Multiwavelength observations of the TeV binary LS i +61° 303 with veritas, Fermi-LAT, and swift/XRT during a TeV outburst

E. Aliu, S. Archambault, B. Behera, K. Berger, M. Beilicke, W. Benbow, R. Bird, A. Bouvier, V. Bugaev, M. Cerruti, X. Chen, L. Ciupik, M. P. Connolly, W. Cui, J. Dumm, A. Falcone, S. Federici, Q. Feng, J. P. Finley, P. FortinL. Fortson, A. Furniss, N. Galante, G. H. Gillanders, S. Griffin, S. T. Griffiths, J. Grube, G. Gyuk, D. Hanna, J. Holder, G. Hughes, T. B. Humensky, P. Kaaret, M. Kertzman, Y. Khassen, D. Kieda, F. Krennrich, M. J. Lang, G. Maier, P. Majumdar, S. McArthur, A. McCann, P. Moriarty, R. Mukherjee, A. O Faoláin De Bhróithe, R. A. Ong, A. N. Otte, N. Park, J. S. Perkins, M. Pohl, A. Popkow, H. Prokoph, J. Quinn, K. Ragan, J. Rajotte, G. Ratliff, P. T. Reynolds, G. T. Richards, E. Roache, G. H. Sembroski, F. Sheidaei, C. Skole, A. W. Smith, D. Staszak, I. Telezhinsky, J. Tyler, A. Varlotta, S. Vincent, S. P. Wakely, T. C. Weekes, A. Weinstein, R. Welsing, A. Zajczyk, B. Zitzer

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18 Scopus citations


We present the results of a multiwavelength observational campaign on the TeV binary system LS I +61°303 with the VERITAS telescope array (>200 GeV), Fermi-LAT (0.3-300 GeV), and Swift/XRT (2-10 keV). The data were taken from 2011 December through 2012 January and show a strong detection in all three wavebands. During this period VERITAS obtained 24.9 hr of quality selected livetime data in which LS I +61°303 was detected at a statistical significance of 11.9σ. These TeV observations show evidence for nightly variability in the TeV regime at a post-trial significance of 3.6σ. The combination of the simultaneously obtained TeV and X-ray fluxes do not demonstrate any evidence for a correlation between emission in the two bands. For the first time since the launch of the Fermi satellite in 2008, this TeV detection allows the construction of a detailed MeV-TeV spectral energy distribution from LS I +61°303. This spectrum shows a distinct cutoff in emission near 4 GeV, with emission seen by the VERITAS observations following a simple power-law above 200 GeV. This feature in the spectrum of LS I +61°303, obtained from overlapping observations with Fermi-LAT and VERITAS, may indicate that there are two distinct populations of accelerated particles producing the GeV and TeV emission.

Original languageEnglish (US)
Article number88
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 10 2013


  • X-rays: binaries
  • acceleration of particles
  • binaries: general
  • gamma rays: stars
  • relativistic processes


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