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: NOT spectroscopy of a blue continuum
GCN Circulars —

GCN Circular 45833
EP261006a: NOT spectroscopy of a blue continuum
From: sqjiang at NAOC
Issued: 2026-10-07 12:40 UTC
Type: X-ray Transient

S.Q. Jiang, D. Xu, J. An (NAOC), L. Lei, S.Y. Fu (HUST), L.B. He, X. Liu, Z.P. Zhu (NAOC), J.P.U. Fynbo (DAWN/NBI), E. Georgiou, A.S. Maartensson (NOT) report:

We performed the spectroscopy of the nucleus of the galaxy, Gaia DR3 2587044864659595392 (Hughes et al. 2022) with a photometric redshift of 0.184 (Duncan et al. 2022), which is within the EP-FXT error circle of EP261006a (Lao, et al., GCN 45826), using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 04:39:42 UT on 2026-10-07, i.e., 10.83 hr after the EP trigger, and 2 x 1200 s exposures were obtained, covering the wavelength range of ~ 3600 - 9200 AA.

The whole spectrum shows a clear blue continuum, without any prominent absorption or emission feature. The spectrum is different from the red one of the galaxy, which is close to an elliptical E0 type.

The spectral difference shows that the optical counterpart of EP261006a is at or very close to the nucleus of the galaxy, as reported in Eyles-Ferris et al. (GCN 45831).

The blue continuum spectrum would be consistent with an early transient such as TDE, FBOT, and so on (e.g., similar to EP260806a).

Further observations are planned.

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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