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Adam Burrows

Publications and source records attributed to Adam Burrows.

At least 73 records · Page 4Linked to original sources
arXiv2020

Core-collapse supernova neutrino emission and detection informed by state-of-the-art three-dimensional numerical models

Based on our recent three-dimensional core-collapse supernova (CCSN) simulations including both exploding and non-exploding models, we study the detailed neutrino signals in representative terrestrial neutrino observatories, Super-Kamiokande (Hyper-Kamiokande), DUNE, JUNO, and IceCube. We find that the physical origin of difference in the neutrino signals between 1D and 3D is mainly proto-neutron-star (PNS) convection. We study the temporal and angular variations of the neutrino signals and discuss the detectability of the time variations driven by the spiral Standing Accretion Shock Instability (spiral SASI) when it emerges for non-exploding models. In addition, we determine that there can be a large angular asymmetry in the event rate ($\gtrsim 50 \%$), but that the time-integrated signal has a relatively modest asymmetry ($\lesssim 20 \%$). Both features are associated with the lepton-number emission self-sustained asymmetry (LESA) and the spiral SASI. Moreover, our analysis suggests that there is an interesting correlation between the total neutrino energy (TONE) and the cumulative number of neutrino events in each detector, a correlation that can facilitate data analyses of real observations. We demonstrate the retrieval of neutrino energy spectra for all flavors of neutrino by applying a novel spectrum reconstruction technique to the data from multiple detectors. We find that this new method is capable of estimating the TONE within the error of $\sim$20\% if the distance to the CCSN is $\lesssim 6$ kpc.

astro-ph.HE↗
arXiv2020

The Missing Link in Gravitational-Wave Astronomy: Discoveries waiting in the decihertz range

The gravitational-wave astronomical revolution began in 2015 with LIGO's observation of the coalescence of two stellar-mass black holes. Over the coming decades, ground-based detectors like LIGO will extend their reach, discovering thousands of stellar-mass binaries. In the 2030s, the space-based LISA will enable gravitational-wave observations of the massive black holes in galactic centres. Between LISA and ground-based observatories lies the unexplored decihertz gravitational-wave frequency band. Here, we propose a Decihertz Observatory to cover this band, and complement observations made by other gravitational-wave observatories. The decihertz band is uniquely suited to observation of intermediate-mass ($\sim 10^2$-$10^4 M_\odot$) black holes, which may form the missing link between stellar-mass and massive black holes, offering a unique opportunity to measure their properties. Decihertz observations will be able to detect stellar-mass binaries days to years before they merge and are observed by ground-based detectors, providing early warning of nearby binary neutron star mergers, and enabling measurements of the eccentricity of binary black holes, providing revealing insights into their formation. Observing decihertz gravitational-waves also opens the possibility of testing fundamental physics in a new laboratory, permitting unique tests of general relativity and the Standard Model of particle physics. Overall, a Decihertz Observatory will answer key questions about how black holes form and evolve across cosmic time, open new avenues for multimessenger astronomy, and advance our understanding of gravitation, particle physics and cosmology.

gr-qc↗
arXiv2020

JWST Transit Spectra II: Constraining Aerosol Species, Particle-size Distributions, Temperature, and Metallicity for Cloudy Exoplanets

JWST will provide moderate resolution transit spectra with continuous wavelength coverage from the optical to the mid-infrared for the first time. In this paper, we illustrate how different aerosol species, size-distributions, and spatial distributions encode information in JWST transit spectra. We use the transit spectral modeling code METIS, along with Mie theory and several flexible treatments of aerosol size and spatial distributions to perform parameter sensitivity studies, calculate transit contribution functions, compute Jacobians, and retrieve parameters with Markov Chain Monte Carlo. The broader wavelength coverage of JWST will likely encompass enough non-gray aerosol behavior to recover information about the species and size-distribution of particles, especially if distinct resonance features arising from the aerosols are present. Within the JWST wavelength range, the optical and mid-infrared typically provide information about 0.1-1 $μ$m sized aerosols, while the near-infrared to mid-infrared wavelengths usually provide information about gaseous absorption, even if aerosols are present. Strong gaseous absorption features in the infrared often remain visible, even when clouds and hazes are flattening the optical and NIR portion of the spectrum that is currently observable. For some combinations of aerosol properties, temperature, and surface gravity, one can make a precise measure of metallicity despite the presence of aerosols, but more often the retrieved metallicity of a cloudy or hazy atmosphere has significantly lower precision than for a clear atmosphere with otherwise similar properties. Future efforts to securely link aerosol properties to atmospheric metallicity and temperature in a physically motivated manner will ultimately enable a robust physical understanding of the processes at play in cloudy, hazy exoplanet atmospheres.

