EARTH — The Einstein Probe captured an X-ray transient event from a celestial object named EP240305a on March 5, 2024. This event exhibited characteristics similar to a gamma-ray-dark gamma-ray burst, a type of extragalactic fast X-ray transient.

The EP240305a event included two X-ray flares, separated by approximately 200 seconds. The initial flare lasted about two minutes, and the subsequent flare extended for just over four minutes. No gamma rays were detected from this event.

Following the initial capture, researchers directed both ground-based and space-based telescopes toward the EP240305a source. These observations collected data across X-ray, infrared, optical, and radio wavelengths. X-rays from EP240305a faded within a few days of the initial burst, while radio emissions from the event diminished over several weeks.

The emission patterns observed from EP240305a did not align with those typically seen in tidal disruption events or stellar flares. Other types of X-ray bursts that occur on similar timescales do not typically emit radio signals. The behavior of EP240305a is most consistent with gamma-ray bursts, despite the absence of detected gamma rays.

The scientists involved in the study reported their findings on EP240305a on June 13 in the Monthly Notices of the Royal Astronomical Society. The Einstein Probe, launched in 2024 through a collaboration between the Chinese Academy of Sciences and the European Space Agency, was designed to scan the sky for high-energy X-ray emission events. The spacecraft orbits Earth every 96 minutes and can survey almost the entire night sky approximately every five hours.

In the study, researchers R. Ma et al. wrote, "In the case of EP240305a, the current data do not allow us to firmly establish a GRB origin, and we therefore conservatively classify it as a gamma-ray-dark GRB-like transient or more broadly an extragalactic fast X-ray transient."