Discovery of a redshifted X-ray emission line in the symbiotic neutron   star binary 4U 1700+24
  We present the spectral analysis of an XMM-Newton observation of the X-ray binary 4U 1700+24, performed during an outburst in August 2002. The EPIC-PN spectrum above 1 keV can be modeled by a blackbody plus Comptonization model, as in previous observations. At lower energies, however, we detect a prominent soft excess, which we model with a broad Gaussian centered at ~0.5 keV. In the high resolution RGS spectrum we detect a single emission line, centered at 19.19^{+0.05}_{-0.09} \AA. We discuss two possible interpretations for this line: O VIII at redshift z=0.012^{+0.002}_{-0.004} or Ne IX at redshift z~0.4. 
A. Tiengo, D. K. Galloway, T. di Salvo, M. Mendez, J. M. Miller, J. L.   Sokoloski, M. van der Klis