Hidden X-ray phase revealed in likely neutron star merger

An international team of astronomers, including researchers from the Department of Physics and the Hong Kong Institute for Astronomy and Astrophysics (HKIAA) at The University of Hong Kong (HKU), has discovered a previously hidden phase of high-energy activity following the merger of compact stars. This event, known as EP250704a in X-rays and GRB 250704B in gamma rays, was observed by the China-led Einstein Probe (EP), the Space Variable Objects Monitor (SVOM) and the Insight-Hard X-ray Modulation Telescope (HXMT).

While the gamma-ray burst lasted only about 0.4 seconds, the source continued to shine in soft X-rays for nearly 10 minutes, revealing a phase of activity that conventional gamma-ray observations would likely have missed. The findings have been published as a cover article in Science Bulletin, highlighting how Einstein Probe's continuous monitoring of a wide area of the sky at soft X-ray energies allowed researchers to uncover this hidden high-energy phase following the merger.

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