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Title: The clumpy absorber in the high-mass X-ray binary Vela X-1

Abstract

Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase ~0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannot be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. Finally, these features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.

Authors:
ORCiD logo [1];  [2];  [3];  [4];  [5];  [6];  [7];  [8];  [7];  [9];  [10];  [11];  [6];  [8];  [9];  [8]
  1. ESA European Space Research and Technology Centre (ESTEC), Noordwijk (Netherlands)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Catholic Univ. of Leuven (KU Leuven) (Belgium). Centre for Mathematical Plasma Astrophysics. Dept. of Mathematics
  4. Villanova Univ., PA (United States). Dept. of Physics
  5. Univ. of Potsdam (Germany). Inst. of Physics and Astronomy
  6. Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States). Dept. of Physics. Center for Research and Exploration in Space Science & Technology (CRESST); NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  7. ESA European Space Astronomy Centre (ESAC), Madrid (Spain). Science Operations Dept.
  8. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Kavli Inst. for Astrophysics and Space Research
  9. Univ. of Erlangen-Nuremberg, Bamberg (Germany). Dr. Karl Remeis-Sternwarte. Erlangen Centre for Astroparticle Physics (ECAP)
  10. CSIC Univ. of Cantabria, Santander (Spain). Inst. of Physics of Cantabria
  11. Univ. of Erlangen-Nuremberg, Bamberg (Germany). Dr. Karl Remeis-Sternwarte. Erlangen Centre for Astroparticle Physics (ECAP); Chinese Academy of Sciences (CAS), Shanghai (China). Shanghai Astronomical Observatory
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States); NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); ESA European Space Research and Technology Centre (ESTEC), Noordwijk (Netherlands); Catholic Univ. of Leuven (KU Leuven) (Belgium); Univ. of Erlangen-Nuremberg, Bamberg (Germany)
Sponsoring Org.:
USDOE; National Aeronautic and Space Administration (NASA); European Union (EU); Research Foundation Flanders (FWO) (Belgium); German Research Foundation (DFG)
OSTI Identifier:
1438665
Report Number(s):
LLNL-JRNL-737837
Journal ID: ISSN 0004-6361; TRN: US1900479
Grant/Contract Number:  
AC52-07NA27344; SV3-73016; NAS8-03060; HST-HF2-51343.001-A; 665501; HA 1455/26
Resource Type:
Accepted Manuscript
Journal Name:
Astronomy and Astrophysics
Additional Journal Information:
Journal Volume: 608; Journal ID: ISSN 0004-6361
Publisher:
EDP Sciences
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; x-rays; Vela X-1; binary x-rays; stars; winds; outflows; massive stars

Citation Formats

Grinberg, V., Hell, N., El Mellah, I., Neilsen, J., Sander, A. A. C., Leutenegger, M., Furst, F., Huenemoerder, D. P., Kretschmar, P., Kuhnel, M., Martinez-Nunez, S., Niu, S., Pottschmidt, K., Schulz, N. S., Wilms, J., and Nowak, M. A. The clumpy absorber in the high-mass X-ray binary Vela X-1. United States: N. p., 2017. Web. doi:10.1051/0004-6361/201731843.
Grinberg, V., Hell, N., El Mellah, I., Neilsen, J., Sander, A. A. C., Leutenegger, M., Furst, F., Huenemoerder, D. P., Kretschmar, P., Kuhnel, M., Martinez-Nunez, S., Niu, S., Pottschmidt, K., Schulz, N. S., Wilms, J., & Nowak, M. A. The clumpy absorber in the high-mass X-ray binary Vela X-1. United States. doi:10.1051/0004-6361/201731843.
Grinberg, V., Hell, N., El Mellah, I., Neilsen, J., Sander, A. A. C., Leutenegger, M., Furst, F., Huenemoerder, D. P., Kretschmar, P., Kuhnel, M., Martinez-Nunez, S., Niu, S., Pottschmidt, K., Schulz, N. S., Wilms, J., and Nowak, M. A. Fri . "The clumpy absorber in the high-mass X-ray binary Vela X-1". United States. doi:10.1051/0004-6361/201731843. https://www.osti.gov/servlets/purl/1438665.
@article{osti_1438665,
title = {The clumpy absorber in the high-mass X-ray binary Vela X-1},
author = {Grinberg, V. and Hell, N. and El Mellah, I. and Neilsen, J. and Sander, A. A. C. and Leutenegger, M. and Furst, F. and Huenemoerder, D. P. and Kretschmar, P. and Kuhnel, M. and Martinez-Nunez, S. and Niu, S. and Pottschmidt, K. and Schulz, N. S. and Wilms, J. and Nowak, M. A.},
abstractNote = {Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase ~0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannot be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. Finally, these features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.},
doi = {10.1051/0004-6361/201731843},
journal = {Astronomy and Astrophysics},
number = ,
volume = 608,
place = {United States},
year = {2017},
month = {12}
}

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Figures / Tables:

Fig. 1 Fig. 1: To-scale sketch of the Vela X-1 system. HD 77581 is shown in blue and the orbit of the neutron star is represented by the black ellipse. Orbital phases are marked and labeled; phases covered in the present work are shown in red. We emphasize that the orbital phasesmore » are equidistant in time for the present orbital shape. We assume i = 73°, that is, lower limit for inclination according to Joss & Rappaport (1984), and the distances are thus lower limits. The background shows an indicative image of the variable large-scale structures that are formed through the interactions of the neutron star with the stellar wind of the mass donor. This image is an artistic impression based on simulations published in Manousakis (2011). The observer is towards minus infinity along the y-axis.« less

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