ar X iv : a st ro - p h / 05 12 62 8 v 2 2 9 D ec 2 00 5 Multiwavelength Observations of the Blazar Mrk 421 in December 2002 and January 2003

We report on a multiwavelength campaign on the TeV γ-ray blazar Markarian (Mrk) 421 performed during December 2002 and January 2003. These target of opportunity observations were initiated by the detection of X-ray and TeV Department of Physics, Washington University, St. Louis, MO 63130, USA Physics Department, Tanta University, Tanta, Egypt Department of Physics, University of Massachussetts, Amherst, MA 01003-4525, USA School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, Yorkshire, England, UK Department of Physics and Astronomy, Iowa State University, Ames, IA 50011-3160, USA Department of Physics, University of California, Los Angeles, CA 90095-1562, USA Department of Physics, National University of Ireland, Galway, Ireland Department of Physics, Purdue University, West Lafayette, IN 47907, USA Department of Physics, Grinnell College, Grinnell, IA 50112-1690, USA Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, Il, USA. Physics Department, McGill University, Montreal, QCH3A2T8, Canada Fred Lawrence Whipple Observatory, Harvard-Smithsonian CfA, P.O. Box 97, Amado, AZ 85645-0097 Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA High Energy Astrophysics Institute, University of Utah, Salt Lake City, UT 84112, USA Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA School of Science, Galway-Mayo Institute of Technology, Galway, Ireland Department of Applied Physics and Instrumentation, Cork Institute of Technology, Cork, Ireland University of Michigan, Ann Arbor, MI 48109, USA Boltwood Observatory, Ontario, Canada University of California, Davis, CA 95616, USA Institute for Space Physics, University of Turku, Vaisala, Finland Department of Physics, University of Colorado at Denver and Health Sciences Center, Denver, CO 80208, USA