Abstract
Compact binary mergers involving at least one neutron star are promising sites for the synthesis of the
r
-process elements found in stars and planets. However, mergers can take place at ...significant offsets from their host galaxies, with many occurring several kpc from star-forming regions. It is thus important to understand the physical mechanisms involved in transporting enriched material from merger sites in the galactic halo to the star-forming disk. We investigate these processes, starting from an explosive injection event and its interaction with the halo medium. We show that the total outflow mass in compact binary mergers is too low for the material to travel to the disk in a ballistic fashion. Instead, the enriched ejecta is swept into a shell, which decelerates over ≲10 pc scales and becomes corrugated by the Rayleigh–Taylor instability. The corrugated shell is denser than the ambient medium and breaks into clouds that sink toward the disk. These sinking clouds lose thermal energy through radiative cooling, and are also ablated by shearing instabilities. We present a dynamical heuristic that models these effects to predict the delay times for delivery to the disk. However, we find that turbulent mass ablation is extremely efficient and leads to the total fragmentation of sinking
r
-process clouds over ≲10 pc scales. We thus predict that enriched material from halo injection events quickly assimilates into the gas medium of the halo and that enriched mass flow to the disk could only be accomplished through turbulent diffusion or large-scale inflowing mass currents.
Abstract
We explore neutrino emission from nonrotating, single-star models across six initial metallicities and 70 initial masses from the zero-age main sequence to the final fate. Overall, across ...the mass spectrum, we find metal-poor stellar models tend to have denser, hotter, and more massive cores with lower envelope opacities, larger surface luminosities, and larger effective temperatures than their metal-rich counterparts. Across the mass–metallicity plane we identify the sequence (initial CNO →
14
N →
22
Ne →
25
Mg →
26
Al →
26
Mg →
30
P →
30
Si) as making primary contributions to the neutrino luminosity at different phases of evolution. For the low-mass models we find neutrino emission from the nitrogen flash and thermal pulse phases of evolution depend strongly on the initial metallicity. For the high-mass models, neutrino emission at He-core ignition and He-shell burning depends strongly on the initial metallicity. Antineutrino emission during C, Ne, and O burning shows a strong metallicity dependence with
22
Ne(
α
,
n
)
25
Mg providing much of the neutron excess available for inverse-
β
decays. We integrate the stellar tracks over an initial mass function and time to investigate the neutrino emission from a simple stellar population. We find average neutrino emission from simple stellar populations to be 0.5–1.2 MeV electron neutrinos. Lower metallicity stellar populations produce slightly larger neutrino luminosities and average
β
decay energies. This study can provide targets for neutrino detectors from individual stars and stellar populations. We provide convenient fitting formulae and open access to the photon and neutrino tracks for more sophisticated population synthesis models.
Abstract
Cosmic multimessenger backgrounds include relic diffuse components created in the early universe and contributions from individual sources. Here, we study both type Ia supernovae (SNe Ia) ...and core-collapse supernovae (CCSNe) contributions to the diffuse neutrino and gamma-ray backgrounds in the MeV regime referred to as DSNB and DSGB respectively. We show that the diffuse SN Ia background is 10
6
times lower (for
ν
¯
e
) than the CCSN background making it negligible. Our predicted DSNB
ν
¯
e
flux at earth in the 19.3–32 MeV regime is 0.36
ν
cm
−2
s
−1
. We also find that the DSNB flux in the energy range from 11.3 to 32 MeV varies by +29% with a change in the SFRD model from Madau & Fragos which yielded a minimum predicted flux, to the extragalactic background light reconstruction model (maximum predicted flux). The diffuse SN Ia gamma-ray background and its dependence on the progenitor supernova delay time distribution are also evaluated. Furthermore, we address the origin of the CGB (Cosmic Gamma-ray Background) in the 0.1–7 MeV regime by adding contributions from sources such as SNe Ia, CCSNe, radio-quiet Active Galactic Nuclei, Flat spectrum radio quasars (FSRQs) and Neutron star—neutron star mergers. We find that our modeled background (including uncertainties) matches the observed CGB above 1.0 MeV, but is a factor ≈2 lower than the observed flux in the 0.1–1.0 MeV range, highlighting the need for future MeV missions to establish the CGB spectrum more reliably, and to possibly identify additional sources or even source classes in the underexplored MeV band.
