Unveiling the nature of optically-selected X-ray transients revealed by ART-XC

We propose a single TOO XMM followup observation of the faint hard Xraytransient that will revealed by the ARTXC telescope in the frame of the ongoingallsky survey. The corresponding program is aimed at studies of the Very FaintXray Transients (VFXTs), detected both in Xrays with ARTXC and optics eitherduring public surveys (ZTF, GAIA, etc.) or in dedicated observations. We willsupport this followup effort with groundbased optical telescopes of CMO SAIMSU, RTT150 and AZT33IK telescopes as well as telescopes of the SAAOobservatory in order to perform spectroscopic and photometric observations. Themain purpose of this proposal and the joint Xrayoptical followup program isto constrain physical properties of the binary system and unveil the nature of the compact object. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]