The γ‐ray binary LS 5039: mass and orbit constraints from MOST observations

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 09/2010; 411(2). DOI: 10.1111/j.1365-2966.2010.17757.x
Source: arXiv

ABSTRACT The results of a coordinated space-based photometric and ground-based spectroscopic observing campaign on the enigmatic gamma-ray binary LS 5039 are reported. Sixteen days of observations from the MOST satellite have been combined with high-resolution optical echelle spectroscopy from the 2.3m ANU Telescope in Siding Spring, Australia. These observations were used to measure the orbital parameters of the binary and to study the properties of stellar wind from the O primary. We found that any broad-band optical photometric variability at the orbital period is below the 2 mmag level, supporting the scenario that the orbital eccentricity of the system is near the 0.24 +/- 0.08 value implied by our spectroscopy, which is lower than values previously obtained by other workers. The low amplitude optical variability also implies the component masses are at the higher end of estimates based on the primary's O6.5V((f)) spectral type with a primary mass of ~26 solar masses and a mass for the compact star of at least 1.8 solar masses. The mass loss rate from the O primary was determined to be 3.7E-7 to 4.8E-7 solar masses per year. Comment: Accepted for MNRAS 2010 September 22

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Available from: Werner W. Weiss, Sep 26, 2015
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    ABSTRACT: LS 5039 is a high-mass binary with a period of 4 days, containing a compact object and an O star, one of the few high-mass binaries detected in gamma-rays. Our Chandra ACIS observation of LS 5039 provided a high-significance (~10sigma) detection of extended emission clearly visible for up to 1' from the point source. The spectrum of this emission can be described by an absorbed power-law model with photon index Gamma=1.9pm0.3, somewhat softer than the point source spectrum Gamma=1.44pm0.07, with the same absorption, N_H=(6.4pm0.6)e21 /cm2. The observed 0.5-8 keV flux of the extended emission is 8.8e-14 erg/s/cm2, or 5% of the point source flux; the latter is a factor of ~2 lower than the lowest flux detected so far. Fainter extended emission with comparable flux and a softer (Gamma~3) spectrum is detected at even greater radii (up to 2'). Two possible interpretations of the extended emission are a dust scattering halo and a synchrotron nebula powered by energetic particles escaping the binary. We discuss both of these scenarios and favor the nebula interpretation, although some dust contribution is possible. We have also found transient sources located within a narrow stripe south of LS 5039. We discuss the likelihood of these sources to be related to LS 5039.
    The Astrophysical Journal 03/2011; 735(1). DOI:10.1088/0004-637X/735/1/58 · 5.99 Impact Factor
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    ABSTRACT: Gamma-ray binaries are systems that comprise a young, massive star and a compact object that can be either a young pulsar or a black hole. They emit radiation from radio up to tens of TeV and show flux variability along the whole electromagnetic spectrum. For three of the four detected gamma-ray binaries, the nature of the compact object is unknown. In this thesis we present a study of gamma-ray binaries through three approaches that involve the simultaneous study of these sources in X-rays and very high energy (VHE) gamma-rays. We present the discovery of correlated X-ray and VHE gamma-ray emission from LS I +61 303. The correlation indicates that the emission from these two bands could be originated in the same parent particle population, and we explore this idea through the calculation of a radiative model. This model allows us to significantly constrain the physical properties of the non-thermal emitter in LS I +61 303. For those systems where the compact object is a young pulsar, the interaction between the stellar and pulsar winds will give rise to strong shocks. The shocked pulsar wind is the candidate location for non-thermal emission from these systems. The shocked stellar wind should give rise to a thermal X-ray spectrum, but no such features have been detected in the X-ray spectrum of gamma-ray binaries. We present a model of the thermal emission of the shocked stellar wind and use it to constrain the pulsar properties. We have applied this method to two X-ray observations of LS 5039 and have successfully constrained the pulsar spin-down luminosity. Finally, we present a search for VHE emission from Scorpius X-1 through a simultaneous X-ray and VHE gamma-ray campaign. The X-ray observations allowed us to select black-hole states where non-thermal X-ray emission has been detected. We did not find significant VHE emission in any of the black hole states, but the upper limits derived will prove useful in future modelling of the non-thermal emitter in the source.
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    ABSTRACT: Several binary systems that contain a massive star have been detected in both the radio band and at very high energies. In the dense stellar photon field of these sources, gamma-ray absorption and pair creation are expected to occur, and the radiation from these pairs may contribute significantly to the observed radio emission. We aim at going deeper in the study of the properties, and in particular the morphology, of the pair radio emission in gamma-ray binaries. We apply a Monte-Carlo code that computes the creation location, the spatial trajectory and the energy evolution of the pairs produced in the binary system and its surroundings. The radio emission produced by these pairs, with its spectral, variability and spatial characteristics, is calculated as it would be seen from a certain direction. A generic case is studied first, and then the specific case of LS 5039 is also considered. We find that, confirming previous results, the secondary radio emission should appear as an extended radio structure of a few milliarcseconds size. This radiation would be relatively hard, with fluxes up to ~ 10 mJy. Modulation is expected depending on the gamma-ray production luminosity, system eccentricity, and wind ionization fraction, and to a lesser extent on the magnetic field structure. In gamma-ray binaries in general, the pairs created due to photon-photon interactions can contribute significantly to the core, and generate an extended structure. In the case of LS 5039, the secondary radio emission is likely to be a significant fraction of the detected core flux, with a marginal extension.
    Publications- Astronomical Society of Japan 05/2011; 63(5). DOI:10.1093/pasj/63.5.1023 · 2.07 Impact Factor
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