Abstracts of Interest
Selected by:
Adnaan Thakur
Abstract: 2111.06506
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Title:A black hole detected in the young massive LMC cluster NGC 1850
Download PDFAbstract: We report the detection of a black hole (NGC 1850 BH1) in the $\sim$100 Myr-old massive cluster NGC~1850 in the Large Magellanic Cloud. It is in a binary system with a main-sequence turn-off star (4.9 $\pm$ 0.4 M${_\odot}$), which is starting to fill its Roche Lobe and becoming distorted. Using 17 epochs of VLT/MUSE observations we detected radial velocity variations exceeding 300 km/s associated to the target star, linked to the ellipsoidal variations measured by OGLE-IV in the optical bands. Under the assumption of a semi-detached system, the simultaneous modelling of radial velocity and light curves constraints the orbital inclination of the binary to ($38 \pm 2$)$^{\circ}$, resulting in a true mass of the unseen companion of $11.1_{-2.4}^{+2.1}$ $M_{\odot}$. This represents the first direct dynamical detection of a black hole in a young massive cluster, opening up the possibility of studying the initial mass function and the early dynamical evolution of such compact objects in high-density environments.
Abstract: 2111.06497
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Title:The Gamow Explorer: A gamma-ray burst observatory to study the high redshift universe and enable multi-messenger astrophysics
Download PDFAbstract: The Gamow Explorer will use Gamma Ray Bursts (GRBs) to: 1) probe the high redshift universe (z > 6) when the first stars were born, galaxies formed and Hydrogen was reionized; and 2) enable multi-messenger astrophysics by rapidly identifying Electro-Magnetic (IR/Optical/X-ray) counterparts to Gravitational Wave (GW) events. GRBs have been detected out to z ~ 9 and their afterglows are a bright beacon lasting a few days that can be used to observe the spectral fingerprints of the host galaxy and intergalactic medium to map the period of reionization and early metal enrichment. Gamow Explorer is optimized to quickly identify high-z events to trigger follow-up observations with JWST and large ground-based telescopes. A wide field of view Lobster Eye X-ray Telescope (LEXT) will search for GRBs and locate them with arc-minute precision. When a GRB is detected, the rapidly slewing spacecraft will point the 5 photometric channel Photo-z Infra-Red Telescope (PIRT) to identify high redshift (z > 6) long GRBs within 100s and send an alert within 1000s of the GRB trigger. An L2 orbit provides > 95% observing efficiency with pointing optimized for follow up by the James Webb Space Telescope (JWST) and ground observatories. The predicted Gamow Explorer high-z rate is >10 times that of the Neil Gehrels Swift Observatory. The instrument and mission capabilities also enable rapid identification of short GRBs and their afterglows associated with GW events. The Gamow Explorer will be proposed to the 2021 NASA MIDEX call and if approved, launched in 2028.
Abstract: 2111.06419
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Title:No longer ballistic, not yet diffusive--the formation of cosmic ray small-scale anisotropies
Download PDFAbstract: The arrival directions of TeV-PeV cosmic rays are remarkably uniform due to the isotropization of their directions by scattering on turbulent magnetic fields. Small anisotropies can exist in standard diffusion models, however, only on the largest angular scales. Yet, high-statistics observatories like IceCube and HAWC have found significant deviations from isotropy down to small angular scales. Here, we explain the formation of small-scale anisotropies by considering pairs of cosmic rays that get correlated by their transport through the same realisation of the turbulent magnetic field. We argue that the formation of small-scale anisotropies is the reflection of the particular realisation of the turbulent magnetic field experienced by cosmic rays on time scales intermediate between the early, ballistic regime and the late, diffusive regime. We approach this problem in two different ways: First, we run test particle simulations in synthetic turbulence, covering for the first time the TV rigidities of observations with realistic turbulence parameters. Second, we extend the recently introduced mixing matrix approach and determine the steady-state angular power spectrum. Throughout, we adopt magneto-static, slab-like turbulence. We find excellent agreement between the predicted angular power spectra in both approaches over a large range of rigidities. In the future, measurements of small-scale anisotropies will be valuable in constraining the nature of the turbulent magnetic field in our Galactic neighborhood.
