[en] A detailed series of radio observations at 10.7 GHz have been carried out to search for possible short timescale (less than or equal to 1 day) variations from active galactic nuclei. Studies were made for both approximately 15 minute variability and approximately 24 hour variability from nine such objects, but no significant changes were observed

[en] The CIPHER instrument is a hard X- and soft γ-ray spectroscopic and polarimetric coded mask imager based on an array of cadmium telluride micro-spectrometers. The position-sensitive detector (PSD) will be arranged in 4 modules of 32x32 crystals, each of 2x2 mm² cross section and 10 mm thickness giving a total active area of about 160 cm². The micro-spectrometer characteristics allow a wide operating range from ∼10 keV to 1 MeV, while the PSD is actively shielded by CsI crystals on the bottom in order to reduce background. The mask, based on a modified uniformly redundant array (MURA) pattern, is four times the area of the PSD and is situated at about 100 cm from the CdTe array top surface. The CIPHER instrument is proposed for a balloon experiment, both in order to assess the performance of such an instrumental concept for a small/medium-size satellite survey mission and to perform an innovative measurement of the Crab polarisation level. The CIPHER's field of view allows the instrument to keep a single source within the field of view for a long observation period without requiring a precise pointing system. Herein we describe the instrument design, together with results obtained in our development studies, in particular on CdTe micro-spectrometers and the integrated front-end electronics. Furthermore, we present the expected operational performance in terms of image and spectral quality (angular and energy resolution) and polarimetric capabilities for an observation of the Crab nebula from balloon altitudes

[en] Radio data on GT 0236 + 61 at a frequency of 10.7 GHz have been obtained over the period 1981 May to 1982 April and we confirm the 26.52-day regular behaviour reported by Taylor and Gregory. This source appears to be similar to several other long-period X-ray binaries such as Circinus X-1. (author)

[en] The rotation modulation collimator is an accepted instrument for use in gamma-ray astronomy. Recently an adaption of this technique has been suggested which should improve the angular resolution and sensitivity by introducing some position sensitivity into the detection plane. A prototype of this instrument, the rotation modulation collimator, has been constructed and laboratory images generated in order to assess the potention for astronomical applications. (orig.)

[en] New geometric coded aperture mask designs are proposed, with certain perfect decoding properties. Two of the new designs are compared with a quadratic residue URA mask when used in forming images with a conventional hospital gamma camera. (orig.)

[en] The abberrations present in a coded aperture imaging system have a fundamentally different origin to those found in a focussed optical instrument. A series of laboratory tests is described in which masks with carefully controlled defects were employed to generate non-perfect gamma-ray images, so that the magnitude of the aberrations introduced could be quantitatively investigated. The results of these tests are presented and the extent to which they affect the design of a practical gamma-ray imaging system is discussed. (orig.)

[en] Polarimetric measurements for hard X- and soft gamma-rays are still quite unexplored in astrophysical source observations. In order to improve the study of these sources through Compton polarimetry, detectors should have a good polarimetric efficiency and also satisfy the demands of the typical exigent detection environments for this kind of missions. Herein we present a simple concept for such systems, since we propose the use of a single thick (∝10 mm) monolithic matrix of CdTe of 32 x 32 pixels, with an active area of about 40 cm². In order to predict the best configuration and dimension of detector pixels defined inside the CdTe monolithic piece, a Monte Carlo code based on GEANT4 library modules was developed. Efficiency and polarimetric modulation factor results as a function of energy and detector thickness, are presented and discussed. Q factor of the order of 0.3 has been found up to several hundreds of keV. (orig.)

[en] The IBIS telescope on board the INTEGRAL satellite, while designed to produce high resolution images of the gamma-ray sky, will also be able to measure the polarization of strong high energy sources. We present an estimate of the polarization sensitivities of both the high energy detector (PICsIT) operating in polarization mode and of the IBIS Compton events which scatter from the low energy to the high energy detector, for possible observations of the CRAB pulsar and for the case of a strong gamma-ray burst in the fully coded field of view

[en] Pixellated Imaging CsI Telescope (PICsIT) is the high energy detector plane of Imager on Board INTEGRAL Satellite (IBIS), one of the main instruments on board the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite that will be launched in the year 2001. It consists of 4096 CsI(Tl) individual detector elements and operates in the energy range from 120 to 10,000 keV. PICsIT is made up of 8 identical modules, each housing 512 scintillating crystals coupled to PIN photodiodes (PD). Each crystal, 30 mm long and with a cross-section of 8.55x8.55 mm², is wrapped with a white diffusing coating and then inserted into an aluminium crate. In order to have a compact design, two electronic boards, mounted directly below the crystal/PD assembly, host both the Analogue and Digital Front-End Electronics (FEE). The behaviour of the read-out FEE has a direct impact on the performance of the whole detector in terms of lower energy threshold, energy resolution and event time tagging. Due to the great number of channels to be handled, an Application Specific Integrated Circuit (ASIC), that manages signals coming from groups of 16 detecting units, has been designed. The first reduced model of a PICsIT module has been now constructed and is under intensive tests in order to evaluate the main qualification parameters of the detector. In this paper, after a description of the PICsIT hardware and assembly procedures, the main results on system functionality are presented

[en] An imaging detector in the gamma range has its applications in various and different fields spanning from the medical diagnostic to the gamma astronomy. One of the techniques used in building such kind of 'gamma cameras' is based on the replication of individual pixel, each one being a stand alone detector. This kind of philosophy has been used in the construction of the PICsIT detector. PICsIT is the high-energy detector layer of the Imager IBIS that is one of the major instruments on board the INTEGRAL satellite observatory that the European Space Agency (ESA) will launch next October from Baikonour. PICsIT is made of 4096 CsI(Tl) scintillating detector 8.4 x 8.4 x 30 mm in size coupled to a PIN PD. Its operative range is 180-20400 keV and its operative modes allows to collect the information from both photoelectric events, which involves just one pixel and Compton or Pair events that involves more than one pixel at the same time. PICsIT is operating with a coded mask placed 3 m far from the detector. PICsIT has been integrated in the INTEGRAL satellite since the end of the year 2001 and is now undergoing the test foreseen for this kind of experiments