You can use the *OPC? (operation complete query) command or the
*OPC (operation complete) command to signal when the sweep is
complete. The *OPC? command returns “1” to the output buffer when
the sweep is complete. The *OPC command sets the “operation complete”
bit (bit 0) in the Standard Event register when the burst is complete. 
TRIGger:SOURce? 
Query the present trigger source. Returns “
IMM”, “EXT”, or “BUS”.
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Chapter 4  Remote Interface Reference      
Frequency Sweep Commands   
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