Abstract: 2111.06445
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Title:A standard siren measurement of the Hubble constant using gravitational wave events from the first three LIGO/Virgo observing runs and the DESI Legacy Survey
Download PDFAbstract: We present a new constraint on the Hubble constant $H_0$ using a sample of well-localized gravitational wave (GW) events detected during the first three LIGO/Virgo observing runs as dark standard sirens. In the case of dark standard sirens, a unique host galaxy is not identified, and the redshift information comes from the distribution of potential host galaxies. From the third LIGO/Virgo observing run detections, we add the asymmetric-mass binary black hole GW190412, the high-confidence GW candidates S191204r, S200129m, and S200311bg to the sample of dark standard sirens analyzed. Our sample contains the top $20\%$ (based on localization) GW events and candidates to date with significant coverage by the Dark Energy Spectroscopic Instrument (DESI) Legacy Survey. We combine the $H_0$ posterior for eight dark siren events, finding $H_0 = 79.8^{+19.1}_{-12.8}~{\rm km~s^{-1}~Mpc^{-1}}$ ($68\%$ Highest Density Interval) for a prior in $H_0$ uniform between $[20,140]~{\rm km~s^{-1}~Mpc^{-1}}$. This result shows that a combination of 8 well-localized dark sirens combined with an appropriate galaxy catalog is able to provide an $H_0$ constraint that is competitive ($\sim 20\%$ versus $18\%$ precision) with a single bright standard siren analysis (i.e. assuming the electromagnetic counterpart) using GW170817. When combining the posterior with that from GW170817, we obtain $H_0 = 72.77^{+11.0}_{-7.55}~{\rm km~s^{-1}~Mpc^{-1}}$. This result is broadly consistent with recent $H_0$ estimates from both the Cosmic Microwave Background and Supernovae.
Abstract: 2111.06510
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Title:Supersonic Expansion of the Bipolar Hii Region Sh2-106: A 3,500 Year-Old Explosion?
Download PDFAbstract: Multi-epoch narrow-band HST images of the bipolar Hii region Sh2-106 reveal highly supersonic nebular proper motions which increase with projected distance from the massive young stellar object S106~IR, reaching over ~30 mas/year (~150 km/s at D=1.09 kpc) at a projected separation of ~1.4' (0.44 pc) from S106~IR. We propose that S106~IR experienced a $\sim10^{47}$ erg explosion ~3,500 years ago. The explosion may be the result of a major accretion burst, a recent encounter with another star, or a consequence of the interaction of a companion with the bloated photosphere of S106~IR as it grew from ~10 through ~15 Solar masses at a high accretion rate. Near-IR images reveal fingers of molecular hydrogen emission pointing away from S106~IR and an asymmetric photon-dominated region surrounding the ionized nebula. Radio continuum and Brackett-gamma emission reveal a C-shaped bend in the plasma, either indicating motion of S106~IR toward the east, or deflection of plasma toward the west by the surrounding cloud. The Hii region bends around a ~1' diameter dark bay west of S106~IR that may be shielded from direct illumination by a dense molecular clump. Herbig-Haro (HH) and Molecular Hydrogen Objects (MHOs) tracing outflows powered by stars in the Sh2-106 proto-cluster such as the Class 0 source S106 FIR are discussed.
