On the constraining observations of the dark GRB 001109and the properties of a z= 0.398 radio selected starburst galaxy contained in its error box*

We present optical and NIR (near infrared) follow up observations of the GRB 001109from 1 to 300 days after the burst. No transient emission was found at these wavelengths within this GRB's (Gamma Ray Burst) 50´´ radius BeppoSAX error box. Strong limits (3σ) are set with: $R\ga 21$, 10.2 h after the GRB; $I\ga 23$, 11.4 h after the GRB; $H\ga 20.7$, 9.9 h after the GRB; and $K_{\rm S}\ga 20$, 9.6 h after the GRB. We discuss whether the radio source found in the GRB's error box ([CITE]) might be related to the afterglow. We also present a multiwavelength study of a reddened starburst galaxy, found coincident with the potential radio and the X-ray afterglow. We show that our strong Iband upper limit makes of the GRB 001109the darkest one localised by the BeppoSAX's NFI (Narrow Field Instrument), and it is one of the most constraining upper limits on GRB afterglows to date. Further to it, the implications of these observations in the context of dark GRBs are considered.