An XMM-Newton Spectral and Timing Study of IGR J16207 - 5129: An Obscured and Non-Pulsating HMXB

We report on a ~12 hr XMM-Newton observation of the supergiant high-mass X-ray binary (HMXB) IGR J16207 - 5129. This is only the second soft X-ray (0.4-15 keV, in this case) study of the source since it was discovered by the International Gamma-Ray Astrophysics Laboratory satellite. The average energy spectrum is very similar to those of neutron star HMXBs, being dominated by a highly absorbed power-law component with a photon index of Γ = 1.15^+0.07 _-0.05. The spectrum also exhibits a soft excess below ~2 keV and an iron Kα emission line at 6.39 ± 0.03 keV. For the primary power-law component, the column density is (1.19^+0.06 _-0.05) × 10²³ cm^-2, indicating local absorption, likely from the stellar wind, and placing IGR J16207 - 5129 in the category of obscured IGR HMXBs. The source exhibits a very high level of variability with an rms noise level of 64% ± 21% in the 10^-4-0.05 Hz frequency range. Although the energy spectrum suggests that the system may harbor a neutron star, no pulsations are detected with a 90% confidence upper limit of ~2% in a frequency range from ~10^-4 to 88 Hz. We discuss similarities between IGR J16207 - 5129 and other apparently nonpulsating HMXBs, including other IGR HMXBs as well as 4U 2206+54 and 4U 1700 - 377.