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: LT and NOT discovery of an optical counterpart
GCN Circulars —

GCN Circular 45831
EP261006a: LT and NOT discovery of an optical counterpart
From: Rob Eyles-Ferris at U of Leicester
Issued: 2026-10-07 10:06 UTC
Type: X-ray Transient, Optical Transient

R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), J. A. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), and A. J. Levan (Radboud and Warwick) report on behalf of a larger collaboration:

We observed the field of the fast X-ray transient EP261006a (Lao et al., GCN 45826) with the Liverpool Telescope (LT) and the Nordic Optical Telescope (NOT) equipped with the IO:O and ALFOSC imagers, respectively. Observations started at 2026-10-06 23:26:24 UT (LT) and 2026-10-07 00:26:37 (NOT).

In image subtractions using Pan-STARRS templates, we identify a clear residual spatially consistent with the nucleus of the galaxy Gaia DR3 2587044864659595392. The location is also consistent with the EP-FXT localisation of the transient (GCN 45826). This residual is seen in all our images and we summarise our host-subtracted photometry below.

| t_mid - t0 (hrs) | Telescope | Filter | Exposure time (s) | AB magnitude |
| ------------- | --------- | ------ | ---------------- | ------------ |
| 5.56 | LT | r | 6x150 | 20.22 +/- 0.03 |
| 5.85 | LT | i | 6x150 | 20.78 +/- 0.05 |
| 6.11 | LT | z | 5x150 | 20.59 +/- 0.07 |
| 6.75 | NOT | r | 5x180 | 19.83 +/- 0.03 |

We note the rise in r-band brightness. Our magnitudes are calibrated to Pan-STARRS and not corrected for Galactic extinction. The blue r - i colour and nuclear location of EP261006a are consistent with the tentative classification as a TDE.

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.

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