Related papers: Extreme blazars
We have collected a large amount of multifrequency data for the objects in the Metsahovi Radio Observatory BL Lacertae sample and computed their spectral energy distributions (SED). This is the first time the SEDs of BL Lacs have been…
We reviewed X-ray flux and spectral variability properties studied to date by various X-ray satellites for Mrk 421 and PKS 2155-304, which are TeV emitting blazars. Mrk 421 and PKS 2155-304 are the most X-ray luminous blazars in the…
The TeV-emitting BL Lac object Mkn 421 was observed with very long baseline interferometry (VLBI) at three closely-spaced epochs one-month apart in March-April 1998. The source was also monitored at very-high gamma-ray energies (TeV…
We summarize the results of BeppoSAX ToO observation of blazars that were known to be in a high state from observations carried out in the optical or X-ray or TeV bands.In some of the observed sources, two spectral components were detected,…
PKS 2155-304 is one of the prototypes of BL Lac objects. Its spectral energy distribution is known from the radio to the TeV band and has two peaks, one in the soft X-rays and the other in the TeV region. These may be interpreted within the…
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…
High synchrotron peak (HSP; $\nu_{sy}^{pk} > 10^{15}$ Hz) BL Lacs are some of the most extreme accelerators in the Universe. Those found at high redshifts ($z>1$) challenge our understanding of blazar evolution models and are crucial for…
We present the results of the BeppoSAX observations of two BL Lacs, OQ 530 and S5 0716+714, as part of a ToO program for the simultaneous observation at radio, optical, X-ray and TeV energies. Both sources are detected in the LECS and MECS,…
Many of the extragalactic sources detected in $\gamma$ rays at TeV energies are BL Lac objects. In particular, they belong to the subclass of ``high frequency peaked BL Lacs" (HBLs), as their spectral energy distributions exhibit a first…
In this paper, we identify Cen A and M87, two nearby Fanaroff-Riley I (FRI) radio galaxies, with high-energy-peaked BL Lac-like (HBL-like) objects by investigating their spectral energy distributions (SEDs). The SED peak of Cen A at…
Very-high-energy (VHE) BL Lac spectra extending above $10 \, \rm TeV$ provide a unique opportunity for testing physics beyond the standard model of elementary particle and alternative blazar emission models. We consider the hadron beam, the…
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)…
Very high energy (~ TeV) $\gamma$-rays from blazars are attenuated by photons from the extragalactic background light (EBL). Observations of blazars can therefore provide an ideal opportunity for determining the EBL intensity if their…
Mrk 421 is a high-synchrotron-peaked blazar featuring bright and persistent GeV and TeV emission. We use the longest and densest ongoing unbiased observing campaign obtained at TeV and GeV energies during 5.5 years with the FACT telescope…
We study the quasi-simultaneous near-IR, optical, UV, and X-ray photometry of eleven gamma-ray selected blazars for which redshift estimates larger than 1.2 have been recently provided. Four of these objects turn out to be high-power…
H1426+428 is one of blazars that are observed by $\gamma$-rays in the TeV region. Because TeV $\gamma$-rays from distant sources are subject to attenuation by the extragalactic background light (EBL) via electron-positron pair production,…
Blazar spectral energy distributions (SEDs) are double peaked and follow a self-similar sequence in luminosity. The so-called "blue" blazars, whose first SED component peaks at X-ray energies, are TeV sources, although with a relatively…
We have collected broadband spectral energy distributions (SEDs) of three BL Lac objects, 3FGL J0022.1$-$1855 (z=0.689), 3FGL J0630.9$-$2406 (z >~ 1.239), and 3FGL J0811.2$-$7529 (z=0.774), detected by Fermi with relatively flat GeV…
(Abridged) Very high-energy (VHE, $E>100$ GeV) observations of the blazar Mrk 501 with MAGIC in 2014 provided evidence for an unusual narrow spectral feature at about 3 TeV during an extreme X-ray flaring activity. The one-zone…
Since the first TeV blazar Markarian (Mrk) 421 was detected in 1992, the number of established TeV gamma-ray emitting BL Lac objects has grown to 6, with redshifts ranging from 0.031 (Mrk 421) to 0.129 (H 1426+428). The intensive study of…