Abstract: 2111.06471
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Title:An environment analysis of the Type Ib SN 2019yvr and the possible presence of an inflated binary companion
Download PDFAbstract: SN 2019yvr is the second Type Ib supernova (SN) with a direct detection of its progenitor (system); however, the spectral energy distribution (SED) of the pre-explosion source appears much cooler and overluminous than an expected helium-star progenitor. Using Hubble Space Telescope (HST) images and MUSE integral-field-unit (IFU) spectroscopy, we find the SN environment contains three episodes of star formation; the low ejecta mass suggests the SN progenitor is most likely from the oldest population, corresponding to an initial mass of 10.4$^{+1.5}_{-1.3}$ $M_\odot$. The pre-explosion SED can be reproduced by two components, one for the hot and compact SN progenitor and one for a cool and inflated yellow hypergiant (YHG) companion that dominates the brightness. Thus, SN 2019yvr could possibly be the first Type Ib/c SN for which the progenitor's binary companion is directly detected on pre-explosion images. Both the low progenitor mass and the YHG companion suggest significant binary interaction during their evolution. Similar to SN 2014C, SN 2019yvr exhibits a metamorphosis from Type Ib to Type IIn, showing signatures of interaction with hydrogen-rich circumstellar material (CSM) at >150 days; our result supports enhanced pre-SN mass loss as an important process for hydrogen-poor stars at the low mass end of core-collapse SN progenitors.
Abstract: 2111.06870
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Title:Radiation hydrodynamics modeling of kilonovae with SNEC
Download PDFAbstract: We develop a method to compute synthetic kilonova light curves that combines numerical relativity simulations of neutron star mergers and the \texttt{SNEC} radiation-hydrodynamics code. We describe our implementation of initial and boundary conditions, r-process heating, and opacities for kilonova simulations. We validate our approach by carefully checking that energy conservation is satisfied and by comparing the \texttt{SNEC} results with those of two semi-analytic light curve models. We apply our code to the calculation of color light curves for three binaries having different mass ratios (equal and unequal mass) and different merger outcome (short-lived and long-lived remnants). We study the sensitivity of our results to hydrodynamic effects, nuclear physics uncertainties in the heating rates, and duration of the merger simulations. We also study the impact of shocks possibly launched into the outflows by a relativistic jet. None of our models match AT2017gfo, the kilonova in GW170817. This points to possible deficiencies in the merger simulations and to the need to go beyond the assumption of spherical symmetry adopted in this work.
Abstract: 2111.06844
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Title:The CO-CAVITY pilot survey: molecular gas and star formation in void galaxies
Download PDFAbstract: We present the first molecular gas mass survey of void galaxies. We compare these new data, together with data for the atomic gas mass and star formation rate ($\rm SFR$) from the literature to those of galaxies in filaments and walls in order to better understand how molecular gas and star formation are related to the large-scale environment. We observed at the IRAM 30-m telescope the CO(1-0) and CO(2-1) emission of 20 void galaxies selected from the Void Galaxy Survey (VGS), with a stellar mass range from $\rm 10^{8.5}$ to $\rm 10^{10.3}M_{\odot}$. We detected 15 objects in at least one CO line. We compare the molecular gas mass ($M_{\rm H_2}$), the star formation efficiency ($\rm SFE =SFR/M_{\rm H_2}$), the atomic gas mass, the molecular-to-atomic gas mass ratio, and the specific star formation rate (sSFR) of the void galaxies with two control samples of galaxies in filaments and walls, selected from xCOLD GASS and EDGE-CALIFA, for different stellar mass bins and taking the star formation activity into account. The results for the molecular gas mass for a sample of 20 voids galaxies allowed us, for the first time, to make a statistical comparison to galaxies in filaments and walls.
Abstract: 2111.06545
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Title:Peta-electron volt gamma-ray emission from the Crab Nebula
Download PDFAbstract: The Crab pulsar and the surrounding nebula powered by the pulsar's rotational energy through the formation and termination of a relativistic electron-positron wind is a bright source of gamma-rays carrying crucial information about this complex conglomerate. We report the detection of $\gamma$-rays with a spectrum showing gradual steepening over three energy decades, from $5\times 10^{-4}$ to $1.1$ petaelectronvolt (PeV). The ultra-high-energy photons exhibit the presence of a PeV electron accelerator (a pevatron) with an acceleration rate exceeding 15% of the absolute theoretical limit. Assuming that unpulsed $\gamma$-rays are produced at the termination of the pulsar's wind, we constrain the pevatron's size, between $0.025$ and $0.1$ pc, and the magnetic field $\approx 110 \mu$G. The production rate of PeV electrons, $2.5 \times 10^{36}$ erg $\rm s^{-1}$, constitutes 0.5% of the pulsar's spin-down luminosity, although we do not exclude a non-negligible contribution of PeV protons to the production of the highest energy $\gamma$-rays.
