Research
Understanding and using fast radio bursts
Understanding and using fast radio bursts
Fast radio bursts are powerful and mysterious explosions producing flashes of radio waves visible from across the universe.
Most of my research is made with data from CHIME/FRB, an experiment detecting hundreds of fast radio bursts each year.
On one hand, I work to detect, study, and understand them. On the other hand, I explore new ways to use these sources to increase our knowledge of the universe. Some of my studies are reported in the following (in no particular order).
Knowing the position of a fast radio burst gives us information about its origin, it is useful to follow it up with other instruments and can be used to know its distance by identifying the host galaxy.
The real-time detection of CHIME/FRB measures source positions with low precision of an order of a degree. This can be improved by orders of magnitude by processing the voltages measured by every single one of the 2048 receivers forming the telescope. I have developed software to process this massive data stream and localize fast radio bursts in the sky.
By using the products of this algorithm, we have identified the host galaxy for half a dozen fast radio bursts, with many more that will be presented soon. For example, we have found the closest ever fast radio burst outside of the Milky Way and identified host galaxies with unique characteristics. Other examples include a nearby spiral and other host candidates.
Fast radio bursts are usually polarized. Their polarization can be used to study both the emission geometry and the magnetic fields of ionized media that radio waves cross in their path. In this way, we can study the magnetic fields in the source environment, in the host galaxy, and in the intergalactic medium.
I have discovered that the source of a repeating fast radio burst lives in one of the most extreme magnetic environments ever observed. With this discovery, it was possible to gather information on the fast radio burst progenitor and also measure magnetic fields inside another galaxy. Observing the source for a few months revealed that the magnetic fields or the geometry of the system changed drastically, causing large variations in the polarization properties of the bursts.
The same voltages measured by the receivers of CHIME and used to localize fast radio bursts can be used to measure their polarization. We have developed the software to extract polarization information from CHIME data. This software was applied to a sample of repeating fast radio bursts and, in particular, to a source also displaying variations in the polarization properties over time. The polarization properties of a larger sample will be presented soon.
Usually, fast radio bursts are formed by one or a few flashes of radio waves in quick succession, with a total duration of up to a few milliseconds. Analyzing CHIME/FRB data, I have found one fast radio burst formed by at least 9 (and probably around 14) separate peaks, for a total duration of about 3 seconds. Moreover, the peaks in the signal came at multiple integers of a period of 0.2 seconds, reminiscent of the emission of Galactic radio pulsars.
This discovery gave us important information on the source of at least some fast radio bursts. Moreover, if other similar sources will be found in the future, they may have the characteristics to be used as clocks at cosmological distances to run unprecedented astronomical experiments.
Strong gravitational lensing occurs when multiple images of a background source are produced by a massive object along the line of sight that bends the trajectory of the light to the observer. If the background source is variable in time, the delay between images can be used to infer the mass profile of the lens and to measure parameters of the universe, especially the Hubble constant.
Similar measurements have been performed in the past by using AGNs and supernovae. However, their characteristics limit the precision of the measurements. On the other hand, fast radio bursts, with their short duration and large emission rate, are perfect sources to be used for this kind of experiment. For example, it is estimated that with only 10 fast radio bursts that are strongly lensed the Hubble constant could be measured with one of the highest precision ever achieved.
Strong lensing is a rare phenomenon and detecting a lensed fast radio burst requires a large number of sources from large distances. In addition, measuring a delay requires multiple images to be observed. This makes it challenging to detect strongly lensed fast radio bursts with current instruments.
I am currently developing a project to detect a few strongly lensed fast radio bursts in the next 5 years. More details to follow soon.
The broadband frequency spectrum of fast radio bursts is poorly constrained but there are indications that it could be different for sources observed to repeat. Also, observing fast radio bursts at very low frequencies not only gives us constraints on the emission mechanism but also on the environment of the source.
Measuring the emission of fast radio bursts over a large bandwidth often requires observing with multiple telescopes. Soon after I joined the CHIME/FRB team, I started following up repeating fast radio bursts with the Green Bank telescope down to a frequency of 300 MHz, where no fast radio bursts had been seen before. After years of observations, we detected a fast radio burst at the lowest frequency at the time. In the meantime, we started observing the same source at even lower frequencies, down to 110 MHz, and discovered a few bursts. The characteristics of the emission at such low frequencies gave us important information about the source of these bursts.