arXiv subjects

Richard S. Miller

Publications and source records attributed to Richard S. Miller.

4 recordsLinked to original sources

arXiv2024

Sibling Rivalry: Thermonuclear Diversity and the Hubble Tension

Homogeneity is the hallmark of standard candle-based cosmology investigations. Thermonuclear supernovae (Type-Ia, SNeIa) violate this essential requirement if they develop along multiple evolutionary pathways. In this work, the impact of thermonuclear diversity on cosmological parameter constraints is quantified using Pantheon+, one of the largest ensembles of SNeIa compiled to probe cosmology to date. Evidence of diversity is encoded in supernova light curves. Pantheon+ is shown to be diverse, with features indicative of multiple thermonuclear sub-classes. Diversity-driven systematic effects have been quantified on a supernova-by-supernova basis; event selections based on light curve-derived metrics were subsequently used to characterize diversity-dependent trends and mitigate their impact. A "diversity free" estimate of the Hubble-Lemaître parameter, $H_0$=$67.5\pm3.5$ km s$^{-1}$ Mpc$^{-1}$ (68\% C.L.), was obtained by reanalyzing Pantheon+. The Hubble Tension, an apparent disparity between early- and late-Universe determinations of $H_0$, is eased from $\sim$$5σ$ to $<$$1σ$ after accounting for the diverse thermonuclear scenarios that govern SNeIa. A strategy for precise determination of $H_0$, dominated by statistical rather than systematic uncertainties, is also presented.

astro-ph.CO↗

arXiv2023

Multi-Messenger Diagnostics of the Engine behind Core-Collapse Supernovae

Core-collapse supernova explosions play a wide role in astrophysics by producing compact remnants (neutron stars, black holes) and the synthesis and injection of many heavy elements into their host Galaxy. Because they are produced in some of the most extreme conditions in the universe, they can also probe physics in extreme conditions (matter at nuclear densities and extreme temperatures and magnetic fields). To quantify the impact of supernovae on both fundamental physics and our understanding of the Universe, we must leverage a broad set of observables of this engine. In this paper, we study a subset of these probes using a suite of 1-dimensional, parameterized mixing models: ejecta remnants from supernovae, ultraviolet, optical and infra-red lightcurves, and transient gamma-ray emission. We review the other diagnostics and show how the different probes tie together to provide a more clear picture of the supernova engine.

astro-ph.HE↗

arXiv2020

Gamma-rays from kilonova: a potential probe of r-process nucleosynthesis

The mergers of compact binaries with at least one neutron star component are the potential leading sites of the production and ejection of $r$-process elements. Discoveries of galactic binary pulsars, short gamma-ray bursts, and gravitational-wave detections have all been constraining the rate of these events, while the gravitational wave plus broadband electromagnetic coverage of binary neutron star merger (GW170817) has also placed constraints on the properties (mass and composition) of the merger ejecta. But uncertainties and ambiguities in modeling the optical and infrared emission make it difficult to definitively measure the distribution of heavy isotopes in these mergers. In contrast, gamma rays emitted in the decay of these neutron-rich ejecta may provide a more direct measurement of the yields. We calculate the gamma production in remnants of neutron star mergers, considering two epochs: a kilonova epoch, lasting about two weeks, and a much later epoch of tens and hundreds of thousands of years after the merger. For the kilonova epoch, when the expanding ejecta is still only partially transparent to gamma radiation, we use 3D radiative transport simulations to produce the spectra. We show that the gamma-ray spectra associated with beta- and alpha-decay provide a fingerprint of the ejecta properties and, for a sufficiently nearby remnant, may be detectable, even for old remnants. We compare our gamma spectra with the potential detection limits of next generation detectors, including the Lunar Occultation Explorer (LOX), the All-sky Medium Energy Gamma-ray Observatory (AMEGO), and the Compton Spectrometer and Imager (COSI). We show that fission models can be discriminated via the presence of short-lived fission fragments in the remnant spectra.

astro-ph.HE↗

arXiv2005

CASTER - a concept for a Black Hole Finder Probe based on the use of new scintillator technologies

The primary scientific mission of the Black Hole Finder Probe (BHFP), part of the NASA Beyond Einstein program, is to survey the local Universe for black holes over a wide range of mass and accretion rate. One approach to such a survey is a hard X-ray coded-aperture imaging mission operating in the 10--600 keV energy band, a spectral range that is considered to be especially useful in the detection of black hole sources. The development of new inorganic scintillator materials provides improved performance (for example, with regards to energy resolution and timing) that is well suited to the BHFP science requirements. Detection planes formed with these materials coupled with a new generation of readout devices represent a major advancement in the performance capabilities of scintillator-based gamma cameras. Here, we discuss the Coded Aperture Survey Telescope for Energetic Radiation (CASTER), a concept that represents a BHFP based on the use of the latest scintillator technology.

astro-ph↗