All Figures

$\begin{figure} \par\includegraphics[width=7cm,clip]{4779f1a}\par\vspace*{2mm} \... ...4779f1b}\par\vspace*{2mm} \includegraphics[width=7cm,clip]{4779f1c}\end{figure}$ Figure 1: Observed spectral energy distributions of LS 5039, LS I+61 $\hbox {$^\circ $ }$ 303 and PSR B1259-63. Fluxes have been transformed to spectral luminosities assuming distances of 2.5 kpc (LS 5039, Casares et al. 2005b), 2.3 kpc (LS I+61 $\hbox {$^\circ $ }$ 303, Gregory et al. 1979) and 1.5 kpc (PSR B1259-63, Johnston et al. 1994). The optical-UV emission peaking at $\sim$ 1 eV in the binaries is the light from the stellar companion (uncorrected for absorption by the interstellar medium). Radio to X-ray flux values in LS 5039 are taken from (in order of increasing frequency) Martí et al. (1998b), Clark et al. (2001),Martocchia et al. (2005); flux values in LS I+61 $\hbox {$^\circ $ }$ 303 are taken from Strickman et al. (1998), Martí & Paredes (1995),Maraschi et al. (1981), Leahy et al. (1997), Greiner & Rau (2001); in PSR B1259-63 from Johnston et al. (2005), Skrutskie et al. (2006), Marraco & Orsatti (1982). The RXTE spectrum of PSR B1259-63 obtained during the 2004 periastron passage was kindly provided by B. Giebels. The upper envelope of radio measurements in LS I+61 $\hbox {$^\circ $ }$ 303 and PSR B1259-63 corresponds to values during radio outbursts. The hard X-ray BATSE points in LS 5039 and LS I+61 $\hbox {$^\circ $ }$ 303 are from Harmon et al. (2004); the OSSE bowtie is from Grove et al. (1995) and the HE $\gamma$ -ray EGRET boxes are from Hartman et al. (1999); EGRET upper limits in PSR B1259-63 are from Tavani et al. (1996). The VHE $\gamma$ -ray HESS measurements are from Aharonian et al. (2005a,b) and the Whipple upper limits for LS I+61 $\hbox {$^\circ $ }$ 303 from Fegan et al. (2005).
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In the text

$\begin{figure} \par\includegraphics[width=6cm,clip]{4779f2} \end{figure}$ Figure 2: Timescales at the standoff point as a function of the electron Lorentz factor $\gamma$ in LS 5039. The radiative timescale $t_{\rm rad}^{-1}=t_{\rm sync}^{-1}+t_{\rm IC}^{-1}$ (solid lines) and the escape timescale $t_{\rm esc}$ (dashed lines) are shown at periastron (black) and apastron (grey). Synchrotron cooling dominates above $\gamma _{\rm S}\approx 2 \times 10^6$ . Inverse Compton cooling dominates below, the transition between Thomson and Klein-Nishina regimes occurring at $\gamma _{\rm KN}\approx 6\times 10^4$ . $R_{\rm s}$ is $2 \times 10^{11}$ cm at periastron (d=0.1 AU) and $4\times 10^{11}$ cm at apastron (d=0.2 AU) (see Table 2).
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{4779f3} \end{figure}$ Figure 3: From left to right: evolution in the pulsar nebula of the flow speed, magnetic field and density as a function of the normalised distance z. The rightmost panel shows the time needed to reach a given distance z in the flow. At $z\approx 800$ ( $d=zR_{\rm s}\approx 10$ AU), the elapsed time is equal to the orbital period (dotted line). The model parameters are $\dot{E}=10^{36}$ erg s^-1, $\gamma =10^5$ , $\sigma =0.01$ and $R_{\rm s}=2\times 10^{11}$ cm, appropriate for LS 5039 at periastron.
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In the text

$\begin{figure} \par\includegraphics[width=9.5cm,clip]{4779f4a}\hspace*{4mm} \includegraphics[width=6.2cm,clip]{4779f4b} \end{figure}$ Figure 4: Left: evolution of the emission along the pulsar nebula. The pulsar nebula is divided into sections at various distances z with the corresponding synchrotron (black) and inverse Compton (grey) spectra shown. The first section shown is for z=1 (dz=0.01). The section dz is then increased: the fifth spectrum is at $z\approx 1.5$ , the tenth at $z\approx 15$ , the last spectrum shown is at $z\approx 1000$ . The total spectrum of the pulsar nebula is shown as a thick black line. The model parameters are the same as in Fig. 3. The thermal emission at $\sim$ 1 eV is direct light from the stellar companion. Right: evolution of the particle distribution as the shocked pulsar wind moves out from the system. The sections are the same as those shown in the SED. The initial $\gamma ^{-2}$ power law cools rapidly at high energies due to synchrotron radiation. Adiabatic losses dominate at large distances.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{4779f5} \end{figure}$ Figure 5: Large-scale appearance of the pulsar nebula around LS 5039 at periastron. In practice, limited angular resolution smoothes out the emission from what is shown here (see Fig. 7). The binary is located at the origin. Its size of a few tenths of AU is much smaller than the scale of the map. Material originating from the standoff point travels outwards following the direction of the comet tail at each orbital phase (shown by grey lines; the projected outflow path at apastron is indicated by a dark line). Because of the orbital motion, the emission winds up into a spiral. To illustrate this, dots are plotted at the locations reached by material expelled at regular time intervals along the orbit. The total elapsed timescale represented corresponds to almost an orbital period and a half. The greyscale codes the intensity of the 5 GHz radio emission (square root scale). At large distances, the step of the spiral tends to $\sigma c P_{\rm orb}$ which is $\approx$ 7 AU for the adopted parameters (same as those of Figs. 3, 4). The inclination ( $i=120\hbox {$^\circ $ }$ , corresponding to a retrograde pulsar orbit, see Sect. 6.1.2), and the major axis orientation ( $\omega =226\hbox {$^\circ $ }$ ) used here are consistent with the measurements of the companion star's radial velocity (see orbit schematic in Fig. 6 of Casares et al. 2005b).
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{4779f6} \end{figure}$ Figure 6: Spectral energy distribution of LS 5039 at periastron (dark full line) and apastron (dark dashed line). The corresponding grey lines show the fraction received by the observer after absorption of the VHE $\gamma$ -rays on stellar photons. Parameters are identical to those of Figs. 3, 4 (but using $R_{\rm s}=4\times 10^{11}$ cm at apastron). Changes in the overall SED are limited and only minor variability is expected except at VHE energies where $\gamma \gamma$ absorption strongly modulates the flux on the orbital period.
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In the text

