AN ARECIBO SEARCH FOR PULSARS AND TRANSIENT SOURCES IN M33

We report on a systematic and sensitive search for pulsars and transient sources in the nearby spiral galaxy M33, conducted at 1.4 GHz with the Arecibo telescope's seven-beam receiver system, ALFA. Data were searched for both periodic and aperiodic sources, up to 1000 pc cm(-3) in dispersion measure and on timescales from similar to 50 mu s to several seconds. The galaxy was sampled with 12 ALFA pointings, or 84 pixels in total, each of which was searched for 2-3 hr. We describe the observations, search methodologies, and analysis strategies applicable to multibeam systems, and comment on the data quality and statistics of spurious events that arise due to radio frequency interference. While these searches have not led to any conclusive signals of periodic or transient nature that originate in the galaxy, they illustrate some of the underlying challenges and difficulties in such searches and the efficacy of simultaneous multiple beams in the analysis of search output. The implied limits are less than or similar to 5 mu Jy Mpc(2) in luminosity (at 1400 MHz) for periodic sources in M33 with duty cycles less than or similar to 5%. For short-duration transient signals (with pulse widths less than or similar to 100 mu s), the limiting peak flux density is 100 mJy, which would correspond to a 5 sigma detection of bright giant pulses (similar to 20 kJy) from Crab-like pulsars if located at the distance of M33. We discuss the implications of our null results for various source populations within the galaxy and comment on the future prospects to conduct even more sensitive searches with the upcoming next-generation instruments including the Square Kilometer Array and its pathfinders.