High Resolution Spectroscopy of 4U 1728-34 from a Simultaneous Chandra-RXTE Observation

We report on a simultaneous Chandra and RossiXTE observation of the LMXB atoll bursting source 4U 1728‐34 between 2002 March 3rd and 2002 March 5th. We fitted the 1.2–35 keV continuum with a blackbody spectrum plus a Comptonized component. Absorption edges associated with Fe I and Fe XXV at ∼ 7.1 keV and ∼ 9 keV respectively, are present in our spectrum. Moreover, an overabundance of Si is highly required for a satisfactory fit. We found no evidence in our fits of broad, or narrow Fe Kα lines, between 6 and 7 keV, contrarly to what previous spectral studies pointed out. We tested our study by reanalysing a previous BeppoSAX observation of 4U 1728‐34, finding a general agreement with our new spectral model.