This program was supported by the the Kavli Foundation, Danish National Research Foundation, the Niels Bohr International Academy, and the DARK Cosmology Centre. The UCSC group is supported in part by NSF grant AST-1518052, the Gordon & Betty Moore Foundation, the Heising-Simons Foundation, generous donations from many individuals through a UCSC Giving Day grant, and from fellowships from the Alfred P. Sloan Foundation (R.J.F.), the David and Lucile Packard Foundation (R.J.F. and E.R.) and the Niels Bohr Professorship from the DNRF (E.R.). AMB acknowledges support from a UCMEXUS-CONACYT Doctoral Fellowship. Support for this work was provided by NASA through Hubble Fellowship grants HST-HF-51348.001 (B.J.S.) and HST-HF-51373.001 (M.R.D.) awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This paper includes data gathered with the 1 meter Swope and 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.r (AGILE) The AGILE Team thanks the ASI management, the technical staff at the ASI Malindi ground station, the technical support team at the ASI Space Science Data Center, and the Fucino AGILE Mission Operation Center. AGILE is an ASI space mission developed with programmatic support by INAF and INFN. We acknowledge partial support through the ASI grant No. I/028/12/2. We also thank INAF, Italian Institute of Astrophysics, and ASI, Italian Space Agency.r (ANTARES) The ANTARES Collaboration acknowledges the financial support of: Centre National de la Recherche Scientifique (CNRS), Commissariat a l'energie atomique et aux energies alternatives (CEA), Commission Europeenne (FEDER fund and Marie Curie Program), Institut Universitaire de France (IUF), IdEx program and UnivEarthS Labex program at Sorbonne Paris Cite (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02), Labex OCEVU (ANR-11-LABX-0060) and the A*MIDEX project (ANR-11-IDEX-0001-02), Region Ile-de-France (DIM-ACAV), Region Alsace (contrat CPER), Region Provence-Alpes-Cite d'Azur, Departement du Var and Ville de La Seyne-sur-Mer, France; Bundesministerium fur Bildung und Forschung (BMBF), Germany; Istituto Nazionale di Fisica Nucleare (INFN), Italy; Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO), the Netherlands; Council of the President of the Russian Federation for young scientists and leading scientific schools supporting grants, Russia; National Authority for Scientific Research (ANCS), Romania;...

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Multi-messenger Observations of a Binary Neutron Star

We report on Bayesian parameter estimation of the mass and equatorial radius of the millisecond pulsar PSR J0030+0451, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer X-ray spectral-timing event data. We perform relativistic ray-tracing of thermal emission from hot regions of the pulsar’s surface. We assume two distinct hot regions based on two clear pulsed components in the phase-folded pulse-profile data; we explore a number of forms (morphologies and topologies) for each hot region, inferring their parameters in addition to the stellar mass and radius. For the family of models considered, the evidence (prior predictive probability of the data) strongly favors a model that permits both hot regions to be located in the same rotational hemisphere. Models wherein both hot regions are assumed to be simply connected circular single-temperature spots, in particular those where the spots are assumed to be reflection-symmetric with respect to the stellar origin, are strongly disfavored. For the inferred configuration, one hot region subtends an angular extent of only a few degrees (in spherical coordinates with origin at the stellar center) and we are insensitive to other structural details; the second hot region is far more azimuthally extended in the form of a narrow arc, thus requiring a larger number of parameters to describe. The inferred mass M and equatorial radius R eq are, respectively, and , while the compactness is more tightly constrained; the credible interval bounds reported here are approximately the 16% and 84% quantiles in marginal posterior mass.

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A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation

Theoretical descriptions of two-dimensional (2D) vibrational and electronic spectroscopy are presented By using a coupled multi-chromophore model, some examples of 2D spectroscopic studies of peptide solution structure determination and excitation transfer process in electronically coupled multi-chromophore system are discussed A few remarks on perspectives of this research area are given

