Related papers: Probing photon-ALP oscillations from the flat spec…
The flat-spectrum radio quasar 3C 454.3 underwent an extraordinary 5-day gamma-ray outburst in November 2010 where the daily flux measured with the Fermi Large Area Telescope (LAT) at photon energies E>100 MeV reached (66+/-2) x 10^-6 ph…
Blazars are a subclass of active galactic nuclei (AGN) that emit non-thermal radiation through relativistic jets, characterized by rapid flux and polarization variability. High synchrotron-peaked blazars (HSPs) and extreme high…
Many blazars detected by the Fermi satellite, observed spectroscopically in the optical, are line-less, and have been classified as BL Lac objects. Optical-UV photometry of nearly one hundred of them allowed to determine the redshift for a…
We present e-MERLIN and EVN observations which reveal unambiguous jet activity within radio quiet quasar HS~0810+2554. With an intrinsic flux density of 880~nJy, this is the faintest radio source ever imaged. The findings present new…
Here we report on the detailed analysis of the gamma-ray light curve of a luminous blazar PKS1510-089 observed in the GeV range with the Large Area Telescope (LAT) onboard the Fermi satellite during the period 2011 September -- December. By…
Blazars are among the most variable objects in the universe. They feature energetic jets of plasma that launch from the cores of these active galactic nuclei (AGN), triggering activity from radio up to gamma-ray energies. Spatial…
We use Southern African Large Telescope (SALT) to perform long-slit spectroscopic observations of 23 newly discovered radio-loud quasars (RLQs) at $2.7<z<3.3$. The sample consists of powerful AGN brighter than 200 mJy at 1.4 GHz and is…
Axionlike particles (ALPs) could mix with photons in the presence of astrophysical magnetic fields. Searching for this effect in gamma-ray observations of blazars has provided some of the strongest constraints on ALP parameter space so far.…
We have utilized the largest sample of $\gamma$-ray selected Fermi flat-spectrum radio quasars (FSRQs) ever used (519 sources) to construct the luminosity function and its evolution through the cosmic history. In addition to spanning large…
The association of at least a dozen ultrahigh-energy cosmic-ray (UHECR) events with energy $\gtrsim 55$ EeV detected by the Pierre Auger Observatory (PAO) from the direction of Centaurus-A, the nearest radio galaxy, supports the scenario of…
The flat spectrum radio quasar (FSRQ) 4C +21.35 (PKS 1222+216) displays prominent nuclear infrared emission from ~1200 K dust. A 70 -- 400 GeV flare with ~10 min variations during half an hour of observations was found by the MAGIC…
The $\gamma$-ray spectral feature of the blazar 1ES 0502+675 is investigated by using Fermi Large Area Telescope (Fermi-LAT) Pass 8 data (between 100 MeV and 300 GeV) covering from 2008 August to 2021 April. A significant ($\sim4\sigma$)…
The regular monitoring of flat-spectrum radio quasars (FSRQs) in $\gamma$-rays by Fermi-LAT since past 12 years indicated six sources who exhibited extreme $\gamma$-ray outbursts crossing daily flux of $10^{-5}$ photons/cm$^{2}$/s. We…
We investigate the gamma-ray and X-ray properties of the flat spectrum radio quasar PKS 2149-306 at redshift z = 2.345. A strong gamma-ray flare from this source was detected by the Large Area Telescope on board the Fermi Gamma-ray Space…
We present the $\gamma$-ray observations of the flat-spectrum radio quasar PKS 1441+25 (z=0.939), using the {\it Fermi} large Area Telescope data accumulated during January - December 2015. A $\gamma$-ray flare was observed in January 24,…
Very-high energy (VHE; $>$100 GeV) $\gamma$-ray emission originates via some of the most extreme particle acceleration processes in the universe. Considering beamed active galactic nuclei, i.e., blazars, only a small fraction, mainly high…
By modeling the broadband spectral energy distributions (SEDs) of a typical flat spectrum radio quasar (FSRQ, 3C 279) and two GeV narrow-line Seyfert 1 galaxies (NLS1s, PMN J0948+0022 and 1H 0323+342) in different flux stages with the…
We report on the gamma-ray activity of the high-synchrotron-peaked BL Lacertae object Mrk 421 during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) gamma-ray spectrum…
With the release of the first year Fermi catalogue, the number of blazars detected above 100 MeV lying at high redshift has been largely increased. There are 28 blazars at z>2 in the "clean" sample. All of them are Flat Spectrum Radio…
We report a laboratory search for axion-like particles (ALPs) in the eV-mass range using a variable-angle three-beam stimulated resonant photon collider. The scheme independently focuses and collides three laser beams, providing a…