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Broad relativistic iron lines from neutron star X-ray binaries are importantprobes of the inner accretion disk. The X-ray reflection features can beweakened due to strong magnetic fields or very low iron abundances such as ispossible in X-ray binaries with low mass, first generation stars as companions.Here we investigate the reality of the broad iron line detected earlier fromthe neutron star low mass X-ray binary 4U~1820--30 with a degenerate heliumdwarf companion. We perform a comprehensive, systematic broadband spectralstudy of the atoll source using \suzaku{} and simultaneous \nustar{} \&\swift{} observations. We have used different continuum models involvingaccretion disk emission, thermal blackbody and thermal Comptonization of eitherdisk or blackbody photons. The \suzaku{} data show positive and negativeresiduals in the region of iron K band. These features are well described bytwo absorption edges at $7.67\pm0.14\kev$ and $6.93\pm0.07\kev$ or partialcovering photoionized absorption or by blurred reflection. Though, thesimultaneous \swift{} and \nustar{} data do not clearly reveal the emission orabsorption features, the data are consistent with the presence of eitherabsorption or emission features. Thus, the absorption based models provide analternative to the broad iron line or reflection model. The absorption featuresmay arise in winds from the inner accretion disk. The broadband spectra appearto disfavour continuum models in which the blackbody emission from the neutronstar surface provides the seed photons for thermal Comptonization. Our resultssuggest emission from a thin accretion disk ($kT_{disk} \sim 1\kev$),Comptonization of disk photons in a boundary layer most likely covering a largefraction of the neutron star surface and innermost parts of the accretion disk,and blackbody emission ($kT_{bb} \sim 2\kev$) from the polar regions.

Broadband X-ray emission and the reality of the broad iron line from the Neutron Star - White Dwarf X-ray binary 4U 1820-30