Enterprise Manager :: Cannot Flashback RAW Of The Table

one of my user POM create one table using this statement

12:55:59 SQL> create table hello_world (emp_id number(4), emp_name varchar2(30))
;
Table created.

then insert some raw into this hello_world table

12:56:41 SQL> insert into hello_world values (1, 'Bill Gates');
1 row created.
12:57:51 SQL> insert into hello_world values (2, 'Steve Jobs');
1 row created.
13:00:32 SQL> insert into hello_world values (3, 'Chris Eaton');
1 row created.
13:01:19 SQL> commit;
Commit complete.

then i have drop this hello_world table

13:02:08 SQL> drop table hello_world;
Table dropped.;

then i have to connect with sys user

13:03:03 SQL> conn sys as sysdba
Enter password:
13:08:21 SQL> select current_timestamp from dual;
CURRENT_TIMESTAMP
---------------------------------------------------------------------------
13-MAY-11 01.10.21.691000 PM +05:30

[code].....

i flashback my this HELLO_WORLD table but why i cannot Flashback RAW of this table .what can i do if i want to flashback raw of this table which query i have to run,