Fast Radio Bursts, or FRBs, are currently one of the biggest unsolved and most tantalising mysteries of astrophysics. They were first discovered in 2007 and are the first of their kind to come from possibly halfway across the Universe. They are extremely bright radio flashes in the sky that last about a thousandth of a second and are about a billion times brighter than anything even remotely similar in our Galaxy. As the radio signal travels from the source to the observer on earth, the higher frequencies arrive at the telescope slightly earlier than the lower frequencies representing the total number of electrons that the pulse has traversed, called the dispersion measure (DM). This dispersion of the radio signal due to electrons in the cosmic medium is analogous to white light being dispersed by a prism into the colours of the rainbow.
The approximate locations of FRBs. The large coloured dots are the FRB positions from FRBcat, the colour of the edge of the dot indicates the observatory that detected the FRB and the colour of the dot indicates the measured DM. The DMs of the FRBs range from 176.4 to 2596 pc cm-3. The small white dots show the distribution of pulsars from the ATNF pulsar catalogue. The colour map in the background shows the Galactic DM as modelled by the YMW16 model, both the DM map and the FRBs have the same DM colour scale, shown on the colour bar.
We don’t yet know what causes FRBs, where in the sky they happen and when they happen. What we do know is that about 5 FRBs go off every minute randomly in the sky, but they are quite easy to miss because most telescopes can only see a very small section of the sky at any given time. We know of 34 FRBs so far, but only one has been seen to repeat, allowing for the source to be localised to a dwarf galaxy. However the exact nature of the source remains open to speculation. With the exception of the repeater, the spatial localisation of the FRBs on the sky is no better than a few to tens of arcminutes (an arcminute is about the apparent size of the thickness of a human hair about 5 metres away) making unambiguous association with counterparts (and a potential host galaxy) at other wavelengths quite challenging. In order to identify a potential host galaxy, it is vital to precisely pin down the source location upon discovery.
The two leading theories on what makes FRBs are bursts from pulsars or magnetars. Pulsars are rapidly spinning dense stars in our Galaxy left over from a supernova explosion. They emit jets of radiation along their poles and as one of these jets crosses our line of sight it appears as a pulse. Pulsars are often called "astronomical lighthouses" because of this. The idea for pulsars as FRBs is that these pulsars are halfway across the Universe and only the brightest of bursts are visible to us on earth. Magnetars are stars that have intense magnetic fields associated with them. The magnetar theory for FRBs is that the magnetic fields are cut off from the surface of the magnetar due to a "starquake" and when they reconnect an FRB is given off.
It took 6 billion years for the brightest FRB detected so far to reach us. In comparison, our solar system is only about 4.7 billion years old. This means that when the light left the source we did not exist. The sun, the earth, oceans, life on earth, it all formed while the light was travelling to us and we just happened to be pointing at the right patch of sky at the right time. So if we look back far enough, we can potentially probe the era of the young Universe in which the first stars were formed. This is the era that has only been theorised about and not yet probed observationally. Magnetic fields also play very critical roles in almost every aspect of astrophysics. Unfortunately much remains unknown about how these fields are generated or how they are evolving. The magnetic fields in the Milky Way have been extensively studied using pulsars. FRBs could help us understand and measure the magnetic fields associated with the medium outside our Galaxy for the very first time.
We know 95% of the Universe is dark energy and dark matter and only ~5% of it is "Baryonic Matter", or normal matter. Baryons make up objects of everyday life. 50% of the baryons are accounted for and astrophysicists suspect that the remaining 50% or "missing baryons" is in the form of diffuse hot plasma between galaxies called the Warm Hot Intergalactic Medium (WHIM). Detecting the WHIM has remained a challenge for many years. The dispersion measure of the FRB along with an estimate of redshift of the galaxy (an indication of how far away the galaxy is) can provide a direct measurement of the baryonic matter including the so called "missing baryons".
The MeerTRAP project will undertake high time resolution FRB searches simultaneously with all other on-going projects at MeerKAT thereby resulting in thousands of hours of time on sky. In radio astronomy, the larger the dish the more signal it can collect. Unfortunately this means that it only sees a small patch of sky at any given time. The inverse is true for a smaller dish. So it collects less signal but sees a larger patch of sky. A interferometer is formed by linking many small dishes together electronically to virtually form one large dish with the field of view of a single dish. So in this way it can collect a lot of signal while retaining a large field of view, which is important when performing blind FRB searches. MeerTRAP expects to discover several tens of FRBs in the near future and as an interferometer, MeerKAT will allow for near instantaneous localisation allowing for a more targeted search in radio for repeats and in other wavelengths for counterparts.
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