Millimetre Observations of Gamma-ray Bursts at IRAM

Since 1997, and following our detection of the first mm afterglow, we have followed-up 70 GRBs, mainly with the IRAMś Plateau de Bure Interferometer, what can be considered as the IRAM Legacy GRB Sample. 66 events were observed at 3 mm, with 19 of them being detected (with another 3 having marginal detections). 32 GRBs were followed up at 1 mm, with 6 of them being detected. Redshifts for the GRB afterglowslie in the range z = 0.03–8.3, with measured flux densities (at 3 mm) varying between 0.25 and 60 mJy (but usually <1.5 mJy) with first observations taking place around 1–2 days after the GRB. Forward shock emission expleains the observations with the exception of one particular case ( GRB 090423at z = 8.2) for which reverse shock emission is required.