With the release of its first two images, JAXA’s X-ray telescope XRISM has officially reached the milestone of First Light. The images show the galaxy cluster Abell 2319 and supernova remnant N132D, demonstrating XRISM’s large field-of-view and high spectral resolution. SRON has developed the filter wheel and an X-ray source used to calibrate the energy scale of the Resolve instrument.
X-ray images of the cosmos look very different to the images we are used to seeing in visible and infrared light, such as those from the James Webb and Hubble Space Telescopes. They also convey unique information about the Universe’s biggest dramas, as X-rays are a very high-energy type of light emitted in the hottest and most violent events.
Abell 2319 cluster
The test images were made during the mission’s commissioning phase, when engineers carry out all the tests and checks needed to make sure the spacecraft is working as well as possible. The first one is a wide view of a nearby cluster of galaxies called Abell 2319. In purple we see X-ray light from million-degree gas that permeates between the galaxies in the cluster. Observing this gas helps astronomers measure the total mass of the galaxy cluster, revealing information about the birth and evolution of the Universe.
XRISM’s observations of galaxy clusters will also provide insight into how the Universe produced and distributed the chemical elements that we find on Earth today. The hot gas found within clusters is a remnant of dying stars over the history of the Universe. By studying the X-rays emitted by the gas, XRISM will discover which ‘metals’ (elements heavier than hydrogen and helium) it contains and map how the Universe became enriched with them.
Supernova remnant N132D
The second image shows the remains of a massive star exploding in the nearby Large Magellanic Cloud, a satellite galaxy of our Milky Way. The different colors indicate different energies of X-ray light, with red being lowest energy and blue being highest energy.
Using its Resolve instrument, XRISM complements the image of the supernova remnant taken by Xtend with spectral view of the chemical elements that exist within N132D. This allows scientists to work out where exactly in the supernova remnant each element can be found. XRISM can identify each element by measuring the specific energy of X-ray light that it emits. Within XRISM’s energy range, scientists can distinguish the elements Silicon (Si), Sulphur (S), Argon (Ar), Calcium (Ca) and Iron (Fe) – elements that are made only in supernova explosions. XRISM helps us measure their abundances, velocities, temperature and density. It also lets us put together a 3D map of the motion and distribution of the chemical elements as a result of the interaction between the supernova remnant and its surroundings.
For comparison, the faint grey line shows the same spectrum from JAXA’s Suzaku X-ray telescope. The energy resolution from XRISM is over 40 times better over the energy range shown in this spectrum.
What has happened since launch?
XRISM launched on 7 September 2023. Since then, JAXA engineers and scientists have been working hard to get the telescope ready for science. This included switching on and testing out XRISM’s two instruments, Xtend and Resolve.
The spacecraft is currently in good condition. Checks on onboard systems such as those that control the power supply, the orientation of the spacecraft, and the communication with Earth, confirm that they work as planned. Hardware provided by ESA was tested early in the commissioning phase and is all working as expected.
The Resolve instrument’s energy resolution – the key scientific performance indicator – is exceeding requirements. However, engineers have not yet managed to open a window protecting the detector before, during and after launch. Efforts are ongoing to fix the issue, but the XRISM team has decided that planned scientific observations should assume that the window will remain in place. The N132D spectrum demonstrates that groundbreaking science can still be achieved.
What’s next?
The spacecraft commissioning phase will be finished by the end of January. In February, JAXA will start calibrating the instruments and fully demonstrating their capabilities. Scientists have already been invited to submit proposals for observations that they would like to make starting from August 2024. The deadline is 4 April 2024. Observations made using XRISM will complement those from XMM-Newton, and will be followed up in the future by NewAthena. SRON is also involved in both of those missions.
SRON contribution
The Dutch contribution to XRISM consists of the filter wheel for Resolve. The filter wheel puts different filters in front of the camera, allowing astronomers to select the brightness and wavelengths of the incoming radiation. They will for example use the Molybdenum gray filter if a star or black hole emits more X-rays than the detector can handle. They will choose the Beryllium or Polyimide aluminum filter to block certain wavelengths. A radioactive iron-55 source is included in the filter wheel to calibrate the X-ray camera. Together with the company Exosens (former Photonis), SRON has also developed an electronically controlled X-ray source allowing continuous calibration of the detector.