Chandra Observations of the Gamma-ray Binary LSI+61303: Extended X-ray Structure?

TL;DR

This study presents the highest resolution X-ray observation of LSI+61303, revealing potential extended structure and a very hard photon index, providing new insights into the source's emission and environment.

Contribution

It reports the first evidence of extended X-ray emission around LSI+61303 and characterizes its spectral properties with unprecedented detail.

Findings

Possible extended structure detected at 3.2 sigma significance.

Photon index measured at 1.25, the hardest ever observed for this source.

X-ray flux and hydrogen column density consistent with previous studies.

Abstract

We present a 50 ks observation of the gamma-ray binary LSI+61303 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 arcsec towards the North of LSI+61303 have been found at a significance level of 3.2 sigma. 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^{+1.8}_{-1.4} x 10^{-12} ergs/cm^2/s, and hydrogen column density, N_{H}=0.70+/-0.06 x 10^{22} cm^{-2}, are compatible with previous results, the photon index Gamma=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 LSI+61303.