Abstract: 2111.05864
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Title:Utilizing cosmic-ray positron and electron observations to probe the averaged properties of Milky Way pulsars
Download PDFAbstract: Pulsars have long been studied in the electromagnetic spectrum. Their environments are rich in high-energy cosmic-ray electrons and positrons likely enriching the interstellar medium with such particles. In this work we use recent cosmic-ray observations from the AMS-02, CALET and DAMPE collaborations to study the averaged properties of the local Milky Way pulsar population. We perform simulations of the local Milky Way pulsar population, for interstellar medium assumptions in agreement with a range of cosmic-ray nuclei measurements. Each such simulation contains $\sim 10^{4}$ pulsars of unique age, location, initial spin-down power and cosmic-ray electron/positron spectra. We produce more than $7\times 10^{3}$ such Milky Way pulsar simulations. We account for and study i) the pulsars' birth rates and the stochastic nature of their birth, ii) their initial spin-down power distribution, iii) their time evolution in terms of their braking index and characteristic spin-down timescale, iv) the fraction of spin-down power going to cosmic-ray electrons and positrons and v) their propagation through the interstellar medium and the Heliosphere. We find that pulsars of ages $\sim 10^{5}-10^{7}$ yr, have a braking index that on average has to be 3 or larger. Given that electromagnetic spectrum observations of young pulsars find braking indices lower than 3, our work provides strong hints that pulsars' braking index increases on average as they age, allowing them to retain some of their rotational energy. Moreover, we find that pulsars have relatively uniform properties as sources of cosmic-ray electrons and positrons in terms of the spectra they produce and likely release O($10\%$) of their rotational energy to cosmic-rays in the ISM. Finally, we find at $\simeq$12 GeV positrons a spectral feature that suggests a new subpopulation of positron sources contributing at these energies.
Abstract: 2111.05863
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Title:On the synthesis of heavy nuclei in protomagnetar outflows and implications for ultra-high energy cosmic rays
Download PDFAbstract: It has been suggested that strongly magnetised and rapidly rotating protoneutron stars (PNSs) may produce long duration gamma-ray bursts (GRBs) originating from stellar core collapse. We explore the steady-state properties and heavy element nucleosynthesis in neutrino-driven winds from such PNSs whose magnetic axis is generally misaligned with the axis of rotation. We consider a wide variety of central engine properties such as surface dipole field strength, initial rotation period and magnetic obliquity to show that heavy element nuclei can be synthesised in the radially expanding wind. This process is facilitated provided the outflow is Poynting-flux dominated such that its low entropy and fast expansion timescale enables heavy nuclei to form in a more efficient manner as compared to the equivalent thermal GRB outflows. We also examine the acceleration and survival of these heavy nuclei and show that they can reach sufficiently high energies $\gtrsim 10^{20}\ {\rm eV}$ within the same physical regions that are also responsible for powering gamma-ray emission, primarily through magnetic dissipation processes. Although these magnetised outflows generally fail to achieve the production of elements heavier than lanthanides for our explored electron fraction range 0.4-0.6, we show that they are more than capable of synthesizing nuclei near and beyond iron peak elements.
