Transient Alerts — HabitableZone

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: Optical follow-up observations with Kinder
GCN Circulars —

GCN Circular 45854
EP261006a: Optical follow-up observations with Kinder
From: Amar Aryan at National Central University, Institute of Astronomy (NCUIA)
Issued: 2026-10-08 09:49 UTC
Type: X-ray Transient, Optical Transient

Z.-Y. Chen, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. H. Gillanders (both Oxford), S. Yang (HNAS), A. Sankar.K, K. N.-T. Ho, A. Dutta, M.-H. Lee, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, W.-J. Hou, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), K. W. Smith, H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report:


We observed the field of the fast X-ray transient EP261006a (Lao et al., GCN 45826) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in r-band started at 15:11 UTC on the 07th of October 2026 (MJD 61320.6327), 21.35 hr after the EP-WXT detection.

We used the Python-based AutoPhOT package (Brennan & Fraser 2022, A&A, 667, A62) to perform template subtraction with the Pan-STARRS1 3Pi archive image (Chambers et al. 2016 arXiv:1612.05560) using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm on individual frames. The optical counterpart (Eyles-Ferris et al., GCN 45831; Wu et al., GCN 45852; Bochenek et al., GCN 45853) was detected in each individual frame.

Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the measured photometry from the first frame are as follows:

Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | Seeing | Airmass
LOT | r | 61320.6327 | 21.35 | 300 * 1 | 19.096 +/- 0.039 | 1".3 | 1.06

Our measurements confirm the reported rise by Eyles-Ferris et al. (GCN 45831); however, the source does not vary rapidly over 25 minutes of observations, remaining at ~19.1 mag in the r-band.

The presented magnitude is calibrated using the field stars from the Pan-STARRS1 catalog and is not corrected for the expected Galactic foreground extinction of A_r = 0.096 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69.

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