astro-ph.EP↗
arXiv2020

Neutrino oscillations in supernovae: angular moments and fast instabilities

Recent theoretical work indicates that the neutrino radiation in core-collapse supernovae may be susceptible to flavor instabilities that set in far behind the shock, grow extremely rapidly, and have the potential to profoundly affect supernova dynamics and composition. Here we analyze the nonlinear collective oscillations that are prefigured by these instabilities. We demonstrate that a zero-crossing in $n_{ν_e} - n_{\barν_e}$ as a function of propagation angle is not sufficient to generate instability. Our analysis accounts for this fact and allows us to formulate complementary criteria. Using Fornax simulation data, we show that fast collective oscillations qualitatively depend on how forward-peaked the neutrino angular distributions are.

hep-ph↗
arXiv2020

A systematic study of proto-neutron star convection in three-dimensional core-collapse supernova simulations

This paper presents the first systematic study of proto-neutron star (PNS) convection in three dimensions (3D) based on our latest numerical Fornax models of core-collapse supernova (CCSN). We confirm that PNS convection commonly occurs, and then quantify the basic physical characteristics of the convection. By virtue of the large number of long-term models, the diversity of PNS convective behavior emerges. We find that the vigor of PNS convection is not correlated with CCSN dynamics at large radii, but rather with the mass of PNS $-$ heavier masses are associated with stronger PNS convection. We find that PNS convection boosts the luminosities of $ν_μ$, $ν_τ$, $\barν_μ$, and $\barν_τ$ neutrinos, while the impact on other species is complex due to a competition of factors. Finally, we assess the consequent impact on CCSN dynamics and the potential for PNS convection to generate pulsar magnetic fields.

astro-ph.HE↗
arXiv2020

Statistical Characterization of Hot Jupiter Atmospheres using Spitzer's Secondary Eclipses

We report 78 secondary eclipse depths for a sample of 36 transiting hot Jupiters observed at 3.6- and 4.5 microns using the Spitzer Space Telescope. Our eclipse results for 27 of these planets are new, and include highly irradiated worlds such as KELT-7b, WASP-87b, WASP-76b, and WASP-64b, and important targets for JWST such as WASP-62b. We find that WASP-62b has a slightly eccentric orbit e cos(omega) = 0.00614+/- 0.00064, and we confirm the eccentricity of HAT-P-13b and WASP-14b. The remainder are individually consistent with circular orbits, but we find statistical evidence for eccentricity increasing with orbital period in our range from 1 to 5 days. Our day-side brightness temperatures for the planets yield information on albedo and heat redistribution, following Cowan and Agol (2011). Planets having maximum day side temperatures exceeding ~ 2200K are consistent with zero albedo and distribution of stellar irradiance uniformly over the day-side hemisphere. Our most intriguing result is that we detect a systematic difference between the emergent spectra of these hot Jupiters as compared to blackbodies. The ratio of observed brightness temperatures, Tb(4.5)/Tb(3.6), increases with equilibrium temperature by 100 +/- 24 parts-per-million per Kelvin, over the entire temperature range in our sample (800K to 2500K). No existing model predicts this trend over such a large range of temperature. We suggest that this may be due to a structural difference in the atmospheric temperature profile between the real planetary atmospheres as compared to models.

astro-ph.EP↗
arXiv2020

Profiles of James Peebles, Michel Mayor, and Didier Queloz: 2019 Nobel Laureates in Physics