Abstract: 2111.05869
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Title:Efficient estimation method for time evolution of proto-neutron star mass and radius from supernova neutrino signal
Download PDFAbstract: In this paper we present a novel method to estimate the time evolution of proto-neutron star (PNS) structure from the neutrino signal in core-collapse supernovae (CCSN). Employing recent results of multi-dimensional CCSN simulations, we delve into a relation between total emitted neutrino energy (TONE) and PNS mass/radius, and we find that they are strongly correlated with each other. We fit the relation by simple polynomial functions connecting TONE to PNS mass and radius as a function of time. By combining another fitting function representing the correlation between TONE and cumulative number of event at each neutrino observatory, PNS mass and radius can be retrieved from purely observed neutrino data. We demonstrate retrievals of PNS mass and radius from mock data of neutrino signal, and we assess the capability of our proposed method. While underlining the limitations of the method, we also discuss the importance of the joint analysis with gravitational wave signal. This would reduce uncertainties of parameter estimations in our method, and may narrow down the possible neutrino oscillation model. The proposed method is a very easy and inexpensive computation, which will be useful in real data analysis of CCSN neutrino signal.
Abstract: 2111.05903
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Title:Particle Acceleration by Pickup Process Upstream of Relativistic Shocks
Download PDFAbstract: Particle acceleration at magnetized purely perpendicular relativistic shocks in electron-ion plasmas are studied by means of two-dimensional particle-in-cell simulations. Magnetized shocks with the upstream bulk Lorentz factor $\gamma_1 \gg 1$ are known to emit intense electromagnetic waves from the shock front, which induce electrostatic plasma waves (wakefield) and transverse filamentary structures in the upstream region via the stimulated/induced Raman scattering and the filamentation instability, respectively. The wakefield and filaments inject a fraction of incoming particles into a particle acceleration process, in which particles are once decoupled from the upstream bulk flow by the wakefield, and are piked up again by the flow. The picked-up particles are accelerated by the motional electric field. The maximum attainable Lorentz factor is estimated as $\gamma_{max,e} \sim \alpha\gamma_1^3$ for electrons and $\gamma_{max,i} \sim (1+m_e\gamma_1/m_i)\gamma_1^2$ for ions, where $\alpha \sim 10$ is determined from our simulation results. $\alpha$ can increase up to $\gamma_1$ for weakly magnetized shock if $\gamma_1$ is sufficiently large. This result indicates that highly relativistic astrophysical shocks such as external shocks of gamma-ray bursts can be an efficient particle accelerator.
Abstract: 2111.05927
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Title:COMAP Early Science: I. Overview
Download PDFAbstract: The CO Mapping Array Project (COMAP) aims to use line intensity mapping of carbon monoxide (CO) to trace the distribution and global properties of galaxies over cosmic time, back to the Epoch of Reionization (EoR). To validate the technologies and techniques needed for this goal, a Pathfinder instrument has been constructed and fielded. Sensitive to CO(1-0) emission from $z=2.4$-$3.4$ and a fainter contribution from CO(2-1) at $z=6$-8, the Pathfinder is surveying $12$ deg$^2$ in a 5-year observing campaign to detect the CO signal from $z\sim3$. Using data from the first 13 months of observing, we estimate $P_\mathrm{CO}(k) = -2.7 \pm 1.7 \times 10^4\mu\mathrm{K}^2 \mathrm{Mpc}^3$ on scales $k=0.051-0.62 \mathrm{Mpc}^{-1}$ - the first direct 3D measurement of the clustering component of the CO(1-0) power spectrum. Based on these observations alone, we obtain a constraint on the amplitude of the clustering component (the squared mean CO line temperature-bias product) of $\langle Tb\rangle^2<49$ $\mu$K$^2$ - nearly an order-of-magnitude improvement on the previous best measurement. These constraints allow us to rule out two models from the literature. We forecast a detection of the power spectrum after 5 years with signal-to-noise ratio (S/N) 9-17. Cross-correlation with an overlapping galaxy survey will yield a detection of the CO-galaxy power spectrum with S/N of 19. We are also conducting a 30 GHz survey of the Galactic plane and present a preliminary map. Looking to the future of COMAP, we examine the prospects for future phases of the experiment to detect and characterize the CO signal from the EoR.
