GCN Circular 45416
Subject
EP260731a: SVOM/ECLAIRs detection through offline targeted search
Event
Date
2026-08-21T13:10:00Z (10 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
H. Yang, S. Guillot, O. Godet (IRAP)
report on behalf of the SVOM team:
The SVOM/ECLAIRs telescope detected EP260731a (EP team, GCN 45261), starting at 2026-07-31T00:53:19 UTC (T0), through an offline targeted search with the event-by-event data downloaded via the X-band ground station. The ECLAIRs detection, at T0, occurred 31 s before the EP-WXT detection that began at 2026-07-31T00:53:50 UTC (EP team, GCN 45301).
The burst was detected within several timescales and energy ranges. The best detection is obtained by the image trigger with a signal-to-noise ratio of 6.4 within 8-120 keV over a time window of 82 s starting at T0. This event was not detected onboard because it was too faint.
The localization of the source is RA, Dec = 344.500, -11.872 degrees:
RA (J2000) = 22h58m00s
Dec (J2000) = -11d52m19s
with a 90% C.L. radius of 12.14 arcmin (including systematic error of 2 arcmin added in quadrature). This position is consistent with that measured by EP/FXT, with an angular separation of 7.8 arcmin.
The ECLAIRs lightcurve shows a multi-peaked structure lasting around 82 s in the 4 - 120 keV band.
The time-averaged spectrum from T0 to T0+82 s in the 5-120 keV is well fitted by a power law with a photon index of -1.4 +/- 0.2, a 4-120 keV photon flux of 0.22 +0.02/-0.06 photons/cm^2/s, and a corresponding 4-120 keV fluence of (7 +/- 1)e-7 erg/cm^2.
Using the same extraction time window from T0+31 s to T0+66 s as EP/WXT, the time-averaged spectrum in the 5-120 keV is also well fitted by a power law with a photon index of -1.4 +/- 0.2, a 4-120 keV photon flux of 0.28 +0.02/-0.08 photons/cm^2/s, and a corresponding 4-120 keV fluence of (3.7 +/- 0.8)e-7 erg/cm^2. The spectral properties measured with SVOM/ECLAIRs are broadly consistent with those reported by EP/WXT (EP team, GCN 45301).
All quoted errors are at the 68% confidence level.
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)
Please contact him by email if you require additional information regarding the SVOM follow-up of this burst.