The 2019 Nobel Prize in Physics honors three pioneering scientists for their fundamental contributions to basic cosmic questions - Professor James Peebles (Princeton University), Michel Mayor (University of Geneva), and Didier Queloz (University of Geneva and the University of Cambridge) - "for contributions to our understanding of the evolution of the universe and Earth's place in the cosmos," with one half to James Peebles "for theoretical discoveries in physical cosmology," and the other half jointly to Michel Mayor and Didier Queloz "for the discovery of an exoplanet orbiting a solar-type star." We summarize the historical and scientific backdrop to this year's Physics Nobel.

physics.hist-ph↗
arXiv2019

Prospects for Directly Imaging Young Giant Planets at Optical Wavelengths

In this work, we investigate the properties of young giant planet spectra in the optical and suggest that future space-based direct imaging missions should be considering young planets as a valuable and informative science case. While young planets are dimmer in the optical than in the infrared, they can still be brighter in the optical than a mature planet of similar mass. Therefore, an instrument designed to characterize mature planets should also be suitable for high-precision photometric imaging and spectroscopy of young self-luminous planets in a wavelength range and at a contrast ratio not attainable from the ground. We identify known young self-luminous companions which are feasible targets for WFIRST-CGI and compute spectra for them, including a treatment of scattering and reflected light at optical wavelengths. Using these results, we highlight potentially diagnostic spectral features that will be present in the WFIRST-CGI wavelengths. Expanding to direct imaging missions beyond WFIRST-CGI, we also use evolutionary models across a grid of masses and planet-star separations as inputs to compute spectra of hypothetical objects, exploring when reflected light may contribute to a degree comparable to that of thermal emission from the residual heat of formation.

astro-ph.EP↗
arXiv2019

The Overarching Framework of Core-Collapse Supernova Explosions as Revealed by 3D Fornax Simulations

We have conducted nineteen state-of-the-art 3D core-collapse supernova simulations spanning a broad range of progenitor masses. This is the largest collection of sophisticated 3D supernova simulations ever performed. We have found that while the majority of these models explode, not all do, and that even models in the middle of the available progenitor mass range may be less explodable. This does not mean that those models for which we did not witness explosion would not explode in Nature, but that they are less prone to explosion than others. One consequence is that the "compactness" measure is not a metric for explodability. We find that lower-mass massive star progenitors likely experience lower-energy explosions, while the higher-mass massive stars likely experience higher-energy explosions. Moreover, most 3D explosions have a dominant dipole morphology, have a pinched, wasp-waist structure, and experience simultaneous accretion and explosion. We reproduce the general range of residual neutron-star masses inferred for the galactic neutron-star population. The most massive progenitor models, however, in particular vis à vis explosion energy, need to be continued for longer physical times to asymptote to their final states. We find that while the majority of the inner ejecta have Y$_e = 0.5$, there is a substantial proton-rich tail. This result has important implications for the nucleosynthetic yields as a function of progenitor. Finally, we find that the non-exploding models eventually evolve into compact inner configurations that experience a quasi-periodic spiral SASI mode. We otherwise see little evidence of the SASI in the exploding models.

astro-ph.HE↗
arXiv2019

Towards an Understanding of the Resolution Dependence of Core-Collapse Supernova Simulations

Using our new state-of-the-art core-collapse supernova (CCSN) code Fornax, we explore the dependence upon spatial resolution of the outcome and character of three-dimensional (3D) supernova simulations. For the same 19-M$_{\odot}$ progenitor star, energy and radial binning, neutrino microphysics, and nuclear equation of state, changing only the number of angular bins in the $θ$ and $ϕ$ directions, we witness that our lowest resolution 3D simulation does not explode. However, when jumping progressively up in resolution by factors of two in each angular direction on our spherical-polar grid, models then explode, and explode slightly more vigorously with increasing resolution. This suggests that there can be a qualitative dependence of the outcome of 3D CCSN simulations upon spatial resolution. The critical aspect of higher spatial resolution is the adequate capturing of the physics of neutrino-driven turbulence, in particular its Reynolds stress. The greater numerical viscosity of lower-resolution simulations results in greater drag on the turbulent eddies that embody turbulent stress, and, hence, in a diminution of their vigor. Turbulent stress not only pushes the temporarily stalled shock further out, but bootstraps a concomitant increase in the deposited neutrino power. Both effects together lie at the core of the resolution dependence we observe.

