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(Abridged) We report on ASCA and BeppoSAX observations of the X-ray source 4U1700+24 and on (quasi-)simultaneous spectroscopy of its optical counterpart,V934 Her, from the Loiano 1.5-meter telescope. Archival ROSAT and RXTE data aswell as the RXTE ASM light curve of 4U 1700+24 are also analyzed along with a1985 EXOSAT pointing. The optical spectra are typical of a M2 III star; arevised distance to the object of ~400 pc is inferred. While these spectra donot show either any change between the two epochs or any peculiar feature, theX-ray spectra reveal a complex and long-term variable shape, with a clear softexcess. The X-ray spectral properties of the source are best described by athermal Comptonization spectrum plus a soft energy(<1 keV) excess, which can bemodeled with a blackbody emission with kT_BB ~ 1 keV; the latter component isnot detected at the lowest source flux levels. The ratio between the twocomponents varies substantially with the source flux. The X-ray emission fromthe object appears to become harder as its luminosity increases, and the RXTEdata acquired during an outburst occurred during Fall 1997 display a hard taildetected up to 100 keV. Apart from erratic shot-noise variability on timescalesof tens to thousands of seconds, no significant pulsations or QPOs are foundfrom the timing analysis of the X-ray light curves. With the new distancedetermination, the 2-10 keV X-ray luminosity range spanned in the consideredobservations lies between ~2x10^32 and ~1x10^34 erg/s. All this allows us tosuggest a scenario consisting of a wide binary system in which a neutron staraccretes matter from the wind of an M giant.Comment: 14 pages, 5 figures, to be published on Astronomy & Astrophysics,  Main Journa

X–ray and optical monitoring of the peculiar source 4U 1700+24/V934 Her