INTEGRAL Status Report - February 2005
Operations and Archiving
No clear link between the losses of the 2 (out of 19) SPI detectors and detector annealing, which preceded the failures in both cases, has been established. Failure investigations have focused on the detector preamplifiers, the high voltage power supplies and associated cabling. However, extensive ground tests by the SPI PI using flight spare hardware have been unable to replicate the failures. In addition, ESA supported thermal tests of the high-voltage feed through and computer modelling of the failure characteristics have not revealed any clues as to the nature of the failures. Since annealing is necessary to maintain the SPI high spectral resolution, it has been decided to perform the next annealing, as planned, in January-February 2005. The annealing procedure has been modified in order to minimize the thermal stresses on the preamplifiers.
The ISDC continues to routinely dispatch data products to observers within 6-8 weeks of their observation. As of 3 January 2005, the on-line ISDC public archive includes all observations made until 25 October 2003 - about one year after launch. Following improvements in the INTEGRAL scientific analysis software, the archive now includes scientific products, as well as the input files necessary to run the scientific analysis pipelines. These products include JEM-X, ISGRI and OMC light curves and JEM-X and ISGRI sky images. Additional products will be added as they become available.
The first SPI all-sky 511 keV (e+, e- annihilation) map is now available showing emission from the galactic centre region (http://astro.estec.esa.nl/Integral/POMNov2004.html). The spatial distribution of the emission is equally compatible with galactic bulge or halo distributions, the combination of a bulge and a disk component, or the combination of a number of point sources. Such distributions are expected if the positrons originate either from low-mass X-ray binaries, novae, Type Ia supernovae, or, even more excitingly, light Dark Matter. This exciting new result was reported in the News Focus of Science (2004, vol. 305, p. 1899). The detailed spectral shape of this feature obtained from ultra-deep exposures of the galactic centre region is reported in Churazov et al. (MNRAS in press). The line is un-shifted with energy of 510.954 ± 0.075 keV and a FWHM of 2.37 ± 0.25 keV. These measurements are the most stringent ever obtained. Under the assumption of annihilation in a single-phase ISM, the spectral shape is compatible with annihilation in a warm partially-ionised ISM with an electron temperature between 7000 and 40 000 K.