eROSITA Science Book: Mapping the Structure of the Energetic Universe

Abstract

eROSITA is the primary instrument on the Russian SRG mission. In the first four years of scientific operation after its launch, foreseen for 2014, it will perform a deep survey of the entire X-ray sky. In the soft X-ray band (0.5-2 keV), this will be about 20 times more sensitive than the ROSAT all sky survey, while in the hard band (2-10 keV) it will provide the first ever true imaging survey of the sky at those energies. Such a sensitive all-sky survey will revolutionize our view of the high-energy sky, and calls for major efforts in synergic, multi-wavelength wide area surveys in order to fully exploit the scientific potential of the X-ray data. The design-driving science of eROSITA is the detection of very large samples (~10^5 objects) of galaxy clusters out to redshifts z>1, in order to study the large scale structure in the Universe, test and characterize cosmological models including Dark Energy. eROSITA is also expected to yield a sample of around 3 millions Active Galactic Nuclei, including both obscured and un-obscured objects, providing a unique view of the evolution of supermassive black holes within the emerging cosmic structure. The survey will also provide new insights into a wide range of astrophysical phenomena, including accreting binaries, active stars and diffuse emission within the Galaxy, as well as solar system bodies that emit X-rays via the charge exchange process. Finally, such a deep imaging survey at high spectral resolution, with its scanning strategy sensitive to a range of variability timescales from tens of seconds to years, will undoubtedly open up a vast discovery space for the study of rare, unpredicted, or unpredictable high-energy astrophysical phenomena. In this living document we present a comprehensive description of the main scientific goals of the mission, with strong emphasis on the early survey phases.

Figures (102)

• Figure 1: Schematic view of the eROSITA telescope. On the left, where the front cover is omitted, the seven telescopes with their X-ray baffles are visible. On the right, the view from the bottom reveals the seven CCD housings.
• Figure 2: Simulated images of a series of eROSITA scans over a very bright, point-like source at low ecliptic latitude (0.5-2 keV flux of$10^{-9} \mathrm{erg} \mathrm{cm}^{-2} \mathrm{~s}^{-1}$ ). The left panel shows the tracks of six successive scans in one visit of the region of the sky containing he source during one 6 -months all-sky survey, while the right panel shows all the tracks of that particular source over the course of 4-years (8 all-sky surveys). Courtesy of N. Clerc.
• Figure 3: Left: PANTER test of eROSITA Flight Mirror Module FM1, with 15 inner mirror shells integrated. Shown is the PSF response of the mirror module at various off-axis angles to a point-like Al-K ( 1.5 keV ) source. On-axis HEW is 13.1 arcsec. Right: Computed HEW from a ray-tracing calculation. Red Curve: the PSF HEW as function of the off-axis angle in pointing mode. Blue Curve: the soft energy band PSF HEW averaged within an encircled off-axis angle during a scan, as a function of this off-axis angle (including vignetting): the average over the whole FoV is about 28 ".
• Figure 4: eROSITA CCD-Module. The CCD with its image area ($3 \times 3 \mathrm{~cm}^{2}$ ) and the slightly smaller frame store area (right) is connected via 384 bond wires with three CAMEX read out chips. They are mounted, together with the (passive) front end electronics, on a ceramic printed circuit board (blue). The flexlead on the right connects the CCD-Module with the experiment electronics.
• Figure 5: Schematic representation of the eROSITA Camera with the (warm) Cu-proton shield (brown), the housing (cold, green), and the CCD-Module (grey) which is thermally connected to heat pipes by a Ti-block (blue). An additional graded shield (magenta) suppresses fluorescent$X$-rays generated in the instrument and leading to an enhanced background.