Looking for black-holes in X-ray binaries with XMM-Newton: XTE J1817-330 and XTE J1856+053

The X‐ray binary XTE J1817‐330 was discovered in outburst on 26 January 2006 with RXTE/ASM. One year later, another X‐ray transient discovered in 1996, XTE J1856+053, was detected by RXTE during a new outburst on 28 February 2007. We triggered XMM‐Newton target of opportunity observationson these two objects to constrain their parameters and search for a stellar black holes. We summarize the properties of these two X‐ray transients and show that the soft X‐ray spectra indicate indeed the presence of an accreting stellar black hole in each of the two systems.