The first Wide-Field Snapshots of the X-ray Universe

The first truly wide-field X-ray images of the sky have been taken by a pathfinder mission testing Lobster-Eye technology for the Einstein Probe (EP) satellite, writes Prof. Paul O’Brien.

The EP-Pathfinder instrument is on a Chinese test satellite launched on August 27. The first results including an 800-second X-ray “time-lapse photography” of a region of the Galactic center, a dense area at the core of our home galaxy, the Milky Way. These mark the first wide-field X-ray snapshots of our universe obtained so far using so-called Lobster-eye technology, originally pioneered at the University of Leicester.

The Leicester team includes Professors Paul O’Brien and Ian Hutchinson, and Drs Charly Feldman, Hannan Lerman and Mellisa McHugh. Via ESA funding, the Leicester team have been calibrating and characterising the Chinese built X-ray optics and detectors for EP in collaboration with the Chinese EP team.

Traditional X-ray telescopes, such as those on board XMM-Newton, Chandra or Swift, have fields of view around the size of the full Moon, half a degree in diameter. Each EP module has a field of view of nearly 350 square degrees, and the full mission will carry 12 of them. The EP-Pathfinder has one test module already demonstrating the extraordinary grasp of the new technology.

Comparison between the real observation (left) by EP WXT Pathfinder and the simulated view (right) of the same patch of sky as given in figure 1. The real observation identifies a source that had become obviously much brighter than viewed at a previous observation, as indicated by the red circle on the left. At the lower-right corner of the left image the size of the full Moon (half a degree in diameter) is given for comparison. (Image credit: CAS).

“These results are really impressive. This is the first wide-field X-ray telescope ever! You have made a record,” comments Prof. Paul O’Brien of the University of Leicester, who is the ESA appointed scientist in the EP mission. “We have been waiting for a true wide-field, soft X-ray imager for many decades so it is wonderful to see the WXT test module in flight on EP-WXT Pathfinder,” comments Prof. Richard Willingale, also of the University of Leicester.

EP is currently under construction, before undergoing tests prior to the launch planned for December 2023. Once in orbit EP will provide targets for other facilities, including JWST and Swift, opening a new era in time-domain astronomy. EP will also search for the elusive electromagnetic counterparts to gravitational-wave sources. GW facilities provide poor localisations, often hundreds of square degrees in size, or more, making it very difficult to find the source with other facilities. EP will very quickly search the location region, often in a single exposure, greatly raising the chances to find the electromagnetic “needle in a haystack”.

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