Abstract. Results of simultaneous INTEGRAL and optical observations of the galactic microquasar SS433 in May 2003and INTEGRAL /RXTE observations in March 2004 are presented. Persistent precessional variability with a maximum to minimum uneclipsed hard X-ray flux ratio of ∼4 is discovered. The 18-60 keV X-ray eclipse is found to be in phase with optical and near infrared eclipses. The orbital eclipse observed by INTEGRAL in May 2003 is at least two times deeper and apparently wider than in the soft X-ray band. The broadband 2-100 keV X-ray spectrum simultaneously detected by RXTE/INTEGRAL in March 2004 can be explained by bremsstrahlung emission from optically thin thermal plasma with kT ∼ 30 keV. Optical spectroscopy with the 6-m SAO BTA telescope confirmed the optical companion to be an A5-A7 supergiant. For the first time, spectorscopic indications of a strong heating effect in the optical star atmosphere are found. The measurements of absorption lines which are presumably formed on the non-illuminated side of the supergiant yield its radial velocity semi-amplitude K v = 132 ± 9 km s −1 . The analysis of the observed hard X-ray light curve and the eclipse duration, combined with the spectroscopically determined optical star radial velocity corrected for the strong heating effect, allows us to model SS433 as a massive X-ray binary. Assuming that the hard X-ray source in SS433 is eclipsed by the donor star that exactly fills its Roche lobe, the masses of the optical and compact components in SS433 are suggested to be M v ≈ 30 M and M x ≈ 9 M , respectively. This provides further evidence that SS433 is a massive binary system with supercritical accretion onto a black hole.

In the first paper of this series, we presented a detailed high-resolution spectroscopic study of CPD − 41 • 7742, deriving for the first time an orbital solution for both components of the system. In this second paper, we focus on the analysis of the optical light curve and on recent XMM-Newton X-ray observations. In the optical, the system presents two eclipses, yielding an inclination i ∼ 77 •. Combining the constraints from the photometry with the results of our previous work, we derive the absolute parameters of the system. We confirm that the two components of CPD − 41 • 7742 are main sequence stars (O9 V + B1-1.5 V) with masses (M 1 ∼ 18 M and M 2 ∼ 10 M) and respective radii (R 1 ∼ 7.5 R and R 2 ∼ 5.4 R) close to the typical values expected for such stars. We also report an unprecedented set of X-ray observations that almost uniformly cover the 2.44-day orbital cycle. The X-ray emission from CPD − 41 • 7742 is well described by a two-temperature thermal plasma model with energies close to 0.6 and 1.0 keV, thus slightly harder than typical early-type emission. The X-ray light curve shows clear signs of variability. The emission level is higher when the primary is in front of the secondary. During the high emission state, the system shows a drop of its X-ray emission that almost exactly matches the optical eclipse. We interpret the main features of the X-ray light curve as the signature of a wind-photosphere interaction, in which the overwhelming primary O9 star wind crashes into the secondary surface. Alternatively the light curve could result from a wind-wind interaction zone located near the secondary star surface. As a support to our interpretation, we provide a phenomenological geometric model that qualitatively reproduces the observed modulations of the X-ray emission.

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We have used the relatively long data string of the 1997-1999 NICMOS focus tests on NGC 3603 to extract $J-band light curves for several hundred stars in the cluster core. Given the relatively modest photometric precision [(J ) ! 0:05 mag], we were able to isolate only a half-dozen variable candidates with peak-to-valley amplitudes above $0.2 mag. One of the variables is one of the two outstandingly brightest cluster members, A1, located in the very dense cluster center. A1 shows double eclipses on each orbital cycle, with the same period (P ¼ 3:7724 days) as found previously and independently in unresolved ground-based radial velocity variations of the Wolf-Rayet (WR) emission component in the central core of NGC 3603. Very rough best estimates for the masses of the components of A1 are in the range 30-90 M for the brighter and more massive H-rich WR component (WN6ha) and 25-50 M for its assumed O star companion. A more detailed study is urgently needed, given the potential for this extremely luminous system to harbor the most massive main-sequence star ever ''weighed.'' Another variable, HST 12, escaped the original search, which was based on larger than average standard deviation. It is a probable field-star eclipsing variable with a moderately long period.

Based on multiyear INTEGRAL observations of SS433 in 2003-2011, a composite IBIS/ISGRI 18-60 keV orbital light curve is constructed around zero precessional phases ψ pr = 0 at the maximim accretion disk opening angle. It shows a peculiar shape with significant excess near the orbital phase φ orb = 0.25, which is not seen in the softer 2-10 keV energy band. The 40-60 keV orbital light curve demonstrates two almost equal humps at phases ∼ 0.25 and ∼ 0.75, most likely due to nutation effects of the accretion disk. The nutational variability of SS433 in 15-50 keV with a period of ≃ 6 d .290 is independently found from analysis of Swift/BAT data. The change of the off-eclipse 18-60 keV X-ray flux with the precessional phase shows a doublewave form with strong primary maximum at ψ pr = 0 and weak but significant secondary maximum at ψ pr = 0.6. A weak variability of the 18-60 keV flux in the middle of the orbital eclipse correlated with the disk precessional phase is also observed. The joint analysis of the broadband 18-60 keV orbital and precessional light curves confirms the presence of a hot extended corona in the central parts of the supercritical accretion disk and constrains the binary mass ratio in SS433 in the range 0.5 q 0.3, suggesting the black hole nature of the compact object.