Conveners
AGN: 1
- Hartmut Winkler
AGN: 2
- Eli Kasai (University of Namibia)
AGN: 3
- Markus Boettcher
It is still unclear, where high-energy cosmic neutrinos (detected by IceCube, KM3Net, and other neutrino detectors) originate. Also, it is not clear, which physical processes dominate the emission mechanisms. Blazars seem to play a role but a detailed understanding is still lacking. We find signatures of gravitational lensing in three blazars - all of these three blazars have been reported as...
The Imaging X-Ray Polarimetry Explorer (IXPE), launched in December 2021, has opened a new window on relativistic jets. In this talk, I will review results of IXPE and co-ordinated multi-wavelength observations of blazars. Highlights are the strong evidence for a leptonic origin of the high-energy emission in low-synchrotron-peaked blazars as well as indications of energy stratification in the...
BL Lacertae (BL Lac) objects are a subclass of active galactic nuclei whose emission is dominated by relativistic jets aligned closely with our line of sight. Their X-ray emission arises primarily from synchrotron or inverse Compton processes, and polarization measurements in this regime offer a direct probe of jet magnetic field geometry and emission mechanisms. The Imaging X-ray Polarimetry...
Blazars, a subclass of radio-loud active galactic nuclei characterized by relativistic jets directed towards Earth, exhibit strongly linearly polarized emission and two broad, non-thermal spectral energy distributions (SEDs). These features are sensitive to various parameters, including the observer's viewing direction and the magnetic field orientation relative to the jet axis.
This talk...
We present a multi-wavelength study of the flat-spectrum radio quasar PKS 0446+11, located within the 90% localization region of the IceCube track-like neutrino event IC240105A, detected on 2024-01-05. Although no significant neutrino excess was found, PKS 0446+11 exhibited a major gamma-ray flare in late 2023 and remained X-ray bright in early 2024, suggesting temporally relevant activity. We...
Among active galactic nuclei (AGNi), blazars are the brightest emitters of high- (HE, $E \geq 100$ \,MeV) to very-high-energy (VHE, $E \geq 100$ \,GeV) $\gamma$-rays from their jets. Radio galaxies, being the misaligned parent population of the blazar class, were historically not observed at these frequencies. However, advances in experiments and observatories have led to their detections in...
In this talk I will discuss X-ray timing and spectral characteristics of two fascinating kinds of jetted Active Galactic Nuclei (AGN)—blazars and Fermi-detected Narrow-line Seyfert 1 (NLSy1) galaxies. In the first section, we highlight a two-decade-long X-ray monitoring program of several notable blazars: Mrk 421, 3C 273, and PKS 2155-304, revealing interesting multi-epoch, spectral, and...
Since Enrico Fermi first proposed the stochastic acceleration of protons due to multiple scatterings off of parsec-scale interstellar magnetic fields as a method of cosmic ray acceleration around the time of the 1950s, the theoretical framework of stochastic acceleration in magnetohydrodynamic (MHD) turbulence has undergone significant refinement, although these traditional models often fail...
Radio-loud active galactic nuclei (RLAGN) emit radiation across most of the electromagnetic spectrum. The lower-energy component (Radio - Soft X-rays) is typically dominated by synchrotron emission from non-thermal electrons in a relativistic jet. RLAGN are known to be highly variable on both short (intra-day) and long (months to years) timescales. Most of the variability observed in the...
Radio galaxies play an important role in the formation of structure in the Universe. Studying the physical properties of both classical radio galaxies (FRI and FRII), as well as their more morphologically complex counterparts (NATs, WATs, BTs, X-shaped, etc), can help in understanding their specific role and how their local environment affects their properties, and vice versa. The MERGHERS...
We investigate whether radio emission primarily traces star formation in RQ AGN. Our sample consists of 5223 galaxies detected by the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey with multi-wavelength counterparts up to a z ≈ 6 limit. We classified the sources using the infrared-to-radio luminosity ratio (q$_{\rm IR)}$, X-ray luminosity cuts, and mid-infrared...
