INTEGRAL Status Report - February 2003
The spacecraft commissioning has been completed and went very smoothly. The spacecraft is fully functional with a very high level of performance and no loss of redundancy. The pointing stability (~arc seconds in yaw and pitch) is much better than specified and slews are being performed routinely with high accuracy. The available power from the solar panels is higher than specified, such that large sun aspect angle of 400 can be maintained throughout eclipse season and beyond nominal mission duration. The sky visibility thus is enhanced. The remaining fuel (180 kg), good power margin, and available redundancy mean that the expected lifetime of Integral comfortably exceeds 5 years.
The scientific instruments have also been commissioned and the PV observations (Cygnus and blank fields) have been completedexcept for the Crab Nebula "standard candle" calibration target, which cannot be observed until 2003 February due to solar aspect angle constraints. It is too early to have firm conclusions on the scientific performance of the instruments. In general, the background due to cosmic particle radiation is higher than expected which results in a shortage of available telemetry. The radiation monitor, IREM, is also functioning nominally and being used throughout the orbit.
The energy resolution of the spectrometer, SPI, is excellent and consistent with that measured before launch. The sensitivity at different energies is consistent with, or within a factor ~2, of that expected. To stay within the available telemetry resources, the SPI operating modes have been modified, resulting in a loss of some timing information. The spatial resolution of the imager, IBIS is as expected, and unprecedented for a gamma-ray instrument. The sensitivities of both IBIS detectors are very close to those predicted prior to launch. Shortly after the start of operations of the X-ray monitor, JEM-X, degradation in performance, probably due to damage by heavy ions, was noticed. In order to minimise further losses, the JEM-X anode voltages have been reduced. The reduced degradation rate should allow the instrument to be operated for the nominal mission duration. Because of the risk of degradation, only one of the two detectors is being used for science operations. These changes result in an increase in the JEM-X low-energy threshold from 3 keV to ~4.5 keV and a reduction in sensitivity (at 6 keV), compared to that predicted prior to launch. Otherwise, the instrument meets its science performance goals. The optical monitor, OMC, is working nominally in full compliance with its specification.
Operations and Archiving
The Integral ground segment is working well with data being received from Redu or Goldstone by the MOC at ESOC. Occasional problems are being experienced with data losses from Goldstone. Mission planning timelines are being routinely generated by the Integral Science Operations Centre and sent to the MOC. The AO-1 programme started on 30 December 2002 and the short-term observing plan is available online. Currently four galactic plane scan arcs have been completed (parts of the core programme) as well as open time observations of MR2251-178, the SN 1987A field, 3C 273 (coordinated with XMM-Newton), SN1006 and Cas A. The data from the few remaining PV observations performed between 18 and 29 December 2002 will be made publicly accessible via the ISDC web site.
The Integral Real time science telemetry is being forwarded to the Integral Science Data Centre (ISDC) with delays of only a few seconds. The ISDC quick look and data analysis software is generally working well and being rapidly enhanced as a better understanding of the instrument performances is obtained. Currently there are concerns about the un-expectantly large number of small gaps in the telemetry arriving from MOC. The first release of data and science products to observers is scheduled for March 2003 with the ISDC scientific analysis software and documentation being made publicly available in April 2003.
Science Highlights
Analysis of quasi-simultaneous observations of Cyg X-1 with RXTE and Integral shows a remarkably good spectral agreement between IBIS, SPI and the high-energy instrument on RXTE (HEXTE). This indicates that the Integral ground calibration is fairly representative of the in-flight performance and that the ISDC data analysis is able to reliably extract and process spectra from these two coded-mask instruments.
Two GRBs have been detected in the fields of view of the gamma-ray instruments. For GRB021125 a 30' radius position was provided with 21 hours of the event and a 2' radius position within 4 days. For GRB021219 a 20' radius position was provided within 5 hours and a 4' radius position within 11 hours. The Integral positions are fully consistent with those derived from the IPN. It has been agreed that the Integral burst alert system is now sufficiently reliable for bright GRBs, that alerts will be issued fully automatically resulting in a delay of only ~30 seconds. Approximately, one GRB is being detected in the SPI anti-coincidence system each day.