The frontier of darkness: the cases of GRB 040223, GRB 040422, GRB   040624
  Understanding the reasons for the faintness of the optical/near-infrared afterglows of the so-called dark bursts is essential to assess whether they form a subclass of GRBs, and hence for the use of GRBs in cosmology. With VLT and other ground-based telescopes, we searched for the afterglows of the INTEGRAL bursts GRB 040223, GRB 040422 and GRB 040624 in the first hours after the triggers. A detection of a faint afterglow and of the host galaxy in the K band was achieved for GRB 040422, while only upper limits were obtained for GRB 040223 and GRB 040624, although in the former case the X-ray afterglow was observed. A comparison with the magnitudes of a sample of afterglows clearly shows the faintness of these bursts, which are good examples of a population that an increasing usage of large diameter telescopes is beginning to unveil. 
P. D'Avanzo, P. Filliatre, P. Goldoni, L. A. Antonelli, S. Campana, G.   Chincarini, S. Covino, A. Cucchiara, M. Della Valle...