Fast X-ray transient EP260723a detected by Einstein Probe with optical counterpart confirmed

AI Summary

Einstein Probe WXT detected a fast X-ray transient (EP260723a) on 2026-07-23 lasting ~100 seconds with peak flux of 1.4×10⁻⁹ erg cm⁻² s⁻¹ in the 0.5-4 keV band. The source position (RA 2.938°, Dec -12.112°) was refined through follow-up observations, with an optical counterpart confirmed by multiple ground-based telescopes (Liverpool, NOT, COLIBRÍ, SVOM/VT) showing magnitudes around r~22 and an extended optical plateau or rebrightening observed over ~32 hours. EP-FXT spectral analysis fitted an absorbed power-law model with photon index 2.96, and a potential host galaxy at z~0.91 was identified in the Legacy Survey.

Measurements

Notices (1)

Einstein Probe WXT — GRB · Thu, 23 Jul 2026 18:46:56 GMT

GCN Circulars (8)

GCN-45216 — EP260723a · Sun, 26 Jul 2026 12:17:29 GMT
The Einstein Probe (EP) conducted a second follow-up observation of the X-ray source EP260723a, confirming an uncatalogued X-ray source consistent with optical counterparts reported by multiple telescopes. The source's spectrum was fitted with an absorbed power-law model, and further multi-band follow-up observations are encouraged.

GCN-45212 — EP260723a · Sat, 25 Jul 2026 22:02:47 GMT
The Liverpool Telescope observed the optical counterpart of the fast X-ray transient EP260723a, detecting magnitudes consistent with those from 19 hours earlier, suggesting an extended optical plateau or rebrightening. Further observations are planned to monitor this phenomenon.

GCN-45209 — EP260723a · Sat, 25 Jul 2026 09:24:56 GMT
The Einstein Probe (EP) performed a follow-up observation of the event EP260723a, initially detected by EP-WXT. A weak X-ray excess was found at the position of the optical counterpart reported by multiple telescopes, but its association with EP260723a remains unclear due to low statistical significance.

GCN-45205 — EP260723a · Fri, 24 Jul 2026 12:08:26 GMT
The SVOM/VT telescope detected the optical counterpart of the event EP260723a in both VT_B and VT_R bands, with AB magnitudes of 22.1 and 21.9 respectively. This observation was part of a follow-up to an initial detection by EP/WXT, and the data was collected approximately 10.658 hours after the trigger.

GCN-45204 — EP260723a · Fri, 24 Jul 2026 10:38:47 GMT
The COLIBRÍ telescope observed the optical counterpart of EP260723a, detecting it with preliminary photometry values of r = 22.25 +/- 0.09 and z = 21.57 +/- 0.14. This observation was part of a follow-up effort to confirm the optical transient reported by previous studies.

GCN-45203 — EP260723a · Fri, 24 Jul 2026 07:50:37 GMT
The Nordic Optical Telescope (NOT) detected an uncatalogued source within the error circle of EP260723a, confirming the optical counterpart with a magnitude of 22.10 at a median time of 10.18 hours post-trigger. This detection is consistent with a previously reported optical counterpart, supporting the identification of EP260723a's optical counterpart.

GCN-45202 — EP260723a · Fri, 24 Jul 2026 07:25:20 GMT
The Liverpool Telescope has detected a likely optical counterpart to the fast X-ray transient EP260723a, with a measured AB magnitude of 21.86 in the r-band and a potential host galaxy identified in the Legacy Survey. The detection was made approximately 10.8 hours after the initial X-ray detection, and the source's position and characteristics are detailed in the report.

GCN-45201 — EP260723a · Fri, 24 Jul 2026 06:57:32 GMT
The Einstein Probe (EP) mission detected a fast X-ray transient, EP260723a, on July 23, 2026, lasting about 100 seconds with a peak flux of approximately 1.4 x 10^(-9) erg cm^-2 s^-1. The event's position is R.A. = 2.938 deg, Dec. = -12.112 (J2000) and follow-up observations by EP-FXT are planned.