Research

I am conducting a systematic search for bright Galactic radio transients discovered in VLASS. The population of known radio transients has grown dramatically in the VLASS era, from only ~10s of candidates before 2017 to thousands today. However, systematic transient searches have largely focused on extragalactic populations, in part because the Galactic plane presents a unique set of challenges. Galactic sources often lack reliable distance constraints, while heavy dust extinction and stellar crowding can make optical and infrared counterparts difficult - or impossible - to identify. Despite these challenges, the Galactic plane remains a particularly rich discovery space, where sources such as VT J1906+0849 (Miller et al., submitted) demonstrate that unusual systems can escape recognition until their radio variability reveals them.

Using variability between VLASS epochs and proximity to the Galactic plane (|b| <= 10 deg), I have assembled a sample of 42 candidate Galactic radio transients. Roughly have are associated with known Galactic systems, including a magnetar, a long period radio transient, X-ray binaries, novae, flare stars, and tight binaries; the rest are newly discovered and largely unclassified. I am using broadband (0.2 - 18 GHz) Very Large Array spectroscopy, Very Long Baseline Array high-resolution (~mas precision) imaging, and Keck/MOSFIRE 0.9-2.5 micron imaging and spectroscopy to determine what powers these sources. The campaign is already revealing a surprisingly diverse population, including candidate self-absorbed compact jets from accreting binaries, GHz-peaked transients, a pulsar candidate, and sources with unusual double-peaked radio spectra.

Ultimately, this project aims to build a more complete picture of the transient radio sky in the Milky Way while uncovering rare or previously unrecognized classes of Galactic sources. 

I am leading a project to help design the observing cadence for the Cadenced All-Sky Survey (CASS), one of the major time domain surveys planned for the Deep Synoptic Array (DSA). The DSA will be a next-generation 0.7 - 2 GHz radio interferometer composed of 1,650 x 6.15-m dishes. The observatory's dense uv-coverage will enable high-fidelity snapshot imaging of the radio sky, effectively functioning as the world's first radio camera. The array will be constructed in a radio-quiet valley near Ely, NV, and is expected to detect more than one billion radio sources, including roughly one million radio transients.

A central question for CASS is when to observe. I  will develop simulations of the Galactic and extragalactic transient populations to determine how different survey cadences affect transient discovery and characterization across a wide range of variability timescales. The optimal strategy differs across the sky: rapidly evolving Galactic transients favor denser sampling of the Galactic plane, while slower extragalactic populations can be probed with longer intervals between observations. By quantifying these trade-offs and the resulting selection effects, this project will directly inform the final observing cadence adopted for CASS.

In this recent paper, we present the discovery and multiwavelength characterization of the brightest known radio transient discovered in VLASS. Archival radio observations show that the source first appeared in 2005, brightened to more than 200 mJy by 2014, and subsequently faded before unexpectedly rebrightening in 2025, revealing a slow evolution on decade-long timescales. We find that the transient is likely a distant Galactic system powered by sustained accretion onto a compact object, but its unusual combination of extreme radio luminosity, X-ray non-detection, evolving synchrotron spectrum, and compact, slowly expanding radio-emitting region distinguishes it from known X-ray binaries. Near-infrared spectroscopy also reveals evidence for a persistent, high-velocity outflow. We suggest that the system may be a young analog of the microquasar SS 433, in which interaction between a jet and a dense disk wind confines the radio-emitting outflow and obscures soft X-ray emission. Despite a persistent, luminous optical and infrared counterpart detected in multiple archival surveys over the last 20 yr, the extraordinary nature of the source went unrecognized until its radio variability captured our attention, highlighting the unique discovery power of the dynamic radio sky.

In this work, I led the discovery of a new candidate transitional millisecond pulsar (tMSP) associated with the Fermi gamma-ray source 4FGL J0407.7-5702. TMSPs are rare neutron star binaries that switch between accretion-powered and rotation-powered pulsar states, providing a unique window into how millisecond pulsars form and evovle. Using X-ray observations from XMM-Newton and optical observations from SOAR and Gemini, we found rapid X-ray variability and flaring together with broad, double-peaked emission lines characteristic of an accretion disk. These properties indicate that the system is likely a tMSP in the subluminous disk state. We also found evidence that it may be one of the most distant systems of its kind, and showed that the ratio of X-ray to gamma-ray flux could be a useful way  to identify additional tMSP candidates.