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INTEGRAL Status Report - November 2004

INTEGRAL Status Report - November 2004

Mission StatusINTEGRAL operations continue smoothly with the spacecraft, instruments and ground segment performing well. Two of the instruments have had anomalies recently. The third INTEGRAL Announcement of Opportunity for observing proposals (AO-3) opened on 13 September 2004. The AO covers observations between 18 February 2005 and 17 August 2006 and the results will be known in December 2004. Preparations for the move of the INTEGRAL Science Operations Centre (ISOC) from ESTEC to the ESAC continue.

Operations and Archiving

Shortly before the expected loss of signal due to perigee passage on 2 June, the imager (IBIS) digital electronics stopped responding to commands. Since the IBIS high-voltages (HV) were still on, passage through the radiation belts would have degraded the photo-multiplier tubes of the veto sub-system. Within the 10 minutes available before loss of signal, the Mission Operation Centre (MOC) team correctly analysed the situation and turned off the power to the IBIS peripherals. The problem has not recurred. There were 6 resets of the INTEGRAL Radiation Monitor (IREM) during the summer resulting in the instruments being put into safe-mode/stand-by for a few hours each time. The anomalies are still under investigation and the most probably cause is single event upsets of the RAM by heavy cosmic-ray particles.

The 4th spectrometer (SPI) annealing was successfully completed on 30 June with a full recovery of the pre-launch energy resolution. However, SPI detector #17 failed on 17 July (2 out of 19 detectors are now off) and attempts to recover it have been unsuccessful. To first order, these failures decrease the SPI efficiency by ~10%. It is yet unclear whether the failures are linked to the annealing which preceded the failures in both cases. The failures are most probably in the detector pre-amplifiers, HV power supplies or associated cabling. The instrument team is conducting ground tests using flight spare hardware to see it the failures can be replicated. ESA is supporting these activities with computer modeling. The INTEGRAL Science Working Team will be asked to recommend on future annealing strategy.

The fourth release of the INTEGRAL Science Data Centre (ISDC) public off-line scientific analysis (OSA) software took place in July. This release includes a number of improved data analysis tools that allow for example, better modeling of off-axis sources, as well as improved spectral response matrices. The ISDC continues to routinely dispatch data products to observers within 6-8 weeks of their observation. The first INTEGRAL observations entered the public domain on 17 July 2004 and are made available to the scientific community via the on-line ISDC archive. Currently, observations from approximately the first 8 months of observations are publicly available. The ISDC has also put a bright source catalog on-line (http://isdc.unige.ch/index.cgi?Data+sources). This contains science products from the Imager and Spectrometer (light-curves and fluxes in different energy bands) for the ~70 brightest INTEGRAL sources. It is regularly updated as more data is added to the public archive.

Science Highlights

Results from the INTEGRAL survey showed very hard emission from a region including the anomalous X-ray pulsar (AXP) 1E 1841-045 (Molkov et al, astro-ph/040216). AXPs are thought to be neutron stars where the high-energy emission is powered by an intense magnetic field - hence these sources being referred to as "magnetars". Triggered by the INTEGRAL survey result, Kuiper et al. (ApJ in press) examined R-XTE and XMM-Newton observations of 1E 1841-045 and reported the surprising discovery that the source has an extremely hard spectrum extending to ~150 keV. This was totally unexpected since previous studies of AXPs had revealed only extremely soft spectra. The discovery has major implications on the emission mechanisms of AXPs, their relation to soft gamma-ray repeaters and to the un-identified EGRET sources.

The INTEGRAL-discovered GRB 031202 turned out to be the closest and faintest gamma-ray burst (GRB) observed so far. Two papers in the August issue of Nature (Sazonov et al., vol. 430, p. 646, and Soderberg et al. vol. 430, p. 648) address the nature of this intrinsically sub-energetic event. Its luminosity is comparable to only one other GRB (GRB 980425) observed so far and it is possible that these represent a yet unknown GRB population of very faint events. Finally, by combining INTEGRAL and XMM-Newton observations of a nearby Seyfert galaxy NGC 4388, Beckmann et al. (ApJ in press) have found further evidence that doughnut-shaped gas and dust clouds surround massive black holes. These discoveries were the topics of two ESA Science News Releases (SNR-16-2004 and SNR-18-2004).

Last Update: 1 September 2019
12-Apr-2024 14:40 UT

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