INTEGRAL Status Report - November 2005
Operations and Archiving
July and August 2005 were notable for intervals of strongly increased solar activity. These resulted in a reduced observing efficiency, but did not produce any degradation of the instrument performances. The 6th SPI annealing took place from 2005 June 24 to 29. The SPI switch-on was nominal and the energy resolution recovered as expected. It is worth recalling that following the losses of two (out of 19) SPI detectors approximately two weeks after the ends of previous annealing cycles, extensive ground tests were conducted. However, these did not reveal any link between annealing and the failures and as a precaution, the procedures for the last two annealings were modified to minimize the thermal stresses on the pre-amplifiers. This appears to have been successful as there have been no further failures since 2004 July.
The ISDC continues to routinely dispatch data products to observers within 6-8 weeks of their observation. As of September 2005, the on-line ISDC public archive includes nearly all public observations made until July 2004. In collaboration with the ISDC, the ISOC Science Data Archive (ISDA) was made publicly available in July 2005. The ISDA is based on the technology used to create the ISO and XMM-Newton ESA archives and will provide users experienced with for example, the XMM-Newton archive with a familiar interface by which to access INTEGRAL science products.
The latest version of the Offline Scientific Analysis (OSA-5) was released by the ISDC in July 2005. In comparison with previous versions, OSA-5 provides much improved user friendliness, better documentation, and improved quality of the scientific results that can be obtained. In response to INTEGRAL Users Group recommendations, the instrument and ISDC teams have provided updated science validation reports, a "cookbook" detailing how diffuse emission may be analysed using the INTEGRAL spectrometer, SPI, and a report presenting the spectral cross-calibration of the various INTEGRAL instruments.
As of the end of August 2005, there have been 114 refereed and 289 non-refereed papers containing results from INTEGRAL. SPI has produced the first all-sky map of the 511 keV line emission produced when electrons and their anti-matter equivalents, positrons, collide and annihilate. This shows that the emission is strongly concentrated towards the galactic bulge region, with only a faint component along the galactic plane. Astronomers often investigate the nature of unknown emission by comparing its sky distribution with those of known classes of objects such as hot stars, molecular clouds, old stars etc. However, the 511 keV line sky distribution is unique and cannot be reconciled with that of any of the likely sources of anti-matter such as the decay of radioactive elements, cosmic rays interacting with the interstellar medium, black holes or neutron stars. One intriguing possibility, not excluded by the INTEGRAL results, is that the emission is produced by the annihilation or decay of an exotic form of Dark Matter, yet to be discovered. The nature of the sources responsible for the anti-matter is clearly one of the key areas for further investigation by INTEGRAL over the coming years.
The INTEGRAL imager, IBIS, has been used to detect a new persistent soft gamma-ray source, IGR J18135-1751. This source is coincident with one of the ten objects recently reported by the HESS collaboration as part of the first TeV survey of the inner part of the Galaxy. These extreme sources are of great interest as they may be the sites of cosmic high-energy particle accelerators. Two out of those newly discovered HESS sources, located along the galactic plane, have no known radio or X-ray counterparts raising the possibility that they may be a new class of object. However, the INTEGRAL results reveal that HESS J1813-178 is probably either a pulsar wind nebula embedded in its supernova remnant, or a pulsar in a high-mass binary system – both well known types of objects. In contrast to the anti-matter case, the INTEGRAL results therefore exclude the exiting hypothesis that HESS J1813-178 belongs to a new class of TeV objects, or that it is a cosmic "dark particle" accelerator.