I'm a postdoctoral researcher in Radio Astronomy at Caltech, where I primarily study pulsars, FRBs and other compact radio objects and their interactions with the media that they pass through on their way to Earth. By disentangling these propagation effects from the intrinsic natures of these sources, I hope to learn more about both the sources themselves and the material in our Galaxy, other galaxies, and the intergalactic medium of the Universe.
The 110-element Deep Synoptic Array is currrently under construction at the Owen's Valley Radio Obsevatory in California, and consists of 110 5-m radio dishes. The DSA will find FRBs and pinpoint their locations in the sky, allowing us to determine the galaxies from which these bursts came. These FRB observations will help answer the questions concerning the nature of the sources of FRBs and the distribution of material within and between galaxies.
In order to study pulsar scintillation (variations in a pulsar's observerd flux due to the interference of rays scattered in the interstellar medium) and the small scale plasma structures that cause it, we first need to be able to reconstruct the scattered image of the pulsar. Pulsars themselves would appear as unresolved points on the sky if there were no intervening plasma structures in the way, and even when scattered are very small so that traditional imaging techniques are not sufficient to reconstruct the scattered image of the pulsar. Part of my research is developing the techniques that can be used to extract information, even if the scattering environment is complicated, with multiple different scattering screens between us and the pulsar. To the left is a reconstructed image of PSR B0834+06 I created based on VLBI observations taken by Brisken et al. (2010).
As pulsar radiation travels towards us, it is scattered and lensed by plasma structures in the interstellar medium. Recently, structure has been noted in scintillation patterns that suggests highly anisotropic scattering at one or more screens along our line-of-sight to the pulsar. Along with my advisor, Ue-Li Pen, I developed a model of pulsar scintillation based on the theory that scintillation is due to grazing refraction lensing of the pulsar emission by plasma sheets in the interstellar medium. In this picture, a plasma screen with a slightly different index of refraction than the surrounding interstellar medium is very closely aligned with the line-of-sight to the pulsar, so that only small perturbations on the screen are needed to bend the pulsar light, as shown in the cartoon to the right. Models of this process make clear predictions about the evolution of the scattering with time and frequency. By comparing these predictions to observations of pulsars, we can start to narrow down the causes of pulsar scintillation. Because these models are predictive, they may also be integral in removing the effects of scattering plasma screens in low-frequency observations of pulsars. You can check out a talk I gave on this research here.
In the fall of 2016, we undertook a global VLBI campaign using in order to track the evolution of the scintillation pattern of PSR B0834+06 over 6 weeks. The image on the left shows the secondary spectrum (the power spectrum of the observed interference pattern) over the observation, constructed from the data recorded at Arecibo. We see individual reverse arclets appear in the left hand side of the secondary spectrum and then traverse through the spectrum. This indicates that small, compact regions of the screen are moving in front of the pulsar. The motion of these can be compared to expectations from models, including from the plasma sheet model. We also see a persistent, diffuse parabolic arc of power, which suggests that compact regions aren't the full story of how the plasma sheet scatters the pulsar emission.
During my PhD, I was also involved in the revitalization of the Algonquin Radio Observatory 46-m radio telescope in Ontario, Canada. We observed bright pulsars with the ARO 46-m in order to search for evidence that instellar screens were resolving pulsar emission regions. You can check out a public talk I gave about using ARO for global pulsar VLBI as part of Astronomy on Tap T.O.