FAST and Multi-messenger Astronomy

It’s my pleasure to have a chance to say something about FAST here. Thanks to Dr. Xu and all the organizers.

There are three main parts in today’s talk.

First, I will talk about my superficial understanding of the Multi-messenger Astronomy. There are four kinds of fundamental interactions, corresponding to different messengers. For electromagnetic interaction, the corresponding messenger is photons. For weak interaction, the corresponding messenger is neutrinos. For gravitational interaction, the corresponding messenger is gravitational wave or maybe gravitons? For Strong interaction, the corresponding messenger is cosmic rays.

Now let’s have a look at the brief history of the development of multi-messenger instruments. For a long time, optical light is the only messenger for us to study the universe. Then we have telescopes and satellites in X-ray, infrared bands. No surprise, new parameter space for new discoveries, there came a lot of discoveries, Quasar, Pulsar, X-ray Binaries, Supernova Remnants, Molecular Clouds, Gamma-ray Burst, Fast Radio Burst, etc.

The cosmic ray studies have a long history, but when we talk about large detectors, the cosmic ray detectors and neutrino detectors all begin in the 1960’s. With these detectors, cosmic ray with energy of 10¹⁸-10²⁰ eV, neutrino from the Sun, supernova, and AGN were detected.

The reliable gravitational wave detectors started later in 1990’s, but experiencing rapid development. Up to now, the gravitational wave from black hole-black hole merger and neutron star-neutron star merger has already been detected.

After the brief history of the multi-messenger instruments. Let’s have a look at FAST. FAST stands for Five-hundred-meter Aperture Spherical radio Telescope. When it is not working, the fiducial shape of the reflector is part of a sphere. The aperture is 500 meters, the radius of the sphere is 300 meters.

There are three main features of FAST. First, the site of FAST is a round Karst depression, perfect for FAST. Second, FAST used an active reflector. Third, FAST used a light weighted feed support system.

This is the optics of FAST. During the observation, the illuminated region deforms from a sphere to a parabola. When tracking a source, the deforming region is changing accordingly. The aperture of the deforming region is 300 meters. So the effective aperture of FAST is 300 meters.

Now we have 7 sets of receivers, covering the frequency range of 70 MHz to 3 GHz.

In the past three years, we have used the ultra-wide band receiver and the 19-beam receiver to do observation. This is what these two receivers look like.

The planned science projects for FAST includes Galactic HI (neutral hydrogen) mapping, HI galaxy searching, pulsars, interstellar molecules, VLBI, SETI, and other unexpected sciences.

Up to now, we have observed HI galaxies, pulsars, FRBs and other objects. We have discovered more than one hundred pulsar candidates and most of them have been confirmed to be new pulsars. In these pulsars, there are also several millisecond pulsars. We have also successfully observed pulses from the repeating FRB.

Usually, the most interesting neutrino sources and gravitational sources are transient sources. We have some collaboration with LIGO and Hui Yan (HXMT). When we get the trigger from these instruments, we will point FAST to the targets in several hours.

To summarize, FAST have observed a lot of sources, including pulsars, FRB, HI galaxies. For multi-messenger observation for FAST, the relevant objects should be transient events.