Gravitational Wave Astronomy
(Left) Hubble Space Telescope image from 4 months before the discovery of GW170817. (Right) The Swope discovery image of SSS17a, the optical counterpart to GW170817. SSS17a is marked with the red arrow.
I am involved in all aspects of gravitational wave astronomy from the search for optical counterparts to pan-chromatic follow up to detailed analysis and theoretical understanding of gravitational wave sources. I was involved in the discovery of the optical counterpart to GW170817, the binary neutron star merger gravitational wave signal detected by the joint LIGO/Virgo collaboration. I am actively planning multi-telescope follow-up efforts to future gravitational wave events and how to optimally search for their electromagnetic counterparts.
I am also involved in several follow-up efforts that examine how to use our global telescope resources to observe the radio through X-ray emission from gravitational wave counterparts. I am especially interested in studying the abundances of r-process elements from these events. Can we find "smoking gun" evidence for these elements in spectroscopic features or the decline rate of transients powered by the r-process? Finding this evidence will require simultaneous follow-up across the electromagnetic spectrum to disentangle the various emission processes. State-of-the-art modeling is also needed to understand how these observations relate to our theoretical understanding of gravitational wave sources.
Kilpatrick, Foley, Kasen, et al. Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger. (2017), Science, 358, 1583
Supernova Progenitor Stars
SN 2016gkg (upper panel) from 22 Sep 2016 compared with a Hubble Space Telescope image (bottom panel) from 21 Aug 2001 showing its progenitor star at the same location. From Kilpatrick et al. (2017).
I examine images of nearby supernovae from before they explode to look for evidence of the progenitor star system. This type of analysis was famously performed with SN 1987A, where astronomers identified a single, blue supergiant star, Sanduleak -69 202, as the supernova progenitor. This result was a spectacular confirmation that massive stars produce supernovae via the core-collapse mechanism. Roughly two dozen supernova progenitor stars are known, with more discovered each year, but many observational and theoretical challenges remain in expanding and understanding this sample.
One challenge is obtaining sufficiently high-resolution imaging of the supernova, such as the laser guide star adaptive optics imaging of SN 2016gkg (image above), needed to precisely identify the location of the supernova and associate it with a single star. I have developed image processing and analysis tools to compare supernovae with pre-explosion imaging, especially from the Hubble Space Telescope. As part of this analysis, I recently updated the Keck/OSIRIS geometric distortion terms, which can be used for all archival OSIRIS imaging.
I am also very interested in dust absorption and emission from material in the progenitor star environment and the extent to which dust obscuration biases our understanding of these systems. Dust grains emit most of their radiation at wavelengths greater than 1 micron. Currently, there is a dearth of deep, high-resolution imaging of supernova host galaxies at these wavelengths. I am actively working on new analysis techniques and observing programs using the Spitzer Space Telescope, Hubble Space Telescope, and ground-based infrared telescopes to obtain pre-explosion infrared imaging of supernova progenitor stars. As the James Webb Space Telescope will soon make deep, high-resolution infrared imaging widely available, these data will form a core sample for analysis of dust in progenitor star environments.
Kilpatrick, Foley, Abramson, et al. On the Progenitor of the Type IIb Supernova 2016gkg. (2017), MNRAS, 465, 4650
Kilpatrick, Foley, Drout, et al. Connecting the progenitors, pre-explosion variability, and giant outbursts of luminous blue variables with Gaia16cfr. (2018), MNRAS, 473, 4805
Kilpatrick, Takaro, Foley, et al. A Potential Progenitor for the Type Ic Supernova 2017ein. (2018), MNRAS, 480, 2072
Kilpatrick & Foley. The Dusty Progenitor Star of the Type II Supernova 2017eaw. (2018), MNRAS, 481, 2536
Kilpatrick, Coulter, Dimitriadis, et al. X-ray limits on the progenitor system of the Type Ia supernova 2017ejb. (2018), MNRAS, 481, 4123
I analyze Galactic supernova remnants (SNRs) using millimeter imaging of the interstellar gas in their environments. Most Galactic SNRs explode from massive stars and evolve close to the molecular clouds in which they were born. By looking for the molecular gas near Galactic SNRs, we can often find evidence for molecular shocks in the form of broad molecular lines. I used observations of the 12CO J=2-1 rotational line (at 231 GHz) from the Heinrich Hertz Submillimeter Telescope to find evidence for broad molecular lines near Cassiopeia A (image above). I extended this analysis to 50 Galactic SNRs and found that molecular shocks are rare comopared to previous estimates.
Kilpatrick, Bieging, & Rieke. Interaction Between Cassiopeia A and Nearby Molecular Clouds. ApJ, 796 (2014) 144
Kilpatrick, Bieging, & Rieke. A Systematic Survey for CO Toward Galactic Supernova Remnants. ApJ, 816 (2016) 1