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Einstein Probe detects X-ray transient EP260920a with confirmed afterglow
AI Summary
The Einstein Probe WXT detected an X-ray transient, EP260920a, with a confirmed afterglow through VLT/HAWK-I observations. Key measurements include a net count rate of 0.11 counts/s and a J-band magnitude of 21.57, indicating potential high-redshift origins.
Measurements
| Event | EP260920a |
|---|---|
| Event ID | 01709318515 |
| Source | Einstein Probe WXT |
| Alert type | XRAY |
| Significance | high |
| Trigger time (UTC) | Sun, 20 Sep 2026 00:06:04 GMT |
| Right ascension (J2000) | 26.5298° |
| Declination (J2000) | -13.9825° |
| Position error radius | 0.005555555555555556° (20.0″) |
| Position from | EP-FXT afterglow position, GCN 45649 |
| Net count rate | 0.11 |
| Image SNR | 9.2 |
| GCN notices | 1 |
| GCN circulars | 10 |
Every localisation reported in Circulars (2)
| Instrument | Of | Error | Circular |
|---|---|---|---|
| EP-WXT | burst | 3.0′ (90%) | GCN 45649 |
| EP-FXT | afterglow | 20.0″ (90%) | GCN 45649 |
Observations (17)
Values parsed from the Circular text; each row names its Circular.
| Time since trigger | Band | Value | Telescope | Circular |
|---|---|---|---|---|
| T+0 s | 0.5-10 keV | 5.4 ± 0.15 erg/cm2/s | Einstein Probe (EP) | GCN 45655 |
| T+5 min | 0.5-4 keV | 1.94 ± 0.68 erg/cm2/s | Einstein Probe (EP) | GCN 45655 |
| T+27 min | SDSS r | > 23.5 AB mag (limit) | Nordic Optical Telescope (NOT) | GCN 45660 |
| T+50 min | SDSS z | > 22.6 AB mag (limit) | Nordic Optical Telescope (NOT) | GCN 45660 |
| T+70 min | r | 21.67 mag | — | GCN 45650 |
| T+99 min | VT_B | > 24 AB mag (limit) | SVOM/VT | GCN 45657 |
| T+109 min | VT_R | > 24 AB mag (limit) | SVOM/VT | GCN 45657 |
| T+2.6 h | SDSS g | > 23.8 AB mag (limit) | Nordic Optical Telescope (NOT) | GCN 45659 |
| T+2.6 h | r | > 23.2 AB mag (limit) | Nordic Optical Telescope (NOT) | GCN 45659 |
| T+2.6 h | i | > 22.9 AB mag (limit) | Nordic Optical Telescope (NOT) | GCN 45659 |
| T+2.6 h | z | > 22.1 AB mag (limit) | Nordic Optical Telescope (NOT) | GCN 45659 |
| T+5.4 h | r | > 24 AB mag (limit) | COLIBRÍ | GCN 45654 |
| T+5.4 h | z | > 22.9 AB mag (limit) | COLIBRÍ | GCN 45654 |
| T+5.4 h | r | > 23.5 AB mag (limit) | COLIBRÍ | GCN 45654 |
| T+5.4 h | z | > 22.3 AB mag (limit) | COLIBRÍ | GCN 45654 |
| T+26.9 h | J | 20.72 ± 0.08 Vega mag | ESO/VLT UT4 | GCN 45679 |
| T+2.1 d | J | 21.57 ± 0.06 Vega mag | ESO/VLT UT4 (Yepun) | GCN 45702 |
Notices (1)
Einstein Probe WXT — XRAY · Sun, 20 Sep 2026 00:06:04 GMT
GCN Circulars (10)
GCN-45702 — EP260920a
· Wed, 23 Sep 2026 12:09:55 GMT
A second observation of the field of EP260920a using the VLT/HAWK-I instrument confirmed the detection of a fading afterglow, indicating it is the counterpart of the event. The afterglow has a measured J-band magnitude of 21.57 and a decay slope of 1.22, confirming its association with the initial trigger.
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
nap
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
nap
GCN-45650 — EP260920a
· Sun, 20 Sep 2026 02:33:40 GMT
nap
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.
AI summary generated Thu, 29 Oct 2026 21:06:39 GMT.