The Einstein Probe was launched in January 2024 to look at X-ray transients, among other things. Its power comes from its Wide-field X-ray Telescope (WXT), which can capture 3600 square degrees of the sky in a single go. That’s an area 18,000 times the apparent area of the Moon. That is a huge patch of astronomical sky, so it’s not surprising that just two months later the probe saw a 17-minute burst of soft X-rays. Given the name EP240315a, it is an example of a fast X-ray transient (FXRT).
Because the WXT can pinpoint transients so quickly, other telescopes could make follow-up observations in real time. Within an hour after its first detection, the Asteroid Terrestrial-Impact Last Alert System (ATLAS) captured the event in visible light. Other observations from the Gemini-North telescope in Hawaii and the Very Large Telescope in Chile were able to measure the redshift of the event. They found that the light of EP240315a traveled for 12.5 billion years to reach us. Radio light from the event was captured from the Australian Telescope Compact Array (ATCA). A global team of observatories allowed astronomers to discover something interesting.
To begin with, radio observations of EP240315a were consistent with a gamma-ray burst (GRB). We often see a burst of X-rays before a GRB, but the X-rays usually appear just a few dozen seconds before the gamma rays. But in this case, the X-rays appeared six minutes before the GRB. This suggests that these GRBs occur through a process we don’t understand. The only way to be sure is to gather more data, which is where the Einstein Probe will come in.
One of the reasons we haven’t seen these kinds of early soft X-rays before a GRB is that they are rather faint. The X-ray light dims and fades as it travels billions of light-years, so it takes a sensitive detector such as the Einstein Probe to see them well. Given the rate at which gamma-ray bursts occur and the wide-field observations of the WXT, we should be able to see many more of them in the near future. Combined with the global team of other observatories, our understanding of GRBs may be set to change in the near future.
Reference: Ricci, Roberto, et al. “Long-term Radio Monitoring of the Fast X-Ray Transient EP 240315a: Evidence for a Relativistic Jet.” The Astrophysical Journal Letters 979.2 (2025): L28.