Successful launch of the Spectrum-RG mission
July 13, 2019
After reaching its destination, Spectrum-RG (often abbreviated as SRG) will start a four year long all-sky survey aimed to produce the most detailed map of the X-ray sky ever made. This survey will detect all massive clusters of galaxies in the visible Universe (about 100,000 clusters) and about 3 million supermassive black holes. The science goals of the all-sky survey include fundamental cosmological studies, such as using clusters of galaxies to constrain the nature of dark energy and dark matter, and understanding the growth of supermassive black holes in the Universe and their co-evolution with their host galaxies.
The SRG observatory will also discover a few hundred thousand X-ray emitting stars in the Milky Way, among them many thousands of accreting white dwarfs, neutron stars and stellar mass black holes. Over the course of 4 years, SRG will actually perform 8 independent all-sky surveys, thus allowing the study of variability of the X-ray sky. Moreover, the new map of the X-ray sky, about ~20 times more sensitive than obtained in the early 1990s by the ROSAT satellite, will open an enormous discovery space inaccessible before, promising surprising new findings, which are unforeseeable now. The SRG observatory will be able to follow up some of the most interesting targets in pointed mode observations for 2.5 years after completion of the all-sky survey.
The SRG spacecraft holding two complementary X-ray telescopes was built by Lavochkin Association (Russia). The ART-XC telescope was designed and built under the leadership of the Space Research Institute (IKI, Moscow), while the Max-Planck-Institute for Extraterrestrial Physics (Garching, Germany) produced the eROSITA telescope, thereby making a critical contribution to the scientific payload of the satellite. Roscosmos was responsible for the Proton rocket and its BLOCK-DM-3 upper stage, as well as the launch itself. It also controls the spacecraft and provides the downlink of the scientific data during the expected 6.5 years lifetime of the mission.
The Spectrum-RG project was originally conceived in 1987 and experienced a long and eventful history. Several MPA scientists, in particular Director-emeritus Rashid Sunyaev, Eugene Churazov and Marat Gilfanov, have been actively involved in SRG from the very beginning, when it started in 1987 as a collaboration of the Soviet Union with UK, Italy, Germany, Denmark, USA, and several other countries. Unfortunately, the first version of SRG was delayed and eventually cancelled in 2002.
However, Rashid Sunyaev, supported by leading astronomers and physicists in Russia, continued to actively explore possibilities to revive the project. In 2003, the Russian Academy of Sciences endorsed the concept of a new mission aimed to detect all massive clusters of galaxies in the observable Universe in order to study baryonic acoustic oscillations, and the Russian Space Agency approved it. In 2004, Sunyaev invited Günther Hasinger (then director of MPE, now ESA Director of Science) to join the project. Initially, MPE proposed to re-build the telescope designed for the ABRIXAS mission, however its sensitivity was insufficient for cosmological studies. Günther Hasinger and Peter Predehl from MPE then came up with the concept of the eROSITA telescope, which was able to satisfy the requirement of detecting 100,000 clusters of galaxies. In 2009, these concepts were formalized by an agreement between the Roscosmos and DLR space agencies, making SRG a Russian-German mission. Two eROSITA scientific consortia, a German and a Russian one were formed, sharing the eROSITA data in equal proportions. Given the history of the project and the long-term contribution of Churazov, Gilfanov and Sunyaev to the SRG mission, MPA scientists became part of the Russian consortium. From the very beginning of the project in 1987, Sunyaev is the principal investigator of the SRG mission in Russia, while Churazov and Gilfanov are now chairing key science working groups of the Russian eROSITA consortium. Together with the German eROSITA team led by MPE, the Max-Planck contribution to the scientific analysis of the data will thus be very substantial.
In the first ten days after the launch the satellite has already travelled a distance of about 700,000 km from Earth. During this time, over 100 scientists and engineers at the Lavochnkin Association, the Space Research Institute in Moscow and at three deep-space network stations in Russia have been busy receiving housekeeping data from the spacecraft, monitoring its health, and gradually switching on its various systems and tracking its orbit. Engineers and scientists at MPE and IKI are working with the eRosita and ART-XC telescopes and monitoring their behaviour. Two important milestones have been reached on July 22 and 23 when the first correction of the spacecraft orbit has been performed and the telescope covers have been opened for both instruments. The three months long journey to the point L2 will be used to test and calibrate the eROSITA and ART-XC telescopes. This so-called CalPV phase will be concluded with PV (performance verification) observations in which the telescopes’ performance will be verified in deep observations of various targets, such as the brightest and nearest clusters of galaxies, of extragalactic fields and through scans of the Galactic Plane. It is expected that the SRG observatory will start its all-sky survey in November this year.