GCN Circular 45784
Subject
EP260927a: SVOM/ECLAIRs Upper Limit
Event
Date
2026-09-29T15:15:35Z (18 hours ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
H. Yang, M. Brunet, O. Godet (IRAP)
report on behalf of the SVOM team:
We performed a targeted search to the X-ray transient EP260927a, detected by EP-WXT at 2026-09-27T14:02:35 UTC (T0) lasting for about 800 s (EP team, GCN 45779), 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 + 800 s, we derive a 3-sigma upper limit of 5e-10 erg/cm^2/s in the 4-120 keV energy band, assuming a power-law spectrum with a photon index of -2.28, as measured by EP-FXT for the uncatalogued source (GCN 45779). 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 5.4e-10 erg/cm^2/s in the 4-120 keV energy band. We note that the EP/WXT flux of 2.91e-11 erg/cm^2/s in the 0.5-4 keV (GCN 45779) is more than an order 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)