Chandra Observation of the Persistent Emission from the Dipping Source XB 1916-053

Abstract

We present the results of a 50 ks long Chandra observation of the dipping source XB 1916 - 053. During the observation two X-ray bursts occurred, and the dips were not present at each orbital period. From the zeroth-order image we estimate the precise X-ray coordinates of the source with a 90% uncertainty of 0"6. In this work we focus on the spectral study of discrete absorption features, during the persistent emission, using the High Energy Transmission Grating Spectrometer on board the Chandra satellite. We detect, for the first time in the first-order spectra of XB 1916 - 053, absorption lines associated with Ne X, Mg XII, Si XIV, and S XVI and confirm the presence of the Fe XXV and Fe XXVI absorption lines with a greater accuracy than the previous XMM EPIC pn observation. Assuming that the line widths are due to a bulk motion or a turbulence associated with the coronal activity, we estimate that the lines are produced in a photoionized absorber 4 x 10(10) cm from the neutron star, near the disk edge.