Chandra Observations of the Gamma-Ray Binary [OBJECTNAME STATUS="NOLINK"]LS I +61 303[/OBJECTNAME]: 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 F 0.3-10 keV = 7.1 × 10 -12 ergs cm -2 s -1 and hydrogen column density N H = (0.70 ± 0.06) × 10 22 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.