Papers for Monday, May 17 2021

We present the analysis of multi-wavelength observations of seven extragalactic radio sources, listed as unidentified in the Third Cambridge Revised Catalog (3CR). X-ray observations, performed during Chandra Cycle 21, were compared to VLA, WISE and Pan-STARRS observations in the radio, infrared and optical bands, respectively. All sources in this sample lack a clear optical counterpart, and are thus missing their redshift and optical classification. In order to confirm the X-ray and infrared radio counterparts of core and extended components, here we present for the first time radio maps obtained manually reducing VLA archival data. As in previous papers on the Chandra X-ray snapshot campaign, we report X-ray detections of radio cores and two sources, out of the seven presented here, are found to be members of galaxy clusters. For these two cluster sources (namely, 3CR 409 and 3CR 454.2), we derived surface brightness profiles in four directions. For all seven sources, we measured X-ray intensities of the radio sources and we also performed standard X-ray spectral analysis for the four sources (namely, 3CR 91, 3CR 390, 3CR 409 and 3CR 428) with the brightest nuclei (more than 400 photons in the 2'' nuclear region). We also detected extended X-ray emission around 3CR 390 and extended X-ray emission associated with the northern jet of 3CR 158. This paper represents the first attempt to give a multi-wavelength view of the unidentified radio sources listed in the 3CR catalog.

A significant fraction of white dwarfs (WDs) exhibit signs of ongoing accretion of refractory elements at rates $\sim10^3$--$10^7$ kg s$^{-1}$, among which, 37 WDs were detected to harbor dusty debris disks. Such a concurrence requires not only fertile reservoirs of planetary material, but also a high duty cycle of metal delivery. It has been commonly suggested that this material could be supplied by Solar System analogs of Main Belt asteroids or Kuiper Belt objects. Here we consider the primary progenitors of WD pollutants as a population of residual high-eccentricity planetesimals, de-volatilized during the stellar giant phases. Equivalent to the Solar System's long-period comets, they are scattered to the proximity of WDs by perturbations from remaining planets, Galactic tides, passing molecular clouds, and nearby stars. These objects undergo downsizing when they venture within the tidal disruption limit. We show quantitatively how the breakup condition and fragment sizes are determined by material strength and gravity. Thereafter, the fragments' semi-major axes need to decay by at least $\sim$6 orders of magnitude before their constituents are eventually accreted onto the surface of WDs. We investigate the orbital evolution of these fragments around WDs and show that WDs' magnetic fields induce an Alfv\'en-wave drag during their periastron passages and rapidly circularize their orbits. This process could be responsible for the observed accretion rates of heavy-elements and the generation of circum-WD debris disks. A speculative implication is that giant planets may be common around WDs' progenitors and they may still be bound to some WDs today.

We present X-ray spectral and long-term variability analyses of an unbiased sample of 361 optically selected radio-loud quasars (RLQs) utilizing sensitive serendipitous X-ray data from the Chandra and XMM-Newton archives. The spectral and temporal properties of RLQs are compared with those of radio-quiet quasars (RQQs) matched in $L_\mathrm{2500A}$ and $z$. The median power-law photon index ($\Gamma$) of RLQs is $1.84^{+0.01}_{-0.01}$, which is close to that of matched RQQs ($1.90^{+0.02}_{-0.01}$). No significant correlations between $\Gamma$ and radio-loudness, $L_\mathrm{x}/L_\mathrm{x,rqq}$ (the X-ray luminosity over that expected from the $L_\mathrm{x}$-$L_\mathrm{uv}$ relation for RQQs), redshift, or Eddington ratio are found for our RLQs. The stacked X-ray spectra of our RLQs show strong iron-line emission and a possible Compton-reflection hump. The intrinsic X-ray variability amplitude is $\approx40$% for RLQs on timescales of months-to-years in the rest frame, which is somewhat smaller than for the matched RQQs ($\approx60$%) on similar timescales, perhaps due to the larger black-hole masses and lower Eddington ratios in our RLQ sample. The X-ray spectral and variability results for our RLQs generally support the idea that the X-ray emission of typical RLQs is dominated by the disk/corona, as is also indicated by a recent luminosity correlation study.

We live in momentous times. The science community is empowered with an arsenal of cosmic messengers to study the Universe in unprecedented detail. Gravitational waves, electromagnetic waves, neutrinos and cosmic rays cover a wide range of wavelengths and time scales. Combining and processing these datasets that vary in volume, speed and dimensionality requires new modes of instrument coordination, funding and international collaboration with a specialized human and technological infrastructure. In tandem with the advent of large-scale scientific facilities, the last decade has experienced an unprecedented transformation in computing and signal processing algorithms. The combination of graphics processing units, deep learning, and the availability of open source, high-quality datasets, have powered the rise of artificial intelligence. This digital revolution now powers a multi-billion dollar industry, with far-reaching implications in technology and society. In this chapter we describe pioneering efforts to adapt artificial intelligence algorithms to address computational grand challenges in Multi-Messenger Astrophysics. We review the rapid evolution of these disruptive algorithms, from the first class of algorithms introduced in early 2017, to the sophisticated algorithms that now incorporate domain expertise in their architectural design and optimization schemes. We discuss the importance of scientific visualization and extreme-scale computing in reducing time-to-insight and obtaining new knowledge from the interplay between models and data.

We report the detection of 8.914-hr variability in both optical and ultraviolet light curves of LP 40-365 (also known as GD 492), the prototype for a class of partly burnt runaway stars that have been ejected from a binary due to a thermonuclear supernova event. We first detected this 1.0% amplitude variation in optical photometry collected by the Transiting Exoplanet Survey Satellite. Re-analysis of observations from the Hubble Space Telescope at the TESS period and ephemeris reveal a 5.8% variation in the ultraviolet of this 9800 K stellar remnant. We propose that this 8.914-hr photometric variation reveals the current surface rotation rate of LP 40-365, and is caused by some kind of surface inhomogeneity rotating in and out of view, though a lack of observed Zeeman splitting puts an upper limit on the magnetic field of <20 kG. We explore ways in which the present rotation period can constrain progenitor scenarios if angular momentum was mostly conserved, which suggests that the survivor LP 40-365 was not the donor star but was most likely the bound remnant of a mostly disrupted white dwarf that underwent advanced burning from an underluminous (Type Iax) supernova.

We analyse the post-inflationary contribution to the stochastic gravitational wave background due to a resonant feature in the scalar power spectrum, which is characterised by an oscillation in $\log(k)$, complementing our previous work arXiv:2012.02761 on sharp features. Primordial features signal departures of inflation from the single-field slow-roll paradigm and are motivated by embeddings of inflation in high energy physics. We find that the oscillation in the scalar power spectrum leads to a corresponding modulation in the gravitational wave spectrum that can be understood as a superposition of two oscillatory pieces, one with the original frequency of the scalar oscillations, and one with double frequency. For oscillations with slowly-varying amplitude this oscillatory part can be computed semi-analytically. Our results can be used as templates for the reconstruction of the signal from future data and permit extracting information about the small scale scalar power spectrum from measurements of the stochastic gravitational wave background.

