Related papers: Optical spectroscopy of BL Lac objects: TeV candid…
Observations of the gamma-ray sky with Fermi led to significant advances towards understanding blazars, the most extreme class of Active Galactic Nuclei. A large fraction of the population detected by Fermi is formed by BL Lacertae (BL Lac)…
Blazars, including BL Lacs and FSRQs, are the most luminous extragalactic {\gamma}-ray sources. They account for about 56% of the sources listed in the recent Fermi-LAT catalog (4FGL-DR4). The optical and UV spectra of BL Lacs are nearly…
The TeV emission of low power BL Lac objects has been established by the detection of an handful of them. The knowledge of the level of the TeV emission and its spectrum can shed light on the particle acceleration mechanisms, and it is…
We study the possible detection of and properties of very high-energy (VHE) gamma-ray emission (in the energy band above 100 GeV) from high redshift sources. We report on the detection of VHE gamma-ray flux from blazars with redshifts…
The large majority of sources detected by the Fermi Gamma-ray Space Telescope are blazars, belonging in particular to the blazar subclass of BL Lacertae objects (BL Lacs). BL Lacs often have featureless optical spectra, which make it…
Active galactic Nuclei (AGNs) with their relativistic jets pointed towards the observer, form a subclass of luminous gamma-ray sources commonly known as blazars. The study of blazars is essential to improve our understanding on the AGNs…
The extragalactic $\gamma$-rays sky observed by Fermi-Large Area Telescope (LAT) is dominated by blazars. In the fourth release of the Fermi-LAT Point Source Catalog (4FGL), are sources showing a multifrequency behavior similar to that of…
Context. Blazars are a distinct subclass of active galactic nuclei (AGN), known for their fast variability, high polarization, and intense emission across the electromagnetic spectrum, from radio waves to gamma rays. Gamma-ray blazar…
Due to their almost featureless optical/UV spectra, it is challenging to measure the redshifts of BL Lacs. As a result, about 50% of gamma-ray BL Lacs lack a firm measurement of this property, which is fundamental for population studies,…
Variability is a prominent observational feature of blazars. The high-energy radiation mechanism of jets has always been important but still unclear. In this work, we performed a detailed analysis using Fermi-LAT data across 15 years and…
Blazars, one of the most extreme class of active galaxies, constitute so far the largest known population of $\gamma$-ray sources and their number is continuously growing in the Fermi catalogs. However in the latest release of the Fermi…
We report on VERITAS very-high-energy (VHE; E>100 GeV) observations of six blazars selected from the Fermi Large Area Telescope First Source Catalog (1FGL). The gamma-ray emission from 1FGL sources was extrapolated up to the VHE band,…
Context. Based on their overwhelming dominance among associated Fermi gamma ray catalogue sources, it is expected that a large fraction of the unidentified Fermi objects are blazars. Through crossmatching between the positions of…
We have obtained high dynamic range, good natural seeing i' images of BL Lacertae objects (BL Lacs) to search for the AGN host and thus constrain the source redshift. These objects are drawn from a sample of bright flat-spectrum radio…
We present results of an ongoing program at the ESO VLT for spectroscopy of BL Lac objects lacking a firm redshift estimate and here we report on 15 objects. For 11 sources we confirm the BL Lac classification, and we determine new…
We present a search for high-energy $\gamma$-ray emission from 566 Active Galactic Nuclei at redshift $z > 0.2$, from the 2WHSP catalog of high-synchrotron peaked BL Lac objects with eight years of Fermi-LAT data. We focus on a redshift…
Active galactic Nuclei (AGNs) with their relativistic jets pointed toward the observer, are a class of luminous gamma-ray sources commonly known as blazars. The study of this source class is essential to unveil the physical processes…
We report on 16 BL Lacertae objects that were proposed to be at z > 1. We present spectroscopic observations secured at the 10.4m GTC that allowed us to assess the redshift of these sources. In particular, for five objects we disprove the…
We present the results of the optical spectroscopy follow-up of a sample of 28 unclassified blazars from the Third Fermi-LAT Catalog of High-Energy Sources (3FHL). All the spectra were taken with the 4m Mayall telescope at Kitt Peak. With…
Context. Blazars are the most numerous class of High Energy (HE; E about 50 MeV - few 100 GeV) and Very High Energy (VHE; E about 100 GeV - 10 TeV) gamma-ray emitters. As of today, a measured spectroscopic redshift is available for only…