Related papers: The 2009 multiwavelength campaign on Mrk 421: Vari…
The Large High Altitude Air Shower Observatory (LHAASO) monitors sources within its field of view for up to 7 hours daily, achieving a duty cycle exceeding 98% and an annual point-source sensitivity of 1.5% Crab Units (CU) in the very high…
We report the results of photometric observations of the blazars Mrk 421 and 3C 454.3 designed to search for intraday variability (IDV) and short-term variability (STV). Optical photometric observations were spread over eighteen nights for…
During the observation period 1997, the nearby Blazar Mkn 501 showed extremely strong emission and high variability. We examine multiwavelength aspects of this event using radio, optical, soft and hard X-ray and TeV data. We concentrate on…
The extragalactic VHE gamma-ray sky is rich in blazars. These are jetted active galactic nuclei viewed at a small angle to the line-of-sight. Only a handful of objects viewed at a larger angle are known so far to emit above 100 GeV.…
As part of our multiwavelength campaign of GX 339-4 observations in 1996 we present the rapid X-ray variability observed July 26 using the RXTE when the source was in a hard state (= soft X-ray low state). We found that the source was…
The high-synchrotron-peaked BL Lac object 1ES\,1959+650 exhibited pronounced activity between MJD~60310 -- 60603, including a very high energy (VHE) detection reported by LHAASO. To investigate the underlying emission mechanisms, we…
Particle acceleration mechanisms in supermassive black hole jets, such as shock acceleration, magnetic reconnection, and turbulence, are expected to have observable signatures in the multi-wavelength polarization properties of blazars. The…
We present Fermi-LAT and multi-frequency, multi-epoch VLBA data for the TeV blazar Mrk421. We collected the data during a long and intensive multi-frequency campaign in 2011. We study the gamma-ray light curve, the photon index evolution…
Context: The blazar Markarian 421 is one of the brightest TeV gamma-ray sources of the northern sky. From December 2007 until June 2008 it was intensively observed in the very high energy (VHE, E > 100 GeV) band by the single-dish Major…
The HAWC Observatory collected 6 years of extensive data, providing an ideal platform for long-term monitoring of blazars in the Very High Energy (VHE) band, without bias towards specific flux states. HAWC continuously monitors blazar…
Observations at Very High Energies (VHE, E > 100 GeV) of the BL Lac object Mrk 501 taken with the High Energy Stereoscopic System (H.E.S.S.) in four distinct periods between 2004 and 2014 are presented, with focus on the 2012 and 2014…
High-resolution radio observations are ideal for constraining the value of physical parameters in the inner regions of active-galactic-nucleus jets and complement results on multiwavelength (MWL) observations. This study is part of a wider…
The BL Lac object 1ES 0647+250 is one of the few distant $\gamma$-ray emitting blazars detected at very high energies (VHE, $\gtrsim$100 GeV) during a non-flaring state. It was detected with the MAGIC telescopes during its low activity in…
We present long-term observations of several VHE (E > 100 GeV) blazars with VERITAS, together with contemporaneous Swift and RXTE X-ray data. The observed targets include Mrk 421, Mrk 501, 1ES 2344+514. Strong flux and spectral variability…
We have conducted a new long-term multi-wavelength campaign on one of the most super- Eddington narrow-line Seyfert 1s (NLS1s) known, namely RX J0134.2-4258. In this first paper, we report deep simultaneous X-ray observations performed by…
Utilizing all the 16-year $RXTE$ observations, we analyze the X-ray spectra of 32 TeV blazars, and perform a systematic investigation of X-ray spectral variability for the 5 brightest sources during their major flares that lasted several…
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)…
We report on the gamma-ray activity of the high-synchrotron-peaked BL Lacertae object Mrk 421 during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) gamma-ray spectrum…
Detailed investigation of broadband flux variability in the blazar 3C 273 allows us to probe the location and size of emission regions and their physical conditions. We report the results on correlation studies of the flaring activity…
The BL Lac 1ES 2344+514 is known for temporary extreme properties (e.g., a shift of the synchrotron SED peak energy $\nu_{synch,p}$ above 1keV). While those extreme states were so far observed only during high flux levels, additional…