Session Q14: Supernovae, GRBs, and FRBs

Understanding the Physics of Shock Breakout

The early emission from a supernova blastwave breaking out of its progenitor star provides key insight into the nature of the supernova explosion and its progenitor.  Asymmetries in the supernova engine, inhomogeneities in the stellar envelope and stellar wind, and the structure of the transition region between the stellar envelope and wind all contribute to the emission from this initial shock breakout.  The importance of inhomogeneous radiation-flow (and its subsequent shock-heating) spans many disciplines, leading to the design of a growing number of laboratory experiments to better understand this physics.  In this talk, I will review the astrophysical problem of early-time shock emission, upcoming NASA missions designed to measure it and the laboratory experiments designed to better understand the physics driving this emission.   

Measuring the properties of f-mode oscillations of a protoneutron star by third generation gravitation-wave detectors

Core-collapse supernovae are one of the sources of gravitational waves that could be detected by the third-generation gravitational-wave detectors. We analyze the gravitational-wave strain signals from two and three dimensional simulations of core-collapse supernovae. The dominant source of time changing quadrupole moment is the l= 2 fundamental mode (f−mode) oscillation of the protoneutron star. From the time-frequency spectrogram of the gravitational-wave strain we see that, starting ∼400ms after the core bounce, most of the power lies within a narrow track that represents the frequency evolution of the f−mode oscillations, as is corroborated by linear perturbation analysis of the angle-averaged profile of the protoneutron star. In this work, we explore the measurability of the frequency evolution and energy of f-mode oscillations of a protoneutron star for a supernova signal observed in the third-generation gravitational-wave detectors. Measurement of the frequency evolution can reveal information about the masses and radii of the protoneutron stars. We find that if the third generation detectors observe a supernova within 20 kpc, we can measure these frequencies to within 98% accuracy. We also find that the energy in the f−mode can be measured to within 20% error for simulations with the progenitor mass is higher than 10 solar masses and source distances within 10 kpc.   

Effects of circumstellar shells on long gamma-ray burst afterglow dynamics

Gamma-ray bursts (GRBs) are the most energetic electromagnetic phenomena in the known universe. However, much remains unknown about the specific mechanism driving their long-term evolution. Current models frequently focus on complex behavior involving the GRB progenitor but assume simple circumstellar environments. Many long GRBs, however, show late-time optical and x-ray flares which may indicate a much richer environment. Relativistic hydrodynamics simulations are used to evolve a family of initial data for a relativistic blast wave colliding with a circumstellar shell similar to what an aging star expelling the outer layers of its atmosphere might generate. The possibility that this interaction contributes to late-time variability is tested. Under favorable circumstances, the results indicate the possibility of late-time thermal flares in the optical or x-ray range. Preliminary results on synchrotron radiation from the reverse shock will also be presented, as well as how these results compare to existing observations.   

Turn on the Radio: Challenges to our Understanding of Gamma-ray Burst from their Radio Emission.

Although the standard picture for how we understand gamma-ray bursts (GRBs), the most luminous explosions in our universe, has been remarkably successful at explaining many of their observed properties, it is clear we are missing fundamental pieces of the puzzle.  In the past few years, analyses of their radio emission in particular has brought to light a number of challenges to our standard model. We present recent results showing a dichotomy between long GRBs with and without radio afterglows. These two populations exhibit significantly different observational properties that suggest potentially two distinct progenitor systems.  We explore the possibility that radio bright GRBs originate from massive stars collapsing in interacting binary systems, while radio dark GRBs may come from single (or non-interacting binary) massive stellar deaths.   We also discuss the cosmological evolution of GRB observables in both the radio bright and dark populations, and connect this to their progenitor evolution over cosmic time.     

Lessons learned from the galactic hosts of short gamma-ray bursts

The multimessenger event GW170817 unequivically connected binary neutron star mergers and short gamma-ray bursts (GRBs). Though it will take many years to significantly bolster the number of gravitational-wave events with identified electromagnetic counterparts, the growing number of host-identified short GRBs can fill this void in the interim, as well as probe compact binary merger hosts over a much larger redshift range. In this talk, I'll present new findings from a population of over 50 host-identified short GRBs. Information attained through spectroscopic and photometric observations of the hosts has led to novel constraints on delay-time distributions, binary progenitor properties, supernova kicks at compact binary formation, and host demographics. The demographics of this population will also help inform follow-up strategies for future gravitational-wave events that are potentially accompanied with an electromagnetic counterpart.   

Spectral analysis of PIC simulations of interpenetrating plasmas

Plasma with interpenetrating beams is known to exhibit electromagnetic instabilities such as the filamentation (e.g., Weibel) instability. Extreme astrophysical environments, such as in collisionless shocks of cosmic explosions -- gamma-ray bursts and supernovae, are natural places where such beam-plasma instabilities naturally occur and affect plasma dynamics and observable light. Here we investigate the case of a collisionless, unmagnetized system with relativistic counter-streaming beams with PIC simulations.  We present the spectral analysis of the system as it evolves. We discuss the spectrum, temporal and angular distribution of the generated plasma modes.    

A Synoptic View of Fast Radio Bursts with CHIME

For more than a decade, enigmatic extragalactic flashes called fast radio bursts (FRBs) have defied a definitive explanation for their origin. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is the only radio telescope capable of instantaneously observing hundreds of square degrees with the sensitivity of a 100-meter scale aperture. As a result, its transient search instrument, CHIME/FRB, has detected thousands of FRBs in its first few years of operations, increasing the known sample by an order of magnitude. I will give an update of CHIME/FRB's most recent results, where observations of particular sources and statistical analyses of the FRB population are starting to reveal the nature of this mysterious phenomenon. I will conclude by describing efforts to augment CHIME's capabilities by adding Outrigger telescopes, which will be located across North America and will precisely localize FRB sources using very long baseline interferometry. These localizations will enable multiwavelength followup and studies of the source environments, providing a new handle on FRB progenitors.   

Coherently Searching for Compact Dark Matter using Gravitationally Lensed Fast Radio Bursts with CHIME

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is observing several Fast Radio Bursts (FRBs) a day across a bandwidth of 400-800 MHz. Searches for gravitationally lensed FRBs have the potential to detect dark compact objects, such as primordial black holes. These microlensed FRB searches can constrain the fraction of dark matter from these compact objects at cosmological distances and in a mass regime that is difficult to probe with other techniques. We employ a novel search method to coherently search for lensing signatures by time-lag correlating the fluctuations of the electric field of an FRB and its possible image. This allows for unambiguous image detections in the time-lag domain without needing CHIME to angularly resolve the image positions in the sky. This method searches for gravitationally lensed FRBs on timescales of nanoseconds to milliseconds, corresponding to a search for compact objects between 10^-4 to 10² solar masses. I present the results of the CHIME/FRB gravitational lensing search with our initial set of ~100 FRB events. We find evidence for diffractive scintillation in some FRBs but no detections of a gravitational lens in this initial search. The search will soon be extended on a source sample an order of magnitude larger.