GCN Circular 45876
EP261007b: SVOM/ECLAIRs Upper Limit
From: SVOM_group
Issued: 2026-10-09 14:43 UTC
Type: X-ray Transient

H. Yang, O. Godet (IRAP)
report on behalf of the SVOM team:

We performed a targeted search to the X-ray transient EP261007b, detected by EP-WXT at 2026-10-07T15:05:16 UTC (T0) (EP team, GCN 45847), with the SVOM/ECLAIRs event-by-event data downloaded through the X-band ground station.

At T0, the transient position was within the ECLAIRs field of view. No statistically significant signal was identified in the [T0 - 3000 s, T0 + 1000 s] interval by the ECLAIRs offline trigger.

For the interval from T0 to T0 + 16 s, we derive a 3-sigma upper limit of 1.2e-8 erg/cm^2/s in the 4-120 keV energy band, assuming a power-law spectrum with a photon index of -1.9, as measured by EP-FXT for the uncatalogued source (GCN 45872). Alternatively, assuming a “soft” spectral template (a Band function with Epeak = 25 keV, alpha = -1.5, beta = -3.0), we derive a 3-sigma upper limit of 1.1e-8 erg/cm^2/s in the 4-120 keV energy band. We note that the EP/WXT flux of 7.9e-11 erg/cm^2/s in the 0.5-4 keV (GCN 45872) is more than two orders of magnitude lower than our 3-sigma upper limit.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP.

The SVOM/ECLAIRs point of contact for this event is : Hui Yang (hui.yang@cnrs.fr)

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