An X-ray transient detected by Einstein Probe WXT, followed by Fermi-GBM and optical observations.

AI Summary

The Einstein Probe WXT detected an X-ray transient (EP260316a) with a double-peaked structure, followed by Fermi-GBM detecting a faint sub-threshold signal. Optical follow-up with COLIBRÍ telescope revealed a faint uncatalogued source near the error circle.

Notices (1)

Einstein Probe WXT — GRB · Mon, 16 Mar 2026 20:33:13 GMT

GCN Circulars (7)

GCN-44037 — EP260316a · Tue, 17 Mar 2026 13:06:02 GMT
Astronomers using the COLIBRÍ telescope detected a faint, uncatalogued source located near a gamma-ray burst, EP260316a. The source, with a magnitude of 24.4 and a signal-to-noise ratio of 5.7, is located at the edge of the error circle of the gamma-ray burst and is not yet confirmed as a transient. Further observations and follow-up with other facilities are encouraged.

GCN-44034 — EP260316a · Tue, 17 Mar 2026 08:21:17 GMT
The Einstein Probe (EP) mission detected a new X-ray transient, EP260316a, using its Wide-field X-ray Telescope (WXT) and Follow-up X-ray Telescope (FXT). The transient was observed immediately upon starting the WXT observation and exhibited a double-peaked structure in both the WXT and Fermi/GBM data. The WXT observation lasted for 22 seconds, while the FXT observation had an exposure time of 5.4 ks. The derived unabsorbed fluxes for the WXT and FXT observations were 3.1x10^-8 erg/s/cm^2 and 9.51x10^-12 erg/s/cm^2, respectively. The hydrogen column densities and photon indices were also measured for both observations.

GCN-44032 — EP260316a · Mon, 16 Mar 2026 17:46:14 GMT
The Xinglong Observatory at NAOC reported no detection of an optical transient associated with EP260316a using their 2.16-m and 0.8-m telescopes. The team obtained upper limits of g ~22.00 mag and ～19.9 mag for the 2.16-m and 0.8-m observations, respectively.

GCN-44031 — EP260316a · Mon, 16 Mar 2026 17:23:26 GMT
The Fermi Gamma-ray Burst Monitor (GBM) has detected a long gamma-ray burst (GRB 260316A) at a calculated location of RA = 305.5, Dec = -79.3 (J2000 degrees) with a statistical uncertainty of 3.2 degrees. The angle from the Fermi Large Area Telescope (LAT) boresight is 81.0 degrees. The team at MSFC/Fermi-GBM has provided data including a skymap, HEALPix FITS file, and light curve for further analysis.

GCN-44030 — EP260316a · Mon, 16 Mar 2026 17:12:28 GMT
A team of astronomers led by M.-H. Lee reported non-detection of a new or uncatalogued source in the EP260316a localization circle using the 1m LOT at the Lulin observatory as part of the Kinder collaboration. They obtained a 3-sigma upper limit of g-band magnitude >23.2 for the transient, uncorrected for galactic extinction.

GCN-44029 — EP260316a · Mon, 16 Mar 2026 17:06:07 GMT
Fermi-GBM detected a faint sub-threshold transient signal, EP260316a, approximately 3.6 seconds before the EP-WXT detection. The signal was best-fit with a 'soft' spectral template and had a false alarm rate of 6.5e-05 Hz. The localisation was consistent with the EP location and had a spatial association probability of 98.8%.

GCN-44027 — EP260316a · Mon, 16 Mar 2026 14:23:30 GMT
The Einstein Probe team reported a correction to the trigger time of EP-WXT alert 00199258890, which identified an X-ray transient detected by the Wide-field X-ray Telescope (WXT) on March 16, 2026. The corrected trigger time is 2026-03-16T12:33:13.451 (UTC). An uncatalogued X-ray source was detected by the Follow-up X-ray Telescope (FXT) within the WXT error circle, with a position of R.A. = 226.9840 deg, DEC = 27.4447 deg (J2000) and an uncertainty of 20 arcsec.