arXiv subjects

Anastasia Glykopoulou

Publications and source records attributed to Anastasia Glykopoulou.

5 recordsLinked to original sources

arXiv2026

Discovery of minute-scale polarization angle rotation in a supermassive black hole jet

Relativistic jets from supermassive black holes oriented towards our line of sight called blazars have puzzled the astronomical community for decades. Their fast jets and preferential alignment creates a fog of relativistic effects that obscures their true properties. Optical polarimetry - tracing the uniformity, direction, and evolution of the magnetic field in the jets, has revealed a unique phenomenon to blazars; coherent changes of the magnetic field manifesting as rotations of the polarization angle ($Ψ$). The origin of those rotations has been debated for decades with several proposed models to explain them. We detected an extremely fast - minute time-scale - rotation in the polarization angle of $\sim136^\circ$ over the span of about 80 minutes, making it the fastest known rotation by almost an order of magnitude. Our optical polarization observations combined with radio very long baseline interferometry allow us to reject different models of particle acceleration and strongly point to relativistic effects and the interaction of standing and moving shock waves as the origin of the extreme polarization variations in jets.

astro-ph.HE↗

arXiv2026

Optical polarization variability and its relation to gamma-ray activity in blazars

Optical polarization can be an important probe of particle acceleration and high-energy emission processes in relativistic jets from supermassive black holes. We combined publicly available observations from three past blazar monitoring programs to produce densely sampled light curves for 15 blazars in order to explore the relation of gamma-ray activity to the polarization variability as well as discover new rotations of the polarization angle. We find that the polarization degree does not correlate with the gamma-ray flux for individual sources nor different subsamples of blazars, potentially indicating multiple emission mechanisms. In the combined dataset, we identified a total of 64 rotations in 12 sources, 39 of which are newly identified rotations. We confirm the trend found in previous works for the whole sample: lower polarization degrees during periods of polarization angle rotations. However, looking at the individual sources, we identified cases where the rotation and non-rotation polarization degree distributions are indistinguishable, providing further evidence for the multiple emission mechanism hypothesis.

astro-ph.HE↗

arXiv2026

Automating the detection of polarization angle rotations in blazars. Re-analysis of RoboPol data reveals 27 new rotations

We present an automated pipeline for the detection of EVPA rotations in blazars, integrating correction of the 180$^\circ$ ambiguity, Bayesian Blocks segmentation, and statistical validation. Applied to RoboPol monitoring data, the method identified 48 rotations across 25 sources, including multiple events in RBPLJ2232+1143, RBPLJ1751+0939, RBPLJ1800+7828, and RBPLJ2253+1608. The rotations span amplitudes from 90.8$^\circ$ to 359.7$^\circ$, durations between 7.0 and 111.3 days, and rotation rates averaging 5.0$^\circ$/day. Comparison with previous catalogs reveals systematic differences: Bayesian Blocks rotations are on average $\sim$10\% larger in amplitude, about twice as long in duration, and roughly two-thirds slower in angular velocity, reflecting systematic biases between adaptive binning and manual segmentation. In addition, we report 27 previously unreported rotations, including 11 from the final 2016--2017 season. A correlation analysis with contemporaneous Fermi--LAT $γ$-ray light curves shows that longer rotations tend to coincide with enhanced $γ$-ray activity, while rotation amplitude alone is not predictive of $γ$-ray brightness. Our pipeline minimizes subjective biases, expands the list of known EVPA rotations, and provides a reproducible framework for future multiwavelength studies of blazar jet dynamics and particle acceleration.

astro-ph.HE↗

arXiv2026

Tracking down the broadband polarimetric properties of PG 1553+113

We report on a nine-month monitoring campaign of the blazar PG 1553+113, relying on three observations carried out in 2025 with the Imaging X-ray Polarimetry Explorer (IXPE) and supported by multi-wavelength facilities. The source displayed pronounced variability across the electromagnetic spectrum, with X-ray flux changes by up to a factor of $\sim5$ and complex evolution of the optical polarization properties, including one of the largest (exceeding $150^{\circ}$) and fastest rotations in the electric vector position angle (EVPA) ever recorded. This swing of the EVPA was also accompanied by a temporary drop of the optical polarization degree to nearly zero. Significant X-ray polarization was observed during the third IXPE pointing, with a polarization degree $Π_{\rm X}\,=(\,18.4\,\pm\,5.8)\%$ and $Ψ_{\rm X}\,=\,74^{\circ} \pm 9^{\circ}$ in the 2--8~keV band, while only upper limits were obtained in the first two epochs. The optical data show that the second IXPE observation occurred shortly after a dramatic optical polarization event characterized by a rapid EVPA swing and strong depolarization. Two possible scenarios may explain the broadband polarimetric behavior: (i) the superposition of two emitting regions with nearly orthogonal magnetic field configurations and variable relative contributions, and (ii) the interaction of a single emitting region with a shock that temporarily reorders the magnetic field. In both cases, the data support a picture in which the X-ray and optical emissions arise from closely related but not strictly co-spatial regions within a dynamically evolving, magnetically structured jet.

astro-ph.HE↗

arXiv2025

Intra-night optical polarization monitoring of blazars

Blazars are known for their extreme variability across the electromagnetic spectrum. Variability at very short timescales can push the boundaries between competing models offering us much needed discriminating power. This is particularly true for polarization variability that allows us to probe particle acceleration and high-energy emission models in blazars. Here we present results from the first pilot study of intra-night optical polarization monitoring conducted using RoboPol at the Skinakas Observatory and supplemented by observations from the Calar Alto, Perkins, and Sierra Nevada observatories. Our results show that while variability patterns can widely vary between sources, variability on timescales as short as minutes is prevalent in blazar jets. The amplitude of variations are typically small, a few percent for the polarization degree and less than 20 degrees for the polarization angle, pointing to a significant contribution to the optical emission from a turbulent magnetic field component, while the overall stability of the polarization angle over time points to a preferred magnetic field orientation.

astro-ph.HE↗