Evidence for long-term Gamma-ray and X-ray variability from the unidentified TeV source HESS J0632+057

HESS J0632+057 is one of only two unidentified very-high-energy gamma-ray sources which appear to be point-like within experimental resolution. It is possibly associated with the massive Be star MWC 148 and has been suggested to resemble known TeV binary systems like LS I +61 303 or LS 5039. HESS J0632+057 was observed by VERITAS for 31 hours in 2006, 2008 and 2009. During these observations, no significant signal in gamma rays with energies above 1 TeV was detected from the direction of HESS J0632+057. A flux upper limit corresponding to 1.1% of the flux of the Crab Nebula has been derived from the VERITAS data. The non-detection by VERITAS excludes with a probability of 99.993% that HESS J0632+057 is a steady gamma-ray emitter. Contemporaneous X-ray observations with Swift XRT reveal a factor of 1.8± 0.4 higher flux in the 1-10 keV range than earlier X-ray observations of HESS J0632+057. The variability in the gamma-ray and X-ray fluxes supports interpretation of the object as a gamma-ray emitting binary. Subject headings: acceleration of particles binaries: general gamma rays: observations stars: individual ( HESS J0632+057, MWC 148 ) Corresponding author; [email protected] Fred Lawrence Whipple Observatory, HarvardSmithsonian Center for Astrophysics, Amado, AZ 85645, USA Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA Department of Physics, Washington University, St. Louis, MO 63130, USA School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA School of Physics, University College Dublin, Belfield, Dublin 4, Ireland School of Physics, National University of Ireland, Galway, Ireland Astronomy Department, Adler Planetarium and As-