VLBI observations of the X-ray binary LS I +61 deg 303

Taylor, Andrew; Kenny, H. T.; Spencer, R. E.; Tzioumis, A. K.

doi:10.1086/171648

Cited by 60 publications

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“…The compact object interacts with the Be circumstellar disk, thereby sampling a wide range of physical parameters and producing remarkable, periodic flaring events each orbital cycle. Such a strong orbital modulation in the LS I+61 • 303 emission is observed across the whole electromagnetic spectrum, especially in the radio (Taylor et al 1992), optical (Mendelson & Mazeh 1994, X-ray (Paredes et al 1997;Leahy 2001), HE (Abdo et al 2009), and VHE γ-ray (Albert et al 2009) domains. In the optical, the orbital period signature is evident not only in visible broad band photometry, but also in the spectral properties of the Hα emission line (Zamanov et al 1999;Grundstrom et al 2007).…”

Section: Ls I+61mentioning

confidence: 95%

Connection between orbital modulation of Hαand gamma-rays in the Be/X-ray binary LS I+61°303

Zamanov

Martı́

Stoyanov

et al. 2013

A&A

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We studied the average orbital modulation of various parameters (γ-ray flux, Hα emission line, optical V band brightness) of the radioand γ-ray emitting Be/X-ray binary LS I+61 • 303. Using the Spearman rank correlation test, we found highly significant correlations between the orbital variability of the equivalent width of the blue hump of the Hα and Fermi-LAT flux with a Spearman p-value ∼2 × 10 −5 , and the equivalent widths ratio EW B /EW R and Fermi-LAT flux with p-value ∼9 × 10 −5 . We also found a significant anticorrelation between Fermi-LAT flux and V band magnitude with a p-value ∼7 × 10 −4 . All these correlations refer to the average orbital variability, and we conclude that the Hα and γ-ray emission processes in LS I+61 • 303 are connected. The possible physical scenario is briefly discussed.

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Section: Ls I+61mentioning

confidence: 95%

Connection between orbital modulation of Hαand gamma-rays in the Be/X-ray binary LS I+61°303

Zamanov

Martı́

Stoyanov

et al. 2013

A&A

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“…The hypothesis that the compact object in LS I +61 • 303, which accretes material from the Be wind, undergoes a periodical (P 1 ) increase in the accretion rateṀ at a particular orbital phase along an eccentric orbit has been suggested and developed by several authors (Taylor et al 1992;Marti & Paredes 1995;Bosch-Ramon et al 2006;Romero et al 2007). Recently, the presence of P 1 and P 2 have been confirmed as stable features in more recent Fermi-LAT and OVRO monitorings of the GeV gamma-ray emission (Jaron & Massi 2014) and of the radio emission , respectively.…”

Section: Beat Between P 1 and Pmentioning

confidence: 99%

Origin of the long-term modulation of radio emission of LS I +61°303

Massi

Torricelli‐Ciamponi

2016

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Context. One of the most unusual aspects of the X-ray binary LS I +61 • 303 is that at each orbit (P 1 = 26.4960 ± 0.0028 d) one radio outburst occurs whose amplitude is modulated with P long , a long-term period of more than 4 yr. It is still not clear whether the compact object of the system or the companion Be star is responsible for the long-term modulation. Aims. We study here the stability of P long . Such a stability is expected if P long is due to periodic (P 2 ) Doppler boosting of periodic (P 1 ) ejections from the accreting compact object of the system. On the contrary it is not expected if P long is related to variations in the mass loss of the companion Be star. Methods. We built a database of 36.8 yr of radio observations of LS I +61 • 303 covering more than 8 long-term cycles. We performed timing and correlation analysis. We also compared the results of the analyses with the theoretical predictions for a synchrotron emitting precessing (P 2 ) jet periodically (P 1 ) refilled with relativistic electrons.Results. In addition to the two dominant features at P 1 and P 2 , the timing analysis gives a feature at P long = 1628 ± 48 days. The determined value of P long agrees with the beat of the two dominant features, i.e. P beat = 1/(ν 1 − ν 2 ) = 1626 ± 68 d. Lomb-Scargle results of radio data and model data compare very well. The correlation coefficient of the radio data oscillates at multiples of P beat , as does the correlation coefficient of the model data. Conclusions. Cycles in varying Be stars change in length and disappear after 2-3 cycles following the well-studied case of the binary system ζ Tau. On the contrary, in LS I +61 • 303 the long-term period is quite stable and repeats itself over the available 8 cycles. The long-term modulation in LS I +61 • 303 accurately reflects the beat of periodical Doppler boosting (induced by precession) with the periodicity of the ejecta. The peak of the long-term modulation occurs at the coincidence of the maximum number of ejected particles with the maximum Doppler boosting of their emission; this coincidence occurs every 1 ν 1 −ν 2 and creates the long-term modulation observed in LS I +61 • 303.

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“…In an eccentric orbit this different relationship for density and velocity creates two peaks in the accretion rate curve, one at periastron where the density is at its maximum and a second one when the drop in density is compensated by the decrease in velocity towards apastron. Taylor et al (1992) computed the accretion rate curve for different eccentricities and showed that two peaks begin to appear for an eccentricity above 0.4. Whereas the first peak is always toward periastron, the orbital occurrence of the second accretion peak depends on variations of the wind of the Be star.…”

Section: Ls I +61mentioning

confidence: 99%

Feasibility study of Lense-Thirring precession in LS I +61°303

Massi

Zimmermann

2010

A&A

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Context. Very recent analysis of the radio spectral index and high energy observations have shown that the two-peak accretion/ejection microquasar model applies for LS I +61 • 303. Aims. The fast variations of the position angle observed with MERLIN and confirmed by consecutive VLBA images must therefore be explained in the context of the microquasar scenario. Methods.We calculate what could be the precessional period for the accretion disk in LS I +61 • 303 under tidal forces of the Be star (P tidal−forces ) or under the effect of frame dragging produced by the rotation of the compact object (P Lense−Thirring ). Results. P tidal−forces is more than one year. P Lense−Thirring depends on the truncated radius of the accretion disk, R tr . We determined R tr = 300r g for observed QPO at 2 Hz. This value is much above the few r g , where the Bardeen-Petterson effect should align the midplane of the disk. For this truncated radius of the accretion disk P Lense−Thirring for a slow rotator results in a few days. Conclusions. Lense-Thirring precession induced by a slowly rotating compact object could be compatible with the daily variations of the ejecta angle observed in LS I +61 • 303.

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VLBI observations of the X-ray binary LS I +61 deg 303

Cited by 60 publications

References 0 publications

Connection between orbital modulation of Hαand gamma-rays in the Be/X-ray binary LS I+61°303

Connection between orbital modulation of Hαand gamma-rays in the Be/X-ray binary LS I+61°303

Origin of the long-term modulation of radio emission of LS I +61°303

Feasibility study of Lense-Thirring precession in LS I +61°303

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