η Carinae is a binary system hosting two unusually massive stars,
with masses of about 30 and 100 times that of the Sun. Both stars
exhibit extreme stellar winds, with the mass-loss rate of the primary
star reaching one Solar mass per millenium, the highest known to date.
The two winds collide, forming a shock. Part of the energy released
there, is used to accelerate particles, which then emits in the X- and
γ-rays. As the separation between the two stars varies by a factor of 20
along their orbit, the X/γ-ray emission is maximized when the two stars
are closest to each other.
A campaign of observations of η Carinae was organized in August 2014 to
study the hard X-ray emission from the wind collision zone at its
maximum intensity and to compare these observations with the expectation
from models of the system. A distortion of the thermal emission (brown
dashed lines in the spectrum shown in the left panel of the image) was
detected, corresponding to a spiral structure developing in the
wind collision zone. During these relatively short exposures, NuSTAR
detected the source up to about 30 keV (black dots). INTEGRAL saw the
emission (dot-dashed line) from high-energy electrons accelerated in the
wind collision zone of η Car to much higher energies (green dots).
The IBIS/ISGRI 40-80 keV image of η Car is shown in the right panel of
the image. Even if the coded mask optics of INTEGRAL is intrinsically
less sensitive than the X-ray mirrors of NuSTAR in the energy band
covered by both instruments, the large field of view of INTEGRAL has
allowed to accumulate enormous exposure over more than 15 years. This
has resulted in an excellent grasp on the hard X-ray properties of η Car
and its surroundings.
Reference:
"The environment of the wind–wind collision region of η Carinae",
C. Panagiotou & R. Walter,
A&A 610, A37,
doi:10.1051/0004-6361/201731841
