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 \sim 6 keV ( rest ) with an iron emission line plus a redshifted absorption line ( detected at 3 \sigma 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 \sim 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 .