INTEGRAL Status Report - April 2003
Due to the unexpectedly high background, a shortage of telemetry has been a concern since launch. In order to ameliorate this situation, an onboard software patch is under test that will increase the telemetry rate by around 20%. This is sufficient to recover the lost information. Upgrades to the ground segment necessary to cope with the increased telemetry are being made. It is expected that the increase in telemetry rate can be implemented by the end of May. Occasional loss of guide stars continues to occur, but does not have a major operational impact or result in a significant loss of scientific return. The fuel usage and operational efficiency were recently reviewed. The mean fuel usage of 0.02 kg/day is well within expectations and will comfortably allow for a longer than 5 year mission duration.
The instruments are working well. IBIS is fully operational. Just prior to the Crab observations, an on-board software patch was installed that reduced the IBIS telemetry usage by ~15%. The additional free telemetry has been allocated to SPI to increase the amount of timing information that can be provided. Only one of the two JEM-X instruments is being operated while an anomaly is being investigated. OMC is fully operational. Two anomalies that resulted in the loss of a few hours of OMC observing are being investigated. Following annealing, the SPI energy resolution is fully inline with pre-launch expectations and the instrument is fully operational. IREM is fully operational. A software patch to improve the signals available to the other instruments when INTEGRAL encounters intervals of high background radiation is being prepared.
Operations and Archiving
The INTEGRAL observing programme is proceeding with a good efficiency. As part of the guaranteed time programme a series of scans along the galactic plane and in the galactic centre region have been performed. A number of open time targets have been observed. These cover a wide range of astronomical classes including clusters of galaxies (Perseus and Coma), supernova remnants (SN 1987A, SN1006 and Cas A), accreting binaries (GRS 1915+105), and active galactic nuclei (3C 273, Cen A, and MR 2251-178). In March and April the galactic centre region was visible with INTEGRAL. This is a region of high scientific interest with many bright gamma-ray sources present, many of which are black holes. The highly variable nature of this region resulted in requests to perform 6 different Target of Opportunity programmes (4U 1630-47, Aql X-1, XTE J1720-318, XTE J1550-564, GRS 1915+105 and XT 1741-322). These observations of high-priority targets involved considerable re-planning of the INTEGRAL timeline. This was performed in a reliable and efficient manner demonstrating the overall good performance of the mission planning component.
The INTEGRAL ground segment continues to work well. A large number of telemetry gaps are still being experienced from the Goldstone station. There are a number of different causes for these gaps and solutions are being investigated by the MOC and Goldstone teams. The cause of the numerous short telemetry gaps is now understood and tests of alternative transmission methods, which should solve the problem, are being conducted.
The INTEGRAL short-term observing plan is available up to one month in advance. Delays in reception of the INTEGRAL consolidated data CDs by the ISDC have been fixed. Data from observations performed between 18 and 29 December 2002 are now publicly available on the ISDC web site. The first release of the ISDC scientific data analysis software to the astronomical community occurred at the beginning of April. The release includes software, test data, and data analysis and installation guides. Following confirmation that the data products meet the required quality standards, the first data and processed products will be sent to observers at the end of April.
A total of five confirmed gamma-ray bursts have been detected by INTEGRAL within the fields of view of the gamma-ray instruments in approximately five months of operations. Probably the most interesting of these is GRB030227. A circular was issued to the Gamma-ray burst community within 0.5 hours of the burst allowing for rapid follow-up observations in other wavebands. These revealed a fading optical counterpart while XMM-Newton, observing only 8 hours after the burst, detected a fading X-ray counterpart and provided a high quality spectrum.
A number of new transient high-energy sources have been detected by INTEGRAL creating much interest in the high-energy astronomical community. The first of these, IGR J16318-4848, revealed a highly unusual, line-rich, strongly absorbed spectrum in an XMM-Newton follow-up observation. The good coordination between the two ESA high-energy missions is clearly enhancing the scientific return of both. Another 3 bright gamma-ray sources have been discovered using INTEGRAL scanning and open time data. One of these, IGR J16358-4726, was found to exhibit 5850 sec pulsations during a serendipitous Chandra observation. These pulsations are also seen by INTEGRAL. It is unclear whether they represent the spin or orbital period of the system.