Related papers: Modelling rapid TeV variability of PKS 2155-304
The TeV blazar PKS 2155--304 was the subject of an intensive 2 week optical and near-infrared observing campaign in 2004 August with the CTIO 0.9m telescope. During this time, simultaneous X-ray data from RXTE were also obtained. We compare…
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…
A time-dependent Synchrotron Self Compton model (SSC) which is able to motivate the used electron spectra of many SSC models as a balance of acceleration and radiative losses is introduced. Using stochastic acceleration as well as Fermi-I…
PKS 2155-304 is a blazar located in the Southern Hemisphere, monitored with the High Energy Stereoscopic System (H.E.S.S.) at very high energy (VHE, E>100 GeV) $\gamma$ rays every year since 2002. Thanks to the large data set collected in…
We have performed an optical observation campaign on PKS 2155-304, whose aim was to determine the variability properties of this object on very short time scales in several photometric bands. We detected variability on time scales as short…
We investigate the formation of TeV spectrum of a distant blazar PKS 1424+240 residing at a redshift $z\geq0.6$ in two scenarios in the frame of a lepto-hadronic jet model taking both the uncertainties of the extragalactic background light…
We present optical light curves for the period 1996-2000, of two of the brightest known EGRET BL Lac objects: PKS 2005-489 and PKS 2155-304, the latter also one of the few known TeV sources. For both objects, quiescent epochs of low level…
Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the…
Recent Cerenkov observations of the two BL Lac objects PKS 2155-304 and Mkn 501 revealed TeV flux variability by a factor ~2 in just 3-5 minutes. Even accounting for the effects of relativistic beaming, such short timescales are challenging…
The rapid variability of the VHE emission reported for some TeV blazars implies Doppler factors well in excess of those inferred from superluminal motions and unification schemes. We propose that those extreme flares may result from…
Recent observations in the TeV band challenge the simplest models developed to describe the overall emission of blazars and radiogalaxies. In particular, the observation of variable TeV emission from M87 and the fast variability shown by…
We propose a new model for the description of ultra-short flares from TeV blazars by compact magnetized condensations (blobs), produced when red giant stars cross the jet close to the central black hole. Our study includes a simple…
Simultaneous HESS/CHANDRA/optical observations were performed on the BL Lac object PKS 2155-304 in the night of July 29-30 2006, when the source underwent its second major gamma-ray outburst in Summer 2006. This event took place about 44…
In May 1994 the BL Lac object PKS 2155-304 was observed continuously for ~10 d with IUE and EUVE and for 2 d with ASCA, as well as with ROSAT and with ground- based radio, IR, and optical telescopes. The light curves show a well-defined…
We report on the first simultaneous observations that cover the optical, X-ray, and high energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 25 August and 6 September 2008,…
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…
Radio-to-TeV observations of the bright nearby (z=0.034) blazar Markarian 501 (Mrk 501), performed from December 2012 to April 2018, are used to study the emission mechanisms in its relativistic jet. We examined the multi-wavelength…
Highly energetic, variable and distant sources such as Active Galactic Nuclei provide a good opportunity to evaluate effects due to the emission and the propagation of high energy photons. In this note, a study of possible energy-dependent…
The observations of TeV blazars published recently show an unexpected quadratic or even cubic correlation between the X-ray and gamma-ray emission. A standard model of the synchrotron self-Compton emission of a compact source inside a jet…
We present a model of the spectra of gamma-ray emitting blazars in which a single homogeneous emission region both emits synchrotron photons directly and scatters them to high (gamma-ray) energy before emission (a ``synchrotron…