Coherent Two-Dimensional Optical Spectroscopy

We explore in a parameterized manner a very large range of physically plausible equations of state (EOSs) for compact stars for matter that is either purely hadronic or that exhibits a phase transition. In particular, we produce two classes of EOSs with and without phase transitions, each containing one million EOSs. We then impose constraints on the maximum mass ($Ml2.16\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$) and on the dimensionless tidal deformability ($\stackrel{\texttildelow{}}{\mathrm{\ensuremath{\Lambda}}}l800$) deduced from GW170817, together with recent suggestions of lower limits on $\stackrel{\texttildelow{}}{\mathrm{\ensuremath{\Lambda}}}$. Exploiting more than $1{0}^{9}$ equilibrium models for each class of EOSs, we produce distribution functions of all the stellar properties and determine, among other quantities, the radius that is statistically most probable for any value of the stellar mass. In this way, we deduce that the radius of a purely hadronic neutron star with a representative mass of $1.4\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ is constrained to be $12.00l{R}_{1.4}/\mathrm{km}l13.45$ at a $2\ensuremath{\sigma}$ confidence level, with a most likely value of ${\overline{R}}_{1.4}=12.39\text{ }\text{ }\mathrm{km}$; similarly, the smallest dimensionless tidal deformability is ${\stackrel{\texttildelow{}}{\mathrm{\ensuremath{\Lambda}}}}_{1.4}g375$, again at a $2\ensuremath{\sigma}$ level. On the other hand, because EOSs with a phase transition allow for very compact stars on the so-called ``twin-star'' branch, small radii are possible with such EOSs although not probable, i.e., $8.53l{R}_{1.4}/\mathrm{km}l13.74$ and ${\overline{R}}_{1.4}=13.06\text{ }\text{ }\mathrm{km}$ at a $2\ensuremath{\sigma}$ level, with ${\stackrel{\texttildelow{}}{\mathrm{\ensuremath{\Lambda}}}}_{1.4}g35.5$ at a $3\ensuremath{\sigma}$ level. Finally, since these EOSs exhibit upper limits on $\stackrel{\texttildelow{}}{\mathrm{\ensuremath{\Lambda}}}$, the detection of a binary with a total mass of $3.4\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ and ${\stackrel{\texttildelow{}}{\mathrm{\ensuremath{\Lambda}}}}_{1.7}g461$ can rule out twin-star solutions.

New Constraints on Radii and Tidal Deformabilities of Neutron Stars from GW170817.

We report on Bayesian parameter estimation of the mass and equatorial radius of the millisecond pulsar PSR J0030$+$0451, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer (NICER) X-ray spectral-timing event data. We perform relativistic ray-tracing of thermal emission from hot regions of the pulsar's surface. We assume two distinct hot regions based on two clear pulsed components in the phase-folded pulse-profile data; we explore a number of forms (morphologies and topologies) for each hot region, inferring their parameters in addition to the stellar mass and radius. For the family of models considered, the evidence (prior predictive probability of the data) strongly favors a model that permits both hot regions to be located in the same rotational hemisphere. Models wherein both hot regions are assumed to be simply-connected circular single-temperature spots, in particular those where the spots are assumed to be reflection-symmetric with respect to the stellar origin, are strongly disfavored. For the inferred configuration, one hot region subtends an angular extent of only a few degrees (in spherical coordinates with origin at the stellar center) and we are insensitive to other structural details; the second hot region is far more azimuthally extended in the form of a narrow arc, thus requiring a larger number of parameters to describe. The inferred mass $M$ and equatorial radius $R_\mathrm{eq}$ are, respectively, $1.34_{-0.16}^{+0.15}$ M$_{\odot}$ and $12.71_{-1.19}^{+1.14}$ km, whilst the compactness $GM/R_\mathrm{eq}c^2 = 0.156_{-0.010}^{+0.008}$ is more tightly constrained; the credible interval bounds reported here are approximately the $16\%$ and $84\%$ quantiles in marginal posterior mass.

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A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation.

We study the mass-radius curve of hybrid stars, assuming a single first-order phase transition between nuclear and quark matter, with a sharp interface between the quark matter core and nuclear matter mantle. We use a generic parametrization of the quark matter equation of state, which has a constant, i.e. density-independent, speed of sound. We argue that this parametrization provides a framework for comparison and empirical testing of models of quark matter. We obtain the phase diagram of possible forms of the hybrid star mass-radius relation, where the control parameters are the transition pressure, energy density discontinuity, and the quark matter speed of sound. We find that this diagram is sensitive to the quark matter parameters but fairly insensitive to details of the nuclear matter equation of state (EoS). We calculate the maximum hybrid star mass as a function of the parameters of the quark matter EoS, and find that there are reasonable values of those parameters that give rise to hybrid stars with mass above $2{M}_{\ensuremath{\bigodot}}$.

/pdf/generic-conditions-for-stable-hybrid-stars-wpac9ud0ml.pdf

Generic conditions for stable hybrid stars

We demonstrate experimentally that visible-visible sum-frequency generation in the bulk of a chiral liquid is observable near electronic resonant transitions. Although the process is electric dipole allowed, it is rather weak because the orientational average over molecules effectively reduces the bulk chiral nonlinearity.

