GRB 251208D

General information

GRB 251208D is a faint/possible GRB candidate triggered by SVOM/ECLAIRs at 2025-12-08 16:51:43 UT, with follow-up reporting no convincing counterpart so far (GCN 43032, 43043, 43047, 43037, 43049).

Wavelength coverage

• Gamma-rays: Detected by SVOM/ECLAIRs (8–120 keV) via Image Trigger with best-image SNR 6.64 over an 81.92 s window (GCN 43032).
• X-rays: Swift/XRT observed T0+5.2 ks to T0+11 ks (2.4 ks exposure), finding two field sources with no evidence for fading; subsequent analysis associates them with a star and a known QSO (GCN 43043, 43047).
• Optical: Non-detections/upper limits reported by LCO (r, z), LAST (clear), and MASTER-Net (clear) within/around the reported region (GCN 43037, 43049, 43036). No observations mentioned in: ultraviolet, infrared, radio, very-high-energy/TeV.

Lightcurve and spectrum

The prompt emission is reported from T0-82 s to T0 in 8–120 keV with a featureless light curve (GCN 43457/43458). The time-averaged 8–120 keV spectrum is fit by a power law with photon index 1.8 ± 0.4 and a 4–120 keV fluence of (1.1 ± 0.3)×10^-6 erg cm^-2 (GCN 43457/43458).

Redshift

A field source consistent with SDSS J223038.66-003108.3 is a known QSO at z = 1.32, but follow-up suggests it is not related to the SVOM high-energy transient (GCN 43047).

What’s special vs typical

The trigger is explicitly described as a faint/possible GRB with an IMT-only detection and SNR below SVOM’s slew threshold, and follow-up has not identified a convincing fading counterpart (GCN 43032, 43043, 43047).