Discovery of a redshifted X-ray emission line in the symbiotic neutron star binary 4U 1700+24
Sokoloski, J. L.; Tiengo, A.; Miller, J. M.; van der Klis, M.; Méndez, M.; Galloway, D. K.; di Salvo, T.
Italy, United States, Netherlands
Abstract
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 Å. 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.