Multiwavelength observations of the previously unidentified blazar RX J0648.7+1516

We report on the VERITAS discovery of very-high-energy (VHE) gamma-ray emission above 200 GeV from the high-frequency-peaked BL Lac object RXJ0648.7+1516 (GBJ0648+1516), associated with 1FGL J0648.8+1516. The photon spectrum above 200 GeV is fit by a power law dN/dE = F0(E/E0)-Gamma with a photon index of 4.4 ± 0.8stat ± 0.3syst and a flux normalization F0 of (2.3± 0.5stat ±1.2sys)×10^-11 TeV^-1cm^-2s^-1 with E0 = 300 GeV. No VHE variability is detected during VERITAS observations of RXJ0648.7+1516 between 2010 March 4 and April 15. Following the VHE discovery, the optical identification and spectroscopic redshift were obtained using the Shane 3–m Telescope at the Lick Observatory, showing the unidentified object to be a BL Lac type with a redshift of z = 0.179. Broadband multiwavelength observations contemporaneous with the VERITAS exposure period can be used to sub-classify the blazar as a high-frequency-peaked BL Lac (HBL) object, including data from the MDM observatory, Swift -UVOT and XRT, and continuous monitoring at photon energies above 1 GeV from the Fermi Large Area Telescope (LAT). We find that in the absence of undetected, high-energy rapid variability, the one-zone synchrotron self-Compton model (SSC) overproduces the high-energy gamma-ray emission measured by the Fermi -LAT over 2.3 years. The SED can be parameterized satisfactorily with an external-Compton or lepto-hadronic model, which have two and six additional free parameters, respectively, compared to the one-zone SSC model. Fil: Aliu, E.. Columbia University; Estados Unidos Fil: Aune, T.. University of California; Estados Unidos Fil: Beilicke, M.. University of Washington; Estados Unidos Fil: Benbow, W.. Harvard-Smithsonian Center for Astrophysics; Estados Unidos Fil: Bottcher, M.. Ohio University; Estados Unidos Fil: Bouvier, A.. University of California; Estados Unidos Fil: Bradbury, S. M.. University of Leeds; Reino Unido Fil: Buckley, J. H.. Washington University; Estados Unidos Fil: Bugaev, V.. Washington University; Estados Unidos Fil: Cannon, A.. University College Dublin,; Irlanda Fil: Cesarini, A.. National University of Ireland Galway; Irlanda Fil: Ciupik, L.. Adler Planetarium and Astronomy; Estados Unidos Fil: Connolly, M. P.. National University of Ireland Galway; Irlanda Fil: Cui, W.. Purdue University; Estados Unidos Fil: Decerprit, D.. Desy; Alemania Fil: Dickherber, R.. Washington University; Estados Unidos Fil: Duke, C.. Grinnell College; Estados Unidos Fil: Errando, M.. Columbia University; Estados Unidos Fil: Falcone, A.. Pennsylvania State University; Estados Unidos Fil: Feng, Q.. Purdue University; Estados Unidos Fil: Finnegan, G.. University of Utah; Estados Unidos Fil: Fortson, L.. University of Minnesota; Estados Unidos Fil: Furniss, A.. University of California; Estados Unidos Fil: Galante, N.. Harvard-Smithsonian Center for Astrophysics; Estados Unidos Fil: Gall, D.. University of Iowa; Estados Unidos Fil: Gillanders, G. H.. National University of Ireland Galway; Irlanda Fil: Godambe, S.. University of Utah; Estados Unidos Fil: Griffin, S.. McGill University; Canadá Fil: Grube, J.. Adler Planetarium and Astronomy Museum; Estados Unidos Fil: Pichel, Ana Carolina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: The Veritas Collaboration.