An international team of astrophysicists has identified a potential origin for fast X-ray transients (FXTs), which are short-lived bursts of X-rays from distant galaxies. The study, led by Northwestern University and the University of Leicester, examined the closest FXT associated with a supernova to date. The researchers discovered that a jet of high-energy particles trapped within a massive star's outer layer produced the FXT.
FXTs have been detected since the 1970s, but their origins remained unclear until now. When jets break through a massive star's layers, they cause gamma-ray bursts (GRBs). However, when these jets are contained, they emit lower energy levels detectable as X-ray signals. This new observation suggests that "failed" jets may be responsible for FXTs.
The research is significant in understanding cosmic explosions and connecting FXTs with GRBs and supernovae. Two studies detailing this event have been accepted by The Astrophysical Journal Letters. "Our work definitively shows that FXTs can originate from the explosive death of a massive star," said Jillian Rastinejad from Northwestern University.
The Einstein Probe, launched in January 2024 by the Chinese Academy of Sciences in partnership with other agencies, played a crucial role in this discovery by significantly increasing known FXT events. Shortly after its launch, it captured EP 250108a, an FXT located 2.8 billion light-years away within the constellation Eridanus.
Astronomers used multiple telescopes to track EP 250108a's evolution across various wavelengths. They found that EP 250108a was linked to a supernova dubbed SN 2025kg or "the kangaroo." This supernova increased in brightness before fading and provided evidence of helium and carbon presence.
Analysis indicated that EP 250108a is likely a "failed" GRB where jets did not escape the dying star's outer layer but remained trapped inside. Rob Eyles-Ferris noted that this outcome is more common than previously thought.
With upcoming astronomical surveys like those from the Vera C. Rubin Observatory, scientists expect to gain further insights into stellar explosions and FXTs' roles within them.
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