Magnetic fields are fundamental to the accretion dynamics of protoplanetary disks and they likely affect planet formation. Typical methods to study the magnetic field morphology observe the polarization of dust or spectral lines. However, it has recently become clear that dust-polarization in ALMA's spectral regime not always faithfully traces the magnetic field structure of protoplanetary disks, which leaves spectral line polarization as a promising method of mapping the magnetic field morphologies of such sources. We aim to model the emergent polarization of different molecular lines in the ALMA wavelength regime that are excited in protoplanetary disks. We explore a variety of disk models and molecules to identify those properties that are conducive to the emergence of polarization in spectral lines and may therefore be viably used for magnetic field measurements in protoplanetary disks. Methods. We use PORTAL (POlarized Radiative Transfer Adapted to Lines) in conjunction with LIME (Line Emission Modeling Engine). Together, they allow us to treat the polarized line radiative transfer of complex three-dimensional physical and magnetic field structures. We present simulations of the emergence of spectral line polarization of different molecules and molecular transitions in the ALMA wavelength regime and we comment on the observational feasibility of ALMA linear polarization observations of protoplanetary disks. We find that molecules that thermalize at high densities, such as HCN, are also most susceptible to polarization. We find that such molecules are expected to be significantly polarized in protoplanetary disks, while molecules that thermalize at low densities, such as CO, are only significantly polarized in the outer disk regions.

We derive the first constraints on the time delay distribution of binary black hole (BBH) mergers using the LIGO-Virgo Gravitational-Wave Transient Catalog GWTC-2. Assuming that the progenitor formation rate follows the star formation rate (SFR), the data favor that $43$--$100\%$ of mergers have delay times $<4.5$ Gyr (90\% credibility). Adopting a model for the metallicity evolution, we derive joint constraints for the metallicity-dependence of the BBH formation efficiency and the distribution of time delays between formation and merger. Short time delays are favored regardless of the assumed metallicity dependence, although the preference for short delays weakens as we consider stricter low-metallicity thresholds for BBH formation. For a $p(\tau) \propto \tau^{-1}$ time delay distribution and a progenitor formation rate that follows the SFR without metallicity dependence, we find that $\tau_\mathrm{min}<2.2$ Gyr, whereas considering only the low-metallicity $Z < 0.3\,Z_\odot$ SFR, $\tau_\mathrm{min} < 3.0$ Gyr (90\% credibility). Alternatively, if we assume long time delays, the progenitor formation rate must peak at higher redshifts than the SFR. For example, for a $p(\tau) \propto \tau^{-1}$ time delay distribution with $\tau_\mathrm{min} = 4$ Gyr, the inferred progenitor rate peaks at $z = 5.4^{+3.0}_{-3.2}$ (90\% credible interval). Finally, we explore whether the inferred formation rate and time delay distribution vary with BBH mass.

The central regions of star-forming barred spiral galaxies can be devoid of star formation because of the redistribution of gas along the length of the bar. However, there can be gas outside the length of the bar that can host star formation. We study a sample of barred disc galaxies in the local Universe with an aim to discriminate between centrally quenched and globally quenched galaxies based on their positions on star-formation-rate(SFR)--stellar mass plots and to find a connection between the SFR of quenched galaxies and the length of their bar. We classified barred galaxies as centrally quenched and globally quenched based on their position on SFR--stellar mass plots, with SFRs derived from H$\alpha$ flux and spectral energy distribution fits on combined ultraviolet and optical flux. We selected galaxies as passive based on the distance from the main sequence relation. From a total 2514 barred galaxies studied here, we present 651 with suppressed star formation in their central region but hosting star formation outside. We also find a possible correlation between bar length and SFR for the galaxies that are fully quenched because of the stellar bar.

Rapidly spinning, deformed neutron stars have long been considered potential gravitational-wave emitters. However, so far only upper limits on the size of the involved quadrupole deformations have been obtained. For this reason, it is pertinent to ask how large a mountain can be before the neutron star crust fractures. This is the question we consider in this paper, which describes how mountains can be calculated in relativistic gravity. Formally, such a calculation requires a fiducial force to source the mountain. Therefore, we consider three simple examples and increase their deforming amplitudes until the crust yields. We demonstrate how the derived mountains depend on the equation of state by considering a range of models obtained from chiral effective field theory. We find that the largest mountains depend sensitively on both the mechanism that sources them and the nuclear-matter equation of state.

A complete understanding of Gamma Ray Bursts (GRBs) has been difficult to achieve due to our incomplete knowledge of the radiation mechanism that is responsible for producing the prompt emission. This emission, which is detected in the first tens of seconds of the GRB, is typically dominated by hard X-ray and gamma ray photons although, there have also been a few dozen prompt optical detections. These optical detections have the potential to discriminate between plausible prompt emission models, such as the photospheric and synchrotron shock models. In this work we use an improved MCRaT code, which includes cyclo-synchrotron emission and absorption, to conduct radiative transfer calculations from optical to gamma ray energies under the photospheric model. The calculations are conducted using a set of two dimensional relativistic hydrodynamic long GRB jet simulations, consisting of a constant and variable jet. We find that correlations between the optical and gamma ray light curves can provide insight into the observer viewer angle as well as the variability of GRB jets. Furthermore, we find that there should be optical prompt precursors that precedes the main gamma ray emission for observers located far from the jet axis. Additionally, the detected optical emission originates from dense regions of the outflow such as shock interfaces and the jet-cocoon interface. These results show the importance of conducting global radiative transfer simulations using hydrodynamically calculated jet structures as well as the potential information that optical prompt detections can provide on GRB jets under the photospheric model.

The aim of this work is to create a long (410 years) series of average annual total sunspot areas AR - physically-based index of sunspot activity. We used telescopic observations of the AR index in 1832-1868 and 1875-2020, as well as the relationship between AR and long series of sunspot indices SN (ISN version 2.0) and sunspot groups GN (Svalgaard and Schatten (2016) GSN version). The Royal Greenwich observatory series after 1976 is extended by the Kislovodsk Mountain Astronomical Station data. When reconstructing AR from SN, it is taken into account that the function AR = f (SN) has a nonlinear systematic character and uncertainty associated with the heterogeneity of these indices. Therefore, in addition to modeling the most probable AR values, predictive limits of reconstruction uncertainty are determined. In the interval 1610-1699 the reconstruction we carried out on the basis of the GN series using the previously proposed decomposition in pseudo-phase space method (DPS). The resulting series NO21y is freely available online. We show that for this series the empirical Gnevyshev-Ohl rule and Waldmeier effect are fulfilled. Wavelet analysis reveals periodicities of 8.4-13.8 years for the main cycle (with a sharp decrease of the period before the global Maunder and Dalton minima) and a two-component Gleissberg cycle with typical periods of 50-60 years and 90-110 years.

We present a ground-based optical transmission spectrum for the warm Saturn-mass exoplanet WASP-110b from two transit observations made with the FOcal Reducer and Spectrograph (FORS2) on the Very Large Telescope (VLT). The spectrum covers the wavelength range from 4000 to 8333\AA, which is binned in 46 transit depths measured to an averaged precision of 220 parts per million (ppm) over an averaged 80\AA~bin for a Vmag=12.8 star. The measured transit depths are unaffected by a dilution from a close A-type field dwarf, which was fully resolved. The overall main characteristic of the transmission spectrum is an increasing radius with wavelength and a lack of the theoretically predicted pressure-broadened sodium and potassium absorption features for a cloud-free atmosphere. We analyze archival high-resolution optical spectroscopy and find evidence for low to moderate activity of the host star, which we take into account in the atmospheric retrieval analysis. Using the AURA retrieval code, we find that the observed transmission spectrum can be best explained by a combination of unocculted stellar faculae and a cloud deck. Transmission spectra of cloud-free and hazy atmospheres are rejected at a high confidence. With a possible cloud deck at its terminator, WASP-110b joins the increasing population of irradiated hot-Jupiter exoplanets with cloudy atmospheres observed in transmission.

Coma Berenices (Coma Ber), an open cluster about the same age as Praesepe and the Hyades (700-800 Myr) is, despite being only 85 pc away, less well studied than its famous cousins. This is due principally to its sparseness and low proper motion, which together made Coma Ber's membership challenging to establish pre-Gaia. We have curated a new list of its members based on Gaia DR2 astrometry, derived its metallicity and interstellar reddening using LAMOST data, and inferred the cluster's age by fitting PARSEC isochrones to its color$-$magnitude diagram. We then measured rotation periods for Coma Ber's low-mass members using TESS and ZTF photometry. Our isochrone fitting and the TESS- and ZTF-derived rotation periods confirm that Coma Ber is coeval with the Hyades and Praesepe. This work is the first step toward re-establishing Coma Ber as another valuable benchmark cluster for age$-$rotation$-$activity studies.

