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   81402
   Unique absorption line features around 4.1 keV have been detected in
   the burst spectra from at least three low-mass X-ray binaries. If they
   are a gravitationally redshifted atomic line and the responsible
   element is identified, the observed redshift factor will directly give
   the mass to radius ratio of the neutron stars. We propose a detailed
   investigation of the absorption line for the bursts from X1608-52 with
   ASCA SIS. For two week observations, we expect to detect more than 10
   X-ray bursts with moderate strength in high telemetry bit rate. This
   may be the last chance to investigate the absorption line features in
   the bursts with the high resolution spectrometers.
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