Chandra observations of the gamma-ray binary LSI+61303: extended X-ray Structure?

Abstract

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+1.8-1.4×10-12 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.