Scientists Uncover Source of Fast X-Ray Transients from Supernova

A significant breakthrough in astrophysics has emerged with the detection of fast X-ray transients (FXTs) linked to a supernova, providing insights into these mysterious cosmic phenomena. Researchers from an international team, led by Northwestern University and the University of Leicester, have identified the closest FXT to Earth, located approximately 2.8 billion light-years away in the constellation Eridanus. This discovery sheds light on the potential origins of FXTs, which have puzzled astronomers for decades.

Through a combination of advanced telescopes on Earth and in space, the team observed a high-energy particle geyser, or jet, that emerged from a massive star during its explosive death. While FXTs have been detected since the 1970s, their origins remained largely unexplained until now. The new findings suggest that these emissions can result from “failed” jets that do not escape the star’s outer layers, as opposed to the more energetic gamma-ray bursts (GRBs) typically associated with successful jet emissions.

The event, designated as EP 250108a, represents a pivotal moment in understanding the relationship between supernovae and FXTs. The research indicates a causal link where GRBs arise from successful jets, and FXTs originate from weak jets that are trapped. This connection clarifies the previously elusive nature of FXTs, offering a new perspective on stellar explosions.

The Einstein Probe, launched in January 2024 by the Chinese Academy of Sciences in collaboration with the European Space Agency and the Max Planck Institute for Extraterrestrial Physics, played a crucial role in this discovery. Equipped with specialized instruments for observing X-ray sources, the Einstein Probe quickly captured the FXT associated with the supernova.

A comprehensive analysis of the event involved multiple observatories. The FLAMINGO-2 spectrograph from the Gemini South telescope and the Gemini Multi-Object Spectrograph from the Gemini North telescope provided valuable near-infrared and optical data. Additionally, the W.M. Keck Observatory in Hawaii, the MMT Observatory in Arizona, and the renowned James Webb Space Telescope contributed to the extensive data collection.

As astronomers focused on EP 250108a, they identified the remnants of a supernova, later named SN 2025kg or affectionately referred to as “the kangaroo.” Over several weeks, the supernova’s brightness increased before gradually fading. Detailed examinations confirmed that “the kangaroo” is a broad-lined Type Ic supernova, typically associated with high-energy events like GRBs. However, in this instance, there was no evidence of a GRB, indicating that EP 250108a is likely a “failed” GRB.

The progenitor star that led to the supernova is estimated to have a mass between 15 to 30 times that of the Sun. This research not only enhances our understanding of FXTs but also opens new avenues for studying the life cycles of massive stars and their explosive ends.

Two companion studies detailing various aspects of the discovery have been accepted for publication in The Astrophysical Journal Letters. These papers, titled “The kangaroo’s first hop: the early fast cooling phase of EP250108a/SN 2025kg” and “EP 250108a/SN 2025kg: Observations of the most nearby Broad-Line Type Ic Supernova following an Einstein Probe Fast X-ray Transient,” highlight the collaborative effort that has resulted in this groundbreaking research.

As scientists continue to unravel the complexities of cosmic phenomena, this discovery marks a significant step forward in our quest to understand the universe and its many mysteries.