Abstract: 2111.06033
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Title:Dense Molecular Clouds in the Crab Supernova Remnant
Download PDFAbstract: Molecular emission was imaged with ALMA from numerous components near and within bright H3-emitting knots and absorbing dust globules in the Crab Nebula. These observations provide a critical test of how energetic photons and particles produced in a young supernova remnant interact with gas, cleanly differentiating between competing models. The four fields targeted show contrasting properties but within them, seventeen distinct molecular clouds are identified with CO emission; a few also show emission from HCO+, SiO and/or SO. These observations are compared with Cloudy models of these knots. It has been suggested that the Crab filaments present an exotic environment in which H3 emission comes from a mostly-neutral zone probably heated by cosmic rays produced in the supernova surrounding a cool core of molecular gas. Our model is consistent with the observed CO J=3-2 line strength. These molecular line emitting knots in the Crab present a novel phase of the ISM representative of many important astrophysical environments.
Abstract: 2111.06199
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Title:Reshaping our understanding on structure formation with the quantum nature of the dark matter
Download PDFAbstract: We study the non-linear structure formation in cosmology accounting for the quantum nature of the dark matter (DM) particles in the initial conditions at decoupling, as well as in the relaxation and stability of the DM halos. Differently from cosmological N-body simulations, we use a thermodynamic approach for collisionless systems of self-gravitating fermions in General Relativity, in which the halos reach the steady state by maximizing a coarse-grained entropy. We show the ability of this approach to provide answers to crucial open problems in cosmology, among others: the mass and nature of the DM particle, the formation and nature of supermassive black holes in the early Universe, the nature of the intermediate mass black holes in small halos, and the core-cusp problem.
Abstract: 2111.05905
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Title:Model independent search for transient multimessenger events with AMON using outlier detection methods
Download PDFAbstract: The Astrophysical Multimessenger Observatory Network (AMON) receives subthreshold data from multiple observatories in order to look for coincidences. Combining more than two datasets at the same time is challenging because of the range of possible signals (time windows, energies, number of events...). However, outlier detection methods can circumvent this issue by identifying any signal divergent from the background (e.g. scrambled data). We propose to use these methods to make a model independent combination of the subthreshold data of neutrino and gamma ray experiments. Using the python outlier detection (PyOD) package, it allows us to test several methods from a simple "k-nearest neighbours" algorithm to a more sophisticated Generative Adversarial Active Learning neural networks which generates data points to better discriminate inliers from outliers.
Abstract: 2111.06024
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Title:Searching for Quasi-periodic Oscillations in Active Galactic Nuclei of the Chandra Deep Field South
Download PDFAbstract: Recent X-ray observations have revealed growing evidence of quasi-periodic oscillation (QPO) in the light curve of active galactic nuclei (AGNs), which may serve as a useful probe of black hole physics. In this work, we present a systematic search for X-ray QPOs among ~ 1000 AGNs of the Chandra Deep Field South (CDF-S) in a homogeneous fashion. Dividing the 7-Ms Chandra observations into four epochs, we search for periodic signals that are persistent throughout any of these epochs, using two independent methods: Lomb-Scargle periodogram and Gregory-Loredo Algorithm. No statistically significant periodic signal is found with either method on any of the four epochs. Our extensive simulations of source light curves suggest that this non-detection is primarily due to a moderate sensitivity of the CDF-S data in QPO detection. Using the simulation-predicted detection efficiency, we are able to provide a meaningful constraint on the intrinsic occurrence rate of persistent QPOs, < (15-20) %, provided that they share a similar power spectral density with a handful of currently known AGN QPOs. The true intrinsic occurrence rate might be significantly below this upper limit, however, given the non-detection among the CDF-S sources. Our additional search for short-lived QPOs that are only detected over a small subset of all observations results in two candidates, one in source XID 643 at a period of ~ 13273 s and the other in source XID 876 at a period of ~ 7065 s.
