TITLE:   GCN CIRCULAR
NUMBER:  35940
SUBJECT: X-ray transient EP240315a: orphan FXT?
DATE:    24/03/17 10:04:11 GMT
FROM:    Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>


V.Lipunov (Lomonosov MSU, Perevoschikov Moscow Observatory)

The recently launched space mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES Einstein Probe mission (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics) reported the discovery of the fast soft X-ray transient (FXT) EP240315a (Zhagn et al., GCN 35931).

Publication is about an event lasting ~1600 seconds. The spectrum of the ATLAS optical counterpart AT2024eju (Srivastav et al., GCN 35932) unambiguously establishes the cosmological nature of EP240315a with redshift z = 4.859 and a possible connection with Gamma Ray Bursts (Saccardi et al., GCN 35936).

Note that the phenomenon of fast X-ray flares was actually predicted within the framework of the Spinar paradigm (Lipunov & Gorbovskoy, 2007, ApJ, v.665, L97; Lipunov & Gorbovskoy, 2008, MNRAS, v.383, 1397.; Lipunova et al., 2009, MNRAS, v.397,1695).

In the case of core collapse, which has an increased spin monentum and a weak magnetic field, the phenomenon of fast X-ray bursts can occur without the phenomenon of a gamma-ray burst at all. The corresponding diagram is available at http://observ.pereplet.ru/images/spinar_dogma.jpg)