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We continue to study the fast X-ray transient XTE J1901+014 discovered in2002 by the RXTE observatory, whose nature has not yet been established. Basedon the XMM-Newton observations of the source in 2006, we have obtained itsenergy spectrum, light curves, and power spectrum in the energy range 0.5-12keV, which are in good agreement with our results obtained previously from thedata of other observatories. In turn, this suggests that the source's emissionis stable in the quiescent state. The XMM-Newton observations also allowed thesource's localization accuracy to be improved to <2", which subsequentlyenabled us to search for its optical companion with the RTT-150 and 6-m BTA(Special Astrophysical Observatory) telescopes. Combining optical, X-ray, andinfrared observations, we have concluded that the optical companion in thesystem under study can be either a later-type star at a distance of several kpcor a very distant red giant or an A or F star. Thus, XTE J1901+014 may be thefirst low-mass fast X-ray transient.

XTE J1901+014 - the First Low-Mass Fast X-ray Transient?