Abstract: 2111.06388
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Full Text: [ PostScript, PDF]
Title:Compact Object Mergers in Hierarchical Triples from Low-Mass Young Star Clusters
Download PDFAbstract: A binary star orbited by an outer companion constitutes a hierarchical triple system. The outer body may excite the eccentricity of the inner binary through the von~Zeipel-Lidov-Kozai (ZLK) mechanism, triggering the gravitational wave (GW) coalescence of the inner binary when its members are compact objects. Here, we study a sample of hierarchical triples with an inner black hole (BH) -- BH binary, BH -- neutron star (NS) binary, and BH -- white dwarf (WD) binary, formed via dynamical interactions in low-mass young star clusters. Our sample of triples was obtained self-consistently from direct N-body simulations of star clusters which included up-to-date stellar evolution. We find that the inner binaries in our triples cannot merge via GW radiation alone, and the ZLK mechanism is essential to trigger their coalescence. Contrary to binaries assembled dynamically in young star clusters, binary BHs merging in triples have preferentially low mass ratios (q ~ 0.3) and higher primary masses (m_p > 40 MSun). We derive a local merger rate density of 0.60, 0.11 and 0.5 yr^-1 Gpc^-3 for BH-BH, BH-NS and BH-WD binaries, respectively. Additionally, we find that merging binaries have high eccentricities across the GW spectrum, including the LIGO-Virgo-KAGRA (LVK), LISA, and DECIGO frequencies. About 7% of BH-BH and 60% of BH-NS binaries will have detectable eccentricities in the LVK band. Our results indicate that the eccentricity and the mass spectrum of merging binaries are the strongest features for the identification of GW mergers from triples.
Abstract: 2111.06197
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Full Text: [ PostScript, PDF]
Title:The Second Love Number of Dark Compact Planets and Neutron Stars with Dark Matter
Download PDFAbstract: We study the mass-radius relation and the second Love number of compact objects made of ordinary matter and non-selfannihilating fermionic dark matter for a wide range of dark matter particle masses, and for the cases of weakly and strongly interacting dark matter. We obtain stable configurations of compact objects with radii smaller than 10 km and masses similar to Earth- or Jupiter-like stellar objects. In certain parameter ranges we find second Love numbers which are markedly different compared to those expected for neutron stars without dark matter. Thus, by obtaining the compactness of these compact objects and measuring their tidal deformability from gravitational wave detections from binary neutron star mergers, the extracted value of second Love number would allow to determine the existence of dark matter inside neutron stars irrespective of the equation of state of ordinary matter.
Abstract: 2111.05860
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Full Text: [ PostScript, PDF]
Title:X-Ray Evidence Against the Hypothesis that the Hyper-Luminous z=6.3 Quasar J0100+2802 is Lensed
Download PDFAbstract: The $z=6.327$ quasar SDSS J010013.02+280225.8 (hereafter J0100+2802) is believed to be powered by a black hole more massive than $10^{10}\ {\rm M}_\odot$, making it the most massive black hole known in the first billion years of the Universe. However, recent high-resolution ALMA imaging shows four structures at the location of this quasar, potentially implying that it is lensed with a magnification of $\mu\sim450$ and thus its black hole is significantly less massive. Furthermore, for the underlying distribution of magnifications of $z\gtrsim6$ quasars to produce such an extreme value, theoretical models predict that a larger number of quasars in this epoch should be lensed, implying further overestimates of early black hole masses. To provide an independent constraint on the possibility that J0100+2802 is lensed, we re-analyzed archival XMM-Newton observations of the quasar and compared the expected ratios of X-ray luminosity to rest-frame UV and IR luminosities. For both cases, J0100+2802's X-ray flux is consistent with the no-lensing scenario; while this could be explained by J0100+2802 being X-ray faint, we find it does not have the X-ray or optical spectral features expected for an X-ray faint quasar. Finally, we compare the overall distribution of X-ray fluxes for known, typical $z\gtrsim6$ quasars. We find a $3\sigma$ tension between the observed and predicted X-ray-to-UV flux ratios when adopting the magnification probability distribution required to produce a $\mu=450$ quasar.
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