A ug 2 00 8 VERITAS Discovery of > 200 GeV Gamma-ray Emission from the Intermediate-frequency-peaked BLLac Object W

We report the detection of very high-energy γ-ray emission from the intermediate-frequencypeaked BLLacertae object WComae (z = 0.102) by VERITAS, an array of four imaging atmospheric-Cherenkov telescopes. The source was observed between January and April 2008. A strong outburst of γ-ray emission was measured in the middle of March, lasting for only four days. The energy spectrum measured during the two highest flare nights is fit by a power-law and is found to be very steep, with a differential photon spectral index of Γ = 3.81±0.35stat±0.34syst. The integral photon flux above 200 GeV during those two nights corresponds to roughly 9% of the flux from the Crab Nebula. Quasi-simultaneous Swift observations at X-ray energies were triggered by the VERITAS observations. The spectral energy distribution of the flare data can be described by synchrotron-self-Compton (SSC) or external-Compton (EC) leptonic jet models, with the latter offering a more natural set of parameters to fit the data. Subject headings: BL Lacertae objects: individual (W Comae) — gamma-rays: observations Fred Lawrence Whipple Observatory, HarvardSmithsonian Center for Astrophysics, Amado, AZ 85645, USA Department of Physics, Washington University, St. Louis, MO 63130, USA Department of Physics, University of Massachusetts, Amherst, MA 01003-4525, USA School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA Department of Physics, Purdue University, West Lafayette, IN 47907, USA Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA Physics Department, University of Utah, Salt Lake City, UT 84112, USA Physics Department, McGill University, Montreal, QC