Related papers: Optical spectroscopy of blazars for the Cherenkov …
In this paper, we discuss an artificial intelligence based approach to constrain the redshift of blazars using combined $\gamma$--ray observations from the \emph{Fermi} Large Area Telescope (LAT) and ground based atmospheric Cherenkov…
We have recently proposed a simplified scenario for blazars in which these sources are classified as flat-spectrum radio quasars or BL Lacs according to the prescriptions of unified schemes, and to a varying combination of Doppler boosted…
In the period between 2009 and 2015, several very high-energy (VHE $> 100$ GeV) gamma-ray flaring events from the BL Lac object PKS 1424+240 were observed by the Cerenkov telescopes VERITAS and MAGIC. It had uncertain redshift ($z$) and…
The classification of gamma-ray-detected blazar candidates of uncertain type (BCU) is a relevant problem in extragalactic gamma-ray astronomy. Here we report the optical spectroscopic characterization, using two 3-4~m class telescopes,…
We have searched for very high energy (VHE) gamma rays from four blazars using the CANGAROO-III imaging atmospheric Cherenkov telescope. We report the results of the observations of H 2356-309, PKS 2155-304, PKS 0537-441, and 3C 279,…
We recently started a systematic search of low-energy counterparts of the unidentified gamma-ray sources (UGSs) listed in the Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) and the Fermi-LAT 2-Year Source Catalog (2FGL).} The…
We report redshift measurements for 12 BL Lacertae objects from a program aimed at obtaining high signal to noise (up to ~ 500) optical spectroscopy of a mixed sample of objects. The new observations, gathered with the 8 m ESO Very Large…
We report the results of optical monitoring for a sample of 11 blazars including 10 BL Lacs and 1 Flat Spectrum Radio Quasar (FSRQ). We have measured the multiband optical flux and colour variations in these blazars on intra-day and…
We present the results of near-infrared H band (1.65 microns) imaging of 11 BL Lac objects with redshifts ranging from z = 0.05 to 0.9. We are able to clearly detect the host galaxy in seven low redshift (z<=0.24) BL Lacs, while the four…
Determining redshifts for BL Lacertae (BL Lac) objects using the traditional spectroscopic method is challenging due to the absence of strong emission lines in their optical spectra. We employ the photometric dropout technique to determine…
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…
A significant fraction ($\sim 30$ %) of the gamma-ray sources listed in the second $\textit{Fermi}$ LAT (2FGL) catalog is still of unknown origin, being not yet associated with counterparts at lower energies. Using the available information…
The VERITAS array of Cherenkov telescopes was used to observe ~130 blazars from 2007 to 2012. Of these, 25 were detected as very-high-energy (VHE; E > 100 GeV) sources. We present here the results of the analysis of 65 VERITAS non-detected…
Following the great success of the current Imaging Atmospheric Cherenkov Telescopes, the next generation gamma-ray telescope arrays, Cherenkov Telescope Array (CTA), is being prepared. CTA will have an order of magnitude higher sensitivity…
\textbf{Context.} Deep optical surveys open the avenue for find large numbers of BL Lac objects that are hard to identify because they lack the unique properties classifying them as such. While radio or X-ray surveys typically reveal dozens…
We present results of observations in the UV to near-IR range for eight blazars, three of which have been recently discovered at Very High Energies (VHE) and five appearing as interesting candidates for VHE {\gamma}-ray detection. We focus…
The very high energy (VHE) gamma-ray spectral indices of blazars show strong correlation with the source redshift. Absence of any such correlation in low energy gamma rays and X-rays indicate the presence of Extragalactic Background Light…
We have measured multi-band optical flux and colour variations for a sample of 12 low energy peaked blazars on short, day-to-month, timescales. Our sample contains six BL Lacertae objects and six flat spectrum radio quasars. These…
There is mounting evidence that ultra-energetic neutrinos of astrophysical origin may be associated with blazars. Here we investigate a unique sample of 47 blazars, $\sim 20$ of which could be new neutrino sources. In particular, we focus…
We are carrying out a multi-purpose program of high signal to noise optical spectroscopy at medium resolution of 30 BL Lac objects. Here we report the detection of three new redshifts, and the discovery of three misclassified sources. The…