Related papers: First Multi-wavelength Campaign on the Gamma-ray-l…
We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift UVOT, X-ray observations by the Swift X-ray…
The TeV BL Lac object Markarian 501 has been the subject of a 4.5 month multi-instrument campaign conducted in 2009, which provided an excellent temporal and energy coverage from radio to very high energy gamma rays (>100 GeV, VHE). During…
Mrk 421 was in its most active state around early 2010, which led to the highest TeV gamma-ray flux ever recorded from any active galactic nuclei. We aim to characterize the multiwavelength behavior during this exceptional year for Mrk 421,…
Following the detection of strong TeV gamma-ray flares from the BL Lac object 1ES 1959+650 with the Whipple 10 m Cherenkov telescope on May 16 and 17, 2002, we performed intensive Target of Opportunity (ToO) radio, optical, X-ray and TeV…
In this paper, we present results of TeV $\gamma$--ray observations of the high synchrotron peaked BL Lac object 1ES 1218+304 (z=0.182) with the $TACTIC$ (TeV Atmospheric Cherenkov Telescope with Imaging Camera). The observations are…
The detection of very-high-energy (VHE; $>$100 GeV) $\gamma$-ray radiation from misaligned jetted Active Galactic Nuclei (AGN) challenges the emission models that primarily explain VHE emissions from beamed AGN, i.e., blazars. Using over 16…
We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211 observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral flux above 200 GeV measured with the nightly-binned light curve is $(8.8 \pm 0.4)…
Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and…
We have observed Markarian 501 in Very High Energy (VHE) gamma-ray wavelength band for 70.6 hours from 15 April to 30 May, 2012 using TACTIC telescope. Detailed analysis of $\sim$66.3 hours of clean data revealed the presence of a TeV…
We present the discovery of very high energy (VHE) gamma-ray emission from the high-frequency-peaked BL Lac object 1ES 0806+524 (z=0.138) and the intermediate-frequency-peaked BL Lac object W Comae (z=0.102) with VERITAS. VHE emission was…
Non-blazar Active Galactic Nuclei (AGN) have emerged as a new gamma-ray emitting source class on the extragalactic sky and started to deepen our understanding of the physical processes and the nature of AGN in general. The detection of…
Motivated by the Costamante & Ghisellini (2002) predictions we investigated if the blazar 1ES 1727+502 (z=0.055) is emitting very high energy (VHE, E>100 GeV) gamma rays. We observed the BL Lac object 1ES 1727+502 in stereoscopic mode with…
Jets associated with Active Galactic Nuclei (AGN) have been observed for almost a century, initially at optical and radio wavelengths. They are now widely accepted as "exhausts" produced electromagnetically by the central, spinning, massive…
Active galactic nuclei are the most luminous persistent (non-transient, even if often variable) objects in the Universe. They are bright in the entire electromagnetic spectrum. Blazars are a special class where the jets point nearly to our…
M87 is the first extragalactic source detected at the TeV that is not a blazar. To account for the recent observations of M87 made by the High Energy Stereoscopic System (H.E.S.S.) telescope array, we developed a new multi-blob synchrotron…
It is notoriously difficult to organize simultaneous observations from space and from the ground. This is particularly so at GeV-TeV energies where the space observations from all sky telescopes and the ground-based observations (mostly…
An updated analysis of a targeted search for high-energy neutrinos from Markarian 421 and Markarian 501 is reported. They are two of the closest and brightest extragalactic sources in the TeV band. In contrast to other types of active…
Large number of Active Galactic Nuclei (AGN) producing Very-High-Energy (VHE) gamma-rays (energies above 100~GeV) has been revealed using observations with Imaging Atmospheric Cherenkov Telescopes (IACTs). However, our knowledge of the VHE…
With the arrival of powerful, ground-based gamma-ray detectors, we can now begin to seriously probe, via simultaneous X-ray/TeV observations, the origin of the gamma-ray emission in the blazars Mrk 421 and 501. If the synchrotron-Compton…
[Abridged] Context. To construct and interpret the spectral energy distribution (SED) of BL Lacertae objects, simultaneous broad-band observations are mandatory. Aims. We present the results of a dedicated multi-wavelength study of the…