The KM3NeT neutrino telescope is a research infrastructure currently under construction in the Mediterranean Sea. It consists of two deep-sea detectors: ORCA, near Toulon, France, and ARCA, off the coast of Sicily, Italy. ORCA is designed for precision study of atmospheric neutrinos in the GeV range, whereas for ARCA the aim is to detect and study cosmic neutrinos of higher energies. KM3NeT...
With the successful observations and synergies of golbal instruments and observatories, the multi-messenger has shown great ability and potential to solve the mystery of cosmic-ray origin. However, there are still quite some challenges, which may need the next-generation neutrino telescope with better angular resolution and bigger effective area. In this talk, I will present our proposal of...
The IceCube neutrino observatory first detected high-energy neutrinos of extraterrestrial origin in 2013, marking a significant milestone for multimessenger astronomy. However, due to its limited angular resolution and sensitivity, only a few neutrino events can be associated with known sources observed in other bands. The exact production mechanisms of celestial neutrinos remain elusive....
The Event Horizon Telescope (EHT) is a network of antennas across the globe currently used to image supermassive black holes (SMBHs) at a frequency of 230 GHz. Since the release of the image of M87 in 2019 and, subsequently, that of Sgr A in 2022 by the EHT collaboration, the focus has shifted towards dynamically imaging SMBHs. This has led to a search for potential sites to extend and fill...
Modern radio interferometers generate vast volumes of raw data, demanding efficient processing to enable real-time or quasi-real-time astronomical analysis. A critical challenge is the detection of transient sources within wide-field interferometric images, which requires rapid imaging and robust discrimination between true transients and false positives.
In this talk, we present a Fast...
The worldwide network of gravitational-wave (GW) detectors, comprised of the Advanced LIGO, Advanced Virgo, and KAGRA detectors has been increasing in sensitivity, range, and hence quantity and quality of detected GW signals from compact binary coalescences.
We present the compact binary signals observed and included in the GW Transient Catalog 4 (GWTC-4), i.e. up to and including the first...
The dual detection of a short gamma-ray burst (GRB 170817A) (Goldstein et al., 2017) and a gravitational wave (GW170817) (Abbott et al., 2017) signal marked the first direct confirmation that both phenomena can originate from the same astrophysical event. While the GW and SGRB signals give valuable insights into the properties of the merging neutron stars, they offer little information about...
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...
In our investigation, we pioneer the development of geometrically deformed strange stars within the framework of teleparallel gravity theory through gravitational decoupling via the complete geometric deformation (CGD) technique. The significant finding is the precise solution for deformed strange star (SS) models achieved through the vanishing complexity factor scenario. Further, we introduce...
The detection of KM3-230213A, the most-energetic neutrino ever detected at an estimated energy of 220 PeV, by the KM3NeT neutrino telescope in the Mediterranean Sea, is a landmark discovery. Given its near horizontal direction and exceptionally high energy, the most likely explanation is that the muon resulted from interaction of a muon neutrino of cosmic origin. In this talk I will provide an...
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...
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...
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 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...
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,...
We will take a journey together beyond our galaxy to learn about Fast Radio Bursts, our attempts to discover thousands of them, the physics that drives them and how they teach us about the universe on local and large scales.
Fast Radio Bursts (FRBs) are millisecond radio transients of extragalactic origin that have emerged as valuable tools for both astrophysics and cosmology. In this talk, I present recent advances on two complementary fronts: the use of machine learning techniques to classify FRB populations and the application of localized FRBs as model-independent probes of the cosmic expansion. These results...
Gamma-Ray Bursts (GRBs), the most luminous explosions in the cosmos, are promising tools for cosmology due to their potential as standardizable candles. Among the empirical correlations proposed for this purpose, the Yonetoku relation, which connects the intrinsic peak energy ($E_{i, p})$ to isotropic peak luminosity ($L_{iso}$), provides a means to probe distances beyond the range of Type Ia...
Gamma-Ray Burst (GRB) afterglows arise from the interaction of relativistic ejecta with the circumburst medium and are observed across the electromagnetic spectrum. Polarisation is expected during the early and late phases of the afterglow depending on the presence of reverse shocks and the viewing geometry of the jet. Polarimetric observations of GRB afterglows serve as a unique diagnostic...
The radiation mechanisms powering Gamma-ray bursts (GRBs) and their physical processes remain one of the unresolved questions in high-energy astrophysics. Spectro-polarimetric observations of exceptionally bright GRBs provide a powerful diagnostic tool to address these challenges. GRB 230307A, the second-brightest long-duration GRB ever detected, exhibits a rare association with a Kilonova,...
