X-Ray Imaging Observations of the High-mass γ-Ray Binary HESS J0632+057

Abstract

Abstract The Chandra X-Ray Observatory (CXO) imaged the high-mass γ-ray binary HESS J0632+057 with the Advanced CCD Imaging Spectrometer (ACIS). We analyzed the CXO data together with 967 ks of archival Swift-XRT observations. On arcsecond scales we find a hint of asymmetric extended emission. On arcminute scales, a region of extended emission (“the blob”), located ≈ 5 .′ 5 east of the binary, is seen in both the CXO-ACIS and the Swift-XRT images. The blob does not have a counterpart in the radio, near-IR, IR, or optical images. The ACIS spectrum of the blob fits either an absorbed power-law model with Γ ≃ 2.6, or a thermal plasma model with kT ≃ 3 keV. Since the blob’s N H is significantly higher than that of the binary we conclude that the blob and binary are not directly related. The somewhat larger, very deep XRT image suggests that the binary may be located within a shell (or cavity). The four ACIS spectra taken within the ∼20 day interval near the light-curve minimum suggest that N H varies on timescales of days, possibly due to the inhomogeneous circumbinary environment. The XRT spectra extracted from wider orbital phase intervals support significant changes in N H near the light-curve maximum/minimum, which may be responsible for the substantial systematic residuals seen near 1 keV, and provide tentative evidence for an Fe line at 6.4 keV. We find no significant periodic signal in the ACIS data up to 0.156 Hz.