Magnetic flux rope, formed by the helical magnetic field lines, can sometimes remain its shape while carrying significant plasma flow that is aligned with the local magnetic field. We report the existence of such structures and static flux ropes by applying the Grad-Shafranov-based algorithm to the Parker Solar Probe (PSP) in-situ measurements in the first five encounters. These structures are detected at heliocentric distances, ranging from 0.13 to 0.66 au, in a total of 4-month time period. We find that flux ropes with field-aligned flows, although occur more frequently, have certain properties similar to those of static flux ropes, such as the decaying relations of the magnetic fields within structures with respect to heliocentric distances. Moreover, these events are more likely with magnetic pressure dominating over the thermal pressure. About one-third of events are detected in the relatively fast-speed solar wind. Taking into account the high Alfvenicity, we also compare with switchback spikes identified during three encounters and interpret their inter-relations. We find that some switchbacks can be detected when the spacecraft traverses flux rope-like structures. The cross-section maps for selected events are presented via the new Grad-Shafranov type reconstruction. Finally, the possible evolution of the magnetic flux rope structures in the inner heliosphere is discussed.

The Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha camera on the SOlar and Heliosphere Observer (SOHO) satellite makes daily images of the entire sky to monitor the three-dimensional distribution of solar wind and solar radiation via its imprint on the stream of interstellar hydrogen that flows through the solar system. In the process it also records the distribution of the hydrogen comae of comets. We report here the analyses of six comets originally from the Oort Cloud observed during the 2017-2020 period by SWAN: C/2015 V2 (Johnson), C/2019 Y1 (ATLAS), C/2017 T2 (PanSTARRS), C/2020 F8 (SWAN), C/2019 Y4 (ATLAS), and C/2019 U6 (Lemmon). Of these the nuclei of C/2019 Y4 (ATLAS) and C/2020 F8 (SWAN) both broke up on their inbound orbit before perihelion. The water production rates over the detectable portion of each comet's orbit are determined and discussed in light of the comet's dynamical sub-class of Oort Cloud comets.

One of the top remaining science challenges in astronomical optics is the direct imaging and characterization of extrasolar planets and planetary systems. Directly imaging exoplanets from ground-based observatories requires combining high-order adaptive optics with a stellar coronagraph observing at wavelengths ranging from the visible to the mid-IR. A limiting factor in achieving the required contrast (planet-to-star intensity ratio) is quasi-static speckles, caused largely by non-common path aberrations (NCPA) in the coronagraph. Starting with a realistic simulator of a telescope with an AO system and a coronagraph, this article provides simulations of several closely related millisecond regression models requiring inputs of the measured wavefronts and science camera images. The simplest regression model, called the naive estimator, does not treat the noise and other sources of information loss in the WFS. The naive estimator provided a useful estimate of the NCPA of $\sim$ 0.5 radian RMS, with an accuracy of $\sim$ 0.06 radian RMS in one minute of simulated sky time on a magnitude 8 star. The bias-corrected estimator generalizes the regression model to account for the noise and information loss in the WFS. A simulation of the bias-corrected estimator with four minutes of sky time included an NCPA of $\sim 0.05 \,$ radian RMS and an extended exoplanet scene. The joint regression of the bias-corrected estimator simultaneously achieved an NCPA estimate with an accuracy of $\sim 5\times10^{-3} \,$radian and contrast of $\sim 10^{-5}$ on the exoplanet scene. In addition, the estimate of the exoplanet image was completely free of the subtraction artifacts that always plague differential imaging. The estimate of the exoplanet image obtained by the joint regression was nearly identical to the image obtained by subtraction of a perfectly known point-spread function.

The leading difficulty in achieving the contrast necessary to directly image exoplanets and associated structures (eg. protoplanetary disks) at wavelengths ranging from the visible to the infrared are quasi-static speckles, and they are hard to distinguish from planets at the necessary level of precision. The source of the quasi-static speckles is hardware aberrations that are not compensated by the adaptive optics system. These aberrations are called non-common path aberrations (NCPA). In 2013, Frazin showed how, in principle, simultaneous millisecond (ms) telemetry from the wavefront sensor (WFS) and the science camera behind a stellar coronagraph can be used as input into a regression scheme that simultaneously and self-consistently estimates the NCPA and the sought-after image of the planetary system (the exoplanet image). The physical principle underlying the regression method is rather simple: the wavefronts, which are measured by the WFS, modulate the speckles caused by the NCPA and therefore can be used as probes of the optical system. The most important departure from realism in the author's 2013 article was the assumption that the WFS made error-free measurements. The simulations in Part I provide results on the joint regression on the NCPA and the exoplanet image from three different methods, called the ideal, the naive, and the bias-corrected estimators. The ideal estimator is not physically realizable but is a useful as a benchmark for simulation studies, but the other two are, at least in principle. This article provides the regression equations for all three of these estimators as well as a supporting technical discussion. Briefly, the naive estimator simply uses the noisy WFS measurements without any attempt to account for the errors, and the bias-corrected estimator uses statistical knowledge of the wavefronts to treat errors in the WFS measurements.

We study properties of an accretion ring in a steady mass flow from a companion star to a compact object in an X-ray binary. The accretion ring is a place where matter inflowing from a companion star sojourns for a while to bifurcate to accretion and excretion flows due to angular momentum transfer in it. The matter in the accretion ring rotates along the Keplerian circular orbit determined by the intrinsic specific angular momentum of the inflowing matter and forms a thick ring-envelope. Two internal flows are expected to appear in the thick envelope. One is a mass spreading flow bifurcating to a thick accretion flow and a thick excretion flow, as a result of the angular momentum transfer within the ring-envelope. The other is a cooling flow toward the envelope center governed by radiative cooling under an effect of X-ray irradiation. This cooling flow eventually forms a core in the torus, from which a thin accretion disk and a thin excretion disk spread out as a result of the angular momentum transfer there again. Evaluating and comparing the time scales for the two internal flows, the accretion ring is shown to generally originate a two-layer accretion flow in which a thin accretion disk is sandwiched by a thick accretion flow, unless the accretion rate is very low. Properties of the thin excretion disk and the thick excretion flow are also investigated. The thin excretion disk is expected to terminate at a distance 4 times as large as the accretion ring radius and to form another ring there, unless tidal effects from the companion star exist. The thick excretion flow is, on the other hand, likely to turn to a super-sonic wind-flow reaching the infinity.

Observed reddening in the circum-galactic medium (CGM) indicates a significant abundance of small grains, of which the origin is still to be clarified. We examine a possible path of small-grain production through shattering of pre-existing large grains in the CGM. Possible sites where shattering occurs on a reasonable time-scale are cool clumps with hydrogen number density $n_\mathrm{H}\sim 0.1$ cm$^{-3}$ and gas temperature $T_\mathrm{gas}\sim 10^4$ K, which are shown to exist through observations of Mg II absorbers. We calculate the evolution of grain size distribution in physical conditions appropriate for cool clumps in the CGM, starting from a large-grain-dominated distribution suggested from theoretical studies. With an appropriate gas turbulence model expected from the physical condition of cold clumps (maximum eddy size and velocity of $\sim$100 pc and 10 km s$^{-1}$, respectively), together with the above gas density and temperature and the dust-to-gas mass ratio inferred from observations (0.006), we find that small-grain production occurs on a time-scale (a few $\times 10^8$ yr) comparable to the lifetime of cool clumps derived in the literature. Thus, the physical conditions of the cool clouds are favrourable for small-grain production. We also confirm that the reddening becomes significant on the above time-scale. Therefore, we conclude that small-grain production by shattering is a probable cause for the observed reddening in the CGM. We also mention the effect of grain materials (or their mixtures) on the reddening at different redshifts (1 and 2).

