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Peter Kretschmar (ISDC/MPE) Masha Chernyakova (ISDC)Sandro Mereghetti (IASF Milano) Roland Walter (ISDC) Simon Shaw (ISDC)Marc Tuerler (ISDC)PSR B1259-63 is a unique binary system composed by a radio millisecondpulsar orbiting a Be star in a very eccentric orbit. The periastronpassage occurs every 3.4 years and offers the possibility of studyingthe interaction of the relativistic wind from the pulsar with the windand circumstellar disk of the companion.The current periastron occurred on March 7 2004. A few days earlier PSRB1259-63 has been detected for the first time at E > 200 GeV with the HESStelescope (IAU Circ. n. 8300) at a flux level of ~0.1 Crab. The time ofthe detection corresponds to the first pulsar crossing of the equatorialdisk which surrounds the Be companion. The next crossing of such a diskwill occur between March 20 and 25 and further high energy emission isexpected at that time.The HESS detection is possibly the confirmation of models predicting theacceleration of relativistic particles at the relativistic shock betweenpulsar and Be wind (Tavani and Arons 1997 Kirk et al. 1999 Chernyakova and Illarionov 2000). The interpretation of these observations would benefitfrom a wide energy coverage and spectral measurement with INTEGRALconstraining the physics of the different models.We propose an INTEGRAL TOO to extend the HESS coverage of that event downto the MeV and possibly lower energy range.After the radio discovery in 1990 only the 1994 periastron passage had agood multiwavelength coverage at high energy thanks to CGRO leading to adetection with OSSE in the 50-200 keV range (Grove et al. 1995 Tavani etal. 1996). The source spectrum was a hard powerlaw with slope 1.8+-0.6 anda flux of ~4 mCrab. [truncated! Please see actual data for full text]