Einstein Probe First Light

Images confirm new X-ray satellite’s revolutionary capability to detect and follow-up explosive events in the high-energy Universe

April 27, 2024

The Einstein Probe science team has released the first images taken by this new scientific satellite, launched on January 9, 2024, demonstrating excellent performance sometime exceeding the design expectations for its two instruments. The Wide-Field X-ray Telescope (WXT) is able to scan half the sky within 5 hours, systematically searching for new X-ray sources associated with highly energetic transient phenomena around black holes and neutron stars. The Follow-up Telescope (FXT) performs follow-up observations of the most exciting events with deeper exposures. The satellite project, led by the Chinese Academy of Sciences (CAS), features major contributions from the Max Planck Institute for Extraterrestrial Physics (MPE), in particular for the FXT instrument, which is based on the design of the eROSITA telescope, giving a new lease of life to the X-ray imaging technology developed at MPE.

The first images taken by the Einstein Probe satellite were revealed to the public following the 7th Joint Workshop of the Einstein Probe Consortium held in Beijing from 24 to 26 April 2024. Since launch, the satellite and its instruments have been undergoing a phase of commissioning during which their functionalities and performance have been evaluated and calibrated. 

“WXT has a unique combination of field of view, monitoring capability, and high sensitivity designed to make new discoveries in the transient X-ray sky. With these first light data, we now know that this promise will be realized,” says Arne Rau, an astrophysicist at MPE and member of the Einstein Probe Science Management Committee. By now, 10 of the 12 modules of the WXT have completed their calibration. The instrument meets and sometimes exceeds its science requirements with a positional accuracy of ~2 arcmin, an angular resolution of 4-5 arcmin, and a light-collecting area of approximately 3 cm2 (at the energy of 1 keV). The WXT optics in-orbit performance was well predicted by the ground calibration at MPE’s PANTER facility.

In-orbit tests for the FXT have similarly verified the performance of its two units, which closely resemble the design of MPE’s eROSITA X-ray telescope. For Einstein Probe’s FXT, MPE supplied the spare mirror module from eROSITA and worked with ESA and industry partners to provide the second mirror module. “It is very gratifying to see that both mirror modules of the FXT in orbit show the performance that we have measured in our X-ray tests on the ground,” says Peter Friedrich, who led MPE’s optics contribution to Einstein Probe, “Personally, I am very pleased that the eROSITA replacement spare module has now also found a novel scientific use.”

MPE also contributed the state-of-the-art pnCCD detector modules for both FXT units, based on the Max Planck Society's Semiconductor Laboratory sensor technology also used for eROSITA. “The FXT CCD detector modules developed at MPE for spatially and time-resolved spectroscopy of X-ray photons have fulfilled the high expectations we had in them before the satellite launch. We are very happy to have made a decisive contribution to the success of the Einstein Probe mission,” adds Norbert Meidinger, who was responsible for the detectors at MPE. The mirror-detector combination provides a source positioning accuracy of <10 arcsec and a light-collecting area of ~300 cm2 at 1.25 keV, along with excellent performance in terms of energy and time resolution. Like the WXT, the FXT achieved and sometimes exceeded its science requirements.

Even during this early checkout phase, Einstein Probe has started making new discoveries. “The WXT started finding new transients almost as soon as it was turned on. By now we have discovered more than a dozen new X-ray transients and over a hundred flares from stars in our Galaxy,” adds Rau. These findings were quickly reported to the community in over 20 global telegrams, leading to a worldwide follow-up effort with ground- and space-based telescopes, including MPE’s own GROND instrument at the 2.2m MPG telescope in La Silla. These early results confirm Einstein Probe’s potential to uncover new sources and potentially new astrophysical phenomena, especially energetic events associated with black holes, neutron stars and their mergers.

The project is the first major space collaboration between MPE and CAS, combining unique technologies from China and Europe towards a common scientific goal. “Einstein Probe leverages the instrument developments we made for eROSITA to open up new scientific opportunities,” says Paul Nandra, Director of the MPE high-energy group, who adds, “The collaboration has worked perfectly – we’re looking forward to the next one!”

Over the coming months, the satellite will continue to carry out its in-orbit calibration activities before entering the operational phase, starting around mid-June 2024.

Einstein Probe is a space science mission led by the Chinese Academy of Sciences (CAS) in collaboration with MPE, the European Space Agency (ESA), and the French space agency, Centre National D'Etudes Spatiales (CNES).

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