author={Deirdre Horan and V. A. Acciari and Stella Bradbury and James Henry Buckley and Viatcheslav Bugaev and Karen Lynn Byrum and A. Cannon and O. Celik and Andrea Cesarini and Y. C. K. Chow and L. Ciupik and Peter Cogan and Abraham D. Falcone and Stephen Fegan and J. P. Finley and Pascal D. Fortin and Lucy Fortson and Daniel Gall and G. H. Gillanders and Jeff Grube and Geza Gyuk and David Hanna and E. Hays and M. P. Kertzman and John Kildea and Alexander K. Konopelko and Henric Krawczynski and F. and M. J. Lang and K. Lee and Patrick J. Moriarty and T. N. Nagai and Jacek Niemiec and R. A. Ong and J. S. Perkins and Martin Pohl and J. Quinn and Philip T. Reynolds and Harry J. Rose and Glenn H. Sembroski and Andrew William Smith and D. Steele and Simon P. Swordy and John Toner and Vladimir V. Vassiliev and Scott Patrick Wakely and Trevor C. Weekes and R. J. White and D. A. Williams and Matthew Wood and Benjamin Zitzer and Hugh D. Aller and M. F. Aller and Mark Baker and David Aldington Levin Barnaby and Michael T. Carini and Patrick Charlot and Jonathan Dumm and N. E. Fields and T. Hovatta and B. Jordan and Yu. A. Kovalev and Yuri Y. Kovalev and H A Krimm and O. M. Kurtanidze and Anne Lahteenmaki and Jean Francois Le Campion and Jeremy D. Maune and Teresa Montaruli and Alberto Carlo Sadun and S. M. Smith and Merja Tornikoski and Matti Turunen and R. Walters},
  journal={The Astrophysical Journal},
Since 2005 September, the Whipple 10 m Gamma-ray Telescope has been operated primarily as a blazar monitor. The five northern hemisphere blazars that have already been detected at the Whipple Observatory, Markarian 421 (Mrk 421), H1426+428, Mrk 501, 1ES 1959+650, and 1ES 2344+514, are monitored routinely each night that they are visible. We report on the Mrk 421 observations taken from 2005 November to 2006 June in the gamma-ray, X-ray, optical, and radio bands. During this time, Mrk 421 was… 
Simultaneous Multiwavelength Observations of Markarian 421 During Outburst
We report on the results of two coordinated multiwavelength campaigns that focused on the blazar Markarian 421 during its 2006 and 2008 outbursts. These campaigns obtained UV and X-ray data using the
Multiwavelength study of the TeV blazar Mrk 421 during a giant flare
Aims. The nearby (z = 0.031) TeV blazar Mrk 421 was reported to be in a high state of flux activity since November, 2009. We aim to investigate possible changes in the physical parameters of Mrk 421
VHE observation of Mrk 421 with TACTIC during 2012; multiwavelength study
Abstract The nearby ( z = 0.031 ) TeV γ-ray emitter BL Lac object Mrk 421 has been observed with the TACTIC telescope for nearly 118 hours during 01 February to 26 April, 2012 (MJD 55958–56044).
