Einstein Probe detects X-ray transient EP260306a with high redshift (z=4.773)

AI Summary

An X-ray transient was detected by Einstein Probe's WXT, followed by identification of an optical counterpart and confirmation of a redshift of z=4.773, indicating a highly significant cosmological event.

Notices (1)

Einstein Probe WXT — GRB · Fri, 06 Mar 2026 01:29:20 GMT

GCN Circulars (7)

GCN-43959 — EP260306a · Wed, 11 Mar 2026 10:31:25 GMT
The IKI-GRB-FuN team reported no detection of the optical counterpart of fast X-ray transient EP260306a using the AZT-33IK 1.5m telescope at Mondy observatory from March 7 to 9. The team took several 120-second frames in the R band and did not detect the previously reported optical counterpart. The photometry is based on nearby USNO-B1.0 stars and is not corrected for Galactic extinction.

GCN-43937 — EP260306a · Sat, 07 Mar 2026 02:34:23 GMT
Astronomical alert: EP260306a: refined analysis of the EP-WXT and EP-FXT observations

GCN-43934 — EP260306a · Fri, 06 Mar 2026 13:36:30 GMT
Astronomers using the Gemini-North telescope have identified the redshift of a fast X-ray transient, EP260306a, as z = 4.773 based on optical spectroscopy. The observation revealed significant continuum detection and various absorption features, confirming the transient's distance and establishing its cosmological significance.

GCN-43933 — EP260306a · Fri, 06 Mar 2026 10:21:37 GMT
The Space Variable Objects Monitor (SVOM) team, led by the Chinese National Space Administration and the French National Center for Space Studies, reported a Target of Opportunity observation of gamma-ray burst EP260306a using the SVOM/VT instrument. The team detected the optical counterpart of the burst in both VT_B and VT_R bands, with AB magnitudes of 23.1±0.2 and 21.7±0.1, respectively. The observation began 2.268 hours after the trigger.

GCN-43931 — EP260306a · Fri, 06 Mar 2026 04:38:09 GMT
A team of astronomers using the COLIBRÍ telescope at the Observatorio Astronómico Nacional in Mexico observed the optical counterpart of a transient event (EP260306a) reported earlier by Li et al. The team obtained 1 hour 53 minutes of data in the r, i, and z filters and detected the transient with preliminary magnitudes of r = 23.27 ± 0.25 and z = 21.58 ± 0.12. The transient has faded since its initial detection, and the team estimates a temporal decay index of α ≈ 1. A preliminary spectral energy distribution fit suggests a high-redshift event, possibly between z=4 and z=5, but cannot rule out a redder source at a lower redshift. The team encourages further spectroscopic observations.

GCN-43930 — EP260306a · Fri, 06 Mar 2026 02:47:52 GMT
The Einstein Probe mission, launched in 2024, has detected an X-ray transient, EP260306a, using its Wide-field X-ray Telescope (WXT). The transient's position was determined to be R.A. = 145.955 deg, DEC = 15.685 deg (J2000) with an uncertainty of 3 arcmin. A follow-up observation with the Follow-up X-ray Telescope (FXT) identified an uncatalogued X-ray source at R.A. = 145.9478 deg, DEC = 15.6963 deg (J2000) with an uncertainty of 20 arcsec. The location of the reported optical counterpart is consistent with the X-ray source. Further information will be provided once telemetry data is received.

GCN-43929 — The EP-WXT trigger 01709258759 · Fri, 06 Mar 2026 02:31:14 GMT
Astronomers at NAOC, TAU, and University of Arizona observed an uncataloged optical source using a Las Cumbres 1m telescope at McDonald Observatory, 20 minutes after an EP/WXT trigger. The source, located at RA 145.949, Dec 15.6937, has an initial magnitude of 21.6.