Research

I am an observational astronomer studying cosmic explosions. I am interested in transient sources within our own Galaxy, and those occurring in a galaxy far, far away.

Credit: George Lucas

Gamma-ray Bursts

Short gamma-ray bursts (GRBs) are brief flashes of gamma-rays emanating from cosmic explosions capable of releasing the amount of energy that our sun radiates throughout its entire lifetime in the span of a few seconds. These powerful explosions are produced by the merger of two neutron stars, and are so extreme that they trigger a rare nuclear reaction chain, known as the r-process, which synthesizes heavy metals, such as gold and platinum. The environments in which they form and merge shed light on their progenitor evolution and formation channels.

Long duration GRBs, on the other hand, are produced by the collapse of a massive star, and, therefore, trace the star formation history of the Universe. I recently led a study of GRB 221009A - the most energetic and brightest of all time. A similar event is not expected for another millenia.

Selected Publications:

O'Connor et al. 2020 - Constraints on the circumburst environments of short gamma-ray bursts
O'Connor et al. 2022 - A deep survey of short GRB host galaxies over z∼0−2: implications for offsets, redshifts, and environments
O'Connor et al. 2023 - A structured jet explains the extreme GRB 221009A

doomed-neutron-stars-create-blast-of-light-and-gravitational-waves.jpg

Credit: NASA

Credit: NASA/Swift/UVOT - AT2017gfo

Kilonovae

Following a neutron star merger, neutron rich material undergoes a rapid decompression, triggering the rapid neutron capture process. This r-process nucleosynthesis rapidly heats the merger ejecta, leading to a bright optical and infrared transient known as a kilonova. Kilonovae mark the conclusive electromagnetic signature of neutron star mergers, and remain a primary focus of modern astrophysics. These transients mark a dominant channel for heavy element production in the Universe. Our team has recently unexpectedly identified kilonovae associated with two long duration GRBs (GRBs 211211A and 230307A), changing forever the landscape of the GRB phenomenon.

Selected Publications:

Ricci et al. 2020 - Searching for the radio remnants of short-duration gamma-ray bursts
O'Connor et al. 2021 - A tale of two mergers: constraints on kilonova detection in two short GRBs at z~0.5
Bruni, O'Connor et al. 2021 - Late-time radio observations of the short GRB 200522A: constraints on the magnetar model
Chase, O'Connor et al. 2022 - Kilonova Detectability with Wide-field Instruments
Troja, Fryer, O'Connor et al. 2022 - A nearby long gamma-ray burst from a merger of compact objects
Yang, Troja, O'Connor et al. 2023 - A lanthanide-rich kilonova in the aftermath of a long gamma-ray burst
Gillanders et al. 2023 - Heavy element nucleosynthesis associated with a gamma-ray burst

Gravitational Waves

Gravitational radiation represents a pathway for the localization and discovery of otherwise invisible objects, such as the merger of two black holes. Moreover, gravitational waves can assist in uncovering electromagnetic transients (e.g., GW170817). Their electromagnetic counterparts include gamma-ray bursts, kilonovae, or other previously undiscovered transient phenomena.

A timeline for the next LIGO, Virgo, and KAGRA observing run can be found here.

Fermi-LIGO_INTEGRAL_Graph_Still_print_edited_edited_edited_edited.jpg

Credit: NSF/LIGO

Credit: LIGO/NASA/L. Singer

Credit: Swinburne/J. Josephides

Fast Radio Bursts

Fast radio bursts (FRBs) are a mystery of modern astrophysics. They are fleeting pulses of energy lasting for milliseconds at radio wavelengths. Their progenitor systems remain elusive, and a variety of pathways still remain plausible candidates for their production (e.g., magnetars). A powerful clue towards their progenitors lies in the environments in which they are produced.

Selected Publications:

Piro et al. 2021 - The fast radio burst FRB 20201124A in a star-forming region: Constraints to the progenitor and multiwavelength counterparts

The Swift Deep Galactic Plane Survey

The Swift Deep Galactic Plane Survey (DGPS) utilized the X-ray Telescope (XRT) on-board the Neil Gehrels Swift Observatory to systematically observe the Galactic Plane of our Galaxy. In total Phase-I of the Survey covers 40 sq. deg of the Plane, searching for variable and transient X-ray sources.

Selected Publications:

O'Connor et al. 2023 - The Swift Deep Galactic Plane Survey Phase-I Catalog
O'Connor et al. 2023 - Swift Deep Galactic Plane Survey Classification of Swift J170800−402551.8 as a Candidate Intermediate Polar Cataclysmic Variable
O'Connor et al. 2023 - Identification of 1RXS J165424.6-433758 as a polar cataclysmic variable

Credit: NASA/CXC/M. Weiss

Galactic X-ray Binaries

The majority of the known Galactic population of compact objects (black holes, neutron stars, and white dwarfs) reside in binary systems comprised of a compact object and a companion star. Accretion from the companion onto the compact object leads to radiation across the electromagnetic spectrum. A main avenue for the identification of these sources is in X-ray surveys, such as the DGPS.

Selected Publications:

O'Connor et al. 2022 - Identification of an X-Ray Pulsar in the BeXRB System IGR J18219−1347
Gorgone et al. 2021 - Swift/XRT Deep Galactic Plane Survey Discovery of a New Intermediate Polar Cataclysmic Variable, Swift J183920.1-045350

Magnetars

Magnetars are highly magnetized, rapidly rotating, young neutron stars. Magnetars constitute a rare class of objects, and only ~30 are known within our Galaxy. They represent an extreme state of matter, which is irreproducible on Earth, and are often invoked to explain a variety of astrophysical phenomena from gamma-ray bursts to fast radio bursts.

Selected Publications:

Enoto et al. 2021 - A Month of Monitoring the New Magnetar Swift J1555.2−5402 during an X-Ray Outburst

Credit: OzGrav/C. Knox