{
  "createdOn": 1787317800486,
  "eventId": "EP260731a",
  "submitter": "SVOM_group <svomgroup@bao.ac.cn>",
  "format": "text/plain",
  "eventType": [
    "X-ray Transient"
  ],
  "circularId": 45416,
  "subject": "EP260731a: SVOM/ECLAIRs detection through offline targeted search",
  "body": "H. Yang, S. Guillot, O. Godet (IRAP)\n\nreport on behalf of the SVOM team:\n\nThe 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).\n\nThe 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.\n\nThe localization of the source is RA, Dec = 344.500, -11.872 degrees:\n\nRA (J2000) = 22h58m00s     \nDec (J2000) = -11d52m19s\n\nwith 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. \n\nThe ECLAIRs lightcurve shows a multi-peaked structure lasting around 82 s in the 4 - 120 keV band.\n\nThe 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. \n\nUsing 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).\n\nAll quoted errors are at the 68% confidence level.\n\nThe 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.\n\nThe SVOM/ECLAIRs point of contact for this event is : Hui Yang (hui.yang@cnrs.fr) \n\nPlease contact him by email if you require additional information regarding the SVOM follow-up of this burst.",
  "submittedHow": "web"
}