We report results of an analysis of the black hole (BH) candidate source X1755-338 in 1989, 1990, and 1991 with Ginga, and in 1995 with ASCA. The spectra were well represented by a model consisting of a soft thermal emission from an accretion disk and a hard X-ray tail. The normalization of the multi-color disk model, relating to the inner disk radius, was similar to each other. The unabsorbed X-ray fluxes from the disk component in the 0.01-10 keV band were estimated to be 1.3x10^{-9}, 3.0x10^{-9}, 9.8x10^{-10}, and 2.4x10^{-9} erg s^{-1} cm^{-2} in 1989, 1990, 1991, and 1995, respectively, and are proportional to kT_{in}^4, where kT_{in} is a temperature at the inner disk radius. Based on the standard accretion disk model for a non-rotating BH, our results suggest either a small BH mass or a large inclination angle. Otherwise, X1755-338 is a rotating BH. The hard X-ray intensity was found to be variable, while the soft X-ray intensity was stable. Although the previous work showed the existence of an iron line at 6.7 keV, no clear iron line feature was found in all the spectra. We infer that most of the iron line flux reported in the previous work was due to contamination of the Galactic diffuse X-ray emission.

A black hole image contains a bright ring of photons that have closely circled the black hole on their way from the source to the detector. Here, we study the photon ring of a rotating black hole which is pierced by a global hyper-light axion-type cosmic string. We show that the coupling $\phi F \tilde{F}$ between the axion $\phi$ and the photon can give rise to a unique polarimetric structure of the photon ring. The structure emerges due to an Aharonov-Bohm type effect that leads to a change of the polarization directions of linear polarized photons when they circle the black hole. For several parameter choices, we determine concrete polarization patterns in the ring. Measuring these patterns can provide us with a way of determining the value of the coefficient of the mixed anomaly between electromagnetism and the symmetry that gave rise to the cosmic string. Finally, we briefly review a possible formation mechanism of black holes that are pierced by cosmic strings and discuss under which conditions we can expect such objects to be present as supermassive black holes in the center of galaxies.

We calculate overstable convective (OsC) modes of $2M_\odot$, $4M_\odot$, and $20M_\odot$ main sequence stars. To compute non-adiabatic OsC modes in the core, we assume $(\nabla\cdot\vec{F}_C)^\prime=0$ as a prescription for the approximation called frozen-in convection in pulsating stars where $\vec{F}_C$ is the convective energy flux and the prime $^\prime$ indicates Eulerian perturbation. We find that the general properties of the OsC modes are roughly the same as those obtained by Lee \& Saio (2020) who assumed $\delta (\nabla\cdot\vec{F}_C)=0$, except that no OsC modes behave like inertial modes when they tend toward complete stabilization with increasing rotation frequency where $\delta$ indicates the Lagrangian perturbation. As the rotation frequency of the stars increases, the OsC modes are stabilized to resonantly excite $g$-modes in the envelope when the core rotates slightly faster than the envelope. The frequency of the OsC modes that excite envelope $g$-modes is approximately given by $\sigma\sim |m\Omega_c|$ in the inertial frame and hence $\sigma_{m=-2}\approx2\sigma_{m=-1}$ where $m$ is the azimuthal wavenumber of the modes and $\Omega_c$ is the rotation frequency of the core. We find that the modal properties of OsC modes do not strongly depend on the mass of the stars. We discuss angular momentum transport by OsC modes in resonance with envelope $g$-modes in the main sequence stars. We suggest that angular momentum transfer takes place from the core to the envelope and that the OsC modes may help the stars rotate uniformly and keep the rotation frequency of the core low during their evolution as main sequence stars.

We investigate the magnetic reconnection in an MHD simulation of a coronal magnetic flux rope (MFR) confined by a helmet streamer, where a prominence-cavity system forms. This system includes a hot cavity surrounding a prominence with prominence horns and a central hot core above the prominence. The evolution of the system from quasi-equilibrium to eruption can be divided into four phases: quasi-static, slow rise, fast rise, and propagation phases. The emerged MFR initially stays quasi-static and magnetic reconnection occurs at the overlying high-Q (squashing factor) apex region, which gradually evolves into a hyperbolic flux tube (HFT). The decrease of the integrated magnetic tension force (above the location of the overlying reconnection) is due to the removal of overlying confinement by the enhanced overlying reconnection between the MFR and the overlying fields at the apex HFT, thus engines the slow rise of the MFR with a nearly constant velocity. Once the MFR reaches the regime of torus instability, another HFT immediately forms at the dip region under the MFR, followed by the explosive flare reconnection. The integrated resultant force (above the location of the flare reconnection) exponentially increases, which drives the exponential fast rise of the MFR. The system enters the propagation phase, once its apex reaches the height of about one solar radius above the photosphere. The simulation reproduces the main processes of one group of prominence eruptions especially those occurring on the quiet Sun.

We present the SEMLA (Signal Extraction using Machine Learning for ALTO) analysis method, developed for the detection of $\rm E>200\,GeV$ $\gamma$ rays in the context of the ALTO wide-field-of-view atmospheric shower array R&D project. The scientific focus of ALTO is extragalactic $\gamma$-ray astronomy, so primarily the detection of soft-spectrum $\gamma$-ray sources such as Active Galactic Nuclei and Gamma Ray Bursts. The current phase of the ALTO R&D project is the optimization of sensitivity for such sources and includes a number of ideas which are tested and evaluated through the analysis of dedicated Monte Carlo simulations and hardware testing. In this context, it is important to clarify how data are analysed and how results are being obtained. SEMLA takes advantage of machine learning and comprises four stages: initial event cleaning (stage A), filtering out of poorly reconstructed $\gamma$-ray events (stage B), followed by $\gamma$-ray signal extraction from proton background events (stage C) and finally reconstructing the energy of the events (stage D). The performance achieved through SEMLA is evaluated in terms of the angular, shower core position, and energy resolution, together with the effective detection area, and background suppression. Our methodology can be easily generalized to any experiment, provided that the signal extraction variables for the specific analysis project are considered.

We find evidence for large-scale clustering amongst Fermi-selected BL Lac objects but not amongst Fermi-selected FSRQs. Using two-point correlation functions we have investigated the clustering properties of different classes of objects from the Fermi LAT 4FGL catalogue. We wanted to test the idea based on optical polarization observations that there might be large volumes of space in which AGN axes are aligned. To do this we needed a clean sample of blazars as these are objects with their jet axes pointing towards the observer and Fermi sources provide such a sample. We find that high latitude Fermi sources taken as a whole show a significant clustering signal on scales up to 30 degrees. To investigate if all blazars behave in the same way we used the machine learning classifications of Kovacevic, et al. (2020), which are based only on gamma-ray information, to separate BL Lac-like objects from FSRQ-like objects. A possible explanation for the clustering signal we find amongst the BL Lac-like objects is that there are indeed large volumes of space in which AGN axes are aligned. This signal might be washed out in FSRQs since they occupy a much larger volume of space. Thus our results support the idea that large scale polarization alignments could originate from coherent alignments of AGN axes. We speculate that these axis alignments may be related to the well-known intrinsic alignments of galaxy optical position angles.

