Electromagnetic followup of gravitational waves

I work with ZTF and WINTER teams to follow-up gravitational wave alerts detected by the LIGO collaboration to search for their electromagnetic counterparts - the elusive kilonovae.

ZTF's large FOV is well-suited to search for the fast-fading kilonovae associated with binary neutron star or neutron star-black hole mergers. ZTF conducted GW followup campaigns during LIGO-O3 (paper), and will continue to do so during the LIGO's ongoing O4 observing run.

WINTER's NIR sensitivity is well-suited to search for kilonovae, as they are expected to be brighter and longer-lasting at infrared wavelengths. Using realistic GW simulations, we found that WINTER is capable of efficiently searching for kilonovae during LIGO O4 (paper).

Stellar Mergers and Common-Envelope Evolution

Luminous Red Novae (LRNe) are transients associated with the final stages of common-envelope evolution in stellar binaries - a stellar merger or common-envelope ejection. LRNe have low intrinsic luminosities, making them observationally rare.

I use a systematic, volume-limited survey of transients discovered by ZTF to search for LRNe and study their demographics. With ZTF, we constructed the first systematic sample of LRNe and constrained their rates and luminosity function (paper).

I am now searching for LRNe using WINTER, to uncover the dustiest stellar mergers that are being missed by optical telescopes like ZTF. I also led an approved program on JWST to conduct mid-IR observations of LRNe during Cycle 2 to study their dust properties.

R-Coronae-Borealis stars - Remnants of low-mass white-dwarf mergers

The remnants of low-mass white dwarf (WD) mergers are expected to spend a significant part of their lives as puffed-up supergiant stars. R-Coronae Borealis (RCB) stars are an enigmatic class of supergiants that have chemical compositions consistent with being WD merger remnants. Adding to their mystery, RCB stars show rapid brightness declines due to dust-formation around them.

I am conducting a systematic infrared search for RCB stars using the PGIR. I use PGIR infrared lightcurves of millions of stars to identify those showing RCB-like erratic variations in their lightcurves. I then use NIR spectroscopy to confirm their nature (paper). I also use the spectra to study the chemical abundances of RCB stars (paper).

Low luminosity type Iax supernovae

Type Iax supernovae (SNe Iax) are a peculiar class of thermonuclear supernovae, that are thought to be the result of the partial deflagration of a white dwarf (WD) accreting from a companion. There is a sub-population of SNe Iax that are intrinsically fainter than the rest and cannot be explained by the standard WD deflagration model.

With ZTF, we discovered the lowest luminosity SN Iax to date, SN 2021fcg (paper). This SN had a peak absolute magnitude of a mere -12.5 mag and could not be explained by the standard WD deflagration model. A promising alternative model was the merger of an ONe WD with a CO WD.

I am now accumulating a systematic sample of low luminosity SNe Iax using ZTF. I also led a successful HST proposal to observe SN 2021fcg to search for its remnant, and constrain its progenitor system.

Data processing pipelines for time-domain surveys

I co-created mirar (Modular Image Reduction and Analysis Resource) - an open-source python package for processing and analyzing images from time-domain surveys. The modular and flexible design of mirar allows for reducing images and detecting transients by performing image subtraction on images from any optical/infrared telescope. Originally built to process WINTER data, mirar is now being used to process data from four other telescopes.