Detection of the gamma-ray binary LS I +61 303 in a low flux state at Very High Energy gamma-rays with the MAGIC Telescopes in 2009

Abstract

We present very high energy (VHE, E > 100 GeV) γ-ray observations of the γ-ray binary system LS I+61 303 obtained with the MAGIC stereo system between 2009 October and 2010 January. We detect a 6.3σ γ-ray signal above 400 GeV in the combined data set. The integral flux above an energy of 300 GeV is F(E>300 GeV)=(1.4 +- 0.3stat +- 0.4syst) * 10^{-12} cm^{-2} s^{-1}, which corresponds to about 1.3% of the Crab Nebula flux in the same energy range. The orbit-averaged flux of LS I +61 303 in the orbital phase interval 0.6--0.7, where a maximum of the TeV flux is expected, is lower by almost an order of magnitude compared to our previous measurements between 2005 September and 2008 January. This provides evidence for a new low emission state in LS I +61 303. We find that the change to the low flux state cannot be solely explained by an increase of photon-photon absorption around the compact star.

Corresponding authors: T. Jogler and O. Blanch; accepted for publication in ApJ, 6 pages and 3 figures

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• Multiwavelength Observations of The TeV Binary LS I +61 303 with VERITAS, Fermi-LAT and Swift-XRT During a TeV Outburst
• The Multi-wavelength Characteristics of the TeV Binary LS I +61${}^{\circ }$ 303
• A precessing stellar disk model for superorbital modulations of the gamma-ray binary LS I+61${}^{\circ }$ 303
• Optical microflares in LS I +61 303 and the search for their multiwavelength counterpart
• VERITAS observations of exceptionally bright TeV flares from LS I +61${}^{\circ }$ 303
• VHE observations of binary systems performed with the MAGIC telescopes
• VERITAS monitoring of LS I +61${}^{\circ }$ 303 in conjunction with X-ray, and GeV observation campaigns
• INTEGRAL View of TeV Sources: A Legacy for the CTA Project