The extragalactic radio background in the universe is mainly due to emission from the radio galaxies and normal galaxies. This emission is synchrotron radiation by relativistic electrons gyrating in the magnetic field of the galaxies. Synchrotron self-absorption and free-free absorptions by hot ionised gas in the interstellar medium play an important role to modify radio emission. In this...
On the 28th of January, an orphan very-high-energy γ-ray flare from 3C279
was detected, not accompanied by flaring in the adjacent GeV gamma-ray
regime. Orphan flares have to be caused by different processes than normal
γ-ray flares. Specifically, the Hadronic Synchrotron Mirror Model has been
proposed to provide a consistent explanation of this flare. The expected tar-
get photon...
Most research on blazar variability focuses on individual flares to explain acceleration
and radiation mechanisms and improve on current models. These short-time events
(being minutes, hours, or days) might not be representative of the underlying mecha-
nisms causing small-amplitude variability and/or continuous emission which is present
most of the time. We will therefore investigate...
The FSRQ CTA 102 (z=1.032) has been tremendously active over the last few years. During its peak activity lasting several months in late 2016 and early 2017, the gamma-ray and optical fluxes rose by up to a factor 100 above the quiescence level. We have interpreted the peak activity as the ablation of a gas cloud by the relativistic jet, which can nicely account for the months-long lightcurve...
We present the results of a preliminary investigation of a potential association of a blazar
candidate behind the Large Magellanic Cloud (LMC) and a gamma-ray transient object.
The hint of flaring activity appeared at the position (RA,dec)∼(86.60 deg,-69.02 deg), while
the J0545-6846 blazar candidate is located at (RA,dec)=(86.47 deg,-68.77 deg). J0545-6846 is characterised by a...
FSRQs are important to study cosmic evolution of AGN jet and also interesting how they contribute to the cosmic MeV gamma-ray background. Past studies with hard X-ray (Swift/BAT 22 month catalog) and GeV gamma-ray (Fermi/LAT) reported the X-ray and gamma-ray luminosity function, but predicts a different evolution between X-ray and GeV gamma-ray. Here we used the Swift/BAT 105 month catalog to...
We test different physically motivated models for the spectral shape of the gamma-ray emission in a sample of 128 blazars with known redshifts detected by Fermi-LAT at energies above 50 GeV. The first nine years of LAT data in the energy range from 300 MeV to 2 TeV are analyzed in order to extend the spectral energy coverage of the 2FHL blazars in our sample. We compare these spectral data to...
The quasar 1156+295 (4C 29.45, Ton599) underwent a dramatic nonthermal outburst in late 2017, with detection at energies > 100 GeV. The outburst was essentially simultaneous at gamma-ray and optical bands, indicating co-spatiality of the emission regions. We present multi-epoch optical spectra of 1156+295 obtained with the 4.3 m Lowell Discovery Telescope at various times, including the...
QSO B0218+357 is currently the only gravitationally lensed source from which both high-energy (HE, >~100 MeV) and very-high-energy (VHE,>~100GeV) gamma-ray emission has been detected.
We report the Fermi/LAT and multiwavelength monitoring observations of this source in radio interferometry, optical and X-rays performed between 2016 and 2020. During the monitoring, individual flares in the...
According to radiative models, radio galaxies are predicted to produce gamma rays since the first stages of their evolution. The study of the high-energy emission from young radio sources is crucial for providing information on the most energetic processes associated with these sources, the actual region responsible for this emission, as well as the structure of the newly born radio jets....
The Circinus galaxy is a composite starburst/Seyfert galaxy which exhibits radio lobes inflated by kpc scale outflows along its minor axis. Its proximity (4 Mpc) makes it a unique target to study the physical nature of these outflows. We investigate if they originate from nuclear star formation activity or if they are jets from an active galactic core. The MeerKAT radio observations allow us...
Phenomenological spectral analysis of S5 1803+784 was done in both the high state and the low state using leptonic jet models. The jet energetic and spectral properties using single zone synchrotron-self Compton (SSC) and SSC with external photons (SSC+EC) jet models are presented. S5 1803+784 is a low synchrotron peak (LSP) blazar with the characteristics weak emission lines
(EW < 5A )....
Radio-loud sources with blazar-like properties, but having a jet that does not directly point in the direction of the observer are among the most interesting classes of gamma-ray emitters. These sources are known as Misaligned Active Galactic Nuclei (MAGN). We searched for new MAGN candidates among the remaining blazars of uncertain type detected by the Fermi Large Area Telescope (LAT) using a...
Galaxies and galaxy clusters are separated by large distances of nearly empty
space called the intergalactic space. In these large, nearly empty regions a weak magnetic field of strength < 10 nG is present that is predicted to be of primordial (early universe) origin. This is called the intergalactic magnetic field (IGMF) and knowledge about its strength, coherence length, origin etc. is...
