GRB 260706A

General information

GRB 260706A is a likely long GRB detected by Fermi/GBM and SVOM/ECLAIRs on 2026-07-06, with additional SVOM/GRM detection and extensive follow-up. An uncatalogued fading X-ray source was found by EP-FXT, and ATCA later reported a possible radio counterpart within the EP-FXT uncertainty region.

Wavelength coverage

• Gamma-ray: Fermi/GBM, SVOM/ECLAIRs, and SVOM/GRM detected the prompt burst; reported T90 values range from about 17 s to 31 s, with fluences of order 3–4e-6 erg/cm2.
• X-ray: EP-FXT found an uncatalogued 0.5–10 keV source about 1.5 hr after trigger with flux 6.21e-12 erg/s/cm2, fading to 2.5e-13 erg/s/cm2 by about 27.1 hr.
• Optical/NIR: LCO, REM, SVOM/VT, and GRANDMA reported non-detections, including LCO r > 22.3 AB at 16.14 hr and SVOM/VT limits of 22.0 AB in both channels at 17.43 hr.
• Radio: ATCA detected a roughly 0.2 mJy source at 8 GHz about 5.1 days post-burst, 2.7 arcsec from the EP-FXT source and within its positional uncertainty; no previous RACS source was present at that position. No observations were mentioned in UV, submillimeter, GeV/TeV, neutrino, or gravitational-wave bands.

Lightcurve and spectrum

• Fermi/GBM reported two prompt peaks and T90 about 17 s in 50–300 keV.
• SVOM/GRM initially reported a multiple-peaked light curve with T90 about 22.9 s, later refined to T90 = 31 (+12,-8) s in 15–5000 keV.
• SVOM/ECLAIRs measured T90 = 23.41 (+0.64,-0.89) s in 4–120 keV.
• Fermi/GBM time-averaged spectrum was fit by a cutoff power law with index -1.13 +/- 0.01 and Epeak 47.1 +/- 0.6 keV; an equally good Band fit gave Epeak 39.1 +/- 0.5 keV, alpha -0.71 +/- 0.01, and beta -2.63 +/- 0.03.
• SVOM/GRM refined spectrum was fit by a cutoff power law with index -1.47 (+0.16,-0.15) and Epeak 53.98 (+5.09,-4.96) keV.
• SVOM/ECLAIRs spectrum was fit by a cutoff power law with alpha = -1.4 +/- 0.1 and Epeak = 38.1 +/- 6.4 keV.
• EP-FXT X-ray flux declined from 6.21e-12 erg/s/cm2 at about 1.5 hr to 2.5e-13 erg/s/cm2 at about 27.1 hr.

Redshift

What’s special vs typical

• The event has a credible fading X-ray counterpart candidate plus a later possible radio counterpart, while multiple optical/NIR searches found no counterpart to relatively deep limits.