investigate the structures present in the innermost regions of planet-forming discs. MATISSE provides spatial resolutions sufficient to resolve the innermost disc regions for sources in nearby star formation regions (∼100 pc).
I apply data reduction and parametric modelling to give astrophysical interpretations of the interferometric observations. First, I explore the circumstellar discs of the HD 142527 binary system, where a close passing (periapsis∼5 au) stellar companion greatly perturbs the disc around the primary. Using a a disc model with an off-centre Gaussian asymmetric component, I find a time-variable structure around the primary at a separation of∼1– 1.2 au over the course of our observations (2021, 2022, and 2023) close to periapsis. The complex structure in the disc seems to be strongly influenced by the companion passage and warrants further observations to enable more detailed modelling. Subsequently, I perform a statistical analysis of∼60 sources from the MATISSE GTO YSO survey. I derive L- vs. N -band sizes from modelling and combine them with simple disc models. In doing so, I find that many discs in the survey sample show signs of gaps or truncations. Here, the sizes increase when the gaps in the disc become larger, up to the point of no significant N -band emission (i.e. truncated), which show smaller sizes than for continuous discs. The sample contains many strongly asymmetric sources from which disc substructures are deduced.
Supervisor: Thomas Henning (MPIA)