  Recently we discovered an unprecedented supermassive black hole binary
(SMBHB) candidate in the nearby Seyfert galaxy SDSS J1430+2303, which is
predicted to merge within three years. X-ray spectroscopy may bring unique
kinematic evidence for the last inspiraling stage, when the binary is too close
to allow each of them to hold an individual broad line region. We try to
confirm the unique SMBHB merger event and understand the associated high-energy
processes from a comprehensive X-ray view. We observed SDSS J1430+2303 with
XMM-Newton, NuSTAR, Chandra, and Swift spanning the first ~200 days since its
discovery. X-ray variability, up to a factor of 7, has been detected on a
timescale of a few days. The broadband spectrum from 0.2-70 keV can be well
fitted with a model consisting of a power law and a relativistic reflection
covered by a warm absorber. The properties of the warm absorber changed
dramatically, for example, with a decrease in the line-of-sight velocity from
~0.2c to ~0.02c, between the two XMM-Newton observations separated by only 19
days, which can be naturally understood in the context of the SMBHB; although,
the clumpy wind scenario cannot be completely excluded. Broad Fe Kalpha
emission has been robustly detected, though its velocity shift or profile
change is not yet measurable. Further longer X-ray observations are highly
encouraged to detect the expected orbital motion of the binary.