High-energy gamma rays are one of the most promising tools to constrain or reveal the nature of Dark Matter (DM). During the almost two decades of the Fermi satellite mission, the data from its Large Area Telescope (LAT) were used to set constraints on Weakly Interacting Massive Particles (WIMP) and Axion -Like-Particle (ALP) models as well as to perform various searches for new physics. As...
In this work, we aim to compute the radio flux from the decay of axions close to Saggitarius A*, the supermassive black hole at the center of our galaxy. These particles can undergo stimulated decay in the presence of photons with energies of half the axion mass. We make use of an observed spectrum for Sgr A emission in the frequency range of SKA and the VLBA, to find the effect of stimulated...
The fundamental nature of dark matter (DM), which constitutes a significant fraction of the universe's mass-energy budget, remains one of the foremost challenges in modern astrophysics and particle physics. Due to their weak interactions and cosmological origins, high-energy neutrinos serve as sensitive probes for potential neutrino-DM scattering processes. Specifically, dense accumulations of...
High-energy neutrino detectors such as IceCube and ANTARES have followed up several bright gamma-ray bursts but have not found any associated neutrino signals, instead placing upper limits on the neutrino flux. In this work, we study the photo-hadronic interaction model during the prompt phase of GRBs and estimate the resulting neutrino flux both analytically and numerically using the publicly...
In 2010, the Fermi Gamma-ray Space Telescope observed two gamma-ray emitting structures, the Fermi Bubbles (FBs), that extend up to 55° above and below the Galactic plane and that seem to emanate from the Galactic center region. Although the spectrum at latitudes |b| > 10° has a softening or a cutoff around 100 GeV, the one at the base of the FBs, |b| <10°, extends up to about 1 TeV without a...
The timing residuals of pulsar emissions have been used before to search for a stochastic Gravitational Wave Background (GWB), with several PTA collaborations recently reporting strong evidence for the Hellings and Downs correlation curve that would be characteristic of a GWB signal. In a similar manner, we analyse the polarisation data of a large population of pulsars observed with MeerKAT...
Pulsars are rapidly rotating neutron stars that emit electromagnetic radiation over a broad energy band. The third pulsar catalogue (3PC) of the Fermi Large Area Telescope (LAT) contains more than 300 gamma-ray pulsars and pulsar candidates. However, phase-resolved spectroscopy has been performed on only a few of them, which was not sufficient to reveal new trends that could help constrain the...
In an ongoing study we interpret the curved spectrum of the Vela pulsar as seen by H.E.S.S. II (up to ~100 GeV) and the Fermi Large Area Telescope to be the result of synchro-curvature radiation due to the acceleration of primary particles in a dissipative magnetosphere, within an extended separatrix region that leads into the current-sheet outside the light cylinder. We investigate the...
White dwarf radio pulsars (WD pulsars) are a fascinating, newly established class of compact binary systems. To date, only three have been confirmed: AR Sco, J1912–4410 and J2306+2440. Like their neutron star counterparts, they exhibit radio pulsations driven by rapid rotation and intense magnetic fields. Since its discovery in 2016, AR Sco has spurred significant debate regarding the nature...
We report the possible detection of pulsed 𝛾-ray emission from one confirmed white dwarf
pulsar J191213.72-441045.1 and a candidate white dwarf pulsar EUVE J0317-85.5 using ∼15
years of data from the Fermi-LAT observatory. Pulsed 𝛾-ray emission in the 0.5-10 GeV energy
range from J191213.72-441045.1 were found at a period of 𝑃=319.99±0.35s with a -log(Pr)=6.76 which corresponds to a...
Galaxy clusters, the largest gravitationally bound structures in the Universe, provide a unique laboratory for
studying various astrophysical processes. This study focuses on diffuse radio emission associated with low-mass
Atacama Cosmology Telescope galaxy clusters observed using the MeerKAT telescope within the MeerKAT
Galaxy Cluster Legacy Survey (MGCLS). Our investigation aims to...
We present a comprehensive phase-resolved photometric, spectroscopic, and polarimetric analysis of the intermediate polar (IP) 1RXS J080114.6–462324, based on multi-instrument observations. These include data from the HIgh-speed Photo-POlarimeter (HIPPO), the Southern African Large Telescope (SALT), and the SAAO 1.0-m and 1.9-m telescopes, complemented by archival photometry from the...
