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Trapped Jets in Massive Stars Revealed as Source of Fast X-Ray Transients

Frequent Einstein Probe detections followed by Rubin Observatory surveys will allow researchers to probe how jets fail to break through collapsing stars

This image shows the cosmic field in which the fast X-ray transient EP 250108a, and the supernova that followed it, were detected by Einstein Probe (EP) in early 2025. Using a combination of telescopes, including the International Gemini Observatory, funded in part by the U.S. National Science Foundation and operated by NSF NOIRLab, and the SOAR telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF NOIRLab, a team of astronomers studied the evolving signal of EP 250108a/SN 2025kg to uncover details about its origin. Their analysis reveals that fast X-ray transients can result from the ‘failed’ explosive death of a massive star. Credit: International Gemini Observatory/NOIRLab/NSF/AURA Acknowledgment: PI: J. Rastinejad (Northwestern University) Image processing: J. Miller & M. Rodriguez (International Gemini Observatory/NSF NOIRLab), M. Zamani (NSF NOIRLab)
Credit: International Gemini Observatory/NOIRLab/NSF/AURA
Dying Star's Strangled Jets Solve 50-Year-Old X-Ray Mystery
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Overview

  • Detailed observations of EP 250108a and its associated supernova SN 2025kg confirm that fast X-ray transients originate from jets that stall inside the outer layers of collapsing massive stars.
  • Since its 2024 launch, the Einstein Probe has detected FXTs several times per month, vastly outpacing the roughly annual gamma-ray burst rate and suggesting failed-jet explosions are common.
  • Rapid multi-wavelength follow-ups with the International Gemini Observatory’s FLAMINGOS-2 and GMOS instruments, along with SOAR Telescope data, tracked the evolving X-ray, optical and infrared signals of the event.
  • Spectroscopic analysis identifies EP 250108a/SN 2025kg as a Type Ic broad-lined supernova from a progenitor star of about 15–30 solar masses.
  • Researchers are gearing up to exploit the upcoming Vera C. Rubin Observatory LSST to expand transient surveys and deepen understanding of jet-failure mechanisms.