ESA Science & Technology - Publication Archive
Aims. Our goal is to understand the characteristics of highly absorbed sgHMXB and in particular the companion stellar wind, which is thought to be responsible for the strong absorption.
Methods. We monitored IGR J17252-3616, a highly absorbed system featuring eclipses, with XMM-Newton to study the variability of the column density and the Fe K-alpha emission line along the orbit and during the eclipses. We also compiled a 3D model of the stellar wind to reproduce the observed variability.
Results. We first derive a refined orbital solution based on INTEGRAL, RXTE, and XMM-Newton data. We find that the XMM-Newton monitoring campaign reveals significant variations in the intrinsic absorbing column density along the orbit and the Fe K-alpha line equivalent width around the eclipse. The origin of the soft X-ray absorption is associated with a dense and extended hydrodynamical tail, trailing the neutron star. This structure extends along most of the orbit, indicating that the stellar wind has been strongly disrupted.
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Aims. We study the massive stars in OB associations and their surrounding interstellar medium environment, using a population synthesis code.
Methods. We developed a new population synthesis code for groups of massive stars, where we model the emission of different forms of energy and matter from the stars of the association. In particular, the ejection of the two radioactive isotopes 26Al and 60Fe is followed, as well as the emission of hydrogen ionizing photons, and the kinetic energy of the stellar winds and supernova explosions. We investigate various alternative astrophysical inputs and the resulting output sensitivities, especially effects due to the inclusion of rotation in stellar models. As the aim of the code is the application to relatively small populations of massive stars, special care is taken to address their statistical properties. Our code incorporates both analytical statistical methods applicable to small populations, as well as extensive Monte Carlo simulations.
Context. The Scorpius-Centaurus association is the most-nearby group of massive and young stars. As nuclear-fusion products are ejected by massive stars and supernovae into the surrounding interstellar medium, the search for characteristic g-rays from radioactivity is one way to probe the history of activity of such nearby massive stars on a My time scale through their nucleosynthesis. 26Al decays with a radioactivity lifetime t~1 My, 1809 keV g-rays from its decay can be measured with current g-ray telescopes.
Soft gamma repeaters (SGRs) and anomalous x-ray pulsars form a rapidly increasing group of x-ray sources exhibiting sporadic emission of short bursts. They are believed to be magnetars, that is, neutron stars powered by extreme magnetic fields, B ~ 1014 to 1015 gauss. We report on a soft gamma repeater with low magnetic field, SGR 0418+5729, recently detected after it emitted bursts similar to those of magnetars. X-ray observations show that its dipolar magnetic field cannot be greater than 7.5 × 1012 gauss, well in the range of ordinary radio pulsars, implying that a high surface dipolar magnetic field is not necessarily required for magnetar-like activity. The magnetar population may thus include objects with a wider range of B-field strengths, ages, and evolutionary stages than observed so far.