In the 1990s, the ROSAT X-ray satellite performed the first deep all-sky survey with an imaging telescope in the 0.1-2.4 keV energy band, increasing the number of known X-ray sources by a factor of approximately 100. The intention of the new analysis was to improve the reliability of the catalogue, by re-analysing the original photon event files, using an advanced detection algorithm and a complete screening process.
An important feature of the new catalogue is a statistical assessment of the reliability of the sources. Because of the extreme sensitivity and low background of the ROSAT PSPC instrument, cosmic X-ray sources can be identified with the detection of just a few photons. These are sometimes difficult to distinguish from random fluctuations, and the new catalogue provides an assessment of this effect, based on simulated data.An artist’s impression of ROSAT, a satellite X-ray telescope launched 1 June 1990, on what was initially designed as an 18-month mission. ROSAT actually operated until 12 February 1999 and re-entered the Earth’s atmosphere on 23 October 2011. Image credit: DLR.The catalogue contains more than just a list of sources, for example X-ray images and overlaid X-ray contour lines for each of the detections are provided. For many sources, X-ray light curves were created to shows how the sources vary in brightness on intra-day timescales. For the brightest sources X-ray spectral fits were performed based on three basic spectral models, a power law, a thermal-plasma and a black-body emission model. This is important because it can distinguish what kind of cosmic source produces the X-rays. These include powerful accreting black holes, giant clusters of galaxies, active stars and the remnants of stars that exploded in supernova explosions.
With the new catalogue, the astrophysical community will now be able to explore these objects in the X-ray sky with more confidence, and with considerably more information.
Additionally, the experience gained by the high-energy group at MPE in creating the new ROSAT all-sky survey X-ray source catalogue will be integrated in the data reduction analysis and scientific exploration of the forthcoming eROSITA all-sky survey. The eROSITA X-ray survey telescope currently built by MPE will be launched in 2017 to scan the whole sky with even higher precision than ROSAT, reaching 30 times deeper into the universe. One of its main goals is to measure the distribution of about 100,000 galaxy clusters, containing thousands of galaxies each. The 2RXS catalogue is the deepest and most reliable X-ray all-sky survey before eROSITA.
Zooming in on black holes is the main mission for the newly installed GRAVITY instrument at ESO’s Very Large Telescope in Chile. During its first observations, GRAVITY successfully combined starlight using all four 1.8-metre Auxiliary Telescopes. The first observations using GRAVITY with the four 8-metre VLT Unit Telescopes are planned for later in 2016.
The Atacama Pathfinder Experiment (APEX) is a 12-metre radio telescope for observations at submillimetre wavelengths, operating 5,100 metres above sea level in the Atacama Desert. On 25-26 January, the project’s 10th anniversary was celebrated at the APEX base station in Sequitor, San Pedro de Atacama. A number of special guests were present at the occasion.
Although there are no seasons in space, this cosmic vista invokes thoughts of a frosty winter landscape. It is, in fact, a region called NGC 6357 where radiation from hot, young stars is energizing the cooler gas in the cloud that surrounds them.
