GRB 051022 was detected at 13:07:58 on 22 October 2005 by HETE-2 .
The location of GRB 051022 was determined immediately by the flight localization system .
This burst contains multiple pulses and has a rather long duration of about 190 seconds .
The detections of candidate X-ray and radio afterglows were reported , whereas no optical afterglow was found .
The optical spectroscopic observations of the host galaxy revealed the redshift { z } = 0.8 .
Using the data derived by HETE-2 observation of the prompt emission , we found the absorption N _ { H } = ( 8.8 _ { -2.9 } ^ { +3.1 } ) \times 10 ^ { 22 } cm ^ { -2 } and the visual extinction A _ { V } = 49 _ { -16 } ^ { +17 } mag in the host galaxy .
If this is the case , no detection of any optical transient would be quite reasonable .
The absorption derived by the Swift XRT observations of the afterglow is fully consistent with those obtained from the early HETE-2 observation of the prompt emission .
Our analysis implies an interpretation that the absorbing medium may be outside the external shock at R \sim 10 ^ { 16 } cm , which could be a dusty molecular cloud .