Hi Ramesh,
The STDXXX files are not considered 'Agent' logs and therefore are not targets for cleanup. If space is an issue, here are some thoughts on how it can be managed to reduce it.
First, are you creating unique output files for each run or appending output to the existing output? That will definitely keep growing.
If the only the last run is important, you could use a specific name for each job and overwrite it for each job run.
Second, if you need to maintain the output for each run for some period of time, then I would suggest have a standard location for the output files.
For long term storage requirements, you could zip/tar up the directories contents and move them to another location on a regular basis.
For short term requreiments, you could use a 'find' command to locate the files older than X and delete them.
Hope that helps,
Mike