General information
GRB 260704A was triggered by SVOM/ECLAIRs at 2026-07-04 03:41:05 UTC and was subsequently associated with an uncatalogued X-ray source detected by SVOM/MXT and Einstein Probe/FXT. A faint, fading optical source detected by COLIBRI is a possible counterpart.
Wavelength coverage
- Gamma-ray/hard X-ray: ECLAIRs detected a precursor and delayed main pulse, with T90 = 166 (+10/-7) s in 4-120 keV.
- Soft X-ray: MXT found an uncatalogued source 139 s after the trigger; FXT independently detected a consistent source about one hour after the trigger with an average unabsorbed 0.5-10 keV flux of 1.49 (-0.22/+0.26) x 10^-12 erg/s/cm^2.
- Optical: NOT obtained i-band imaging at 23.1 hr and found no new source to i > 22.5. COLIBRI detected a tentative source in r and z at 27.7-31.7 hr and measured fading in both bands at 51.6-54.1 hr.
No radio, ultraviolet, infrared, neutrino, or gravitational-wave observations are mentioned.
Lightcurve and spectrum
- The ECLAIRs light curve has multiple peaks, comprising a precursor from T0-41 s to T0 and a main pulse from T0+105 s to T0+160 s.
- The duration is T90 = 166 (+10/-7) s in 4-120 keV.
- The precursor spectrum is fitted by a power law with alpha = -2.71 +/- 0.31; its reported 4-120 keV fluence is 1.7 (+0.1/-0.7) erg/cm^2 and photon flux is 0.29 (+0.01/-0.11) ph/cm^2/s.
- The main-pulse spectrum is fitted by a power law with alpha = -1.96 +/- 0.12; its reported 4-120 keV fluence is 6.1 (+0.5/-0.7) erg/cm^2 and photon flux is 0.48 (+0.01/-0.05) ph/cm^2/s.
- The optical candidate faded from r = 23.54 +/- 0.22 and z = 22.70 +/- 0.27 to r = 24.08 +/- 0.23 and z = 23.19 +/- 0.28 between the two COLIBRI epochs.
Redshift
What’s special vs typical
The ECLAIRs spectral slopes may imply a peak energy below 5 keV, making GRB 260704A a possible X-ray flash. Its unusually delayed main pulse and the tentative fading counterpart detected independently in two optical bands add interest, although both the counterpart association and X-ray-flash classification remain provisional.