‘Spider’ binary systems – black widow and redback binaries consisting of a millisecond pulsar and a low-mass companion in a compact orbit, are important types of pulsar system exhibiting various key features, including radio eclipses, optical light curves from the heated companion, and X-ray and GeV orbital light curves and spectra. In these systems, the intense pulsar wind heats and may...
Gamma-ray binaries are a rare class of high-mass binary systems where the peak of their spectral energy distribution occurs in the gamma-ray energy range. These systems have proven to be excellent laboratories for studying particle acceleration mechanisms. One such system is LMC P3, the most luminous gamma-ray binary discovered to date and, so far, the only one found outside the Milky Way. It...
We report the detection of a Low Synchrotron Peaked (LSP) blazar PKS 0346-27 at redshift 0.99 by the High Energy Stereoscopic System (H.E.S.S.) on 3rd November, 2021 with a significance above 5σ. The spectral energy distribution (SED) consists of the simultaneous observations by Fermi-LAT, Swift XRT/UVOT and ATOM during the H.E.S.S detection period while the multiwavelength light curve...
The spectral width (W) is proposed as a new measure to address the complexities in the GRB prompt phase spectral studies. We carried out a detailed procedure to redefine the Band function with W as one of the parameters, to study the GRB spectra. This model was convolved with the XSPEC, and the temporal evolution of W, for the case of GRB 220426A and GRB 230812B using the Fermi/ GBM data, was...
Blazars, a subclass of active galactic nuclei with collimated jets of matter oriented at the observer, Earth. These jets produce radiation across the entire electromagnetic spectrum, in the form of two broad, non-thermal peaks. There are competing models capable of reproducing this radiation, which can be broadly categorised into two types: leptonic and lepto-hadronic, based on the exclusion...
Namibia stands out as an exceptional location for astronomical research, offering pristine night skies and ideal observation conditions. Home to Africa's first International Dark Sky Reserve, the country boasts an arid climate with minimal rainfall, resulting in abundant cloudless nights perfect for extended viewing hours. This environment is ideal for facilities like the High Energy...
Blazars make up the largest fraction of Fermi-LAT-detected sources of high-energy gamma-ray emission. At the same time, their emission is known to be highly variable throughout the electromagnetic spectrum. With hints of their highest fractional variability in the radio regime being present at the highest radio frequencies, monitoring blazars at mm-wavelengths shall be one of the key science...
Gamma-ray binaries are high-mass binary systems that emit predominantly in the high-energy and very-high-energy gamma-ray regimes. LMC P3 is the only known gamma-ray binary located outside our galaxy and consists of an O5,III companion star and a compact object with a mass in the range of a neutron star or a black hole. The leading theory is that all gamma-ray binaries contain a young,...
We present phase-resolved analysis of the polar QS Telescopii using photometry, spectroscopy, Doppler tomography, photopolarimetry, and circular spectropolarimetry collected between 2017 and 2025. We report the first detection of quasi-periodic oscillations (QPOs) in QS Tel, with timescales of 6–10 minutes, revealing dynamic accretion behavior. Doppler tomography of Hα and HeII (4686 Å) lines...
A discrete jet component (blob) ejection and its subsequent deceleration were observed in the 2019/2020 outburst of the low-mass X-ray binary MAXI J1348–630. A first kinematic analysis of the deceleration due to an abrupt transition from an evacuated cavity to the interstellar medium suggested a kinetic energy exceeding $10^{46}$ erg, surpassing estimates of the available total ejection...
Context. Gamma-ray binaries are a rare subclass of high-mass binary systems composed of a compact object (either a neutron star or a black hole) and an O- or B-type stellar companion. These systems exhibit broadband non-thermal emission that peaks in the gamma-ray regime and serve as ideal laboratories for studying relativistic particle acceleration, wind–wind interactions, and extreme...
Magnetically controlled accreting white dwarf binaries, which includes polars and intermediate polars, provide unique laboratories for high-energy particle acceleration in compact stellar systems. Their strong magnetic fields, rapid accretion flows, and dynamic magnetospheres enable distinct acceleration channels. In polars, which rotate synchronously with strong magnetic locking, unipolar...
The Large High Altitude Air Shower Observatory (LHAASO) has recently reported five Galactic microquasars as Ultra-High-Energy (UHE) gamma-ray emitters (>100 TeV), an unexpected result that challenges conventional models of Galactic particle acceleration. Among these sources, the microquasar V4641 Sgr exhibits gamma-ray emission up to ~0.8 PeV, as well as the hardest UHE spectrum. The...
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...
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...
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...
