The XMM-Newton spectrum of a candidate recoiling supermassive black
  hole: an elusive inverted P-Cygni profile
  We present a detailed spectral analysis of new XMM-Newton data of the source
CXOC J100043.1+020637, also known as CID-42, detected in the COSMOS survey at z
= 0.359. Previous works suggested that CID-42 is a candidate recoiling
supermassive black holes showing also an inverted P-Cygni profile in the X- ray
spectra at ~6 keV (rest) with an iron emission line plus a redshifted
absorption line (detected at 3sigma in previous XMM-Newton and Chandra
observations). Detailed analysis of the absorption line suggested the presence
of ionized material inflowing into the black hole at high velocity. In the new
long XMM-Newton observation, while the overall spectral shape remains constant,
the continuum 2-10 keV flux decreased of ~20% with respect to previous
observation and the absorption line is undetected. The upper limit on the
intensity of the absorption line is EW<162 keV. Extensive Monte Carlo
simulations show that the non detection of the line is solely due to variation
in the properties of the inflowing material, in agreement with the transient
nature of these features, and that the intensity of the line is lower than the
previously measured with a probability of 98.8%. In the scenario of CID-42 as
recoiling SMBH, the absorption line can be interpreted as due to inflow of gas
with variable density and located in the proximity of the SMBH and recoiling
with it. New monitoring observations will be requested to further characterize
this line.
