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INTEGRAL observations of SS433: new results
Anatol Cherepashchuk Sternberg Astronomical Institute, Moscow University, Russia
In collaboration with: Rashid Sunyaev (IKI), Konstantin Postnov, Eleonora Antokhina, Nikolai Shakura, Darja Kosenko, Elena Seifina,Sergey Molkov (IKI)
1


Overview
· Introduction
· · · · Observations Analysis of hard X-ray spectra Analysis of hard X-ray eclipses Discussion and conclusions

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INTRODUCTION:
· · A massive eclipsing binary system Consists of a mass donor star and a compact object, surrounded by the precessing accretion disk Narrow -collimated relativistic jets (v ~ 0.26 c) Precessional period P=162.5 d Orbital period p=13.082 d A problem w ith spectral classification of the optical star (the disk is significantly more luminous)

SS 4 3 3

· · · ·

One of the main questions - the nature of the relativistic object (BH or NS ?)
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First INTEGRAL observations




SS433 was observed in AO1-AO3 First observations gave a surprise: SS433 is a hard Xray source with emission clearly detected up to 100 keV We concluded that SS433 is galactic microquasar with hard X-ray spectrum (Cherepashchuk et al 2003)

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Observations: Multivawelength campaign






Radio (RATAN-600: S. Trushkin)-IR (Pulkovo: Yu. Gnedin et al.) ­ Optical (SAO RAS 6-m: S. Fabrika et al.; RTT150, Kazan and TUBITAK: N.Sakhibullin et al) ­ Xray (RXTE: M. Revnivtsev et al.) ­ Gamma (INTEGRAL: A. Cherepashchuk et al.) ­ analysis of the nature of hard X-rays (Cherepashchuk et al. 2005, A&A) Radial velocity curve of the optical companion was measured and binary parameters reassessed; conclusion ­ SS433 is most likely a HMXB with BH. BUT uncertainties with radial velocity measurements are still high, so mass ratio Mx/Mo remains poorly constrained from optical data only. These results have recently been confirmed by high resoluiton optical spectroscopy on Gemini-North telescope (Hillwig & Gies 2007)
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All INTEGRAL observations

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Precessional variability





Strong precessional 162-d variability was found with a maximum to minimum flux ratio of ~7 Flux at primary minima is nonzero: ~ 3 mCrab, suggesting extended hard X-ray emitting region
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Orbital eclipses
primary max. crossover I



Several orbital eclispses were observed at different precessional phases

Second. max. crossover II
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Eclipses at prec. phase 0


Most informative are eclispses at the maximum disk opening angle (moment T3 =prec=0) Hard X-ray eclipse is wider than softer one Eclipse ingress appears stable; egress is unstable and variable (as in Ginga observations)





We believe that only eclipse ingress is due to true eclipse, and ignored egress in our analysis
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Analysis of hard X-ray spectra



To increase statistical significance, we splitted the precessional light curve on two parts: "high" (maximum Xrya flux) and "low" (<10 mCrab). Both are consistent with power law.
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Spectral analysis results




Individual ISGRI spectra can be fitted by a multitemperature thermal jet with adiabatic cooling But the unchanged shape of the X-ray spectrum over precessional period and broad X-ray eclipse hints on the presence of a wide corona (formal spectral fit by a comptonization model can be obtained, but gives an unacceptably low temperature kT~14 keV and large optical depth ~4) We conclude that either jets are thick (to match the observed eclipse) or a mildly hot broad corona is present around thin jets.
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Spectrum up to 100 keV (reliable points) can be fitted by multi component emisson model: thermal jet + hot comptonizing corona (T~20 keV, =1.5) See Yura Krivosheev's poster for more detail. Assuming a corona size of 1012cm, this gives electron number denisty ne~1012cm-3, This suggests a mildly hot compatible with density at corona around jets heated by the photospheric radius of collision of the high-velocity jet outflowing wind with matter (0.26 c) with slower dM/dt~10-5 Msun/yr wind (~3000 km/s) from the supercritical accretion disk
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Model for variability
· The optical star fills it Roche lobe · The accretion disk is approximated by an oblate spheroid · X-ray flux is emitted by the hot "corona" around the base of the narrow relativistic jets · The "corona" is approximated by the spheroid and precesses along with disk · The "corona" is placed inside the "funnel" at the inner parts of the disk · During the orbital and precessional moving the "corona" is eclipsed by the star and disk bodies
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Joint analysis of orbital eclipses (ingress only) and precessional variability

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Results of the joint variability analysis






Precessional light curve only does not allow the binary mass ratio q=Mx/Mo to be chosen: equally well fit solutions can be found for q=0.05-1 Analysis of the orbital X-ray eclipse ingress only, observed at prec=0.1 allows to take q=0.1-0.6, with a difference of only 10% in the fit accuracy Joint analysis of both precessioal and orbital variabilitites of SS433 constrains q = 0.3-0.5

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Recent results (Hillwig

from Gemini North & Gies, 2007)
Radial velocity semi-amplitude Ko~60 km/s and Kx~170 km/s Mx=4.3+/-0.8M Mo=12.3+/-3.3M q=0.3

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Discussion


Mass function of the compact star:
mv sin i f X (M ) = 2 (1 + q)
q 0.3 0.5 fx=10.1 MS m mx v 5.4 fx=7.7 M mx mv
S

3

fx=2.0 M mx mv

S

18.1 4.1

13.8 1.1 18.4 2.4

3.6 4.8
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12.1 24.1 9.2
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Summa r y


1) INTEGRAL orbital and precessional light curves of SS433 can be interpreted by an extended corona above the superaccreting disk around the compact object. Thin relativistic jets shining in soft X-rays are launched from the center of the corona that is observed in hard Xrays

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2) Mass ratio as inferred from joint modeling of hard X-ray eclipse (ingress only) and precessional variability is q=0.3-0.5. This implies for the probable mass function fX(M)=8-10 Msun optical star mass compact star mass Mv = 14-24 Msun Mx = 4-12 Msun

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This supports our earlier conclusion that the compact star in SS433 is a black hole
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New observations of SS433 in 2007: May 2007 surprize:
Looks very much Like Ginga! Flux, mCrab

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New observations in October 2007:

Confirm q=0.3-0.5
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Mean precession light curve from INTEGRAL data (2003-2007)

90% CL

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Future prospects






The nature of the compact star in SS433 seems to be finally established from X-ray and optical observations ­ a BH with mass 4-8 M_sun Reliable determination of the mass function is still crucial. SUBARU observed SS433 in October 2007 and obtained high-resolution spectra of the optical star (Fabrika et al., in preparation). INTEGRAL measurements of the form of the primary Xray eclipse in SS433 have been crucial in establishing the nature of the compact star and hard X-ray emitting corona around supercritical accretion disk Hard X-ray monitoring is necessary to establish the nature of the hot extended corona

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