Candidate Identification and Interference Removal in Seti

SETI@home, a search for signals from extraterrestrial intelligence, has been recording data at the Arecibo radio telescope since 1999. These data are sent via the Internet to the personal computers of volunteers who have donated their computers' idle time toward this search. The SETI@home client software, which runs on these computers, corrects the data for a wide variety of possible accelerations of the transmitter or receiver ranging from -100 Hz/s to 100 Hz/s. At each possible Doppler drift rate, the software performs a sensitive analysis to detect four types of potential signals: 1) narrow band continuous wave signals, 2) narrow band signals which match the Gaussian profile expected as an extraterrestrial signal drifts through the telescope field of view, 3) repeating pulses found using a fast folding algorithm, and 4) signals representing a series of three signals at constant frequency, evenly spaced in time (Korpela, Werthimer, Anderson, Cobb and Lebofsky 2001). To date, SETI@home volunteers have detected over 4.2 billion potential signals. (http://setiathome.berkeley.edu/sci_status.html) While essentially all of these potential signals are due to random noise processes, radio frequency interference (RFI) or interference processes in the SETI@home instrumentation, it is possible that a true extraterrestrial transmission exists within this database. Herein we describe the process of interference removal being implemented in the SETI@home post-processing pipeline, as well as those methods being used to identify candidates worthy of further investigation.