Abstract
Core-collapse supernova explosions play a wide role in astrophysics by producing compact remnants (neutron stars or 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 one-dimensional, parameterized mixing models: ejecta remnants from supernovae, ultraviolet, optical and infrared light curves, 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. Join us in improving and evolving this document through active community engagement. Instructions are provided at this link:
https://github.com/clfryer/MM-SNe
.
Could a Kilonova Kill: A Threat Assessment Perkins, Haille M. L.; Ellis, John; Fields, Brian D. ...
Astrophysical journal/The Astrophysical journal,
02/2024, Volume:
961, Issue:
2
Journal Article
Peer reviewed
Open access
Abstract
Binary neutron star mergers produce high-energy emissions from several physically different sources, including a gamma-ray burst (GRB) and its afterglow, a kilonova (KN), and, at late times, ...a remnant many parsecs in size. Ionizing radiation from these sources can be dangerous for life on Earth-like planets when located too close. Work to date has explored the substantial danger posed by the GRB to on-axis observers; here we focus instead on the potential threats posed to nearby off-axis observers. Our analysis is based largely on observations of the GW170817/GRB 170817A multi-messenger event, as well as theoretical predictions. For baseline KN parameters, we find that the X-ray emission from the afterglow may be lethal out to ∼1 pc and the off-axis gamma-ray emission may threaten a range out to ∼4 pc, whereas the greatest threat comes years after the explosion, from the cosmic rays accelerated by the KN blast, which can be lethal out to distances up to ∼11 pc. The distances quoted here are typical, but the values have significant uncertainties and depend on the viewing angle, ejected mass, and explosion energy in ways we quantify. Assessing the overall threat to Earth-like planets, KNe have a similar kill distance to supernovae, but are far less common. However, our results rely on the scant available KN data, and multi-messenger observations will clarify the danger posed by such events.
Abstract
The detection of gravitational waves from the binary neuron star merger GW170817 and electromagnetic counterparts GRB170817A and AT2017gfo kick-started the field of gravitational-wave ...multimessenger astronomy. The optically red to near-infrared emission (“red” component) of AT2017gfo was readily explained as produced by the decay of newly created nuclei produced by rapid neutron capture (a kilonova). However, the ultraviolet to optically blue emission (“blue” component) that was dominant at early times (up to 1.5 days) received no consensus regarding its driving physics. Among many explanations, two leading contenders are kilonova radiation from a lanthanide-poor ejecta component and shock interaction (cocoon emission). In this work, we simulate AT2017gfo-like light curves and perform a Bayesian analysis to study whether an ultraviolet satellite capable of rapid gravitational-wave follow-up, could distinguish between physical processes driving the early “blue” component. We find that ultraviolet data starting at 1.2 hr distinguishes the two early radiation models up to 160 Mpc, implying that an ultraviolet mission like Dorado would significantly contribute to insights into the driving emission physics of the postmerger system. While the same ultraviolet data and optical data starting at 12 hr have limited ability to constrain model parameters separately, the combination of the two unlocks tight constraints for all but one parameter of the kilonova model up to 160 Mpc. We further find that a Dorado-like ultraviolet satellite can distinguish the early radiation models up to at least 130 (60) Mpc if data collection starts within 3.2 (5.2) hr for AT2017gfo-like light curves.
Abstract
We present an updated model for the extragalactic background light (EBL) from stars and dust, over wavelengths ≈0.1–1000
μ
m. This model uses accurate theoretical stellar spectra, and tracks ...the evolution of star formation, stellar mass density, metallicity, and interstellar dust extinction and emission in the universe with redshift. Dust emission components are treated self-consistently, with stellar light absorbed by dust reradiated in the infrared as three blackbody components. We fit our model, with free parameters associated with star formation rate and dust extinction and emission, to a wide variety of data: luminosity density, stellar mass density, and dust extinction data from galaxy surveys; and
γ
-ray absorption optical depth data from
γ
-ray telescopes. Our results strongly constraint the star formation rate density and dust photon escape fraction of the universe out to redshift
z
= 10, about 90% of the history of the universe. We find our model result is, in some cases, below lower limits on the
z
= 0 EBL intensity, and below some low-
z
γ
-ray absorption measurements.
