Graduate Student
California Institute of Technology
I am a graduate student in astronomy at the California Institute of Technology. My interests lie primarily in radio astronomy, particularly the study of fast radio bursts (FRBs). I am currently leading the development and construction of a new instrument to search for FRBs in the local universe.
A map of STARE2 stations.
STARE2 station at Goldstone.
Fast Radio Bursts (FRBs) are millisecond bursts of GHz frequency radio emission of extragalactic origin, and their progenitors are hotly debated. They are typically observed from distant galaxies. However, the Survey for Transient Astronomical Radio Emission 2 (STARE2) is designed to find FRBs that originate from our own galaxy.
STARE2 consists of three stations located at the Owens Valley Radio Observatory (OVRO), the Goldstone Deep Space Communications Complex (GDSCC), and near the town of Delta, UT. The purpose of having multiple stations is the filter out radio frequency interference, ensure robust claims of detection, and provide some localization. It has sensitivity to approximately a quarter of the sky and is sensitive to 1 ms radio bursts >300 kJy.
On April 28th, 2020 we detected FRB 200428 (=ST 200428A) with all three stations. This burst had a fluence of 1.5 MJy ms, implying that its energy is similar to that of extragalactic FRBs. This is the first FRB detected in the Milky Way. More interestingly, it is associated with the Galactic magnetar SGR 1935+2154. This is direct evidence that magnetars produce the FRBs we see at extragalactic distances.
Fast radio transient phase space.
I developed a novel technique for comparing samples of transient host galaxies in order to robustly compare samples of transient host galaxies. I applied this to a sample of FRB host galaxies and determined they are consistent with the magnetar hypothesis.
Type Ia-CSM supernovae have similar spectra to Type Ia supernovae, but with superimposed narrow hydrogen lines from a surrounding circumstellar medium (CSM). I analyzed the data from the first type Ia-CSM supernova found in X-rays, a new probe of the CSM. I was able to infer that the CSM is likely asymmetric and similar to that around Type IIn supernovae.
I looked at 10 years of data on Terzan 5A, a millisecond pulsar in a tight eclipsing binary system, to help determine the eclipse mechanism. Although I was unable to determine the eclipse mechanism, I did find a few clues: 1) The eclipse is longer if you only look at linearly polarized light. 2) The rotation measure varies significantly at the edges of the eclipse. 3) During observations with "mini-"eclipses (shown above), there is a small burst of linearly polarized light at the egress of the eclipse.
Black widow pulsars are binary millisecond pulsars in tight orbits with small companions. Their orbits are highly variable, and in order to precisely time them so they can be used to detect gravitational waves, this orbital variability must be modeled out. However, since the same data are used to determine the timing parameters and search for gravitational waves, modeling more parameters opens the door to losing the gravitational wave signal. I was able to show that the orbital variability in black widow pulsars can be modeled without removing much of the gravitational wave signal, opening the door to using them to detect gravitational waves.
It is well known that the phase averaged spectrum of gamma-ray pulsars is harder than expected assuming the gamma-rays are produced from curvature radiation. This can be explained if the spectrum in each phase bin is different and has a shape consistent with curvature radiation, as the phase averaged spectrum is the sum of the spectrum in each phase bin and many different curvature radiation spectra add to give the observed hard phase averaged spectrum. However, I showed that in the Geminga and Vela pulsars, each phase bin also has a spectrum harder than expected from curvature radiation. This likely means there are multiple emission regions contributing to each pulse phase, or perhaps an unstable potential across one emission region.