This study explores the implications of joint spectral analysis using data from Fermi's Gamma-ray Burst Monitor (GBM), Large Area Telescope (LAT), and LAT Low Energy (LLE) on phenomenological correlations in Gamma-Ray Bursts (GRBs). Combining spectral data from these three Fermi instruments, we aim to enhance our understanding of GRB characteristics and their potential as cosmological probes....
The recent detection of very high-energy gamma-ray emission (VHE, $>$ 100 GeV) from a subset of gamma-ray bursts (GRBs) has opened new opportunities for GRB research. The temporal and spectral evolution of VHE GRB afterglows requires comprehensive modeling and high-cadence, multi-wavelength observations across the electromagnetic spectrum (radio to VHE). Standard afterglow emission from VHE...
Extreme-TeV blazars represent a distinct sub-class of BL Lac type Active Galactic Nuclei with very hard spectra and a high-energy bump peaking above ~1 TeV. The multi-wavelength emission from such objects is difficult to interpret with standard emission models. The very narrow electron distribution and unusually low value of the jet magnetization that are required for a good fit are difficult...
The intricate polarization patterns seen in blazar jets, particularly highlighted by findings from the Imaging X-ray Polarimetry Explorer (IXPE), require multizone model frameworks to describe polarization behavior in blazar jets accurately. Single-zone models, which assume a uniform magnetic field and particle distribution, cannot explain the significant polarization degree and angle...
Blazars are a special type of AGN, with jets that happen to
point very close to the direction towards Earth. The powerful
gamma-ray beam from distant blazars represents a unique tool to
explore the environment along its path, and allows us to probe opacity
both inside the source and in the intergalactic medium. Internally,
gamma-rays experience attenuation due to photon-photon absorption,...
Blazars are the brightest persistent sources in the high-energy and very-high-energy (VHE) gamma-ray sky. Because their UV/optical radiation is often dominated by non-thermal, and, in the case of BL Lacs, featureless continuum radiation, the determination of their redshift is extremely difficult. Only about 50% of gamma-ray blazars have a firm measurement of their redshift. This strongly...
Pulsar Wind Nebulae are highly intriguing astrophysical objects in many respects. They are the brightest and closest class of relativistic sources, and hence the ultimate laboratory for the physics of relativistic plasmas, where we can study in unique detail processes such as acceleration and collimation of relativistic outflows, or the acceleration of particles at relativistic shocks. In...
We report the possible detection of γ-ray pulsations from both the recently
discovered ∼4.03 hour binary system J1912-4410 which consists of a white dwarf
rotating at Pspin=319.34903(8)s (∼5.32 minutes, Pelisoli et al. 2023) with an M-
dwarf companion and the 725.5(8)s (∼12 minutes, Ferarrio et al. 1997) rotating,
isolated white dwarf EUVE J0317-855 using ∼15 years of observations from...
We report the detection of steady and pulsed gamma-ray emission from AR Scorpii and AE Aquarii using data from the Fermi Large Area Telescope (LAT). Both sources exhibit a detection significance above Fermi LAT threshold (5 $\sigma$), despite not being listed in the Fermi LAT catalog due to the standard analysis approach rendering them insignificant. Previous studies have indicated a detection...
The faint radio population contains a higher proportion of star-forming galaxies (SFGs) and radio-quiet or non-jetted active galactic nuclei (AGN) below radio flux densities of approximately 100 microJy. It is commonly understood that radio emission in SFGs is primarily thermal and for radio-loud AGN, it is mainly non-thermal. The radiative mechanisms producing radio emission in non-jetted...
$\gamma$-ray emitting narrow-line Seyfert 1 galaxies ($\gamma$-NLS1) are jetted, $\gamma$- and radio-loud sources of a very puzzling sub-class of Active Galactic Nuclei (AGN), exhibiting properties similar to low power flat-spectrum radio quasars (FSRQs), but not quite identical. They are characterised by relatively low black hole masses and extremely high, near-Eddington accretion rates, with...
Hydra A is a FR-I type radio galaxy located at the centre of the Abell 780 cluster with a redshift of $ z = 0.054$. Previous observations of the radio galaxy have been conducted at low frequencies by the Very Large Array (VLA) telescope and using the L-band frequencies of the MeerKAT array telescope. The Chandra X-ray observatory also carried out a detailed survey of the X-ray emission from...
This paper is the second instalment in our study of the observed time delay in the arrival times of radio photons emanating from Gamma-ray Bursts (GRBs). The mundane assumption in contemporary physics as to the cause of these pondersome time delays is that they are a result of the photon being endowed with a non-zero mass. While we do not rule out the possibility of a non-zero mass for the...
The Friedmann-Lemaître-Robertson-Walker (FLRW) model, which forms the foundation of the Lambda Cold Dark Matter (LCDM) framework, is a key pillar in cosmology. It has effectively explained the formation and evolution of cosmic structures in line with most observational data. Central to the FLRW model is the cosmological principle, asserting that the universe is homogeneous and isotropic on...
