Transcript INTEGRAL observations of SS433: new results Anatol Cherepashchuk Sternberg Astronomical Institute, Moscow

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)
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Overview
1. Introduction
2. Observations
3. Analysis of hard X-ray spectra
4. Analysis of hard X-ray eclipses
5. Discussion and conclusions
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INTRODUCTION: SS
433
• 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 with spectral
classification of the optical star
(the disk is significantly more
luminous)
One of the main questions - the nature of
the relativistic object (BH or NS ?)
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First INTEGRAL observations
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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
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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) – X-ray (RXTE:
M. Revnivtsev et al.) – Gamma (INTEGRAL: A.
Cherepashchuk et al.) – analysis of the nature of hard Xrays (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
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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.
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Several orbital
eclispses were
observed at different
precessional phases
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crossover I
Second. max. crossover II
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Eclipses at prec. phase 0
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Most informative are
eclispses at the maximum
disk opening angle
(moment T3 =prec=0)
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 Hard X-ray eclipse is
wider than softer one
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 Eclipse ingress appears
stable; egress is unstable
and variable (as in Ginga
observations)
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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
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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
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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, τ=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 wind
dM/dt~10-5 Msun/yr
(~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
s
• 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
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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 from Gemini North
(Hillwig & 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
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Mass function of the compact star:
3
mv sin i
f X (M ) 
2
(1  q)
q
fx=10.1 MS fx=7.7 MS fx=2.0 MS
mx
mv
0.3
5.4
0.5
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mx
mx
mv
18.1 4.1
13.8 1.1
3.6
12.1 24.1 9.2
18.4 2.4
4.8
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mv
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Summary
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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 X-rays
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2) Mass ratio as inferred from joint
modeling of hard X-ray eclipse (ingress
only) and precessional variability is q=0.30.5. This implies for the probable mass
function fX(M)=8-10 Msun
optical star mass
Mv = 14-24 Msun
compact star mass
Mx = 4-12 Msun
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:
Flux, mCrab
Looks very much
Like Ginga!
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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
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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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