MAGIC observation of the GRB 080430 afterglow

Gamma-ray bursts are cosmological sources emitting radiation from the gamma-rays to the radio band. Substantial observational efforts have been devoted to the study of gamma-ray bursts during the prompt phase, i.e. the initial burst of high-energy radiation, and during the longer- lasting afterglows. In spite of many successes in interpreting these phenomena, there are still several open key questions about the fundamental emission processes, their energetics and the environment. Aims. Independently of specific gamma-ray burst theoretical recipes, spectra in the GeV/TeV range are predicted to be remarkably simple, be- ing satisfactorily modeled with power-laws, and therefore offer a very valuable tool to probe the extragalactic background light distribution. Furthermore, the simple detection of a component at very-high energies, i.e. at ∼ 100 GeV, would solve the ambiguity about the importance of various possible emission processes, which provide barely distinguishable scenarios at lower energies. Methods. We used the results of the MAGIC telescope observation of the the moderate resdhift (z ∼ 0.76) GRB 080430 at energies above about 80 Gev, to evaluate the perspective for late-afterglow observations with ground based GeV/TeV telescopes. Results. We obtained an upper limit of F95% CL = 5.5 × 10− 11 erg cm− 2 s− 1 for the very high-energy emission of GRB 080430, which cannot set fur- ther constraints on the theoretical scenarios proposed for this object. Nonetheless, our observations show that Cherenkov telescopes have already reached the required sensitivity to detect the GeV/TeV emission of GRBs at moderate redshift (z 0.8), provided the observations are carried out at early times, close to the onset of their afterglow phase