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S.D. Vrtilek, J.E. McClintock, J.C. Raymond (Harvard-Smithsonian Center for Astrophysics)
We will present a preliminary analysis of the 1-10 keV spectrum of the low-mass X-ray binary, 4U1735-44, obtained with the High-energy Transmission Grating Spectrometer on Chandra. The source was observed for 26.2ks (1.6 binary periods) and the orbital modulation is clearly seen in the X-ray lightcurve. The presence of emission features at 0.72 and 0.83 keV with no noticeable emission at 0.77 keV suggests collisionally ionized plasma if we use a diagnostic defined by Liedahl et al. (1991). This is consistent with the lack of the RRC features detected by Paerels (2000) in Cyg X-3 and considered a signature of photoionized plasma. Several emission features observed with the Einstein Objective Grating Spectrometer (Vrtilek et al. 1991) are detected, notably those attributed to Fe XVII-XVIII at 13.5 and 14.3 angstroms as well as a feature that may be due to OVII at 17.7 angstroms. Fluorescent Fe emission at 6.4 keV is considerably weaker than expected. The data are of sufficient quality to allow us to search for variability of the emission features as a function of orbital phase.
Support for this work was provided by NASA through grant NAG5-6711.