高能暂现源 · 每日文献综述

We present the discovery and multiwavelength follow-up of gamma-ray bursts (GRB) 250818B, detected by the Space Variable Objects Monitor (SVOM) and localized by the Gravitational-wave Optical Transient Observer. We compile X-ray, optical/near-infrared, and radio data into broad-band light curves and spectral energy distributions. Despite being initially reported as short, the public prompt light-curve figure suggests a duration of <inline-formula><tex-math>$\sim 5$</tex-math></inline-formula> s, arguing against a secure short-duration classification. The afterglow is unusually bright relative to short-GRB samples: in X-rays and optical it is broadly consistent with the long-GRB population, while in the radio it is among the most luminous events in the short-GRB comparison sample and remains within the long-GRB range. MeerKAT detects the source at 3.1 GHz, while the Atacama Large Millimetre/submillimetre Array provides deep higher-frequency limits. Keck/LRIS spectroscopy shows continuum and metal absorption (Fe II, Mg II, Mg I), giving <inline-formula><tex-math>$z=1.216$</tex-math></inline-formula>. Synchrotron forward-shock modelling favours a constant-density medium and refreshed (energy-injection) emission, well described by a two-component jet with core isotropic-equivalent kinetic energy <inline-formula><tex-math>$E_{0}\sim 8\times 10^{52}$</tex-math></inline-formula> erg, ambient number density <inline-formula><tex-math>$n_0\sim 12\, \mathrm{cm^{-3}}$</tex-math></inline-formula>, jet half-opening angle <inline-formula><tex-math>$\theta _j\simeq 0.13$</tex-math></inline-formula> rad (<inline-formula><tex-math>$\sim 7.4^\circ$</tex-math></inline-formula>), and electron index <inline-formula><tex-math>$p\simeq 1.67$</tex-math></inline-formula>. We do not identify a host conclusively: the data admit either a faint LS DR10 galaxy at <inline-formula><tex-math>$\sim 4\, {\rm arcsec}$</tex-math></inline-formula> (<inline-formula><tex-math>$\sim 34$</tex-math></inline-formula> kpc) as an offset candidate, or a fainter, near-coincident uncatalogued host. GRB 250818B highlights the power of rapid counterpart identification in the SVOM era, while uncertain prompt classification and inconclusive host association still limit progenitor interpretation.