PALFA Survey
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PALFA is a large-scale survey for radio pulsars at 1.4 GHz using the Arecibo 305-meter telescope and the ALFA multibeam receivers. It is the largest and most sensitive survey of the Galactic plane to date.[1]
Most of the advances in pulsar astronomy were due to the discovery of new objects. A major increase in search sensitivity has already started a new era of discovery at the Arecibo Observatory.
This increase in search sensitivity is due first and foremost by the ALFA receiver and the pulsar surveys it makes possible, which are now being carried by the Pulsar Consortium using the Arecibo 305 m radio telescope. Preliminary estimates (see below) indicate that the Arecibo Galactic plane survey using ALFA could find many hundreds of new pulsars. As of November 2019, the survey had already discovered a total of 192 new pulsars.
The survey is targeting low Galactic latitudes (|b|≤5°) in the Galactic longitude ranges accessible by the Arecibo telescope (32°<l<77°) and 168°<l<214°). Upon completion, it is expected to find hundreds of new pulsars. Highlights from the survey include the discoveries of the second most relativistic binary pulsar known, PSR J1906+0746,[2] and the first eccentric binary millisecond pulsar in the Galactic plane, PSR J1903+0327[3] In addition, PALFA has produced the first pulsar discovery by volunteer computing, PSR J2007+2722, through the Einstein@Home distributed computing project.[4] The discoveries include all known varieties of rotation-powered neutron stars: millisecond pulsars,[5][6] relativistic binaries, mildly recycled,[4] normal, and energetic young pulsars.[7] Fourteen of the ALFA objects have been identified through their intermittent single pulses and are likely rotating radio transients (RRATs).[8] The rest have been discovered via blind periodicity searches. Follow-up radio timing observations are carried out through a coordinated effort between Arecibo, Jodrell Bank, Greenbank, and Nançay to obtain phase-connected timing solutions for these pulsars.
The first fast radio burst to be discovered by a telescope other than the Parkes radio telescope was identified in a PALFA pointing in the Galactic anti-center.[9] This was the first repeating fast radio burst ever discovered.
The PALFA survey is carried out by an international consortium of scientists from the United States, Canada, Germany, Netherlands, United Kingdom, Australia, and France. The Principal Investigator of the PALFA survey is Prof. Victoria Kaspi of McGill University.
Data acquisition
With ALFA, 47 pointings are needed to cover one square degree, compared to about 330 pointings needed to cover one square degree with similar density with a single-pixel feed. Initially, the survey used the Wideband Arecibo Pulsar Processors (WAPPs) to detect the signal from ALFA's seven beams. These cover 100 MHz of band (with dual polarization capability), initially centered at 1420 MHz and now at 1440 MHz. For search purposes, 256-channel spectra are produced every 64 microseconds. In 2009, the survey transitioned to new and improved back-ends, the Mock polyphase filterbank spectrometers, which are capable of covering 300 MHz (from 1225 MHz to 1525 MHz, the bandwidth covered by ALFA) for each of the seven beams (see detailed technical specifications here). This has led to greatly increased search sensitivity and better means to deal with all the radio frequency interference.
