Chandra observations of the gamma-ray binary LS I +61 303: Extended X-ray structure?

We present a 50 ks observation of the gamma-ray binary LS I +61 303 carried out with the ACIS-I array aboard the Chandra X-Ray Observatory. This is the highest resolution X-ray observation of the source conducted so far. Possible evidence of an extended structure at a distance between 5″ and 12″ toward the north of LS I +61 303 has been found at a significance level of 3.2 σ. The asymmetry of the extended emission excludes an interpretation in the context of a dust-scattered halo, suggesting an intrinsic nature. On the other hand, while the obtained source flux of F0.3-10keV = 7.1 -1.4+1.8 × 10-12 ergs cm-2 s-1 and hydrogen column density NH = (0.70 ± 0.06) × 1022 cm-2 are compatible with previous results, the photon index Γ = 1.25 ± 0.09 is the hardest ever found. In light of these new results, we briefly discuss the physics behind the X-ray emission, the location of the emitter, and the possible origin of the extended emission ∼0.1 pc away from LS I +61 303. © 2007. The American Astronomical Society. All rights reserved.