The Galactic Plane Pulsar Snapshot (GPPS) survey

by using the FAST

Fig.1: The four steps of beam-switching for the 19 beams of the L-band receivers of the FAST can completely cover a sky area for a survey.

Considering that the 19-beam receiver can be slightly moved in the beam-switching mode, every step of such beam-switching costs only or 20 seconds, we therefore designed and successfully tested the snapshot mode in March 2019 so that the four steps of small movements of the feeds make the four pointings which make observations to completely cover a sky area of 0.157 square degree, as seen in Fig.1.

Based on this high efficiency snapshot mode observations, for the risk-share open session of the FAST in 2019, we designed the the Galactic Plane Pulsar Snapshot (GPPS) survey. The goal of the GPPS survey is to make the most sensitive pulsar survey on the Galactic plane in +-5 degree of the Galactic latitudes with the highest priority, and later the survey will extend to +-10 degree (see Fig.2 and Fig.3). The integration time for each pointing is 5 minutes (i.e. 300 seconds). A cover can be surveyed by the 4 pointings made by the beam-switching, which costs 21 minutes in total, including 4*5 minutes for pointing plus 3*20 seconds for beam-switching. It is expected to discover about 1000 pulsars in this sky region of the Galactic plane visible by the FAST. The best wishes include the discovery of pulsars with extremely short rotating periods or extremely short orbit periods if they are in binary.

Fig.2: The pulsar distribution in the sky and the Galactic plane visible to the FAST.

We carried out a series of test observations. Initial efforts were dedicated to examine the data acquisition system and test the pointing accuracy, and to design the data convert software. We designed and later continuously improved the pipelines for data-processing. Radio frequency interference (RFI) has been excused various method, such as ArPLS-ST. We discovered some pulsars in 2019. At the end of 2019, the GPPS project has been officially accepted by the Science Committee of the FAST, as one of five hi-priority major projects of the FAST.

Fig.3: The covers of GPPS survey to observe: observation progress.

In 2020, extensive observations have been made (see Fig.3), and we have already detected several hundreds of known pulsars, and have discovered pulsars in the following table.