In this discussion we will be focusing on the changes of the dispersion measure (DM), rotation measure (RM) and scattering characteristics of PSR J1748-2446A. PSR J1748-2446A is a "spider” binary in Terzan 5 where the pulsar blasts the surface of its orbiting companion star away. We used data from the MeerKAT telescope at L-band frequencies to look at the complex eclipse of this spider...
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...
The pioneering underwater neutrino observatory, ANTARES, was in operation almost continuously in the Mediterranean Sea from its establishment in 2008 until its recent decommissioning in 2022. This presentation will shed light on its inception, principal findings in particle physics and astrophysics, including its extensive multi-messenger initiative. This encompassed sending alerts and...
Neutrinos, while often considered as Majorana fermions, can also behave as effectively Dirac fermions, making them candidates for pseudo-Dirac particles. This concept introduces the possibility of oscillations between active and sterile neutrinos, driven by a small mass-squared difference. This phenomenon differs from the standard oscillation scenario involving only the three active neutrino...
As experiments continue to narrow the viable WIMP parameter
space, axions have become an increasingly popular candidate
for dark matter. The nature of the axion coupling to the Standard
Model makes them far more difficult to constrain, especially in
the mass ranges usually considered for cold dark matter. So far,
astrophysical experiments have struggled to place strong limits
on such...
In the theory of relativity, the notion of a particle is based on the irreducible representation of the Poincaré group. However, there are post-relativistic theories which generalize the relativistic notions, including that of a particle. One such theory is the theory of superfluid vacuum, which describes the physical vacuum as a Euclidean 3D superfluid; whereas Lorentzian 4D spacetime and...
Presenting the Containerized Automated Radio Astronomy Calibration (CARACal) pipeline, a system and telescope agnostic reduction pipeline for radio interferometer data. CARACal leverages the portability and flexibility enabled by the Stimela framework (Makhathini, 2016) to provide a simple yet powerful pipeline for both experienced and novice users.
Unlike other pipelines, which are...
The Cherenkov Telescope Array gamma-ray Observatory (CTAO) is working on developing two large telescopes, each with a diameter of 23 meters, that will be installed in Paranal, Chile. They are referred to as Large Size Telescope South, LST-S. These telescopes will use a single mirror parabolic shape to capture images with moderate angular resolution. 198 hexagonal reflecting panels will be...
We present an analysis of the optical and GeV gamma-ray behaviour of the flat-spectrum radio quasar 3C 279 during four phases of significant gamma-ray flux variability between 2014 – 2019. Multiple flares were observed during this period, with the most rapid flare exhibiting a flux doubling time of 2.66 hr. A ZDCF analysis of the optical and gamma-rays light curves show a near-zero time-lag...
Black Hole X-ray binaries (BHXRBs) represent a unique class of astrophysical systems where a stellar-mass black hole accretes matter from a companion star via accretion disks. The accretion disk emits X-ray and UV because of the radiative losses. The transfer of matter can occur through continuous donor supply or episodic capturing of material from stellar winds, leading to sudden enhancements...
Gamma-ray binaries are a subclass of high-mass binary stellar binary systems consisting of a compact object (neutron star/ black hole) and an O- or B-type stellar companion. They emit across the entire electromagnetic spectrum, with a characteristic energy spectrum that peaks in the gamma-ray energy range. Currently, only ten such systems have been discovered.
1GLJ1018.6-5856 and LMC P3...
Some accreting white dwarf (WD) systems show dwarf nova (DN) outbursts. These are characterized by an outburst amplitude of a few magnitudes and a duration of days to weeks in optical bands, as explained in the thermal instability model. We report the detailed optical and X-ray observations of the 2021 outburst in MASTER OT J030227.28+191754.5 (hereafter J0302). The X-ray spectrum at outburst...
This project explores the complex emission patterns and instabilities in the post-shock accretion columns (PSACs) of magnetic cataclysmic variables (mCVs). Utilizing the PLUTO code, the study integrates bremsstrahlung and cyclotron radiation mechanisms to simulate these phenomena under various initial conditions, such as white dwarf mass and magnetic field strengths. The findings reveal...
Blazars are a class of Active Galactic Nuclei (AGN), found in the centres of elliptical galaxies, that are radio loud and have a small angle between the jet and the observer’s line of sight. In some cases, flaring events in one frequency band are not accompanied by flaring in other bands. Such events are called orphan flares. The causes of this variability and conditions in and location of the...
**We report the detection of a TeV 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 5 σ. The spectral energy distribution (SED) consists of the simultaneous observations by Fermi-LAT, Swift XRT and UVOT during the H.E.S.S detection period. We show that a hadronic one-zone model (modified by strong EBL...
Be X-ray binaries, which make up the largest subclass of the high mass X-ray binary systems, comprise a neutron star in an eccentric orbit around Be star companion with a geometrically thin Keplerian disc. The interaction of the neutron star with the Be disc results in the accretion of matter leading to X-ray outbursts. The X-ray outbursts occur in two flavours: Type I (or normal outbursts,...
