GRB 260903A

General information

GRB 260903A was detected by SVOM/ECLAIRs at 2026-09-03T12:37:20 UTC with SNR 7.70, T90 = 21 +6/-4 s, and a 90% ECLAIRs error radius of 10.20 arcmin. A refined analysis reports a 4-120 keV fluence of (1.6 +0.3/-0.2)e-7 erg/cm^2 and says the burst could be classified as an X-ray flash.

Wavelength coverage

• Gamma-ray/X-ray prompt: SVOM/ECLAIRs triggered and provided refined prompt duration and fluence measurements.
• Optical: SVOM/VT, LCO, NOT/ALFOSC, OHP/T193, SAO RAS, and Liverpool Telescope reported detections of the counterpart, with later observations confirming fading.
• X-ray: EP-FXT detected an uncatalogued fading X-ray source within the SVOM/VT error region, with 0.5-10 keV flux 9.76e-13 erg/cm^2/s.
• Near-infrared: WINTER observed in J band at 17.1 hr and reported a non-detection with J > 19.07 AB. No radio, millimeter, ultraviolet, neutrino, or gravitational-wave observations are mentioned.

Lightcurve and spectrum

• SVOM/ECLAIRs measured T90 = 21 +6/-4 s in 4-20 keV.
• The prompt 4-120 keV fluence was (1.6 +0.3/-0.2)e-7 erg/cm^2 for a power-law fit.
• The initial LCO optical source at r = 17.91 +/- 0.02 and z = 17.69 +/- 0.13 AB was retracted after positional drift showed it matched the known minor planet 2000 OQ52.
• SVOM/VT measured the later counterpart at VT_B = 21.9 +/- 0.2 and VT_R = 20.7 +/- 0.1 AB at 2.18 hr.
• LCO measured r = 20.92 +/- 0.19 AB at 38.66 min, r = 20.46 +/- 0.19 AB at 2.30 hr, and r = 21.8 +/- 0.4 AB at 2.74 hr, with no strong variability reported in that interval.
• NOT/ALFOSC detected fading at 11.45 hr with r = 22.88 +/- 0.16 AB.
• OHP/T193 detected the counterpart near 11 hr with r' = 23.0 +/- 0.2 AB.
• SAO RAS measured Rc = 22.45 +/- 0.09 Vega mag at 8.1358 hr.
• Liverpool Telescope measured r = 22.73 +/- 0.26 AB at 12.6 hr, with limits g > 22.37 and z > 21.38 AB.
• WINTER reported J > 19.07 AB at 17.1 hr.

Redshift

What’s special vs typical

• The burst may be an X-ray flash according to the refined SVOM/ECLAIRs analysis.
• The event has a confirmed fading optical counterpart and a fading X-ray counterpart, but no redshift or multi-messenger association is reported.