arXiv subjects

Eleni Antonopoulou

Publications and source records attributed to Eleni Antonopoulou.

5 recordsLinked to original sources

arXiv2026

Modeling MAD Sgr A* flares and their dependence on spin

Aims: This study aims to place constraints on the spin of Sgr A* from recent flare observations. It models the flare kinematics in the vicinity of a supermassive black hole, evaluates their dependence on black hole spin, and assesses the correlation between the spin of the black hole and the astrometric observations in the Galactic center. Methods: Our study extends the work of Antonopoulou et al. 2025 to a range of black hole spins. A prominent flux eruption is identified in the simulation, and the evolution of the active region on the equatorial plane is tracked during the event. The flare model consists of a spherical hot spot ejected along the flux tube with a relativistic velocity. Results: In MAD simulations, the flux tube wraps around the jet funnel in the opposite direction to the black hole's spin. This dependence is imprinted on the flare trajectory and provides a strong correlation between the spin of the black and the flare kinematics. This analysis favors Kerr black holes, with a preference towards larger spin magnitude. Although prograde simulations show a consistent clockwise motion in the sky regardless of disk rotation, retrograde models require a clockwise accretion disk to account for the observations of July 22, 2018. Conclusions: A maximally rotating Kerr black hole is the most promising candidate for reproducing the observed flare trajectory in the vicinity of Sgr A*, illustrating a pass faction surpassing $90\%$ among the investigated flare models. In particular, determining spin orientation within this model is linked to the rotation of the accretion disk. Assuming a counterclockwise accretion disk, a prograde black hole with $a\geq1/2$ is able to reproduce the observed flare kinematics in the Galactic center. Conversely, assuming a clockwise rotation for the disk, the observations support both prograde and retrograde Kerr black holes with a large spin.

astro-ph.HE↗

arXiv2026

Broadband multiwavelength properties of the archetypal blazar 3C 279 during the 2017 Event Horizon Telescope campaign

The archetypal blazar 3C 279 hosts a prominent relativistic jet and exhibits strong broadband variability across the electromagnetic spectrum. In April 2017, the Event Horizon Telescope (EHT) observed 3C 279, alongside one of the most extensive quasi-simultaneous multiwavelength (MWL) campaigns ever conducted. With the aim of investigating the physical processes governing 3C 279, we analyzed individual observations and multiband light curves, and constructed a new quasi-simultaneous MWL spectrum. We also performed phenomenological modeling using the turbulent extreme multi-zone (TEMZ) model to constrain the fundamental physical properties of the source. The EHT observations reveal a clear flux increase in the innermost core between April 5 and 11, 2017. Over a broader timescale, radio measurements at longer wavelengths show concurrent enhancements in core flux and polarization around mid-April, coinciding with the ejection of a superluminal knot. Record UV-optical flares with strong polarization variability occurred in late March, followed by gamma-ray activity that declined before the end of the EHT observing period. During this interval, the source remained in a low X-ray state and showed no detectable VHE emission. The TEMZ modeling suggests that the broadband spectrum and variability of 3C 279 can be explained within a jet scenario in which turbulent plasma cells are compressed by a stationary conical shock. However, alternative interpretations, such as magnetic reconnection or a moving shock-in-jet event, remain plausible. This coordinated MWL campaign advances our understanding of the origin of jet and gamma-ray emission in 3C 279, while also providing a comprehensive publicly available dataset that will serve as a valuable reference for future studies.

astro-ph.HE↗

arXiv2026

Dynamics and geometry of the inner sub-parsec-scale jet in 3C 279 observed with the Event Horizon Telescope

The 2021 Event Horizon Telescope observations resolve the innermost jet region of the blazar 3C279 with unprecedented detail. The reconstructed images consistently reveal a compact core elongated nearly orthogonal to the large-scale jet axis. This rarely observed morphology recurs across multiple epochs and from 22-230 GHz and is therefore intrinsic rather than an imaging artifact. Geometric model fitting identifies several components with apparent speeds up to 10c, requiring bulk Lorentz factors greater than 10.3 and constraining viewing angles to extremely small values (smaller than one degree). Rest-frame brightness temperatures are systematically low (between 10^9 and 10^10 K), consistent with optically thin emission at 230 GHz. These results suggest that the jet bends toward the observer on sub-parsec scales, producing strong relativistic beaming. Possible drivers of the observed jet bending and temporal evolution include the jet's interaction with the interstellar medium, kink or Kelvin--Helmholtz instabilities, magnetic reconnection near the horizon, or binary-induced precession. However, the current temporal coverage of VLBI data remains insufficient to distinguish between these mechanisms. Continued multifrequency VLBI monitoring will be essential to constraining the dynamics and geometry of the jet base in 3C279.

astro-ph.GA↗

arXiv2025

Magnetically arrested disk flux eruption events to describe SgrA* flares

Context. Magnetically arrested disks are among the most suitable candidates for describing the gas accretion and observed emission in the vicinity of supermassive black holes. Aims. This work aims to provide a direct correlation between the quasi-periodic flux eruption events, characteristic of MAD accretion disk simulations, and the observed flaring behavior in the Galactic center. Methods. We employ a MAD accretion disk with a distinct counter-clockwise rotation and investigate the evolution of magnetized flux tubes generated during a prominent flux eruption event. Although these flux tubes demonstrate a clockwise pattern, they experience significant dragging by the accretion disk's rotation. This study models the motion of hot spots, formed on the disk's equatorial plane due to magnetic reconnection, as they travel along the magnetized flux tubes at a fraction of the speed of light. Results. Hot spots with a relativistic ejection velocity are able to balance out the counter-clockwise dragging of the flux tube's foot-point on the disk and demonstrate a clockwise motion in the sky, that is in good agreement with the NIR flares in the Galactic center. In addition, our flare models favor face-on inclinations in the range $[0^\circ, 34^\circ]$ and $[163^\circ, 180^\circ]$ for SgrA*. Conclusions. The flux eruption events that arise naturally in the MAD accretion state provide a promising framework for reproducing the observed flaring behavior in the vicinity of SgrA*.

astro-ph.HE↗

arXiv2024

Parameter study for hot spot trajectories around Sgr$A*$

Intense flaring events in the near-infrared and X-ray wavebands of our Galactic Center have been the subject of research for decades. In recent years, the GRAVITY instrument of the Very Large Telescope captured the motion and polarimetric signature of such a flare in close proximity to the supermassive black hole. This study aims to investigate a broad parameter space for hot spot motion in the vicinity of Sgr$A*$ and reproduce the observed flaring behavior. To this end, we have developed a General Relativistic Radiative Transfer code and conducted a parameter study including both planar and ejected hot spot configurations around supermassive black holes. Super-Keplerian orbital frequencies are favored by circular equatorial, cylindrical and parabolic models, whereas conical hot spot trajectories provide a better fit for orbital frequencies below the Keplerian value. Additionally, a distant observer cannot effectively differentiate between Schwarzschild and Kerr black holes, as well as face-on orbits at different observation angles.

astro-ph.HE↗