A sub-class of narrow-line Seyfert 1 galaxies with exceptionally strong Fe II emission lines named after the prototype I Zw 1 show high variability in X-rays. Despite this, and in contrast with many other Seyferts, variations in the optical are comparatively small. I have collected Las Cumbres Observatory robotic telescope network BVugr photometry of 20 I Zw 1 type AGN over 2-3 years and can...
Blazars, a class of active galactic nuclei with relativistic jets oriented close to our line of sight, dominate the extragalactic γ-ray sky and are well known for their strong variability across the electromagnetic spectrum. Millimetre observations are of particular interest because they probe emission regions near the jet base, where high-energy flares are likely originating.
In this work,...
In this report, we present SAO RAS radio/optical observations of high-energy neutrino candidates - bright blazars. Extensive research has shown that the arrival directions of ultra-high-energy (UHE) neutrinos statistically coincide with bright blazar positions, while the timing of neutrino events coincides with powerful synchrotron flares in these objects. AGN have emerged as compelling...
In this report we present results of multi-wavelength investigations of brights blazars sample provided mainly with SAO RAS optical telescopes - 6-meter reflector and 1-meter class instruments. The campaign of optical monitoring spans over 20 years. The sample consists of almost two dozens sources in wide brightness range (optical R band) - between 14th and 20th magnitudes. The statistical...
We present a study of the radio and optical properties of the high-frequency peaker (HFP) blazar PKS 1614+051 at $z=3.21$ based on the data covering the time period of 1997–2024. The radio data are represented by the instantaneous 1–22 GHz measurements from the SAO RAS RATAN-600 radio telescope, the 5 and 8 GHz data from the IAA RAS RT-32 telescopes, and the 37 GHz data from the RT-22...
PKS 0903−57 is a little-studied γ-ray blazar that has recently attracted considerable interest due to the strong flaring episodes observed since 2020 in high energy (HE; 100 MeV ≤ E ≤ 100 GeV) and very high-energy (VHE; 100 GeV ≤ E ≤ 10 TeV) γ-rays. Its nature and properties have not been well determined until recently by Goldoni et al. (2024), which this talk is based on. The main challenge...
Blazars are among the most luminous and variable sources in the universe, producing emission up to TeV energies. The lower-energy component of the emission is dominated by non-thermal leptonic synchrotron radiation from the jet. However, the high energy component is not yet fully understood, as it can be reproduced by both leptonic and hadronic models. Polarization measurements at optical and...
The very bright Flat Spectrum Radio Quasar (FSRQ) 3C 279 (z = 0.536) is the first source of this class to be detected at very high energy gamma-rays and is characterised by an abundance of bright multi-wavelength (MWL) flaring events, especially at highest energies, where the amplitude and variability timescales are most extreme. The source is particularly known for its complex spectral...
Active galactic nuclei (AGNs) are powered by accretion onto supermassive black holes (SMBHs), yet the mechanisms governing their energy output and the growth of SMBHs, particularly at high redshift, remain incompletely understood. Blazars, a subclass of AGNs with relativistic jets oriented close to our line of sight, are detectable across the electromagnetic spectrum, from radio to gamma rays,...
Centaurus A (Cen A), is the nearest known radio galaxy to Earth, and it is a significant source of γ-ray emission, offering an excellent opportunity to study high-energy astro-physical processes. The objective of this study is to investigate the particle acceleration to very high energies (VHE) along the jet of Cen A, using data from the High Energy Stereoscopic System (H.E.S.S.) collected...
We demonstrate that the simplest three-dimensional superflow of logarithmic quantum Bose liquid can generate a four-dimensional relativistic quinton system, which comprises the dilaton and a combination of quintessence and the tachyonic phantom; the last two being non-minimally coupled to each other. Both gravity and these scalar fields are thus shown to be "infrared" projections of the...
