GCN Circular 45885
EP261006a / AT 2026aetp: Multiband optical follow-up with the PKU 60cm Telescope
From: Y.C. Kang at Peking University
Issued: 2026-10-10 13:01 UTC
Type: X-ray Transient, Optical Transient
Yacheng Kang (PKU), Qiang Wang (PKU), Ruize Shi (PKU), Chenxi Bao (PKU), Xinmiao Zhao (PKU), Yuhan Yao (PKU), and Fangzhou Ren (PKU) report on behalf of the PKU HiTF (High-energy Transients Follow-up) group:
We observed the field of EP261006a (Lao et al., GCN 45826; T0 = 2026-10-06T17:49:57), which has been classified as a possible TDE (Eyles-Ferris et al., GCN 45831; Jiang et al., GCN 45833), using the PKU 60cm telescope at Xinglong Observatory, NAOC. Observations were conducted over multiple epochs on 2026 October 7 and 8, approximately 21–49 hours after the EP-WXT detection, in the g, r, and i bands.
In the stacked images, we clearly detect the optical counterpart in the difference images at a position consistent with that of AT 2026aetp (Eyles-Ferris et al., GCN 45831; Jiang et al., GCN 45833; Wu et al. GCN 45852; Bochenek et al., GCN 45853; Chen et al. GCN 45854; Zhang et al., GCN 45877; Bochenek et al., GCN 45883). Preliminary photometry is calibrated against nearby Pan-STARRS field stars and reported in the AB magnitude system, without correction for Galactic extinction.
The observation log is summarized below following the time sequence:
| Date | Start_UT | T_mid - T0 (days) | Filter | Exposure (s) | Magnitude (AB) |
| :--------: | :------: | :---------------: | :----: | :----------: | :------------: |
| 2026-10-07 | 13:55:42 | 0.88 | g | 12 * 600 | 18.76 +/- 0.03 |
| 2026-10-07 | 16:02:32 | 0.94 | r | 4 * 600 | 19.07 +/- 0.04 |
| 2026-10-07 | 17:43:52 | 1.02 | r | 6 * 600 | 19.02 +/- 0.04 |
| 2026-10-07 | 18:49:21 | 1.08 | i | 11 * 600 | 19.23 +/- 0.06 |
| 2026-10-08 | 13:21:12 | 1.86 | g | 12 * 600 | 18.46 +/- 0.03 |
| 2026-10-08 | 15:23:32 | 1.92 | r | 7 * 600 | 18.79 +/- 0.04 |
| 2026-10-08 | 16:57:40 | 1.97 | r | 3 * 600 | 18.79 +/- 0.04 |
| 2026-10-08 | 17:29:48 | 2.03 | i | 12 * 600 | 19.05 +/- 0.04 |
Further analysis and follow-up observations are ongoing.
The PKU 60cm Telescope is operated by the Department of Astronomy, Peking University. The PKU HiTF group is dedicated to rapid follow-up observations of high-energy transients.
Filter: only the top 10% of the past year's X-ray transients are posted, ranked by the number of GCN Circulars written about them (now ≥ 11). Thresholds are recalculated monthly. Only events first reported within the past 7 days can start a thread.
Relayed automatically from NASA's General Coordinates Network.
Transient Alerts » in reply to EP261006a — X-ray Transient
In plain words Notable
On 6 October 2026 the Einstein Probe, a space X-ray telescope, spotted a sudden flash of X-rays at the position of a galaxy, with a measured redshift of 0.1853 (very roughly 2-3 billion light-years away). Optical telescopes then found a bright, blue, new light source right at the galaxy's centre that was not there two days earlier and has brightened to about 18th magnitude over several days. Its blue colour and central location fit a tidal disruption event, where a black hole tears apart a passing star, but the spectra show no clear features to confirm this, and a fast-fading exploding star remains possible. The X-rays faded by about a factor of 300 within a day, while the visible light kept rising, so the two may not come from the same process. Radio telescopes (VLA and MeerKAT) detected nothing.
How unusual is it? A measured distance, an optical counterpart at the galaxy's centre and a rising blue light curve make this a well-characterised fast X-ray transient, with a likely tidal disruption event, which is more than the typical alert. It is not exceptional, since such events are being found regularly, and the classification is still unconfirmed; clear emission lines or radio emission would settle the nature, and a different type of explosion would change the picture.
Written by an AI model (claude-sonnet-5-5) from the official reports in this thread, and rewritten as new reports arrived (version 7); last updated . It may contain mistakes: the reports themselves are the authority.
EP261006a / AT 2026aetp: Multiband optical follow-up with the PKU 60cm Telescope
The whole thread (20 posts)
- EP261006a — X-ray Transient
- EP261006a / AT 2026aetp: Optical follow-up with the 1.3-m DFOT
- EP261006a : MeerKAT radio observations.
- EP261006a: 10 GHz VLA observations
- EP261006a / AT 2026aetp: Luminance-band optical follow-up with small-aperture telescopes
- EP261006a: Kilonova-Catcher optical follow-up and detection
- Updated explainer: what the latest reports add (AI-written)
- EP261006a / AT 2026aetp: Multiband optical follow-up with the PKU 60cm Telescope
- EP261006a: Liverpool Telescope optical follow-up
- Explainer: what this is and why it matters (AI-written)
- EP261006a: Xinglong 2.16m/BFOSC optical follow-up observations
- EP261006a: Optical follow-up observations with MATCH
- EP261006a / AT 2026aetp: VLT/X-shooter spectroscopic redshift z = 0.1853
- EP261006a: Swift/XRT detection of the fading X-ray counterpart
- EP261006a: Optical follow-up observations with Kinder
- EP261006a: Liverpool Telescope optical observations
- EP261006a: Early Optical Observations by WFST
- EP261006a: NOT spectroscopy of a blue continuum
- EP261006a: LT and NOT discovery of an optical counterpart
- EP261006a: SVOM/VT optical upper limits