Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039
A few high-mass X-ray binaries–consisting of an OB star plus compact companion– have been observed by Fermi and ground-based Cerenkov telescopes like High Energy Stereoscopic System (HESS) to be sources of very high energy (VHE; up to 30 TeV) γ-rays. This paper focuses on the prominent γ-ray sour...
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| Format: | Article |
| Language: | English |
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The Korean Space Science Society
2012-03-01
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| Series: | Journal of Astronomy and Space Sciences |
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| Online Access: | http://ocean.kisti.re.kr/downfile/volume/kosss/OJOOBS/2012/v29n1/OJOOBS_2012_v29n1_51.pdf |
| _version_ | 1797331645838131200 |
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| author | Stan Owocki Atsuo Okazaki Gustavo Romero |
| author_facet | Stan Owocki Atsuo Okazaki Gustavo Romero |
| author_sort | Stan Owocki |
| collection | DOAJ |
| description | A few high-mass X-ray binaries–consisting of an OB star plus compact companion–
have been observed by Fermi and
ground-based Cerenkov telescopes like High Energy Stereoscopic System (HESS) to be sources of very high energy (VHE;
up to 30 TeV) γ-rays. This paper focuses on the prominent γ-ray source, LS 5039, which consists of a massive O6.5V star
in a 3.9-day-period, mildly elliptical (e ≈ 0.24) orbit with its companion, assumed here to be an unmagnetized compact
object (e.g., black hole). Using three dimensional smoothed particle hydrodynamics simulations of the Bondi-Hoyle accretion
of the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very
closely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model,
wherein intrinsic emission of γ-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of
the phase variation of γ-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the
HESS Cerenkov telescope,
it is important to account also for photon-photon interactions between the γ-rays and the stellar
optical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included,
we find that this simple BHL accretion model also quite naturally
fits the HESS light curve, thus making it a strong alternative
to the pulsar-wind-shock models commonly invoked to explain such VHE γ-ray emission in massive-star binaries. |
| first_indexed | 2024-03-08T07:37:31Z |
| format | Article |
| id | doaj.art-cdbe436457ca4cf4a4eae5b1881a33b1 |
| institution | Directory Open Access Journal |
| issn | 2093-5587 2093-1409 |
| language | English |
| last_indexed | 2024-03-08T07:37:31Z |
| publishDate | 2012-03-01 |
| publisher | The Korean Space Science Society |
| record_format | Article |
| series | Journal of Astronomy and Space Sciences |
| spelling | doaj.art-cdbe436457ca4cf4a4eae5b1881a33b12024-02-02T18:25:44ZengThe Korean Space Science SocietyJournal of Astronomy and Space Sciences2093-55872093-14092012-03-01291515510.5140/JASS.2012.29.1.051Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039Stan Owocki0Atsuo Okazaki1Gustavo Romero2Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USAFaculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062-8605, JapanFacultad de Ciencias Astronomicas y Geofısicas, Universidad Nacional de La Plata, Paseo del Bosque, 1900 La Plata, ArgentinaA few high-mass X-ray binaries–consisting of an OB star plus compact companion– have been observed by Fermi and ground-based Cerenkov telescopes like High Energy Stereoscopic System (HESS) to be sources of very high energy (VHE; up to 30 TeV) γ-rays. This paper focuses on the prominent γ-ray source, LS 5039, which consists of a massive O6.5V star in a 3.9-day-period, mildly elliptical (e ≈ 0.24) orbit with its companion, assumed here to be an unmagnetized compact object (e.g., black hole). Using three dimensional smoothed particle hydrodynamics simulations of the Bondi-Hoyle accretion of the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very closely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model, wherein intrinsic emission of γ-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of the phase variation of γ-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the HESS Cerenkov telescope, it is important to account also for photon-photon interactions between the γ-rays and the stellar optical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included, we find that this simple BHL accretion model also quite naturally fits the HESS light curve, thus making it a strong alternative to the pulsar-wind-shock models commonly invoked to explain such VHE γ-ray emission in massive-star binaries.http://ocean.kisti.re.kr/downfile/volume/kosss/OJOOBS/2012/v29n1/OJOOBS_2012_v29n1_51.pdfX-rays: binariesgamma-rays: starshydrodynamics |
| spellingShingle | Stan Owocki Atsuo Okazaki Gustavo Romero Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039 Journal of Astronomy and Space Sciences X-rays: binaries gamma-rays: stars hydrodynamics |
| title | Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039 |
| title_full | Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039 |
| title_fullStr | Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039 |
| title_full_unstemmed | Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039 |
| title_short | Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039 |
| title_sort | modeling gamma ray emission from the high mass x ray binary ls 5039 |
| topic | X-rays: binaries gamma-rays: stars hydrodynamics |
| url | http://ocean.kisti.re.kr/downfile/volume/kosss/OJOOBS/2012/v29n1/OJOOBS_2012_v29n1_51.pdf |
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