Einstein Probe detects X-ray transient EP260920a with possible high-redshift near-infrared counterpart

AI Summary

The Einstein Probe WXT detected an uncatalogued X-ray transient (EP260920a) on 2026-09-20 at 00:06:04 UTC with a position of RA 26.557°, Dec -13.967° and 3 arcmin localization uncertainty. The source shows a 0.5-4 keV spectrum consistent with an absorbed power-law (photon index 2.61) and an average unabsorbed flux of 1.94×10⁻¹⁰ erg s⁻¹ cm⁻². Multiple optical follow-ups detected no counterpart down to limits of r > 23.5-24.0 mag within hours of the trigger, but a near-infrared source was subsequently identified by VLT/HAWK-I at J ~ 20.72 mag approximately 1.1 days post-trigger, suggesting a high-redshift origin for this event.

Measurements

Notices (1)

Einstein Probe WXT — GRB · Sun, 20 Sep 2026 00:06:04 GMT

GCN Circulars (9)

GCN-45679 — EP260920a · Mon, 21 Sep 2026 10:34:38 GMT
A new near-infrared source, potentially associated with the event EP260920a, was detected by the VLT/HAWK-I instrument at coordinates RA 01:46:06.91, Dec -13:58:49.83. The source, with a magnitude of J ~ 20.72, is believed to be a high-redshift candidate due to its lack of detection in historical surveys.

GCN-45660 — EP260920a · Sun, 20 Sep 2026 16:14:12 GMT
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GCN-45659 — EP260920a · Sun, 20 Sep 2026 12:04:25 GMT
The Nordic Optical Telescope (NOT) observed the field of EP260920a, detected by the Einstein Probe, but found no new optical sources down to specific magnitude limits. This non-detection suggests that EP260920a could be a high-redshift event, prompting a recommendation for near-infrared follow-ups.

GCN-45657 — EP260920a · Sun, 20 Sep 2026 10:35:29 GMT
The SVOM/VT telescope conducted follow-up observations of the event EP260920a, starting approximately 43 minutes after the trigger, but did not detect any new optical sources within the error box. The observations, consistent with non-detections from other facilities, provide upper limits on the optical brightness of the event.

GCN-45655 — EP260920a · Sun, 20 Sep 2026 08:34:10 GMT
The X-ray transient EP260920a, detected by the Einstein Probe (EP) mission, was analyzed with refined data showing it started approximately 300 seconds before the initial trigger. The event's X-ray spectrum and position were further detailed, with an optical transient candidate reported nearby, though not within the refined error circle. Further multi-wavelength observations are encouraged to determine the nature of this event.

GCN-45654 — EP260920a · Sun, 20 Sep 2026 08:00:28 GMT
The COLIBRÍ telescope observed the field of EP260920a and did not detect the tentative source reported by Li et al. down to 3-sigma limits of r > 24.0 and z > 22.9. Additionally, no uncatalogued source was detected within the FXT region down to 5-sigma limits of r > 23.5 and z > 22.3.

GCN-45653 — EP260920a · Sun, 20 Sep 2026 05:35:25 GMT
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GCN-45650 — EP260920a · Sun, 20 Sep 2026 02:33:40 GMT
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GCN-45649 — EP260920a · Sun, 20 Sep 2026 01:22:23 GMT
The Einstein Probe (EP) mission detected an X-ray transient, designated EP260920a, on September 20, 2026, using its Wide-field X-ray Telescope (WXT). A follow-up observation with the Follow-up X-ray Telescope (FXT) confirmed an uncatalogued X-ray source within the WXT error circle, highlighting the EP's capability to monitor and follow up on X-ray transients.