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Abstract. It has been suggested that young pulsars, with ages less than a million years, are possible counterparts of some of the Galactic unidentified gamma-ray sources detected by the EGRET instrument on-board the Compton Gamma Ray Observatory. In this work, we compare different aspects of the EGRET unidentified (EUI) source distribution in the Galactic plane with those of the pulsar distribution. An EUI source Log N-Log S analysis is presented and compared with the Galactic radio pulsar Log N-Log S distribution. A number of systematic effects that could introduce errors to the EGRET Log N-Log S relation are discussed. A two-point angular correlation analysis of the EUI sources and Galactic pulsars is performed. We find that the global distribution properties of the plane EUI sources do not follow those of the young pulsar population. We conclude that even though a fraction of the EUI sources may have young pulsar counterparts, the majority of them follow a distribution that is similar to the molecular cloud distribution in nearby spiral arms.

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Abstract. The polarisation of astrophysical source emission in the energy range from a few tens of keV up to the MeV region is an almost unexplored field of high-energy astrophysics. Till date, polarimetry in astrophysics-in the energy domain from hard X-rays up to soft γ -rays-has not been pursued due to the difficulties involved in obtaining sufficient sensitivity. Indeed for those few instruments that are capable of performing this type of measurement (e.g. the COMPTEL instrument on the Compton Gamma-ray Observatory and the IBIS instrument on INTEGRAL), polarimetry itself plays a secondary role in the mission objectives, as the efficiencies (0.5% and 10% maximum, respectively) and polarimetric Q factors (0.1 and 0.3, respectively) are relatively limited. In order to perform efficient polarimetric measurements for hard X-ray and soft gamma-ray sources, with an instrument of relatively robust and simple design, a CdTe based telescope (CIPHER: Coded Imager and Polarimeter for High Energy Radiation) is under study. This instrument is based on a thick (10 mm) CdTe position-sensitive spectrometer comprising four modules of 32 × 32 individual pixels, each with a surface area of 2 × 2 mm 2 (about 160 cm 2 total detection area). The polarimetric performance and design optimisation of the CIPHER detection surface have been studied by use of a Monte Carlo code. This detector, due to its intrinsic geometry, can allow efficient polarimetric measurements to be made between 100 keV and 1 MeV. In order to predict the polarimetric performance and to optimise the design and concept of the CIPHER detection plane, a Monte Carlo code based on GEANT4 library modules was developed to simulate the detector behaviour under a polarised photon flux. The Compton double event efficiency, as well bi-dimensional double event distribution maps and the corresponding polarimetric modulation factor will be presented and discussed. Modulation Q factors better than 0.50 and double event total efficiencies greater than 10% were calculated in the energy range between 100 keV and 1 MeV. Herein we will present and discuss the general problems that affect polarimetric measurements in space, such as the inclination of the source with respect to the telescope optical axis and background radiation. Q factor calculations for several beam inclinations as well as for background together with simulated astronomical sources will be presented and discussed.

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