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Register a new userExploring the powering source of the TeV X-ray binary LS 5039
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J. Moldon
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LS 5039 is one of the four TeV emitting X-ray binaries detected up to now. The powering source of its multi-wavelength emission can be accretion in a microquasar scenario or wind interaction in a young non-accreting pulsar scenario. These two scenarios predict different morphologic and peak position changes along the orbital cycle of 3.9 days, which can be tested at milliarcsecond scales using VLBI techniques. Here we present a campaign of 5 GHz VLBA observations conducted in June 2000 (2 runs five days apart). The results show a core component with a constant flux density, and a fast change in the morphology and the position angle of the elongated extended emission, but maintaining a stable flux density. These results are difficult to fit comfortably within a microquasar scenario, whereas they appear to be compatible with the predicted behavior for a non-accreting pulsar.
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LS 5039 is one of the four TeV emitting X-ray binaries detected up to now. The powering source of its multi-wavelength emission can be accretion in a microquasar scenario or wind interaction in a young non-accreting pulsar scenario. These two scenarios predict different morphologic and peak position changes along the orbital cycle of 3.9 days, which can be tested at milliarcsecond scales using VLBI techniques. Here we present a campaign of 5 GHz VLBA observations conducted in June 2000 (2 runs five days apart). The results show a core component with a constant flux density, and a fast change in the morphology and the position angle of the elongated extended emission, but maintaining a stable flux density. These results are difficult to fit comfortably within a microquasar scenario, whereas they appear to be compatible with the predicted behavior for a non-accreting pulsar.
We study mechanisms of multi-wavelength emissions (X-ray, GeV and TeV gamma-rays) from the gamma-ray binary LS~5039. This paper is composed of two parts. In the first part, we report on results of observational analysis using four year data of fermi Large Area Telescope. Due to the improvement of instrumental response function and increase of the statistics, the observational uncertainties of the spectrum in $sim$100-300 MeV bands and $>10$GeV bands are significantly improved. The present data analysis suggests that the 0.1-100GeV emissions from LS~5039 contain three different components; (i) the first component contributes to $<$1GeV emissions around superior conjunction, (ii) the second component dominates in 1-10GeV energy bands and (iii) the third component is compatible to lower energy tail of the TeV emissions. In the second part, we develop an emission model to explain the properties of the phase-resolved emissions in multi-wavelength observations. Assuming that LS~5039 includes a pulsar, we argue that both emissions from magnetospheric outer gap and inverse-Compton scattering process of cold-relativistic pulsar wind contribute to the observed GeV emissions. We assume that the pulsar is wrapped by two kinds of termination shock; Shock-I due to the interaction between the pulsar wind and the stellar wind and Shock-II due to the effect of the orbital motion. We propose that the X-rays are produced by the synchrotron radiation at Shock-I region and the TeV gamma-rays are produced by the inverse-Compton scattering process at Shock-II region.
We report on long-term stability of X-ray modulation apparently synchronized with an orbital period of 3.9 days in the gamma-ray binary LS 5039. Recent observations with the Suzaku satellite in the year 2007, which covered continuously more than one orbital period, have provided us with detailed characterization of X-ray flux and spectral shape as a function of orbital phase. Motivated by the results from Suzaku, we have re-analyzed the X-ray data obtained with ASCA, XMM-Newton, and Chandra between 1999 and 2005, to investigate long-term behavior of LS 5039 in the X-ray band. We found that the modulation curves in 1999--2007 are surprisingly stable. Even fine structures in the light curves such as spikes and dips are found to be quite similar from one orbit to another. The spectral characteristics observed in the past are consistent with those seen with Suzaku for some orbital phase segments. We suggest that magneto-hydrodynamical collisions between the relativistic outflow from a compact object and the stellar wind from the O star explain the clock-like non-thermal X-ray emission over eight years through remarkably stable production of high-energy particles near the binary system.
LS 5039 is a gamma-ray binary system observed in a broad energy range, from radio to TeV energies. The binary system exhibits both flux and spectral modulation as a function of its orbital period. The X-ray and very-high-energy (VHE, E > 100 GeV) gamma-ray fluxes display a maximum/minimum at inferior/superior conjunction, with spectra becoming respectively harder/softer, a behaviour that is completely reversed in the high-energy domain (HE, 0.1 < E < 100 GeV). The HE spectrum cuts off at a few GeV, with a new hard component emerging at E > 10 GeV that is compatible with the low-energy tail of the TeV emission. The low 10 - 100 GeV flux, however, makes the HE and VHE components difficult to reconcile with a scenario including emission from only a single particle population. We report on new observations of LS 5039 conducted with the High Energy Stereoscopic System (H.E.S.S.) telescopes from 2006 to 2015. This new data set enables for an unprecedentedly-deep phase-folded coverage of the source at TeV energies, as well as an extension of the VHE spectral range down to ~120 GeV, which makes LS 5039 the first gamma-ray binary system in which a spectral overlap between satellite and ground-based gamma-ray observatories is obtained.
Gamma-ray binaries allow us to study physical processes such as particle acceleration up to TeV energies and VHE gamma-ray emission and absorption with changing geometrical configurations on a periodic basis. These sources produce outflows of radio-emitting particles whose structure can be imaged with VLBI. LS 5039 is a gamma-ray binary that has shown variable VLBI structures in the past. We aim to characterise the radio morphological changes of LS 5039 and discriminate if they are either repeatable or erratic. We observed LS 5039 with the VLBA at 5 GHz during five consecutive days to cover the 3.9-day orbit and an extra day to disentangle between orbital or secular variability. We also compiled the available high-resolution radio observations of the source to study its morphological variability at different orbital phases. We used a simple model to interpret the obtained images. The new observations show that the morphology of LS 5039 up to projected distances of 10 milliarcseconds changes in 24 h. The observed radio morphological changes display a periodic orbital modulation. Multifrequency and multiepoch VLBI observations confirm that the morphological periodicity is stable on timescales of years. Using a simple model we show that the observed behaviour is compatible with the presence of a young non-accreting pulsar with an outflow behind it. The morphology is reproduced for inclinations of the orbit of 60-75 deg. For masses of the companion star in the range 20-50 Msun, this range of inclinations implies a mass of the compact object of 1.3-2.7 Msun. The periodic orbital modulation of the radio morphology of LS 5039 suggests that all gamma-ray binaries are expected to show a similar behaviour. The changes in the radio structure of LS 5039 are compatible with the presence of a young non-accreting neutron star, which suggests that the known gamma-ray binaries contain young pulsars.
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