CRAFTS Observing Modes

CRAFTS is a commensal drift scan survey. The CRAFTS mode (drfit-scan with an angle plus high-cadence CAL) provides efficient, super Nyquist-sampled coverage of large sky area. It is now a relatively mature, well-tested observing mode supported by the telescope and is accompanied by extensive, existing calibration pipelines. The CRAFTS team is offering to share the observing mode, provide observation planning assistance, and share the associated calibration pipelines with other FAST users.

The CRAFTS observing mode consists of a drift map where the telescope is held fixed at the meridian while the sky drifts past. The receiver is rotated at an angle of 23.4 degrees and individual drift scans are separated by 21.67 arcminutes in Dec to produce a highly uniform, Nyquist-sampled map.

The backend systems output three sets of data products simultaneously, all of which are full- stokes and calibratable. The pulsar backend outputs 4k channels over a 500MHz band with ~98us sampling. The HI backend outputs wideband (64k channels over 500MHz) and narrowband (64k channels over 31.125 MHz around the 21 cm line) spectra sampled every 0.2s.

An innovative high-cadence noise injection system is used whereby a weak white noise signal of known intensity is periodically injected in order to calibrate the data. This is the fastest noise injection system ever developed and is unique to FAST. It can track electronics gain fluctuations on timescales as short as 100us to provide extremely stable results. This noise injection system does not interfere with Pulsar, or FRB observations.

CRAFTS team requires no access to your data or science collaboration. To better utilize the service, we recommend the following.

Prior to observations: Upon request, given a sky region and the number of passes, the CRAFTS team can generate all the necessary telescope setup and observing instructions necessary for your observations in the correct format.

After observations: Upon request, CRAFTS team will share their calibration pipelines that can perform much of the initial calibration and data processing.

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