Supermassive black holes lying in the center of galaxies can launch relativistic jets of
plasma along their polar axis. The physics of black-hole jets is a very active research topic in …

This article reviews the recent observational results regarding γ-ray emission from active
galaxies. The most numerous discrete extragalactic γ-ray sources are AGNs dominated by …

Markarian 421 (Mrk 421 hereafter) is a nearby active galaxy with a featureless optical
spectrum devoid of prominent emission or absorption lines, strongly polarized variable …

Blazars are a peculiar class of active galactic nuclei that enlighten the sky at all
wavelengths. The electromagnetic emission of these sources is jet-dominated, resulting in a …

Blazars are some of the most energetic sources in our universe and among the most
prominent objects in the γ-ray sky. The new era of multimessenger and multiwavelength …

Context. Markarian 501 (Mrk 501) is a very high-energy (VHE) gamma-ray blazar located at
z= 0.034, which is regularly monitored by a wide range of multi-wavelength instruments …

Diffusive shock acceleration (DSA) at relativistic shocks is widely thought to be an important
acceleration mechanism in various astrophysical jet sources, including radio-loud active …

Quasi-periodic oscillations (QPO) originating from innermost regions of blazars can provide
unique perspective of some of the burning issues in blazar studies including disk–jet …

Context. Investigation of the hard X-ray emission properties of blazars is key to the
understanding of the central engine of the sources and associated jet process. In particular …

Context. We present an extensive study of the BL Lac object Mrk 501 based on a data set
collected during the multi-instrument campaign spanning from 2009 March 15 to 2009 …