This paper describes the architecture and demonstrates the capabilities of a newly developed, physically-based imaging simulator environment called SISPO, developed for small solar system body fly-by and terrestrial planet surface mission simulations. The image simulator utilises the open-source 3D visualisation system Blender and its Cycles rendering engine, which supports physically based rendering capabilities and procedural micropolygon displacement texture generation. The simulator concentrates on realistic surface rendering and has supplementary models to produce realistic dust- and gas-environment optical models for comets and active asteroids. The framework also includes tools to simulate the most common image aberrations, such as tangential and sagittal astigmatism, internal and external comatic aberration, and simple geometric distortions. The model framework's primary objective is to support small-body space mission design by allowing better simulations for characterisation of imaging instrument performance, assisting mission planning, and developing computer-vision algorithms. SISPO allows the simulation of trajectories, light parameters and camera's intrinsic parameters.

We report a $\approx 400$-hour Giant Metrewave Radio Telescope (GMRT) search for HI 21 cm emission from star-forming galaxies at $z = 1.18-1.39$ in seven fields of the DEEP2 Galaxy Survey. Including data from an earlier 60-hour GMRT observing run, we co-added the HI 21 cm emission signals from 2,841 blue star-forming galaxies that lie within the full-width at half-maximum of the GMRT primary beam. This yielded a $5.0\sigma$ detection of the average HI 21 cm signal from the 2,841 galaxies at an average redshift $\langle z \rangle \approx 1.3$, only the second detection of HI 21 cm emission at $z\ge1$. We obtain an average HI mass of $\langle {\rm M_{HI}} \rangle=(3.09 \pm 0.61) \times 10^{10}\ {\rm M}_\odot$ and an HI-to-stellar mass ratio of $2.6\pm0.5$, both significantly higher than values in galaxies with similar stellar masses in the local Universe. We also stacked the 1.4 GHz continuum emission of the galaxies to obtain a median star-formation rate (SFR) of $14.5\pm1.1\ {\rm M}_\odot \textrm{yr}^{-1}$. This implies an average HI depletion timescale of $\approx 2$ Gyr for blue star-forming galaxies at $z\approx 1.3$, a factor of $\approx 3.5$ lower than that of similar local galaxies. Our results suggest that the HI content of galaxies towards the end of the epoch of peak cosmic SFR density is insufficient to sustain their high SFR for more than $\approx 2$ Gyr. Insufficient gas accretion to replenish the HI could then explain the observed decline in the cosmic SFR density at $z< 1$.

A numerical detection of the mass-dependent two-fold spin transition of the galaxies is presented. Analyzing a sample of the galaxies with stellar masses in the range of $10^{9}< (M_{\star}/M_{\odot})\le 10^{11}$ from the IllustrisTNG300-1 simulations, we explore the alignment tendency between the galaxy spins and the three eigenvectors of the linearly reconstructed tidal field as a function of $M_{\star}$ and its evolution over a broad range of redshift $0\le z \le 2.5$. Detecting a significant signal of the occurrence of the mass-dependent transition of the galaxy spins not only at $z>1$ but also at $z\le 1$, we show that the type of the galaxy spin transition varies with redshifts. As $M_{\star}$ increases beyond a certain threshold mass, the preferred directions of the galaxy spins transit from the third to the first tidal eigenvectors (type one) at $z\le 1$ but from the third to the second tidal eigenvectors (type two) at $z\ge 2$, unlike those of the DM halos that undergo only the type two transitions at $z\le 1$. It is also shown that both of the threshold mass and the transition type strongly depend on the galaxy status, morphology, star formation rate as well as on the environment. We suggest that the occurrence of the type two transition should be induced by the vorticity effect on the small mas scale, while the type one transition should be closely linked to some hydrodynamical mechanism which is effective most for the quiescent massive galaxies in the passive stage.

Primordial black holes (PBHs) from the early Universe have been connected with the nature of dark matter and can significantly affect cosmological history. We show that coincidence dark radiation and density fluctuation gravitational wave signatures associated with evaporation of $\lesssim 10^9$ g PBHs can be used to explore and discriminate different formation scenarios of spinning and non-spinning PBHs spanning orders of magnitude in mass-range, which is challenging to do otherwise.

Molecular hydrogen is the most abundant molecular species in the Universe. While no doubts exist that it is mainly formed on the interstellar dust grain surfaces, many details of this process remain poorly known. In this work, we focus on the fate of the energy released by the H$_2$ formation on the dust icy mantles, how it is partitioned between the substrate and the newly formed H$_2$, a process that has a profound impact on the interstellar medium. We carried out state-of-art \textit{ab-initio} molecular dynamics simulations of H$_2$ formation on periodic crystalline and amorphous ice surface models. Our calculations show that up to two thirds of the energy liberated in the reaction ($\sim$300 kJ/mol $\sim$3.1 eV) is absorbed by the ice in less than 1 ps. The remaining energy ($\sim$140 kJ/mol $\sim$1.5 eV) is kept by the newly born H$_2$. Since it is ten times larger than the H$_2$ binding energy on the ice, the new H$_2$ molecule will eventually be released into the gas-phase. The ice water molecules within $\sim$4 \AA ~from the reaction site acquire enough energy, between 3 and 14 kJ/mol (360--1560 K), to potentially liberate other frozen H$_2$ and, perhaps, frozen CO molecules. If confirmed, the latter process would solve the long standing conundrum of the presence of gaseous CO in molecular clouds. Finally, the vibrational state of the newly formed H$_2$ drops from highly excited states ($\nu = 6$) to low ($\nu \leq 2$) vibrational levels in a timescale of the order of ps.

We present the analysis of the molecular gas in the nuclear regions of NGC 4968, NGC 4845, and MCG-06-30-15, with the help of ALMA observations of the CO(2-1) emission line. The aim is to determine the kinematics of the gas in the central (~ 1 kpc) region. We use the 3D-Based Analysis of Rotating Object via Line Observations ($^{3D}$BAROLO) and DiskFit softwares. Circular motions dominate the kinematics of the gas in the central discs, mainly in NGC 4845 and MCG-06-30-15, however there is a clear evidence of non-circular motions in the central ($\sim$ 1 kpc) region of NGC 4845 and NGC 4968. The strongest non-circular motion is detected in the inner disc of NGC 4968 with velocity $\sim 115\, \rm{km\,s^{-1}}$. The bisymmetric model is found to give the best-fit for NGC 4968 and NGC 4845. If the dynamics of NGC 4968 is modeled as a corotation pattern just outside of the bar, the bar pattern speed turns out to be at $\Omega_b$ = $52\, \rm{km\,s^{-1}\,kpc^{-1}}$ the corotation is set at 3.5 kpc and the inner Lindblad resonance (ILR) ring at R = 300pc corresponding to the CO emission ring. The 1.2 mm ALMA continuum is peaked and compact in NGC 4968 and MCG-06-30-15, but their CO(2-1) has an extended distribution. Allowing the CO-to-H$_{2}$ conversion factor $\alpha_{CO}$ between 0.8 and 3.2, typical of nearby galaxies of the same type, the molecular mass M(H$_{2}$) is estimated to be $\sim 3-12\times 10^{7} ~{\rm M_\odot}$ (NGC 4968), $\sim 9-36\times 10^{7}~ {\rm M_\odot}$ (NGC 4845), and $\sim 1-4\times 10^{7}~ {\rm M_\odot}$ (MCG-06-30-15). We conclude that the observed non-circular motions in the disc of NGC 4968 and likely that seen in NGC 4845 is due to the presence of the bar in the nuclear region. At the current spectral and spatial resolution and sensitivity we cannot claim any strong evidence in these sources of the long sought feedback/feeding effect due to the AGN presence.

