Scientists have gotten a new look at our sky at X-ray wavelengths, giving us a new picture of the universe. The researchers have revisited the all-sky survey carried out by the ROSAT satellite in order to create a new image of the sky.
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. This increased the number of known X-ray sources by a factor of about 100. This was intended to improve the reliability of the catalogue by re-analyzing the original photon event files with the help of an advanced detection algorithm and a complete screening process.
Now, though, researchers have created a revised and extended version of the catalogue. Called the 2RXS catalogue, it actually provides the deepest and cleanest X-ray all-sky survey to date.
The new catalogue has a statistical assessment of the reliability of the sources. Due to 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.
The catalogue has more than just a list of sources, however. X-ray images and overlaid X-ray contour lines are provided for each of the detections. In addition, X-ray light curves were created for many sources to show how the sources vary in brightness on intra-day timescales.
But why is this new catalogue such a big deal? It will allow the astrophysical community to explore these objects in the X-ray sky with more confidence and with considerably more information.
That's not all, either. In 2017, another survey telescope will be launched, called the eROSITA X-ray survey telescope. It will scan the whole sky with even higher precision than ROSAT, and reach about 30 times deeper into the universe. One of its main goals will be to measure the distribution of about 100,000 galaxy clusters, containing thousands of galaxies each.
The findings reveal a bit more about the universe, and show researchers a bit more about the objects that produce X-rays. This, in turn, may tell scientists a bit more about these cosmic objects.
The findings are published in the March 2016 journal Astronomy & Astrophysics.
