The Advanced Telescope for High-Energy Astrophysics (Athena) has been selected following a very competitive international selection process as second Large Class mission by ESA for a launch in 2031. This telescope is designed to address two fundamental topics:
• Determine how and when large-scale structures formed in the Universe and track their evolution from formation epoch to the present time. A large fraction (30-40%) of the gas has still escaped detection (the so-called missing baryons). As these structures have a typical temperature of 10^5-10^7 K, X-ray observations are mandatory (in short ‘the hot Universe’).
• Perform a complete census of black hole growth in the Universe, determine the physical processes responsible for that growth and its influence on larger scales, and trace these and other energetic and transient phenomena to the earliest cosmic epochs (‘the energetic Universe’).
Athena will enable, for the first time, a complete study of these topics on the relevant evolutionary time scales. It is the only approved X-ray observatory for the early 2030’s and complements other world-class space and ground based facilities (SKA, E-ELT, ALMA, CTA) with matching sensitivity.
The Athena space mission is enabled by three key components. An X-ray collecting mirror with an effective area of 1.4 m^2 and an angular resolution of 5 arcsec (HEW), a Wide Field camera with a Field of View of 40 x 40 arcmin^2 and an integral field unit with an energy resolution ranging between 200 – 3000 over a field of view of 5 arcmin (diameter). This mission can be realized thanks to long-term investments in the telescope technology in combination with the first ever Integral Field Unit in the soft X-ray band (X-IFU), capable to separate spectrally emission lines of highly ionized elements. The achieved breakthroughs in the relevant technology are:
• the innovative telescope using high quality Si wafers as reflecting surfaces. These have been developed on a large scale for the semi-conductor industry. This technology enables an unprecedented collecting area in combination with the superb angular resolution while staying within the mass limits of a space mission.
• The new cryogenic detectors operating at sub-K temperatures with a large array of absorbers, read-out using a transition edge sensor (TES), with a spectral resolution capable of measuring the properties of the hot gas.
Both these technologies have been pioneered in the Netherlands. Implementing this technology in a space mission, with its expected harsh environmental conditions (radiation, thermal loads, launch) in combination with the required high reliability requires experienced partners. The mission includes a large telescope (12 m focal length, mirror with a diameter of 2.6 m) encompassing more than 100.000 accurately aligned wafers (reflectors) and two instruments in the focal plane. Athena has a planned operational lifetime of 5 years with consumables to extend the mission life time to more than 10 years.
The Dutch contribution is at the center of the X-IFU instrument and is recognized by the co-Principal Investigator role (co-PI) for NWO-I/SRON.