ABSTRACT There has been much debate about the origin of the diffuse γ-ray background in the MeV range. At lower energies, AGNs and Seyfert galaxies can explain the background, but not above 0.3 MeV. ...Beyond ∼10 MeV blazars appear to account for the flux observed. That leaves an unexplained gap for which different candidates have been proposed, including annihilations of WIMPS. One candidate is Type Ia supernovae (SNe Ia). Early studies concluded that they were able to account for the γ-ray background in the gap, while later work attributed a significantly lower contribution to them. All those estimates were based on SN Ia explosion models that did not reflect the full 3D hydrodynamics of SN Ia explosions. In addition, new measurements obtained since 2010 have provided new, direct estimates of high-z SN Ia rates beyond z ∼ 2. We take into account these new advances to see the predicted contribution to the gamma-ray background. We use here a wide variety of explosion models and a plethora of new measurements of SN Ia rates. SNe Ia still fall short of the observed background. Only for a fit, which would imply ∼150% systematic error in detecting SN Ia events, do the theoretical predictions approach the observed fluxes. This fit is, however, at odds at the highest redshifts with recent SN Ia rate estimates. Other astrophysical sources such as flat-spectrum radio quasars do match the observed flux levels in the MeV regime, while SNe Ia make up to 30%-50% of the observed flux.
The neutrino-nucleus reaction cross sections of super(4)He and super(12)C are evaluated using new shell model Hamiltonians. Branching ratios of various decay channels are calculated to evaluate the ...yields of Li, Be, and B produced through the v-process in supernova explosions. The new cross sections enhance the yields of super(7)Li and super(11 )B produced during the supernova explosion of a 16.2 M sub(image) star model compared to the case using the conventional cross sections by about 10%. On the other hand, the yield of super(10)B decreases by a factor of 2. The yields of super(6)Li, super(9)Be, and the radioactive nucleus super(10)Be are found at a level of image10 super(-11) M sub(image). The temperature of image - and image - neutrinos inferred from the supernova contribution of super( 11)B in Galactic chemical evolution models is constrained to the 4.3-6.5 MeV range. The increase in the super(7)Li and super(11)B yields due to neutrino oscillations is demonstrated with the new cross sections.
The cosmological origin of at least an appreciable fraction of classical gamma-ray bursts (GRBs) is now supported by redshift measurements for a half-dozen faint host galaxies. Still, the nature of ...the central engine (or engines) that provide the burst energy remains unclear. While many models have been proposed, those currently favored are all based upon the formation of and/or rapid accretion into stellar-mass black holes. Here we discuss a variety of such scenarios and estimate the probability of each. Population synthesis calculations are carried out using a Monte Carlo approach in which the many uncertain parameters intrinsic to such calculations are varied. We estimate the event rate for each class of model as well as the propagation distances for those having significant delay between formation and burst production, i.e., double neutron star (DNS) mergers and black hole-neutron star (BH/NS) mergers. One conclusion is a 1-2 order of magnitude decrease in the rate of DNS and BH/NS mergers compared to that previously calculated using invalid assumptions about common envelope evolution. Other major uncertainties in the event rates and propagation distances include the history of star formation in the universe, the masses of the galaxies in which merging compact objects are born, and the radii of the hydrogen-stripped cores of massive stars. For reasonable assumptions regarding each, we calculate a daily event rate in the universe for (1) merging neutron stars: {approx}100 day-1; (2) neutron star-black hole mergers: {approx}450 day-1; (3) collapsars: {approx}104 day-1; (4) helium star black hole mergers: {approx}1000 day-1; and (5) white dwarf-black hole mergers: {approx}20 day-1. The range of uncertainty in these numbers, however, is very large, typically 2-3 orders of magnitude. These rates must additionally be multiplied by any relevant beaming factor (f{sub {omega}} <1) and sampling fraction (if the entire universal set of models is not being observed). Depending upon the mass of the host galaxy, one-half of the DNS mergers will happen within 60 kpc (for a galaxy with a mass comparable to that of the Milky Way) to 5 Mpc (for a galaxy with negligible mass) from the Galactic center. The same numbers characterize BH/NS mergers. Because of the delay time, neutron star and black hole mergers will happen at a redshift 0.5-0.8 times that of the other classes of models. Information is still lacking regarding the hosts of short, hard bursts, but we suggest that they are due to DNS and BH/NS mergers and thus will ultimately be determined to lie outside of galaxies and at a closer mean distance than long complex bursts (which we attribute to collapsars). In the absence of a galactic site, the distance to these bursts may be difficult to determine. (c) (c) 1999. The American Astronomical Society.
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