GRB 260509A

General information

GRB 260509A triggered SVOM/ECLAIRs at 2026-05-09T21:51:09 UTC with a best-alert position at RA=11:47:32.9, Dec=+00:12:34.2 (J2000; 90% radius 4.72 arcmin). A fading optical counterpart consistent across multiple facilities was identified within a few arcminutes of the ECLAIRs localization.

Wavelength coverage

• Gamma-ray / hard X-ray: SVOM/ECLAIRs prompt temporal and spectral properties reported; SVOM/GRM detection reported.
• Optical: Detected by SVOM/VT, GOTO, Liverpool Telescope, LCO, COLIBRÍ, KAIT, and later reported/marginally detected by SAO RAS; late-time non-detection reported by CrAO.
• Near-IR: MDM/MIRAGE reports low-significance J detection and Hs upper limit.
• X-ray (soft), UV, radio, mm/sub-mm, neutrinos, GW: no observations mentioned.

Lightcurve and spectrum

Redshift

NOT/ALFOSC spectroscopy reports a continuum detected down to ~3600 Å, implying an upper limit z < 1.95 from the lack of HI absorption; no clear metal absorption features are reported in the preliminary reduction. Photometric/qualitative statements from optical detections suggest z<3 and colors consistent with z<4, but no measured redshift is given.

What’s special vs typical

SVOM/ECLAIRs reports a very soft prompt spectrum (photon index −2.20 ± 0.09) and suggests classification as an X-Ray Flash; a precursor starting ~T0−22 s is reported with a very soft spectrum that can also be fit by a blackbody (kT ~1.5 keV).