title: Simultaneous X-Ray and TeV Observations of a Rapid Flare from Markarian 421.
abstract: Mrk 421 was observed for about 2 days with BeppoSAX in 1998 April as part of a worldwide multiwavelength campaign. A large, well-defined flare was observed in X-rays. The same flare was observed simultaneously at TeV energies by the Whipple Observatory gamma-ray telescope. These data provide (1) the first evidence that the X-ray and TeV intensities are well correlated on timescales of hours and (2) the first exactly simultaneous X-ray and TeV spectra. The results imply that the X-ray and TeV photons derive from the same region and from the same population of relativistic electrons. The physical parameters deduced from a homogeneous synchrotron self-Compton model for the spectral energy distribution yield electron cooling times close to the observed variability timescales.
authors.initials: L
authors.lastname: Maraschi
authors.initials: G
authors.lastname: Fossati
authors.initials: F
authors.lastname: Tavecchio
authors.initials: L
authors.lastname: Chiappetti
authors.initials: A
authors.lastname: Celotti
authors.initials: G
authors.lastname: Ghisellini
authors.initials: P
authors.lastname: Grandi
authors.initials: E
authors.lastname: Pian
authors.initials: G
authors.lastname: Tagliaferri
authors.initials: A
authors.lastname: Treves
authors.initials: AC
authors.lastname: Breslin
authors.initials: JH
authors.lastname: Buckley
authors.initials: DA
authors.lastname: Carter-Lewis
authors.initials: M
authors.lastname: Catanese
authors.initials: MF
authors.lastname: Cawley
authors.initials: DJ
authors.lastname: Fegan
authors.initials: S
authors.lastname: Fegan
authors.initials: J
authors.lastname: Finley
authors.initials: J
authors.lastname: Gaidos
authors.initials: T
authors.lastname: Hall
authors.initials: AM
authors.lastname: Hillas
authors.initials: F
authors.lastname: Krennrich
authors.initials: RW
authors.lastname: Lessard
authors.initials: C
authors.lastname: Masterson
authors.initials: P
authors.lastname: Moriarty
authors.initials: J
authors.lastname: Quinn
authors.initials: J
authors.lastname: Rose
authors.initials: F
authors.lastname: Samuelson
authors.initials: TC
authors.lastname: Weekes
authors.initials: CM
authors.lastname: Urry
authors.initials: T
authors.lastname: Takahashi