The visibility of gamma-ray burst afterglows in dusty star-forming regions

Recent observations of the environments of gamma-ray bursts (GRBs) favour m assive stars as their progenitors, which are likely to be surrounded by gas and dust. The visibility of the optical and UV emission of a GRB is expect ed to depend on the characteristics of both the dust and the GRB emission i tself. A reasonable distribution of surrounding dust is capable of absorbin g all the optical and UV emission of the optical flash and afterglow of a G RB, unless the optical flash has a peak isotropic luminosity Lpeak greater than or equal to 10(49) erg s(-1). This means that dark bursts should exist and these bursts will have to be studied at infrared rather than optical w avelengths. In this paper details will be given about the infrared GRB dust emission. The reprocessed dust emission peaks at a rest-frame wavelength o f about 8 mum. Forthcoming space telescopes, in particular the IRAC camera on board the Space Infrared Telescope Facility, could detect this emission out to a redshift of about 2. However, an accurate position of the GRB afte rglow must be provided for this emission to be identified, because the ligh t curve of the reprocessed dust emission does not vary on time-scales less than several years.