The gamma-ray burst GRB 000210 had the highest \gamma -ray peak flux of any event localized by BeppoSAX as yet but it did not have a detected optical afterglow , despite prompt and deep searches down to R _ { lim } \approx 23.5 .
It is therefore one of the events recently classified as dark GRBs , whose origin is still unclear . Chandra observations allowed us to localize the X-ray afterglow of GRB 000210 to within \approx 1 ″ and a radio transient was detected with the VLA .
The precise X-ray and radio positions allowed us to identify the likely host galaxy of this burst , and to measure its redshift , z = 0.846 .
The probability that this galaxy is a field object is \approx 1.6 \times 10 ^ { -2 } .
The X-ray spectrum of the afterglow shows significant absorption in excess of the Galactic one corresponding , at the redshift of the galaxy , to N _ { H } = ( 5 \pm 1 ) \times 10 ^ { 21 } cm ^ { -2 } .
The amount of dust needed to absorb the optical flux of this object is consistent with the above HI column density , given a dust-to-gas ratio similar to that of our Galaxy .
We do not find evidence for a partially ionized absorber expected if the absorption takes place in a Giant Molecular Cloud .
We therefore conclude that either the gas is local to the GRB , but is condensed in small-scale high-density ( n \gtrsim 10 ^ { 9 } cm ^ { -3 } ) clouds , or that the GRB is located in a dusty , gas-rich region of the galaxy .
Finally , we examine the hypothesis that GRB 000210 lies at z \gtrsim 5 ( and therefore that the optical flux is extinguished by Ly _ { \alpha } forest clouds ) , but we conclude that the X-ray absorbing medium would have to be substantially thicker from that observed in GRBs with optical afterglows .