Tricky wobbling of a super-critical accretion disk in the galactic micro-quasar SS433
Over the last 10 years, the super-accreting galactic micro-quasar
SS433 was observed various times in hard X-rays by INTEGRAL. Hard
X-rays (20-60 keV) are thought to mainly arise in a rarefied hot
plasma filling a broad cone around the inner parts of jets as they
protrude through the accretion disk atmosphere. The hard X-ray flux
from SS433 is quite weak, about 5% of the flux from the Crab pulsar,
so it required a time span of about 10 years of INTEGRAL observations,
with a total exposure of 8.5 Ms, to see all three motions of the
accretion disk in this system -- orbital, precessional, and nutational.
The nutational motion (wobbling) with an amplitude of several degrees
is due to the periodic enhancement of gravitational force action on the
disk when the optical star crosses the line of nodes of the precessing
accretion disk. Unlike optical and radio observations which study the
motion of jets and outer parts of the disk, INTEGRAL's hard X-ray
observations allowed to look for the first time inside the hottest
central parts of the super-critical accretion disk. These observations,
independently, also confirmed the high mass of the compact star in
SS433 -- more than 3 solar masses, which suggests the compact object
to be a stellar-mass black hole.
Upper left: Precessional light curve of SS433 observed by IBIS/ISGRI
outside and during the primary eclipse (blue and red points, respectively).
Upper right: Orbital eclipse of SS433 in 18-40 and 40-60 keV bands.
Nutational motion of the disk appears as two additional bumps around
orbital phases ~0.25 and 0.75
Bottom left: Artist impression of the INTEGRAL satellite against the
optical Milky Way background.
Bottom right: A representation of the geometric model of the binary
system SS433 with a precessing accretion disc around the central black
hole. A hot rarefied corona around central parts of the accretion disk
which produces the hard X-ray is shown in red. The model reproduces the
observed precessional (upper left) and orbital (upper right) hard X-ray
light curve of SS433. Nutational motion of the disc cannot be seen in
this scale, but is included in the modelling.
Reference:
INTEGRAL observations of SS433: system's parameters and nutation
of supercritical accretion disc
A.M. Cherepashchuk, R.A. Sunyaev, S.V. Molkov, E.A. Antokhina,
K.A. Postnov, A.I. Bogomazov
http://adsabs.harvard.edu/abs/2013MNRAS.436.2004C,
MNRAS, Volume 436, Issue 3, p.2004-2013