Observation of Markarian 421 in TeV Gamma Rays Over a 14-Year Time Span
Abstract The variability of the blazar Markarian 421 in TeV gamma rays over a 14-year time period has been explored with the Whipple 10 m telescope. It is shown that the dynamic range of its flux
MAGIC TeV gamma-ray observations of Markarian 421 during multiwavelength campaigns in 2006
Context. Wide-range spectral coverage of blazar-type active galactic nuclei is of paramount importance for understanding the particle acceleration mechanisms assumed to take place in their jets. The
TeV Gamma-Ray Observations of Mrk421 and H1426+428 with TACTIC Imaging Telescope
We have observed extragalactic sources Mrk421 (z=0.30) and H1426+428 (z=0.129) in very high energy gamma region using TACTIC telescope at Mount Abu, Rajasthan, India. Mrk421 was observed during 07
Long-term multi-wavelength variability and correlation study of Markarian 421 from 2007 to 2009
We study the multi-band variability and correlations of the TeV blazar Mrk 421 on year time scales, which can bring additional insight on the processes responsible for its broadband emission. We
X-ray/gamma-ray flux correlations in the BL Lacs Mrk 421 and 501 using HAWC data
The HAWC gamma ray observatory is located at the Sierra Negra Volcano in Puebla, Mexico, at an altitude of 4,100 meters. HAWC is a wide field of view array of 300 water Cherenkov detectors that are
Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010
Context. Because of its proximity, Mrk 421 is one of the best sources on which to study the nature of BL Lac objects. Its proximity allows us to characterize its broadband spectral energy
An active state of the BL Lacertae object Markarian 421 detected by INTEGRAL in April 2013
Aims. Multiwavelength variability of blazars offers indirect, but very effective, insight into their powerful engines and on the mechanisms through which energy is propagated from the centre down the


Multiwavelength observations of the blazar Markarian 421 in 2002 December and 2003 January
We report on a multiwavelength campaign on the TeV γ-ray blazar Mrk 421 performed during 2002 December and 2003 January. These target of opportunity observations were initiated by the detection of
Multiwavelength observations of Markarian 421 in 2001 March: an unprecedented view on the X-ray/TeV correlated variability
We present a detailed analysis of week-long simultaneous observations of the blazar Mrk 421 at 2-60 keV X-rays (RXTE) and TeV γ-rays (Whipple and HEGRA) in 2001. Accompanying optical monitoring was
A multiwavelength view of the TeV blazar markarian 421: Correlated variability, flaring, and spectral evolution
We report results from an intensive multiwavelength monitoring campaign on the TeV blazar Mrk 421 over the period of 2003-2004. The source was observed simultaneously at TeV energies with the Whipple
Complex Spectral Variability from Intensive Multiwavelength Monitoring of Markarian 421 in 1998
We conducted a multifrequency campaign for the TeV blazar Markarian 421 in 1998 April. The campaign started from a pronounced high-amplitude flare recorded by BeppoSAX and Whipple; the ASCA
Detection of the BL Lacertae object H1426+428 at TeV gamma-ray energies
A very high energy γ-ray signal has been detected at the 5.5 σ level from H1426+428, an X-ray-selected BL Lacertae object at a redshift of 0.129. The object was monitored from 1995 to 1998 with the
INTEGRAL observations of the blazar Mrk 421 in outburst Results of a multi-wavelength campaign
Context. If one wants to understand the physics of blazars, better simultaneous observations are important at all wavelengths, so it was fortunate that a ToO observation of the TeV-emitting blazar
X-Ray Emission of Markarian 421: New Clues from Its Spectral Evolution. I. Temporal Analysis
Mrk 421 was repeatedly observed with BeppoSAX in 1997 and 1998. This is the first of two papers where we present the results of a thorough temporal and spectral analysis of all the data available to
Multiwavelength Observations of Strong Flares From the TeV-Blazar 1ES 1959+650
Following the detection of strong TeV γ-ray flares from the BL Lac object 1ES 1959+650 with the Whipple 10 m Cerenkov telescope on 2002 May 16 and 17, we performed intensive target of opportunity
TeV observations of Mrk 421 with the TACTIC γ-ray telescope during 2006-8
In this paper, we report on the Markarian 421 results obtained during TeV γ-ray observations from 18 December 2006 to 18 April 2007 and 11 January to 7 May 2008 for 122.68 and 184.82 h, respectively,
Results from the Blazar Monitoring Campaign at the Whipple 10m Gamma-ray Telescope
In September 2005, the observing program of the Whipple 10 m gamma-ray telescope was redefined to be dedicated almost exclusively to AGN monitoring. Since then the five Northern Hemisphere blazars