TITLE: GCN CIRCULAR NUMBER: 45390 SUBJECT: EP260806a: SVOM/ECLAIRs detection through targeted search DATE: 26/08/17 20:11:23 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> H. Yang, S. Guillot (IRAP), A. Coleiro (APC) report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected EP260806a (EP team, GCN 45299), starting at 2026-08-06T20:02:00 UTC (T0), through an offline targeted search with the event-by-event data downloaded via the X-band ground station. The earliest ECLAIRs detection, at T0, occurred almost three hours before the EP-WXT detection that began at 2026-08-06 22:57:37 UTC (EP team, GCN 45305). The transient was detected during two time windows: first, between T0 and 2026-08-06T20:25:20 UTC, and later, between 2026-08-06T21:36:00 UTC and 2026-08-06T22:04:40 UTC. These intervals were interrupted by periods during which the transient was covered by Earth occultation and when the satellite entered regions of high particle background. For example, the transient was occulted by the Earth for ECLAIRs when it was detected by EP-WXT. In both time windows, the transient was detected with several timescales and energy ranges. The best detection was obtained by the image trigger with a signal-to-noise ratio of 6.7 in the 4-20 keV over a time window of 1311 seconds starting at 2026-08-06T21:42:40 UTC. This event was not detected onboard because it was too faint with very long timescales. The localization of the source is RA, Dec = 12.355, 35.380 degrees: RA (J2000) = 00h49m25s Dec (J2000) = 35d22m48s with a 90% C.L. radius of 11.7 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 11 arcmin. The ECLAIRs light curve shows a featureless structure during both time windows, with most of the detected photons below 20 keV. We extracted the time-averaged spectra over the two time windows: T0 – 2026-08-06T20:25:20 and 2026-08-06T21:36:00 – 2026-08-06T22:04:40. The first spectrum in the 5-20 keV is well fitted (chi2/dof=3.1/4) by a power-law model with a photon index of 1.1+0.5-0.6, yielding a corresponding 4-20 keV flux of (5.1+/-1.1)e-10 erg/cm^2/s. The second spectrum in the 5-20 keV is well fitted (chi2/dof=1.1/4) by a power-law model with a photon index of 2.9+/-0.6, yielding a corresponding 4-20 keV flux of (6.5+/-0.9)e-10 erg/cm^2/s. Adopting a redshift of z = 0.089 (de Ugarte Postigo et al., GCN 45302), the luminosities are estimated to be 1e46 erg/s and 1.3e46 erg/s in the 4-20 keV for the two time windows, respectively. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/45390. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...