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Optical Counterpart to the Ultraluminous X-Ray Source in the UGC 6456 Galaxy |
Russian version |
The subject of this study is a binary system in the galaxy UGC6456
(also known as VII Zw 403). It is a highly variable source in both
the X-ray and optical ranges, which, having a peak X-ray luminosity
of Lx=1.7*10^40 erg/s, can be classified as ultraluminous X-ray source
(ULXs). Objects of this type show X-ray luminosities that exceed the
Eddington limit for stellar mass black holes. In most ULXs, accretion
from donor stars onto stellar-mass black holes or neutron stars occurs
in the so-called supercritical regime, which rate is orders of magnitude
higher than those observed in many X-ray binaries of our Galaxy
(reaching 10^-5 - 10^-4 Msun/yr). A key feature of the supercritical
accretion is a powerful matter outflows coming from the central regions
of accretion disks (the so-called supercritical disc wind). However,
many parameters of this phenomenon remain unknown: the geometry of
the outflow, its velocity at different distances from the black hole
or neutron star, the efficiency of energy release, the fractions of
energies advected into a black hole and carried away together with
the wind gas, etc; the values of these parameters can be determined
or at least estimated based on observational data. At the same time,
the available observation and detailed RHD simulations show that most
of the ejected matter has relatively low temperatures (tens of thousands
Kelvin) and emits in the UV-optical range, while the X-ray observations
can elicit only the fastest gas flows (the so-called ultrafast outflows).
Therefore, it is the optical range that is most suitable for studies of
the supercritical disk wind.
![]() Figure 1. Superposition of B, V, and Rc images of the UGC 6456 galaxy taken with BTA/SCORPIO. The inset shows the HST/WFPC2/F555W image of the region around UGC6456 ULX marked by the square; the circle indicate the 0.8" 90%-error box of the ULX position derived from the Chandra data. |