Submillimeter interferometry has the potential to image supermassive black holes on event horizon scales, providing tests of the theory of general relativity and increasing our understanding of black hole accretion processes. The Event Horizon Telescope (EHT) performs these observations from the ground, and its main imaging targets are Sagittarius A* in the Galactic Center and the black hole at the center of the M87 galaxy. However, the EHT is fundamentally limited in its performance by atmospheric effects and sparse terrestrial $(u,v)$-coverage (Fourier sampling of the image). The scientific interest in quantitative studies of the horizon size and shape of these black holes has motivated studies into using space interferometry which is free of these limitations. Angular resolution considerations and interstellar scattering effects push the desired observing frequency to bands above 500 GHz. This paper presents the requirements for meeting these science goals, describes the concept of interferometry from Polar or Equatorial Medium Earth Orbits (PECMEO) which we dub the Event Horizon Imager (EHI), and utilizes suitable space technology heritage. In this concept, two or three satellites orbit at slightly different orbital radii, resulting in a dense and uniform spiral-shaped $(u,v)$-coverage over time. The local oscillator signals are shared via an inter-satellite link, and the data streams are correlated on-board before final processing on the ground. Inter-satellite metrology and satellite positioning are extensively employed to facilitate the knowledge of the instrument position vector, and its time derivative. The European space heritage usable for both the front ends and the antenna technology of such an instrument is investigated. Current and future sensors for the required inter-satellite metrology are listed. Intended performance estimates and simulation results are given.

The first stars are thought to be one of the dominant sources of hydrogen reionization in the early Universe, with their high luminosities and surface temperatures expected to drive high ionizing photon production rates. In this work we take our Geneva stellar evolution model grid of zero-metallicity stars and predict their production rates of photons capable to ionize H, He I and He II. We explore the impact of stellar initial mass, rotation, convective overshooting, and initial mass function of the host population. We have found that ionizing photon production rates increase with increasing initial mass, therefore populations with more top heavy initial mass functions produce more ionizing photons. For the rotational velocities in our model grid we see changes of up to 25% to ionizing photons produced. This varies with ionizing photon species and reflects changes to surface properties due to rotation. We have also found that higher convective overshooting increases ionizing photon production at all initial masses for all ionizing photon species, by approximately 20% for the change in overshooting considered here. For stellar populations, the variations in the slope of the initial mass function and the maximum initial mass have a significant effect on the production of ionizing photons. This work presents ionizing photon production predictions for the most up to date Geneva stellar evolution models of Population III stars ahead of future observations from facilities such as JWST, and provides insight into how key evolutionary parameters impact the contribution of the first stars to reionization.

The concept for space interferometry from Polar or Equatorial Circular Medium Earth Orbits (the PECMEO concept) is a promising way to acquire the image of the "shadow" of the event horizon of Sagittarius A* with an angular resolution of circa 5 microarcseconds. The concept is intended to decrease the size of the main reflector of the instrument to about 3 m using a precise orbit reconstruction based on Global Navigation Satellite System (GNSS) navigation, inter-satellite range and range-rate measurements, and data from the Attitude and Orbit Determination System (AODS). The paper provides the current progress on the definition of the subsystems required for the concept on the basis of simulations, radio regulations, and available technology. The paper proposes the requirement for the localization of the phase centre of the main reflector. The paper provides information about the visibility of GNSS satellites and the needed accuracies of the AODS. The paper proposes the frequency plan for the instrument and its Inter-Satellite Links (ISLs). The concepts for measurement of range and range rate using ISLs (as well as for the data exchange at these ISLs) are presented. The block diagram of the interferometer is described and its sensitivity is estimated. The link budget for both ISLs is given as well as their critical components. The calculated measurement quality factors are given. The paper shows the expected performance of the sub-systems of the interferometer. The requirements for the localization of the main reflectors and the information about the availability of the GNSS satellites are based on the simulations results. (Two sentences have been deleted in order to satisfy the maximum symbol count established by arXiv rules.) The paper provides input information for the development of the orbit reconstruction filter and the whole PECMEO system.

We study the evolution of Eu and Ba abundances in local group dwarf spheroidal and ultra faint dwarf galaxies by means of detailed chemical evolution models and compare our results with new sets of homogeneous abundances. The adopted models include gas infall and outflow and have been previously tested. We investigate several production scenarios for r-process elements: merging neutron stars and magneto-rotational driven supernovae. Production of Ba through the main s-process acting in low- and intermediate- mass stars is considered as well. We also test different sets of nucleosynthesis yields. For merging neutron stars we adopt either a constant and short delay time for merging or a delay time distribution function. Our simulations show that: i) if r-process elements are produced only by a quick source, it is possible to reproduce the [Eu/Fe] vs [Fe/H], but those models fail in reproducing the [Ba/Fe] vs [Fe/H]. ii) If r-process elements are produced only with longer delays the opposite happens. iii) If both a quick source and a delayed one are adopted, such as magneto-rotational driven supernovae and merging neutron stars with a delay time distribution, the [Eu/Fe] abundance pattern is successfully reproduced, but models still fail in reproducing the [Ba/Fe]. iv) On the other hand, the characteristic abundances of Reticulum II can be reproduced only if both the Eu and the r-process fraction of Ba are produced on short and constant time delays during a single merging event. We discuss also other possible interpretations, including an inhomogeneous mixing of gas which might characterize this galaxy.

The central engines of Active Galactic Nuclei (AGNs) are powered by accreting supermassive black holes, and while AGNs are known to play an important role in galaxy evolution, the key physical processes occur on scales that are too small to be resolved spatially (aside from a few exceptional cases). Reverberation mapping is a powerful technique that overcomes this limitation by using echoes of light to determine the geometry and kinematics of the central regions. Variable ionizing radiation from close to the black hole drives correlated variability in surrounding gas/dust, but with a time delay due to the light travel time between the regions, allowing reverberation mapping to effectively replace spatial resolution with time resolution. Reverberation mapping is used to measure black hole masses and to probe the innermost X-ray emitting region, the UV/optical accretion disk, the broad emission line region and the dusty torus. In this article we provide an overview of the technique and its varied applications.

Context. In this paper we present ultra deep images of the compact group of galaxies HCG 86 as part of the VEGAS survey. Aims. Our main goals are to estimate the amount of intragroup light (IGL), to study the light and color distributions in order to address the main formation process of the IGL component in groups of galaxies. Methods. We derived the azimuthally averaged surface brightness profiles in the g,r and i bands with g - r and r - i average colors and color profiles for all group members. By fitting the light distribution, we have extrapolated the contribution of the stellar halos plus the diffuse light from the brightest component of each galaxy. The results are compared with theoretical predictions. Results. The long integration time and wide area covered make our data deeper than previous literature studies of the IGL in compact groups of galaxies and allow us to produce an extended (~160 kpc) map of the IGL, down to a surface brightness level of about 30 mag/arcsec^2 in the g band. The IGL in HCG 86 is mainly in diffuse form and has average colors of g - r ~ 0.8 mag and r - i ~ 0.4 mag. The fraction of IGL in HCG 86 is ~ 16% of the total luminosity of the group, and this is consistent with estimates available for other compact groups and loose groups of galaxies of similar virial masses. A weak trend is present between the amount of IGL and the early-type to late-type galaxy ratio. Conclusions. By comparing the IGL fraction and colors with those predicted by simulations, the amount of IGL in HCG 86 would be the result of the disruption of satellites at an epoch of z ~ 0.4. At this redshift, observed colors are consistent with the scenario where the main contribution to the mass of the IGL comes from the intermediate-massive galaxies.

We report the detection of X-ray pulsations from the rotation-powered millisecond-period pulsars PSR J0740+6620 and PSR J1614-2230, two of the most massive neutron stars known, using observations with the Neutron Star Interior Composition Explorer (NICER). We also analyze X-ray Multi-Mirror Mission (XMM-Newton) data for both pulsars to obtain their time-averaged fluxes and study their respective X-ray fields. PSR J0740+6620 exhibits a broad double-peaked profile with a separation of ~0.4 in phase. PSR J1614-2230, on the other hand, has a broad single-peak profile. The broad modulations with soft X-ray spectra of both pulsars are indicative of thermal radiation from one or more small regions of the stellar surface. We show the NICER detections of X-ray pulsations for both pulsars and also discuss the phase relationship to their radio pulsations. In the case of PSR J0740+6620, this paper documents the data reduction performed to obtain the pulsation detection and prepare for pulse profile modeling analysis.

