Einstein Probe detects fast X-ray transient EP260210a with no optical counterpart

AI Summary

EP260210a, a short-lived X-ray transient detected by Einstein Probe's WXT, showed an average unabsorbed 0.5-4 keV flux of 1.5 × 10^(-10) erg/s/cm^2. Follow-up observations by various ground-based telescopes set stringent upper limits on potential optical counterparts without detecting any new sources.

Notices (1)

Einstein Probe WXT — GRB · Tue, 10 Feb 2026 10:23:01 GMT

GCN Circulars (8)

GCN-43773 — EP260210a · Tue, 17 Feb 2026 15:04:00 GMT
The IKI-GRB-FuN team reports non-detection of a new optical source in the error circle of the fast X-ray transient EP260210a using the AZT-33IK 1.5m telescope at Mondy observatory. The only catalogued source within the error circle, a galaxy at (J2000) 11:19:19.81 +45:23:43.8, was detected and its R-band magnitudes were measured as 20.29±0.05 and 20.31±0.06 on Feb 10 and Feb 14, respectively.

GCN-43697 — EP260210a · Wed, 11 Feb 2026 15:54:23 GMT
An astronomical alert was issued regarding the observation of transient object EP260210a by the MASTER-Tunka robotic telescope in Russia. The team pointed the telescope to the errorbox 1 day after the notice time and obtained upper limits on the object's brightness in clear filter C, ranging from 18.1 to 20.9 mag. The observations are ongoing.

GCN-43696 — EP260210a · Wed, 11 Feb 2026 14:20:01 GMT
The Einstein Probe (EP) mission detected a fast X-ray transient, EP260210a, with its Wide-field X-ray Telescope (WXT). The event started on February 10, 2026, and lasted for approximately 220 seconds. The derived average unabsorbed 0.5-4 keV flux was 1.5 (-0.3/+0.4) × 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed the source a few minutes later and detected an uncatalogued source with an average unabsorbed 0.5-10 keV flux of 6.4 (-1.1/+1.1) × 10^(-12) erg/s/cm^2 and a photon index of 2.7 (-0.1/+0.1). The FXT observation had an effective exposure time of around 5 ks.

GCN-43692 — EP260210a · Wed, 11 Feb 2026 08:35:06 GMT
Astronomical alert: EP260210a: Optical upper limits with Kinder observations

GCN-43687 — EP260210a · Tue, 10 Feb 2026 17:33:25 GMT
The SVOM/VT team performed a Target of Opportunity observation of EP260210a, a transient phenomenon detected by the Einstein Probe. No uncatalogued sources were detected within the error box of EP-FXT, and the 3 sigma limit magnitudes in the VT_B and VT_R channels were found to be greater than 23.2 mag and 22.9 mag, respectively. These limits are consistent with earlier upper limits from SVOM/C-GFT and COLIBRÍ.

GCN-43684 — EP260210a · Tue, 10 Feb 2026 14:47:40 GMT
A team of international researchers using the COLIBRÍ telescope at the Observatorio Astronómico Nacional in Mexico conducted follow-up observations of the transient event EP260210a. They did not detect any new source at the position of the event and reported 5-sigma upper limits for the r and z bands: r > 23.59 and z > 22.15.

GCN-43683 — EP260210a · Tue, 10 Feb 2026 13:35:22 GMT
The SVOM/C-GFT team reported no credible candidate detection within the error box of EP260210a in their g, r, and i-band follow-up imaging using the Chinese Ground Follow-up Telescope (C-GFT). The team obtained upper limits for magnitudes in each band: i-band (20.02), g-band (20.15), and r-band (20.23). These limits were calibrated against the UCAC4 catalogue.

GCN-43681 — EP260210a · Tue, 10 Feb 2026 12:13:39 GMT
The Einstein Probe mission, a space X-ray observatory, has detected an X-ray transient designated EP260210a using its Wide-field X-ray Telescope (WXT). The transient, located at R.A. = 169.840°, DEC = 45.408° (J2000), triggered the WXT on February 10, 2026. An uncatalogued X-ray source was later identified within the error circle using the Follow-up X-ray Telescope (FXT). This discovery marks a significant finding in X-ray astronomy.