$\begin{figure} \par\includegraphics[width=3.4cm,clip]{4779f7a}\hspace*{4mm} \inc... ...]{4779f7c}\hspace*{4mm} \includegraphics[width=3.4cm,clip]{4779f7d} \end{figure}$ Figure 7: Orbital evolution of the 5 GHz radio emission from the pulsar nebula in LS 5039. The maps were composed by summing up the contributions along the spiral nebula, as calculated for the various orbital phases $\phi$ (see Fig. 5 for the $\phi =0$ case). The maps were then smoothed by a Gaussian kernel with a full-width at half maximum (FWHM) of 0.8 mas ( $3\times 10^{13}$ cm at 2.5 kpc). The maps share a common color scale to allow direct comparison, with contours at 50%, 25%, and 10% of the maximum orbital radio emission. The maps at $\phi =0{-}0.25$ are very similar to the one observed by Paredes et al. (2000).
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{4779f8a}\par\vspace*{2mm} \includegraphics[width=7.8cm,clip]{4779f8b} \end{figure}$ Figure 8: Spectral energy distribution of LS I+61 $\hbox {$^\circ $ }$ 303 at periastron (full black lines) and apastron (dashed black lines). The pulsar is assumed to have $\dot{E}=10^{36}$ erg s^-1 and $\gamma =10^5$ as for LS 5039, but a slightly higher $\sigma =0.02$ . Top: the stellar wind is polar with a standoff point at $R_{\rm s}=8\times 10^{11}$ cm (periastron) and $4\times 10^{12}$ cm (apastron). Bottom: the stellar wind is equatorial with $R_{\rm s}=5\times 10^{10}$ cm (periastron) and $2\times 10^{12}$ cm (apastron). Grey lines show the fraction of the emission occurring when $\Delta t>P_{\rm orb}$ (the periastron line is visible in the top panel but not in the bottom panel).
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In the text

$\begin{figure} \par\includegraphics[width=3.5cm,clip]{4779f9a}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{4779f9b} \end{figure}$ Figure 9: Left: map of the 5 GHz radio emission from the pulsar nebula in LS I+61 $\hbox {$^\circ $ }$ 303 at $\phi =0.5$ (i=120 $^\circ$ ). $\phi$ is zero at periastron passage (for which $\phi _{\rm radio}=0.23$ , Gregory 2002). Right: corresponding outflow path (as in Fig. 5 but on a linear greyscale) before smoothing (the projected outflow path at apastron is indicated by a dark line). The stellar wind is assumed to be polar (top panel of Fig. 8). The smoothing Gaussian kernel has an FWHM of 8 mas ( $2.8 \times 10^{14}$ cm at 2.3 kpc). Contours are at 50%, 25%, and 10% of maximum emission. There is a preferred direction to the right, towards apastron.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{4779f10} \end{figure}$ Figure 10: Spectral energy distribution of PSR B1259-63 at periastron (solid line) and apastron (dashed line). The pulsar is assumed to have $\dot{E}=8\times 10^{35}$ erg s^-1, $\gamma =10^5$ , and $\sigma =0.01$ . The stellar wind is polar (same parameters as LS I+61 $\hbox {$^\circ $ }$ 303) with a standoff point at $R_{\rm s}=3\times 10^{12}$ cm (periastron) and $4\times 10^{13}$ cm (apastron). With an equatorial, slow wind, the standoff point at periastron is at $R_{\rm s}=10^{12}$ cm, not different enough from the polar wind case to significantly change the expected SED from that shown above. The grey dashed line shows the summed late time emission ( $\Delta t>P_{\rm orb}$ ) at apastron, which occurs on scales $\protect\ga$ 0.01 pc.
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In the text

$\begin{figure} \par\includegraphics[width=3.5cm,clip]{4779f11a}\hspace*{4mm} \includegraphics[width=3.3cm,clip]{4779f11b} \end{figure}$ Figure 11: Left: map of 5 GHz radio emission from PSR B1259-63 close to periastron passage ( $\phi =0.1$ , i=30 $^\circ$ ), assuming only a polar-type stellar wind. Right: corresponding outflow path on the same scale before smoothing (the projected outflow path at apastron is indicated by a dark line). The smoothing Gaussian kernel has a FWHM of 0.05 $^{\prime \prime }$ ( $1.1 \times 10^{15}$ cm at 1.5 kpc). The contours are at 50%, 25%, and 10% of the maximum intensity. The tail extends to a few arcseconds. The spatial scale is large given the size of the orbit (hence $R_{\rm s}$ ); with an even larger eccentricity than LS I+61 $\hbox {$^\circ $ }$ 303, the preferred direction of the nebula towards apastron is very clear.
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In the text