GRB 251203B

General information

GRB 251203B (SVOM trigger sb25120304) was initially reported as a GRB, but subsequent follow-up indicates the transient is most likely a flare from the star Gaia DR3 2534635509050352256 and is no longer considered a GRB.

Wavelength coverage

• Gamma/X-ray (prompt, 5–20 keV): SVOM/ECLAIRs image-trigger detection with SNR reported.
• X-ray (0.3–10 keV): SVOM/MXT reported an uncatalogued X-ray source; Swift/XRT detected a candidate counterpart coincident with a catalogued 4XMM source.
• Optical: SVOM/VT dual-channel (VT_B/VT_R) imaging; BOOTES-2 clear imaging; LCO r and z imaging (upper limits for new source); MASTER-Net clear imaging (upper limits); AbAO R-band imaging (no new source; bright star detected). No observations were mentioned in radio, millimeter/sub-mm, UV, GeV/TeV gamma rays, or infrared spectroscopy.

Lightcurve and spectrum

• SVOM/ECLAIRs: best image-trigger alert SNR 9.85 in 5–20 keV over an 81.92 s window.
• Swift/XRT: mean flux (0.3–10 keV) (5.76 ± 0.28)e-11 erg cm^-2 s^-1 with a spectral-fit assumption NH=1.00e+21 cm^-2 and photon index Γ=2.03; peak flux (8.8 ± 2.0)e-11 erg cm^-2 s^-1.
• Optical variability: SVOM/VT reports the Gaia star fading from VT_B≈12.4 to 14.0 over ~1 hr; BOOTES-2 reports fading by ~1.8 mag over ~20 min, consistent with a stellar flare.

Redshift

What’s special vs typical

• The trigger was explicitly retracted as non-GRB and attributed to a stellar flare, with consistent evidence from optical fading and an X-ray source matching a catalogued counterpart.