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Register a new userIntrinsic physical properties and Doppler boosting effects in LSI+61303
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Our aim is to show how variable Doppler boosting of an intrinsically variable jet can explain the long-term modulation of 1667 pm 8 days observed in the radio emission of LSI+61303. The physical scenario is that of a conical, magnetized plasma jet having a periodical (P1) increase of relativistic particles, Nrel, at a specific orbital phase, as predicted by accretion in the eccentric orbit of LSI+61303. Jet precession (P2) changes the angle, eta, between jet axis and line of sight, thereby inducing variable Doppler boosting. The problem is defined in spherical geometry, and the optical depth through the precessing jet is calculated by taking into account that the plasma is stratified along the jet axis. The synchrotron emission of such a jet was calculated and we fitted the resulting flux density Smodel(t) to the observed flux density obtained during a 6.5-year monitoring of LSI+61303 by the Green Bank radio interferometer. Our physical model for the system LSI+61303 is not only able to reproduce the long-term modulation in the radio emission, but it also reproduces all the other observed characteristics of the radio source, the orbital modulation of the outbursts, their orbital phase shift, and their spectral index properties. Moreover, a correspondence seems to exist between variations in the ejection angle induced by precession and the rapid rotation in position angle observed in VLBA images. We conclude that the peak of the long-term modulation occurs when the jet electron density is around its maximum and the approaching jet is forming the smallest possible angle with the line of sight. This coincidence of maximum number of emitting particles and maximum Doppler boosting of their emission occurs every 1667 days and creates the long-term modulation observed in LSI+61303.
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The stellar binary system LS I +61303, composed of a compact object in an eccentric orbit around a B0 Ve star, emits from radio up to gamma-ray energies. The orbital modulation of radio spectral index, X-ray, and GeV gamma-ray data suggests the presence of two peaks. This two-peaked profile is in line with the accretion theory predicting two accretion-ejection events for LS I +61303 along the 26.5 d orbit. However, the existing multiwavelength data are not simultaneous. In this paper, we report the results of a campaign covering radio, X-ray, and gamma-ray observations of the system along one single orbit. Our results confirm the two predicted events along the orbit and in addition show that the positions of radio and gamma-ray peaks are coincident with X-ray dips as expected for radio and gamma-ray emitting ejections depleting the X-ray emitting accretion flow. We discuss future observing strategies for a systematic study of the accretion-ejection physical processes in LS I +61303.
We present Very Long Baseline Interferometry (VLBI) observations of the high mass X-ray binary LSI+61303, carried out with the European VLBI Network (EVN). Over the 11 hour observing run, performed 10 days after a radio outburst, the radio source showed a constant flux density, which allowed sensitive imaging of the emission distribution. The structure in the map shows a clear extension to the southeast. Comparing our data with previous VLBI observations we interpret the extension as a collimated radio jet as found in several other X-ray binaries. Assuming that the structure is the result of an expansion that started at the onset of the outburst, we derive an apparent expansion velocity of 0.003 c, which, in the context of Doppler boosting, corresponds to an intrinsic velocity of at least 0.4 c for an ejection close to the line of sight. From the apparent velocity in all available epochs we are able to establish variations in the ejection angle which imply a precessing accretion disk. Finally we point out that LSI+61303, like SS433 and Cygnus X-1, shows evidence for an emission region almost orthogonal to the relativistic jet.
Among the initial results from Kepler were two striking lightcurves, for KOI 74 and KOI 81, in which the relative depths of the primary and secondary eclipses showed that the more compact, less luminous object was hotter than its stellar host. That result became particularly intriguing because a substellar mass had been derived for the secondary in KOI 74, which would make the high temperature challenging to explain; in KOI 81, the mass range for the companion was also reported to be consistent with a substellar object. We re-analyze the Kepler data and demonstrate that both companions are likely to be white dwarfs. We also find that the photometric data for KOI 74 show a modulation in brightness as the more luminous star orbits, due to Doppler boosting. The magnitude of the effect is sufficiently large that we can use it to infer a radial velocity amplitude accurate to 1 km/s. As far as we are aware, this is the first time a radial-velocity curve has been measured photometrically. Combining our velocity amplitude with the inclination and primary mass derived from the eclipses and primary spectral type, we infer a secondary mass of 0.22+/-0.03 Msun. We use our estimates to consider the likely evolutionary paths and mass-transfer episodes of these binary systems.
In this first paper from forthcoming series of works devoted to radio image of relativistic jets from active galactic nuclei the role of internal structure of a flow is discussed. We determine the radial profiles of all physical values for reasonable Michel magnetization parameter $sigma_{rm M}$ and ambient pressure $P_{rm ext}$. Maps of Doppler boosting factor $delta$ and observed directions of linear polarization of synchrotron emission are also constructed.
We present new optical and infrared photometric observations and high resolution H$alpha$ spectra of the periodic radio star lsi. The optical photometric data set covers the time interval 1985-1993 and amounts to about a hundred nights. A period of $sim$26 days is found in the V band. The infrared data also present evidence for a similar periodicity, but with higher amplitude of variation (0rmag 2). The spectroscopic observations include 16 intermediate and high dispersion spectra of lsi collected between January 1989 and February 1993. The H$alpha$ emission line profile and its variations are analyzed. Several emission line parameters -- among them the H$alpha$ EW and the width of the H$alpha$ red hump -- change strongly at or close to radio maximum, and may exhibit periodic variability. We also observe a significant change in the peak separation. The H$alpha$ profile of lsi does not seem peculiar for a Be star. However, several of the observed variations of the H$alpha$ profile can probably be associated with the presence of the compact, secondary star.
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