The peculiar high-mass X-ray binary 1ES 1210-646
  Using data collected with the BeppoSAX, INTEGRAL and Swift satellites, we
report and discuss the results of a study on the X-ray emission properties of
the X-ray source 1ES 1210-646, recently classified as a high-mass X-ray binary
through optical spectroscopy. This is the first in-depth analysis of the X-ray
spectral characteristics of this source. We found that the flux of 1ES 1210-646
varies by a factor of about 3 on a timescale of hundreds of seconds and by a
factor of at least 10 among observations acquired over a time span of several
months. The X-ray spectrum of 1ES 1210-646 is described using a simple powerlaw
shape or, in the case of INTEGRAL data, with a blackbody plus powerlaw model.
Spectral variability is found in connection with different flux levels of the
source. A strong and transient iron emission line with an energy of about 6.7
keV and an equivalent width of about 1.6 keV is detected when the source is
found at an intermediate flux level. The line strength seems to be tied to the
orbital motion of the accreting object, as this feature is only apparent at the
periastron. Although the X-ray spectral description we find for the 1ES
1210-646 emission is quite atypical for a high-mass X-ray binary, the
multiwavelegth information available for this object leads us to confirm this
classification. The results presented here allow us instead to definitely rule
out the possibility that 1ES 1210-646 is a (magnetic) cataclysmic variable as
proposed previously and, in a broader sense, a white dwarf nature for the
accretor is disfavoured. X-ray spectroscopic data actually suggest a neutron
star with a low magnetic field as the accreting object in this system.