PSR J0740$+$6620 has a gravitational mass of $2.08\pm 0.07~M_\odot$, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740$+$6620 is $13.7^{+2.6}_{-1.5}$ km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030$+$0451, the masses of two other $\sim 2~M_\odot$ pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation of state modeling, and find consistent results at $\sim 1.5-3$ times nuclear saturation density. For a given framework, when all measurements are included the radius of a $1.4~M_\odot$ neutron star is known to $\pm 4$% (68% credibility) and the radius of a $2.08~M_\odot$ neutron star is known to $\pm 5$%. The full radius range that spans the $\pm 1\sigma$ credible intervals of all the radius estimates in the three frameworks is $12.45\pm 0.65$ km for a $1.4~M_\odot$ neutron star and $12.35\pm 0.75$ km for a $2.08~M_\odot$ neutron star.

We report on Bayesian estimation of the radius, mass, and hot surface regions of the massive millisecond pulsar PSR J0740$+$6620, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer X-ray Timing Instrument (NICER XTI) event data. We condition on informative pulsar mass, distance, and orbital inclination priors derived from the joint NANOGrav and CHIME/Pulsar wideband radio timing measurements of arXiv:2104.00880. We use XMM European Photon Imaging Camera spectroscopic event data to inform our X-ray likelihood function. The prior support of the pulsar radius is truncated at 16 km to ensure coverage of current dense matter models. We assume conservative priors on instrument calibration uncertainty. We constrain the equatorial radius and mass of PSR J0740$+$6620 to be $12.39_{-0.98}^{+1.30}$ km and $2.072_{-0.066}^{+0.067}$ M$_{\odot}$ respectively, each reported as the posterior credible interval bounded by the 16% and 84% quantiles, conditional on surface hot regions that are non-overlapping spherical caps of fully-ionized hydrogen atmosphere with uniform effective temperature; a posteriori, the temperature is $\log_{10}(T$ [K]$)=5.99_{-0.06}^{+0.05}$ for each hot region. All software for the X-ray modeling framework is open-source and all data, model, and sample information is publicly available, including analysis notebooks and model modules in the Python language. Our marginal likelihood function of mass and equatorial radius is proportional to the marginal joint posterior density of those parameters (within the prior support) and can thus be computed from the posterior samples.

In recent years our understanding of the dense matter equation of state (EOS) of neutron stars has significantly improved by analyzing multimessenger data from radio/X-ray pulsars, gravitational wave events, and from nuclear physics constraints. Here we study the additional impact on the EOS from the jointly estimated mass and radius of PSR J0740+6620, presented in Riley et al. (2021) by analyzing a combined dataset from X-ray telescopes NICER and XMM-Newton. We employ two different high-density EOS parameterizations: a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS). At nuclear densities these are connected to microscopic calculations of neutron matter based on chiral effective field theory interactions. In addition to the new NICER data for this heavy neutron star, we separately study constraints from the radio timing mass measurement of PSR J0740+6620, the gravitational wave events of binary neutron stars GW190425 and GW170817, and for the latter the associated kilonova AT2017gfo. By combining all these, and the NICER mass-radius estimate of PSR J0030+0451 we find the radius of a 1.4 solar mass neutron star to be constrained to the 95% credible ranges 12.33^{+0.76}_{-0.81} km (PP model) and 12.18^{+0.56}_{-0.79} km (CS model). In addition, we explore different chiral effective field theory calculations and show that the new NICER results provide tight constraints for the pressure of neutron star matter at around twice saturation density, which shows the power of these observations to constrain dense matter interactions at intermediate densities.

Context. In exoplanet searches with radial velocity data, the most common statistical significance metrics are the Bayes factor and the false alarm probability (FAP). Both have proved useful, but do not directly address whether an exoplanet detection should be claimed. Furthermore, it is unclear which detection threshold should be taken and how robust the detections are to model misspecification. Aims. The present work aims at defining a detection criterion which conveys as precisely as possible the information needed to claim an exoplanet detection. We compare this new criterion to existing ones in terms of sensitivity and robustness. Methods. We define a significance metric called the false inclusion probability (FIP) based on the posterior probability of presence of a planet. Posterior distributions are computed with the nested sampling package Polychord. We show that for FIP and Bayes factor calculations, defining priors on linear parameters as Gaussian mixture models allows to significantly speed up computations. The performances of the FAP, Bayes factor and FIP are studied with simulations as well as analytical arguments. We compare the methods assuming the model is correct, then evaluate their sensitivity to the prior and likelihood choices. Results. Among other properties, the FIP offers ways to test the reliability of the significance levels, it is particularly efficient to account for aliasing and allows to exclude the presence of planets with a certain confidence. We find that, in our simulations, the FIP outperforms existing detection metrics. We show that planet detections are sensitive to priors on period and semi-amplitude and that letting free the noise parameters offers better performances than fixing a noise model based on a fit to ancillary indicators.

Inverse problems defined naturally on the sphere are becoming increasingly of interest. In this article we provide a general framework for evaluation of inverse problems on the sphere, with a strong emphasis on flexibility and scalability. We consider flexibility with respect to the prior selection (regularization), the problem definition - specifically the problem formulation (constrained/unconstrained) and problem setting (analysis/synthesis) - and optimization adopted to solve the problem. We discuss and quantify the trade-offs between problem formulation and setting. Crucially, we consider the Bayesian interpretation of the unconstrained problem which, combined with recent developments in probability density theory, permits rapid, statistically principled uncertainty quantification (UQ) in the spherical setting. Linearity is exploited to significantly increase the computational efficiency of such UQ techniques, which in some cases are shown to permit analytic solutions. We showcase this reconstruction framework and UQ techniques on a variety of spherical inverse problems. The code discussed throughout is provided under a GNU general public license, in both C++ and Python.

In this paper, using the concept of Lewis Riesenfeld invariant quantum operator method for finding continuous eigenvalues of quantum mechanical wave functions we derive the analytical expressions for the cosmological geometric phase, which is commonly identified to be the Pancharatnam Berry phase from primordial cosmological perturbation scenario. We compute this cosmological geometric phase from two possible physical situations,(1) In the absence of Bell's inequality violation and (2) In the presence of Bell's inequality violation having the contributions in the sub Hubble region ($-k\tau\gg 1$), super Hubble region ($-k\tau\ll 1$) and at the horizon crossing point ($-k\tau= 1$) for massless field ($m/{\cal H}\ll 1$), partially massless field ($m/{\cal H}\sim 1$) and massive/heavy field ($m/{\cal H}\gg 1$), in the background of quantum field theory of spatially flat quasi De Sitter geometry. The prime motivation for this work is to investigate the various unknown quantum mechanical features of primordial universe. To give the realistic interpretation of the derived theoretical results we express everything initially in terms of slowly varying conformal time dependent parameters, and then to connect with cosmological observation we further express the results in terms of cosmological observables, which are spectral index/tilt of scalar mode power spectrum ($n_{\zeta}$) and tensor-to-scalar ratio ($r$). Finally, this identification helps us to provide the stringent numerical constraints on the Pancharatnam Berry phase, which confronts well with recent cosmological observation.

