INTEGRAL observations of SS433: Results of a coordinated campaign

Abstract

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.

Spectroscopic Observations of the Mass Donor Star in SS 433

“…We caution that our estimate of K O may differ from the actual geometric value if the inner hemisphere of the A-type supergiant is significantly heated by flux from the disk (Cherepashchuk et al 2005). The amount of irradiation present is very uncertain, since the disk vertical extensions may be sufficient to block most of the high-energy radiation from the central accretion zone from reaching the facing hemisphere of the supergiant.…”

“…The first potential observations of the mass donor star were reported by Gies et al (2002a), with additional observations published later by Cherepashchuk et al (2005). These studies detected faint absorption lines present in blue spectra of SS 433 that exhibited the Doppler shifts expected for the donor star.…”

SS 433: the accretion disk revealed in Hα

“…Equation (5) assumes a simple disk geometry but it is likely that the volume of the companion opaque to Hα does not fill its Roche lobe, at least not during this episode. This does not seem at odds with the relatively short optical eclipses (Antokhina & Cherepashchuk 1987) but the values of q extracted from longer X-ray eclipses, assuming that the companion fills its Roche lobe (Cherepashchuk et al 2005(Cherepashchuk et al , 2008, are smaller than permitted by the data on the circumbinary and accretion disks. X-ray eclipses are very varied (Cherepashchuk et al 2008) and it may be that the X-rays are eclipsed not only by the limb of the companion but also by an atmosphere, associated gas streams and wind (Fabrika 2004;Cherepashchuk et al 2008).…”

Viscous timescale in high mass X-ray binaries

“…(1) Chakrabarty et al (1993); (2) Cherepashchuk et al (2005); (3) Sadakane et al (1985); (4) Notes. L x is the X-ray luminosity calculated using respective count rates and source distances listed in Table 1.…”