NANOGrav astronomers use the world's most sensitive radio telescopes to observe and discover millisecond pulsars: the Robert C. Byrd Green Bank Telescope located at the National Radio Astronomy Observatory in Green Bank, West Virginia and the William E. Gordon Telescope located at the Arecibo Observatory in Puerto Rico. NANOGrav uses the Green Bank Telescope and Arecibo to observe 79 millisecond pulsars.
The Green Bank Telescope is smaller than Arecibo, but is capably of pointing in any direction unlike its static partner. As such, it can see 85% of the total sky, and is therefore critical to achieve the sky coverage necessary for our project. It is located in the only U.S. National Radio Quiet zone, in which radio transmissions are regulated to limit the amount of interference that might adversely affect our observations. In addition to observing our pulsars twice a month, NANOGrav also uses the Green Bank Telescope to search for possible new additions to our pulsar timing array through the Green Bank North Celestial Cap pulsar survey.
Arecibo is the second largest radio telescope in the world, with a diameter of 305 meters, which is the size of 3 football fields. Because it has so much collecting area, Arecibo can detect extremely weak radio signals, such as those from millisecond pulsars. In fact, Arecibo is the most sensitive radio telescope in the world, by a wide margin, contributing to the search for gravitational waves using pulsar timing. The dish is so large, however, that it must remain fixed in position. This limits the parts of the sky that Arecibo can access—it is capable of seeing the sky directly overhead and 20 degrees to each side. It accomplishes this by using a spherical reflecting dish (as opposed to the more common parabolic shape) and a special optical system housed in its large Gregorian focus dome.
Arecibo is used to search for new pulsars through two large-area pulsar surveys: the Pulsar Arecibo L-band Feed Array (PALFA) survey and Arecibo 327 MHz drift scan pulsar survey.