We investigate the potential of ground-based gravitational-wave detectors to probe the mass function of intermediate-mass black holes (IMBHs) wherein we also include BHs in the upper mass gap $\sim 60-130~M_\odot$. Using the noise spectral density of the upcoming LIGO and Virgo fourth observing (O4) run, we perform Bayesian analysis on quasi-circular non-precessing, spinning IMBH binaries (IMBHBs) with total masses $50\mbox{--} 500 M_\odot$, mass ratios 1.25, 4, and 10, and (dimensionless) spins up to 0.95, and estimate the precision with which the source-frame parameters can be measured. We find that, at $2\sigma$, the source-frame mass of the heavier component of the IMBHBs can be constrained with an uncertainty of $\sim 10-40\%$ at a signal to noise ratio of $20$. Focusing on the stellar-mass gap, we first evolve stars with massive helium cores using the open-source MESA software instrument to establish the upper and lower edges of the mass gap. We determine that the lower edge of the mass gap is $\simeq$ 59$^{+34}_{-13}$ $M_{\odot}$, while the upper edge is $\simeq$ 139$^{+30}_{-14}$ $M_{\odot}$, where the error bars indicate the mass range that follows from the $\pm 3\sigma$ uncertainty in the ${}^{12}\text{C}(\alpha, \gamma) {}^{16} \text{O}$ nuclear rate. We then study IMBHBs with components lying in the mass gap and show that the O4 run will be able to robustly identify most such systems. In this context, we also re-analyze the GW190521 event and show that the 90$\%$ confidence interval of the primary-mass measurement lies inside the mass gap. Finally, we show that the precision achieved with the O4 run (and future O5 run) could be crucial for understanding the mass function, the formation mechanism, and evolution history of IMBHs.

Neutron stars can be destroyed by black holes at their center accreting material and eventually swallowing the entire star. Here we note that the accretion model adopted in the literature, based on Bondi accretion or variations thereof, is inadequate for small black holes -- black holes whose Schwarzschild radius is comparable to, or smaller than, the neutron's de Broglie wavelength. In this case, quantum mechanical aspects of the accretion process cannot be neglected, and give rise to a completely different accretion rate. We show that for the case of black holes seeded by the collapse of bosonic dark matter, this is the case for electroweak-scale dark matter particles. In the case of fermionic dark matter, typically the black holes that would form at the center of a neutron star are more massive, unless the dark matter particle mass is very large, larger than about 10$^{10}$ GeV. We calculate the lifetime of neutron stars harboring a "small" black hole, and find that black holes lighter than $\sim 10^{11}$ kg quickly evaporate, leaving no trace. More massive black holes destroy neutron stars via quantum accretion on time-scales much shorter than the age of observed neutron stars.

Quasi-periodic oscillations, often present in the power density spectrum of accretion disk around black holes, are useful probes for the understanding of gravitational interaction in the near-horizon regime of black holes. Since the presence of an extra spatial dimension modifies the near horizon geometry of black holes, it is expected that the study of these quasi-periodic oscillations may shed some light on the possible existence of these extra dimensions. Intriguingly, most of the extra dimensional models, which are of significant interest to the scientific community, predicts the existence of a tidal charge parameter in black hole spacetimes. This tidal charge parameter can have an overall negative sign and is a distinctive signature of the extra dimensions. Motivated by this, we have studied the quasi-periodic oscillations for a rotating braneworld black hole using the available theoretical models. Subsequently, we have used the observations of the quasi-periodic oscillations from available black hole sources, e.g., GRO J1655 -- 40, XTE J1550 -- 564, GRS 1915 + 105, H 1743 + 322 and Sgr A* and have compared them with the predictions from the relevant theoretical models, in order to estimate the tidal charge parameter. It turns out that among the 11 theoretical models considered here, 8 of them predict a negative value for the tidal charge parameter, while for the others negative values of the tidal charge parameter are also well within the 1-$\sigma$ confidence interval.

Axion-CMB scenario is an interesting possibility to explain the temperature anisotropy of the cosmic microwave background (CMB) by primordial fluctuations of the QCD axion \cite{Iso:2020pzv}. In this scenario, fluctuations of radiations are generated by an energy exchange between axions and radiations, which results in the correlation between the primordial axion fluctuations and the CMB anisotropies. Consequently, the cosmological observations stringently constrain a model of the axion and the early history of the universe. In particular, we need a large energy fraction $\Omega_A^{}$ of the axion at the QCD phase transition, but it must become tiny at the present universe to suppress the isocurvature power spectrum. One of natural cosmological scenarios to realize such a situation is the thermal inflation which can sufficiently dilute the axion abundance. Thermal inflation occurs in various models. In this paper, we focus on a classically conformal (CC) $B$-$L$ model with a QCD axion. In this model, the early universe undergoes a long supercooling era of the $B$-$L$ and electroweak symmetries, and thermal inflation naturally occurs. Thus it can be a good candidate for the axion-CMB scenario. But the axion abundance at the QCD transition is shown to be insufficient in the original CC $B$-$L$ model. To overcome the situation, we extend the model by introducing $N$ scalar fields $S$ (either massive or massless) and consider a novel cosmological history such that the $O(N)$ and the $B$-$L$ sectors evolve almost separately in the early universe. We find that all the necessary conditions for the axion-CMB scenario can be satisfied in some parameter regions for massless $S$ fields, typically $N\sim 10^{19}$ and the mass of $B$-$L$ gauge boson around $5-10$ TeV.

We suggest a new experiment sensitive to a possible difference between the amount of CP violation as measured on the surface of the Earth and in a lower gravity environment. Our proposed experiment is model independent and could yield a $5\sigma$ measurement within tens of days, indicating a dependence of the level of CP violation in the neutral kaon system on the local gravitational potential.

In this work, we construct a five-dimensional spherically-symmetric, charged and asymptotically Anti-de Sitter black hole with its singularity being point-like and strictly localised on our brane. In addition, the induced brane geometry is described by a Reissner-Nordstr\"{o}m-(A)dS line-element. We perform a careful classification of the horizons, and demonstrate that all of them are exponentially localised close to the brane thus exhibiting a pancake shape. The bulk gravitational background is everywhere regular, and reduces to an AdS$_5$ spacetime right outside the black-hole event horizon. This geometry is supported by an anisotropic fluid with only two independent components, the energy density $\rho_E$ and tangential pressure $p_2$. All energy conditions are respected close to and on our brane, but a local violation takes place within the event horizon regime in the bulk. A tensor-vector-scalar field-theory model is built in an attempt to realise the necessary bulk matter, however, in order to do so, both gauge and scalar degrees of freedom need to turn phantom-like at the bulk boundary. The study of the junction conditions reveals that no additional matter needs to be introduced on the brane for its consistent embedding in the bulk geometry apart from its constant, positive tension. We finally compute the effective gravitational equations on the brane, and demonstrate that the Reissner-Nordstr\"{o}m-(A)dS geometry on our brane is caused by the combined effect of the five-dimensional geometry and bulk matter with its charge being in fact a tidal charge.

Current measurements of Standard-Model parameters suggest that the electroweak vacuum is metastable. This metastability has important cosmological implications because large fluctuations in the Higgs field could trigger vacuum decay in the early universe. For the false vacuum to survive, interactions which stabilize the Higgs during inflation -- e.g., inflaton-Higgs interactions or non-minimal couplings to gravity -- are typically necessary. However, the post-inflationary preheating dynamics of these same interactions could also trigger vacuum decay, thereby recreating the problem we sought to avoid. This dynamics is often assumed catastrophic for models exhibiting scale invariance since these generically allow for unimpeded growth of fluctuations. In this paper, we examine the dynamics of such "massless preheating" scenarios and show that the competing threats to metastability can nonetheless be balanced to ensure viability. We find that fully accounting for both the backreaction from particle production and the effects of perturbative decays reveals a large number of disjoint "islands of (meta)stability" over the parameter space of couplings. Ultimately, the interplay among Higgs-stabilizing interactions plays a significant role, leading to a sequence of dynamical phases that effectively extend the metastable regions to large Higgs-curvature couplings.