INTEGRAL Status Report - May 2007
Operations and Archiving
A Mission Extended Operations Review (MEOR) is planned for early May. This has the objective of making recommendations on the mission operations and support appropriate for the interval beyond the 5-year design lifetime of the mission. The MEOR will also examine proposed changes in the operational concept designed to reduce costs while maintaining an acceptable level of scientific return.
The fifth Announcement of Opportunity (AO-5) opened on 12 March 2007 with a deadline of 20 April 2007. This solicits proposals for observations to be made between August 2007 and August 2008 as well for targets in the already defined "Key Programme" fields. Key Programmes are observations that require very long exposures in order to fulfil their scientific objectives. For AO-5, following peer review, three Key Programme fields were selected in the North Ecliptic Pole, Cygnus and Galactic Centre regions and INTEGRAL will spend 2 million seconds observing each region. Due to the large fields of view and high sensitivity of the INTEGRAL instruments, there will be many additional gamma-ray targets visible in the fields that are not needed to fulfil the scientific objectives of the Key Programme proposals. These targets can be proposed for in AO-5 with a higher chance of success since it is already known that these regions of sky will be observed. In fact 160 proposals were received, of which 85 were associated with the three previously announced Key Programme fields. The over-subscription in time is about 5.9. The number of proposals received increased again (AO-3 and AO-4 had 108 and 142 proposals, respectively) reflecting the increasing level of interest and outstanding science return from the mission.
INTEGRAL has performed its fastest ever Target of Opportunity observation. Following receipt of a request to observe the anomalous X-ray pulsar 4U 0142+61, which was undergoing a large burst with characteristics similar to those of a soft gamma-ray repeater flare, INTEGRAL started observing less than 6 hours later.
Science Highlights
INTEGRAL data have been published in a total of 250 refereed papers, of which 11 are from 2007.
Astronomers, using INTEGRAL, have detected what appears to be the fastest spinning neutron star yet. This tiny stellar corpse, probably only 20 km in diameter, is spinning with a frequency of 1122 Hz. The neutron star, known as XTE J1739-285, was discovered during an active phase in October 1999 using NASA's Rossi X-Ray Timing Explorer (RXTE) satellite. In August 2005, whilst INTEGRAL was performing its regular monitoring of the central regions of our galaxy, XTE J1739-285 was observed to be again active. About a month later INTEGRAL discovered X-ray bursts from the object and following an alert from the INTEGRAL team, RXTE was once again used to observe XTE J1739-285. In total the two spacecraft observed around 20 bursts. Previous observations of other neutron stars have shown that the X-rays emitted during bursts can display oscillations that correspond to the rotation rate of the neutron star. The team searched the XTE J1739-285 bursts for evidence of oscillations. What they found was astonishing; in the brightest burst there were indeed oscillations, but they were nearly twice as fast as any previously observed and they indicate that the neutron star is rotating 1122 times every second! This is very close to the fastest possible spin rate of a neutron star - much faster and it would simply fly apart due to centrifugal forces.