COMMISSION 27 OF THE I. A. U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3572

                                                       Konkoly Observatory
                                                       Budapest
                                                       8 March 1991

                                                       HU ISSN 0374 - 0676


               ANALYSIS OF R-RAY ECLIPSES IN SS433

   Detailed X-ray light curves of SS433 (=V1343 Aql) within primary eclipse
for the phases Psi=0.11, 0.33 and 0.5 of the precessional period 162.5d
have been obtained recently (Brinkmann et al.; 1989, Kawai, 1989). Precessional 
phase Psi=0 corresponds to the moment of maximum separation of the
moving emissions.
   Following to the results of the interpretation of the optical light
curves of SS433 (Antokhina and Cherepashchuk, 1987) we try to do an analysis
of these X-ray eclipsing light curves of SS433 in the framework of the Roche
model of close binary system with the precessing thick accretion disk 
containing geometrically thick electron scattering hot nonrelativistic "jets"
in its central parts. Physical grounds for the existence of such a thick
nonrelativistic "jets" in SS433 have been presented by Kawai (1989). It has
been supposed that the shape of X-ray eclipsing light curves is due to the
eclipse of this thick nonrelativistic X-ray "jets" by the external parts of
the accretion disk and by the normal star. Thin relativistic X-ray jets 
going out from the tops of the thick nonrelativistic "jets" are almost 
noneclipsing by the normal star and contribute the third noneclipsing light in
the binary system. External parts of the accretion disk are described by the
spheroid with the ratio of the semiaxes ("thickness") k=b/a (b and a are the
semiaxes of this spheroid). The thin relativistic jets must be rather short
because they have to be eclipsed by the external parts of the accretion disk
(red moving FeXXV line is not observed in the X-ray spectrum of SS433). On
the other hand, the thin jets have to be rather long because they are almost
noneclipsed by the normal star. It helps us to constrain the "thickness" of
accretion disk k=b/a ~0.7. Internal parts of the disk are conic.
   The basic parameters in our model are as follows: the mass ratio for
the relativistic component and for normal star q=M_x/M_v, the "thickness" of
the accretion disk k=b/a, semiaxes of the thick nonrelativistic "jets" a_j,
b_j, the angle of the cone omega describing interior parts of the disk. The
filling factor mu for the normal star in its Roche lobe is supposed to be 1.
Our detailed calculations show that the value of mu less than 1 is in
contradiction with X-ray observations. The value of the semiaxis of the
spheroid a for the external parts of the disk is equal to the distance between
the centrum of the accretion disk and the inner Lagrangian point.


                               [FIGURE 1]

 Figure 1. Observed (point) and theoretical (lines) X-ray light curves at
           different phases of the 162.5-day precessional period Psi = 0.11
           (top), 0.33 (centre), 0.5 (bottom).


   The synthesized X-ray eclipsing light curves for three phases of 
precessional period, Psi=0.11, 0.33, 0.5 have been compared with observational
light curves and values of the parameters q, k, a_, b_j and omega have been 
determined. The shape of eclipsing X-ray light curve may be well described by
the thick and thin disk, but thick disk is more preferable from the point of
view described above. The obtained confidence interval for q is 0.15<=q<=0.25.
   The best solution was obtained for the values of q=0.2, k=0.7, a_j=0.1,
b_j=0.2, omega=60 deg (see Fig. 1). The computer simulated pictures
corresponding to this model are presented in Fig. 2. For the phase Psi=0.5
there is no satisfactory agreement between the observations if omega=60 deg.
But for omega=40 deg we obtained a good agreement with observations (see Fig.
1). This fact can be understood taking into account the probable complicated
shape of the disk.
   For q=0.2 and mass function f(M)=10 M_sun (Crampton and Hutchings, 1981)
the value of mass of the relativistic objects is M_X=3.1 M_sun. The upper
limits for for q and M_x q<=0.25, M_x<=4 M_sun obtained from analysis of X-ray
eclipses are close to the lower limits for q and M_x determined by Antokhina
and Cherepashchuk (1987) from the analysis of the optical light curves of
SS433: q=0.25, M_X> 4 M_sun. It should be noted that because the normal star
overfills its Roche lobe, and the dimension of the Roche lobe is less than
the level of normal star photosphere, the upper limit for q obtained from X-ray
eclipses may be increased up to q=0.3.


                               [FIGURE 2]

 Figure 2. Computer simulated picture of X-ray eclipses in the SS433 system
 for three precessional phases Psi = 0.11 (top), 0.33 (centre), 0.5 (bottom).


   It should be also noted that the value of q=0.2-0.3 corresponds to the
total eclipse of the accretion disk by the normal star which is in conflict
with the optical light curves of SS433. This problem needs further 
investigations.


                       E.A. ANTOKHINA, A.M. CHEREPASHCHUK, E.Y. SEYFINA
                       Sternberg State Astronomical Institute
                       Moscow, USSR



References:

Antokhina, E.A., Cherepashchuk, A.M.: 1987, Soviet Astronomy, 31, 295. [BIBCODE 1987SvA....31..295A ]
Brinkmann, W., Kawai, N., Matsuoka, M.: 1989, Astronomy and Astrophysics,
      218, L.13. [BIBCODE 1989A&A...218L..13B ]
Crampton, D., Hutchings, J.: 1981, Astrophysical Journal., 251, 604. [BIBCODE 1981ApJ...251..604C ]
Kawai, N.: 1989, Proc. 23d ESLAB Symp. on Two-Topics in X-ray Astronomy,
      Bologna, Italy (ed. N.E. White), p. 453. [BIBCODE 1989ESASP.296..453K ]