astro-ph.HE↗
arXiv2019

Temporal and Angular Variations of 3D Core-Collapse Supernova Emissions and their Physical Correlations

We provide the time series and angular distributions of the neutrino and gravitational-wave emissions of eleven state-of-the-art three-dimensional non-rotating core-collapse supernova models and explore correlations between these signatures and the real-time dynamics of the shock and the proto-neutron-star core. The neutrino emissions are roughly isotropic on average, with instantaneous excursions about the mean inferred luminosity of as much as $\pm$20%. The deviation from isotropy is least for the "$ν_μ$"-type neutrinos and the lowest-mass progenitors. Instantaneous temporal luminosity variations along a given direction for exploding models average $\sim$2$-$4%, but can be as high as $\sim$10%. For non-exploding models, they can achieve $\sim$25%. The temporal variations in the neutrino emissions correlate with the temporal and angular variations in the mass accretion rate. We witness the LESA phenomenon in all our models and find that the vector direction of the LESA dipole and that of the inner Y$_\mathrm{e}$ distribution are highly correlated. For our entire set of 3D models, we find strong connections between the cumulative neutrino energy losses, the radius of the proto-neutron star, and the $f$-mode frequency of the gravitational wave emissions. When physically normalized, the progenitor-to-progenitor variation in any of these quantities is no more than $\sim$10%. Moreover, the reduced $f$-mode frequency is independent of time after bounce to better than $\sim$10%. Therefore, simultaneous measurement of gravitational waves and neutrinos from a given supernova event can be used synergistically to extract real physical quantities of the supernova core.

astro-ph.HE↗
arXiv2019

Detection Prospects of Core-Collapse Supernovae with Supernova-Optimized Third-Generation Gravitational-wave Detectors

We optimize the third-generation gravitational-wave detector to maximize the range to detect core-collapse supernovae. Based on three-dimensional simulations for core-collapse and the corresponding gravitational-wave waveform emitted, the corresponding detection range for these waveforms is limited to within our galaxy even in the era of third-generation detectors. The corresponding event rate is two per century. We find from the waveforms that to detect core-collapse supernovae with an event rate of one per year, the gravitational-wave detectors need a strain sensitivity of 3$\times10^{-27}~$Hz$^{-1/2}$ in a frequency range from 100~Hz to 1500~Hz. We also explore detector configurations technologically beyond the scope of third-generation detectors. We find with these improvements, the event rate for gravitational-wave observations from CCSN is still low, but is improved to one in twenty years.

gr-qc↗
arXiv2019

Full Transport Model of GW170817-Like Disk Produces a Blue Kilonova

The 2017 detection of the inspiral and merger of two neutron stars in gravitational waves and gamma rays was accompanied by a quickly-reddening transient. Such a transient was predicted to occur following a rapid neutron capture (r-process) nucleosynthesis event, which synthesizes neutron-rich, radioactive nuclei and can take place in both dynamical ejecta and in the wind driven off the accretion torus formed after a neutron star merger. We present the first three-dimensional general relativistic, full transport neutrino radiation magnetohydrodynamics (GRRMHD) simulations of the black hole-accretion disk-wind system produced by the GW170817 merger. We show that the small but non-negligible optical depths lead to neutrino transport globally coupling the disk electron fraction, which we capture by solving the transport equation with a Monte Carlo method. The resulting absorption drives up the electron fraction in a structured, continuous outflow, with electron fraction as high as $Y_e\sim 0.4$ in the extreme polar region. We show via nuclear reaction network and radiative transfer calculations that nucleosynthesis in the disk wind will produce a blue kilonova.

astro-ph.HE↗
arXiv2019

Characterizing the Gravitational Wave Signal from Core-Collapse Supernovae

We study the gravitational wave signal from eight new 3D core-collapse supernova simulations. We show that the signal is dominated by $f$- and $g$-mode oscillations of the protoneutron star and its frequency evolution encodes the contraction rate of the latter, which, in turn, is known to depend on the star's mass, on the equation of state, and on transport properties in warm nuclear matter. A lower-frequency component of the signal, associated with the standing accretion shock instability, is found in only one of our models. Finally, we show that the energy radiated in gravitational waves is proportional to the amount of turbulent energy accreted by the protoneutron star.