/pdf/sum-frequency-generation-in-chiral-liquids-near-electronic-4fvgm2xmtn.pdf

Sum-Frequency Generation in Chiral Liquids near Electronic Resonance

The neutron star tidal deformability is a critical parameter which determines the premerger gravitational-wave signal in a neutron star merger. In this article, we show how neutron star tidal deformabilities behave in the presence of one or two sharp phase transition(s). We characterize how the tidal deformability changes when the properties of these phase transitions are modified in dense matter equations of state. Sharp phase transitions lead to the smallest possible tidal deformabilities and also induce discontinuities in the relation between tidal deformability and gravitational mass. These results are qualitatively unmodified by a modest softening of the phase transition. Finally, we test two universal relations involving the tidal deformability and show that their accuracy is limited by sharp phase transitions.

Tidal deformability with sharp phase transitions in binary neutron stars

In the context of the massive secondary object recently observed in the compact-star merger GW190814, we investigate the possibility of producing massive neutron stars from a few different equation of state models that contain exotic degrees of freedom, such as hyperons and quarks. Our work shows that state-of-the-art relativistic mean-field models can generate massive stars reaching $\ensuremath{\gtrsim}2.05\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\mathrm{Sun}}$, while being in good agreement with gravitational-wave events and x-ray pulsar observations, when quark vector interactions and nonstandard self-vector interactions are introduced. In particular, we present a new version of the Chiral Mean Field (CMF) model in which a different quark-deconfinement potential allows for stable stars with a pure quark core. When rapid rotation is considered, our models generate stellar masses that approach, and in some cases surpass $2.5\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\mathrm{Sun}}$. We find that in such cases fast rotation does not necessarily suppress exotic degrees of freedom due to changes in stellar central density, but require a larger amount of baryons than what is allowed in the nonrotating stars. This is not the case for pure quark stars, which can easily reach $2.5\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\mathrm{Sun}}$ and still possess approximately the same amount of baryons as stable nonrotating stars. We also briefly discuss possible origins for fast rotating stars with a large amount of baryons and their stability, showing how the event GW190814 can be associated with a star containing quarks as one of its progenitors.

GW190814 as a massive rapidly rotating neutron star with exotic degrees of freedom

We combine the equation of state of dense matter up to twice nuclear saturation density ${n}_{\mathrm{sat}}$ obtained using chiral effective field theory $(\ensuremath{\chi}\mathrm{EFT})$ and recent observations of neutron stars to gain insights about the high-density matter encountered in their cores. A key element in our study is the recent Bayesian analysis of correlated EFT truncation errors based on order-by-order calculations up to next-to-next-to-next-to-leading order in the $\ensuremath{\chi}\mathrm{EFT}$ expansion. We refine the bounds on the maximum mass imposed by causality at high densities and provide stringent limits on the maximum and minimum radii of $\ensuremath{\sim}1.4\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ and $\ensuremath{\sim}2.0\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ stars. Including $\ensuremath{\chi}\mathrm{EFT}$ predictions from ${n}_{\mathrm{sat}}$ to $2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$ reduces the permitted ranges of the radius of a $1.4\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ star, ${R}_{1.4}$, by $\ensuremath{\sim}3.5\phantom{\rule{0.16em}{0ex}}\text{km}$. If observations indicate ${R}_{1.4}l11.2\phantom{\rule{0.16em}{0ex}}\text{km}$, then our study implies that either the squared speed of sound ${c}_{s}^{2}g1/2$ for densities above $2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$ or that $\ensuremath{\chi}\mathrm{EFT}$ breaks down below $2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$. We also comment on the nature of the secondary compact object in GW190814 with mass $\ensuremath{\simeq}2.6\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ and discuss the implications of massive neutron stars $g2.1\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}\phantom{\rule{0.16em}{0ex}}(2.6\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}})$ in future radio and gravitational-wave searches. Some form of strongly interacting matter with ${c}_{s}^{2}g0.35\phantom{\rule{0.16em}{0ex}}(0.55)$ must be realized in the cores of such massive neutron stars. In the absence of phase transitions below $2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$, the small tidal deformability inferred from GW170817 lends support for the relatively small pressure predicted by $\ensuremath{\chi}\mathrm{EFT}$ for the baryon density ${n}_{\mathrm{B}}$ in the range $1\text{--}2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$. Together they imply that the rapid stiffening required to support a high maximum mass should occur only when ${n}_{\mathrm{B}}\ensuremath{\gtrsim}1.5\text{--}1.8\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$.

/pdf/limiting-masses-and-radii-of-neutron-stars-and-their-3gab6dgiuo.pdf

Sophia Han

Papers

Generic conditions for stable hybrid stars

Sum-Frequency Generation in Chiral Liquids near Electronic Resonance

Tidal deformability with sharp phase transitions in binary neutron stars

GW190814 as a massive rapidly rotating neutron star with exotic degrees of freedom

Limiting masses and radii of neutron stars and their implications