Suchergebnisse

Cen X−3 is a compact high-mass X-ray binary likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of two pointed XMM–Newton observations. The first one took place during a normal state of the source, when it has a luminosity LX ∼ 1036 erg s−1. This observation covered orbital phases ϕ = 0.00–0.37, i.e. the egress from the eclipse. The egress light curve is highly structured, showing distinctive intervals. We argue that different intervals correspond to the emergence of different emitting structures. The light-curve analysis enables us to estimate the size of such structures around the compact star, the most conspicuous of which has a size ∼0.3R*, of the order of the Roche lobe radius. During the egress, the equivalent width of Fe emission lines, from highly ionized species, decreases as the X-ray continuum grows. On the other hand, the equivalent width of the Fe K α line, from near-neutral Fe, strengthens. This line is likely formed due to the X-ray illumination of the accretion stream. The second observation was taken when the source was 10 times X-ray brighter and covered the orbital phases ϕ = 0.36–0.80. The X-ray light curve in the high state shows dips. These dips are not caused by absorption but can be due to instabilities in the accretion stream. The typical dip duration, of about 1000 s, is much longer than the time-scale attributed to the accretion of the clumpy stellar wind of the massive donor star, but is similar to the viscous time-scale at the inner radius of the accretion disc. ; This research has been supported by the project ESP2017-85691-P. LMO acknowledges Deutsches Zentrum für Luft und Raumfahrt (DLR) grant FKZ 50 OR 1508 and partial support by the Russian Government Program of Competitive Growth of Kazan Federal University. JJRR acknowledges financial support from the Spanish Ministry of Education, Culture and Sport fellowship PRX17/00114, and also thanks all the staff from SRON for their collaboration and hospitality there. KP acknowledges support from Russian Foundation for Basic Research (RFBR) grant 18-502-12025.

We present an analysis of the first observation of the iconic high-mass X-ray binary 4U 1700−37 with the Chandra High-Energy Transmission Gratings (HETGs) during an X-ray eclipse. The goal of the observation was to study the structure/physical conditions in the clumpy stellar wind through high-resolution spectroscopy. We find the following: (a) Emission-line brightness from K-shell transitions, corresponding to near-neutral species, directly correlates with continuum illumination. However, these lines do not greatly diminish during eclipse. This is readily explained if fluorescence K α emission comes from the bulk of the wind. (b) The highly ionized Fe xxv and Fe xxvi Ly α diminish during eclipse. Thus, they must be produced in the vicinity of the compact object where log ξ > 3. (c) To describe the emission-line spectrum, the sum of two self-consistent photoionization models with low ionization (log ξ ∼ −1) and high ionization (log ξ ∼ 2.4) is required. From their emission measures, the clump-to-interclump density ratio can be estimated to be nc/ni ∼ 300. To fit the complex He-like Si xiii profile, the plasma requires a broadening with vbulk ∼ 840 km s−1. Reproducing the observed r ≈ f line fluxes requires the addition of a third collisionally ionized plasma. (d) Emission-line widths appear unresolved at the HETG resolution with the exception of silicon. There is no clear radial segregation between (quasi-)neutral and ionized species, consistent with cold wind clumps interspersed in a hot rarefied interclump medium. ; This research has been funded under the project ESP2017-85691-P. The research leading to these results has received funding from the European Union's Horizon 2020 Programme under the Activities for the High-Energy Astrophysiscs Domain (AHEAD) project (grant agreement no. 654215). Victoria Grinberg (VG) was supported through the Margarete von Wrangell fellowship by the ESF and the Ministry of Science, Research and the Arts of Baden-Württemberg. Work at LLNL was performed under the auspices of the U.S. Department of Energy under contract no. DE-AC52-07NA27344 and supported through National Aeronautics and Space Administration (NASA) grants to Lawrence Livermore National Laboratory (LLNL). Lida M. Oskinova acknowledges Deutsches Zentrum für Luft und Raumfahrt (DLR) grant FKZ 50 OR 1508 and partial support by the Russian Government Program of Competitive Growth of Kazan Federal University.

