Related papers: Temporal variability and estimation of jet paramet…

The extreme TeV blazar 1ES 0229+200 is a high-frequency-peaked BL Lacertae object. It has not shown intraday variability in extensive optical and X-ray observations. Nor has it shown any significant variability on any measurable timescale…

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…

Mrk 421 is the first TeV blazar found to exhibit significant spectral variability during strong flaring activity, showing hardening of the TeV spectrum in high emission states. Mrk 421 is also known to exhibit flux variability on time…

(Shortened)Context: We analyze the optical variability of the FSRQ Ton 599 using BVRI photometry from the WEBT collaboration (2011-2023), complemented by photometric and spectroscopic data from the Steward Observatory.\\ Aims: To…

The TACTIC $\gamma$-ray telescope has observed Mrk 421 on 66 clear nights from Dec. 07, 2005 to Apr. 30, 2006, totalling $\sim$ 202 hours of on-source observations. Here, we report the detection of flaring activity from the source at $\geq$…

High-redshift ($z>2$) blazars are the most powerful members of the blazar family. Yet, only a handful of them have both X-ray and $\gamma$-ray detection, thereby making it difficult to characterize the energetics of the most luminous jets.…

The well studied blazar 3C 279 underwent a giant $\gamma$-ray outburst in 2014 March-April. The measured $\gamma$-ray flux (1.21 $\pm$ 0.10 $\times$ 10$^{-5}$ ph cm$^{-2}$ s$^{-1}$ in 0.1-300 GeV energy range) is the highest detected from…

We perform a blind search for the variability of the gamma-ray sky in the energy range E>1 GeV using 308 weeks of the Fermi-LAT data. We use the technique based on the comparison of the weekly photon counts and exposures in sky pixels by…

The blazar 3C454.3 exhibited a strong flare seen in gamma-rays, X-rays, and optical/NIR bands during 3--12 December 2009. Emission in the V and J bands rose more gradually than did the gamma-rays and soft X-rays, though all peaked at nearly…

Blazars, a subclass of active galactic nuclei (AGN), are known to be bright $\gamma$-ray sources, frequently exhibiting active (flaring) periods. The blazar PKS~2155-304 is a high synchrotron-peaked BL Lac object located at redshift…

Blazars present highly variable $\gamma$-ray emission. This variability, which can range from a few minutes to several years, is also observed at other wavelengths across the entire electromagnetic spectrum. We make use of the first 12…

In April-May 2003, the blazar 1ES 1959+650 showed an increased level of X-ray activity. This prompted a multiwavelength observation campaign with the Whipple 10 m gamma-ray telescope, the Rossi X-ray Timing Explorer, the Bordeaux Optical…

Flat spectrum radio quasars (FSRQs) are the most luminous blazars at GeV energies, but only rarely emit detectable fluxes of TeV gamma rays, typically during bright GeV flares. We explore the gamma-ray variability and spectral…

Time variability of the photon flux is a known feature of active galactic nuclei (AGN) and in particular of blazars. The high frequency peaked BL Lac (HBL) object PKS 2155-304 is one of the brightest sources in the TeV band and has been…

We present results on multifrequency Very Long Baseline Array (VLBA) monitoring observations of the double-image gravitationally lensed blazar JVAS B0218+357. Multi-epoch observations started less than one month after the gamma-ray flare…

We perform monthly total and polarized intensity imaging of a sample of $\gamma$-ray blazars (33 sources) with the Very Long Baseline Array (VLBA) at 43 GHz with the high resolution of 0.1 milliarcseconds. From Summer 2008 to October 2009…

Very high energy gamma-ray emission from the BL Lac object Markarian 421 has been detected over three observing seasons on 59 nights between April 1992 and June 1994 with the Whipple 10-meter imaging Cherenkov telescope. During its initial…

The Milagro experiment was a TeV gamma-ray observatory designed to continuously monitor the overhead sky in the 0.1-100 TeV energy range. It operated from 2000 and 2008 and was characterized by a large field of view ($\sim$ 2 sr) and a high…

The $\gamma$-ray-loud blazar TXS 2013+370, a powerful multiwavelength emitter at $z = 0.859$, underwent an exceptional GeV outburst in late 2020-early 2021. In this work, we present full-polarization VLBI imaging at 22, 43, and 86 GHz…

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…