astro-ph.HE↗
arXiv2019

Characterization of Exoplanet Atmospheres with the Optical Coronagraph on WFIRST

WFIRST-CGI is a NASA technology demonstration mission that is charged with demonstrating key technologies for future exo-Earth imaging missions in space. In the process, it will obtain images and low-resolution spectra of a handful to a dozen extrasolar planets and possibly protoplanetary disks. Its unprecedented contrast levels in the optical will provide astronomers with their first direct look at mature, Jupiter sized planets at moderate separations. This paper addresses the question: what science can be done with such data? An analytic noise model, which is informed by the ongoing engineering developments, is used to compute maximum achievable signal-to-noise ratios and scientifically viable integration times for hypothetical star planet systems, as well as to investigate the constraining power of various combinations of WFIRST-CGI photometric and spectral observations. This work introduces two simple models for planetary geometric albedos, which are inspired largely by the solar system's gas giants. The first planet model is a hybrid Jupiter-Neptune model, which separately treats the short and long wavelengths where chromophores and methane dominate absorption, respectively. The second planet model fixes cloud and haze properties in CoolTLusty to match Jupiter's albedo spectrum, it then perturbs only the metallicity. MCMC retrievals performed on simulated observations are used to assess the precision with which planet model parameters can be measured subject to different exposure times and observing cases. Fit results for both models' parameterizations of geometric albedo spectra demonstrate that a rough indication of the metallicity or methane content should be possible for some WFIRST-CGI targets. We conclude that real observations will likely be able to differentiate between extreme cases using these models, but will lack the precision necessary to uncover subtle trends.

astro-ph.EP↗
arXiv2019

The Yet-Unobserved Multi-Messenger Gravitational-Wave Universe

Observations with next-generation ground-based detectors further enhanced with multi-messenger (electromagnetic and neutrino) detections will allow us to probe new extreme astrophysics. Target sources included: core-collapse supernovae, continuous emission from isolated or accreting neutron stars, and bursts from magnetars and other pulsars.

astro-ph.HE↗
arXiv2019

Three-Dimensional Supernova Explosion Simulations of 9-, 10-, 11-, 12-, and 13-M$_{\odot}$ Stars

Using the new state-of-the-art core-collapse supernova (CCSN) code F{\sc{ornax}}, we have simulated the three-dimensional dynamical evolution of the cores of 9-, 10-, 11-, 12-, and 13-M$_{\odot}$ stars from the onset of collapse. Stars from 8-M$_{\odot}$ to 13-M$_{\odot}$ constitute roughly 50% of all massive stars, so the explosive potential for this mass range is important to the overall theory of CCSNe. We find that the 9-, 10-, 11-, and 12-M$_{\odot}$ models explode in 3D easily, but that the 13-M$_{\odot}$ model does not. From these findings, and the fact that slightly more massive progenitors seem to explode \citep{vartanyan2019}, we suggest that there is a gap in explodability near 12-M$_{\odot}$ to 14-M$_{\odot}$ for non-rotating progenitor stars. Factors conducive to explosion are turbulence behind the stalled shock, energy transfer due to neutrino-matter absorption and neutrino-matter scattering, many-body corrections to the neutrino-nucleon scattering rate, and the presence of a sharp silicon-oxygen interface in the progenitor. Our 3D exploding models frequently have a dipolar structure, with the two asymmetrical exploding lobes separated by a pinched waist where matter temporarily continues to accrete. This process maintains the driving neutrino luminosty, while partially shunting matter out of the way of the expanding lobes, thereby modestly facilitating explosion. The morphology of all 3D explosions is characterized by multiple bubble structures with a range of low-order harmonic modes. Though much remains to be done in CCSN theory, these and other results in the literature suggest that, at least for these lower-mass progenitors, supernova theory is converging on a credible solution.

astro-ph.SR↗