Context. High-mass X-ray binaries (HMXBs) are exceptional astrophysical laboratories that offer a rare glimpse into the physical processes that govern accretion on compact objects, massive-star winds, and stellar evolution. In a subset of the HMXBs, the compact objects accrete matter solely from winds of massive donor stars. These so-called wind-fed HMXBs are divided in persistent (classical) HMXBs and supergiant fast X-ray transients (SFXTs) according to their X-ray properties. While it has been suggested that this dichotomy depends on the characteristics of stellar winds, they have been poorly studied. Aims. With this investigation, we aim to remedy this situation by systematically analyzing donor stars of wind-fed HMXBs that are observable in the UV, concentrating on those with neutron star (NS) companions. Methods. We obtained Swift X-ray data, HST UV spectra, and additional optical spectra for all our targets. The spectral analysis of our program stars was carried out with the Potsdam Wolf–Rayet model atmosphere code. Results. Our multi-wavelength approach allows us to provide stellar and wind parameters for six donor stars (four wind-fed systems and two OBe X-ray binaries). The wind properties are in line with the predictions of the line-driven wind theory. Based on the abundances, three of the donor stars are in an advanced evolutionary stage, while for some of the stars, the abundance pattern indicates that processed material might have been accreted. When passing by the NS in its tight orbit, the donor star wind has not yet reached its terminal velocity but it is still significantly slower; its speed is comparable with the orbital velocity of the NS companion. There are no systematic differences between the two types of wind-fed HMXBs (persistent versus transients) with respect to the donor stars. For the SFXTs in our sample, the orbital eccentricity is decisive for their transient X-ray nature. The dichotomy of wind-fed HMXBs studied in this work is primarily a result of the orbital configuration, while in general it is likely that it reflects a complex interplay between the donor-star parameters, the orbital configuration, and the NS properties. Based on the orbital parameters and the further evolution of the donor stars, the investigated HMXBs will presumably form Thorne–Żytkow objects in the future. ; The first author of this work (R.H.) is supported by the Deutsche Forschungsgemeinschaft (DFG) under grant HA 1455/28-1. L.M.O. acknowledges support from the Verbundforschung grant 50 OR 1809. J.M.T. acknowledges the research grant ESP2017-85691-P. A.A.C.S. is supported by the Deutsche Forschungsgemeinschaft (DFG) under grant HA 1455/26. F.F., K.S., and A.B. are grateful for support from STScI Grant HST-GO-13703.002-A. T.S. acknowledges support from the European Research Council (ERC) under the European Union's DLV-772225-MULTIPLES Horizon 2020 research and innovation programme.

Among the different types of massive stars in advanced evolutionary stages is the enigmatic WN8h type. There are only a few Wolf–Rayet (WR) stars with this spectral type in our Galaxy. It has long been suggested that WN8h-type stars are the products of binary evolution that may harbor neutron stars (NS). One of the most intriguing WN8h stars is the runaway WR 124 surrounded by its magnificent nebula M1-67. We test the presence of an accreting NS companion in WR 124 using ~100 ks long observations by the Chandra X-ray observatory. The hard X-ray emission from WR 124 with a luminosity of L X ~ 1031 erg s−1 is marginally detected. We use the non-local thermodynamic equilibrium stellar atmosphere code PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star is effectively opaque for X-rays, hence the low X-ray luminosity of WR 124 does not rule out the presence of an embedded compact object. We suggest that, in general, high-opacity WR winds could prevent X-ray detections of embedded NS, and be an explanation for the apparent lack of WR+NS systems. ; Support for this Letter was provided by the National Aeronautics and Space Administration through Chandra award No. G07-18014X issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the NASA contract NAS8-03060. J.A.T., M.A.G., and H.T. are funded by UNAM DGAPA PAPIIT project IA100318. L.M.O. acknowledges support by the DLR grant 50 OR 1508 and partial support by the Russian Government Program of Competitive Growth of Kazan Federal University. A.A.C.S. is supported by the Deutsche Forschungsgemeinschaft (DFG) under grant HA 1455/26 and would like to thank STFC for funding under grant No. ST/R000565/1. Y.-H.C. acknowledges support from the Ministry of Science and Technology of Taiwan. T.S. acknowledges support from the German Verbundforschung (DLR) grant 50 OR 1612. J.M.T. acknowledges support from ESP2017-85691-P.

High mass X-ray binaries are among the brightest X-ray sources in the Milky Way, as well as in nearby Galaxies. Thanks to their highly variable emissions and complex phenomenology, they have attracted the interest of the high energy astrophysical community since the dawn of X-ray Astronomy. In more recent years, they have challenged our comprehension of physical processes in many more energy bands, ranging from the infrared to very high energies. In this review, we provide a broad but concise summary of the physical processes dominating the emission from high mass X-ray binaries across virtually the whole electromagnetic spectrum. These comprise the interaction of stellar winds with the high gravitational and magnetic fields of compact objects, the behaviour of matter under extreme magnetic and gravity conditions, and the perturbation of the massive star evolutionary processes by presence in a binary system. We highlight the role of the INTEGRAL mission in the discovery of many of the most interesting objects in the high mass X-ray binary class and its contribution in reviving the interest for these sources over the past two decades. We show how the INTEGRAL discoveries have not only contributed to significantly increase the number of high mass X-ray binaries known, thus advancing our understanding of the population as a whole, but also have opened new windows of investigation that stimulated the multi-wavelength approach nowadays common in most astrophysical research fields. We conclude the review by providing an overview of future facilities being planned from the X-ray to the very high energy domain that will hopefully help us in finding an answer to the many questions left open after more than 18 years of INTEGRAL scientific observations. ; The INTEGRALteams in the participating countries acknowledge the continuous support from their space agencies and funding organizations: the Italian Space Agency ASI (via different agreements including the latest one, 2019-35HH, and the ASIINAF agreement 2017-14-H.0), the French Centre national d'études spatiales (CNES), the Russian Foundation for Basic Research (KP, 19-02-00790), the Russian Science Foundation (ST, VD, AL; 19-12-00423), the Spanish State Research Agency (via different grants including ESP2017-85691-P, ESP2017-87676-C5-1-R and Unidad de Excelencia María de Maeztu – CAB MDM-2017-0737). IN is partially supported by the Spanish Government under grant PGC2018-093741-B-C21/C22 (MICIU/AEI/FEDER, UE). LD acknowledges grant 50 OG 1902.