Observations Of Thermal Emission Research Articles

Optical Extinctions of Inter-Arm Molecular Clouds in M31: A Pilot Study for the Upcoming CSST Observations

Abstract Recent Submillimeter dust thermal emission observations have unveiled a significant number of inter-arm massive molecular clouds in M31. However, the effectiveness of this technique is limited to its sensitivity, making it challenging to study more distant galaxies. This study introduces an alternative approach, utilizing optical extinctions derived from space-based telescopes, with a focus on the forthcoming China Space Station Telescope (CSST). We first demonstrate the capability of this method by constructing dust extinction maps for 17 inter-arm massive molecular clouds in M31 using the Panchromatic Hubble Andromeda Treasury (PHAT) data. Our analysis reveals that inter-arm massive molecular clouds with an optical extinction (AV) greater than 1.6 magnitudes exhibit a notable AV excess, facilitating their identification. The majority of these inter-arm massive molecular clouds show an AV around 1 magnitude, aligning with measurements from our JCMT data. Further validation using a mock CSST RGB star catalog confirms the method’s effectiveness. We show that the derived AV values using CSST z and y photometries align more closely with the input values. Molecular clouds with AV > 1.6 can also be identified using the CSST mock data. We thus claim that future CSST observation cloud provide an effective way for the detection of inter-arm massive molecular clouds with significant optical extinction in nearby galaxies.

A Combined Ground-based and JWST Atmospheric Retrieval Analysis: Both IGRINS and NIRSpec Agree that the Atmosphere of WASP-77A b Is Metal-poor

Ground-based high-resolution and space-based low-resolution spectroscopy are the two main avenues through which transiting exoplanet atmospheres are studied. Both methods provide unique strengths and shortcomings, and combining the two can be a powerful probe into an exoplanet’s atmosphere. Within a joint atmospheric retrieval framework, we combined JWST NIRSpec/G395H secondary eclipse spectra and Gemini South/IGRINS pre- and post-eclipse thermal emission observations of the hot Jupiter WASP-77A b. Our inferences from the IGRINS and NIRSpec data sets are consistent with each other, and combining the two allows us to measure the gas abundances of H2O and CO, as well as the vertical thermal structure, with higher precision than either data set provided individually. We confirm WASP-77A b’s subsolar metallicity ([(C+O)/H] = −0.61 −0.09+0.10) and solar C/O ratio (C/O = 0.57 −0.06+0.06) . The two types of data are complementary, and our abundance inferences are mostly driven by the IGRINS data, while inference of the thermal structure is driven by the NIRSpec data. Our ability to draw inferences from the post-eclipse IGRINS data is highly sensitive to the number of singular values removed in the detrending process, potentially due to high and variable humidity. We also search for signatures for atmospheric dynamics in the IGRINS data and find that propagated ephemeris error can manifest as either an orbital eccentricity or a strong equatorial jet. Neither are detected when using more up-to-date ephemerides. However, we find moderate evidence of thermal inhomogeneity and measure a cooler nightside that presents itself in the later phases after secondary eclipse.

The Roasting Marshmallows Program with IGRINS on Gemini South I: Composition and Climate of the Ultrahot Jupiter WASP-18 b

We present high-resolution dayside thermal emission observations of the exoplanet WASP-18 b using IGRINS on Gemini South. We remove stellar and telluric signatures using standard algorithms, and we extract the planet signal via cross-correlation with model spectra. We detect the atmosphere of WASP-18 b at a signal-to-noise ratio (S/N) of 5.9 using a full chemistry model, measure H2O (S/N = 3.3), CO (S/N = 4.0), and OH (S/N = 4.8) individually, and confirm previous claims of a thermal inversion layer. The three species are confidently detected (>4σ) with a Bayesian inference framework, which we also use to retrieve abundance, temperature, and velocity information. For this ultrahot Jupiter (UHJ), thermal dissociation processes likely play an important role. Retrieving abundances constant with altitude and allowing the temperature–pressure profile to adjust freely results in a moderately super-stellar carbon-to-oxygen ratio (C/O = ) and metallicity ([M/H] = ). Accounting for undetectable oxygen produced by thermal dissociation leads to C/O = and [M/H] = . A retrieval that assumes radiative–convective–thermochemical equilibrium and naturally accounts for thermal dissociation constrains C/O < 0.34 (2σ) and [M/H] = , in line with the chemistry of the parent star. Looking at the velocity information, we see a tantalizing signature of different Doppler shifts at the level of a few kilometers per second for different molecules, which might probe dynamics as a function of altitude and/or location on the planet disk. Our results demonstrate that ground-based, high-resolution spectroscopy at infrared wavelengths can provide meaningful constraints on the compositions and climate of highly irradiated planets. This work also elucidates potential pitfalls with commonly employed retrieval assumptions when applied to the spectra of UHJs.

Unifying High- and Low-resolution Observations to Constrain the Dayside Atmosphere of KELT-20b/MASCARA-2b

We present high-resolution dayside thermal emission observations of the exoplanet KELT-20b/MASCARA-2b using the MAROON-X spectrograph. Applying the cross-correlation method with both empirical and theoretical masks and a retrieval analysis, we confirm previous detections of Fe i emission lines and we detect Ni i for the first time in the planet (at 4.7σ confidence). We do not see evidence for additional species in the MAROON-X data, including notably predicted thermal inversion agents TiO and VO, their atomic constituents Ti i and V i, and previously claimed species Fe ii and Cr i. We also perform a joint retrieval with existing Hubble Space Telescope/WFC3 spectroscopy and Spitzer/IRAC photometry. This allows us to place bounded constraints on the abundances of Fe i, H2O, and CO, and to place a stringent upper limit on the TiO abundance. The results are consistent with KELT-20b having a solar to slightly supersolar composition atmosphere in terms of the bulk metal enrichment, and the carbon-to-oxygen and iron-to-oxygen ratios. However, the TiO volume mixing ratio upper limit (10−7.6 at 99% confidence) is inconsistent with this picture, which, along with the nondetection of Ti i, points to sequestration of Ti species, possibly due to nightside condensation. The lack of TiO but the presence of a large H2O emission feature in the WFC3 data is challenging to reconcile within the context of 1D self-consistent, radiative-convective models.

Temperature Structures Associated with Different Components of the Atmospheric Circulation on Tidally Locked Exoplanets

Observations of time-resolved thermal emission from tidally locked exoplanets can tell us about their atmospheric temperature structure. Telescopes such as JWST and ARIEL will improve the quality and availability of these measurements. This motivates an improved understanding of the processes that determine atmospheric temperature structure, particularly atmospheric circulation. The circulation is important in determining atmospheric temperatures, not only through its ability to transport heat, but also because any circulation pattern needs to be balanced by horizontal pressure contrasts, therefore implying a particular temperature structure. In this work, we show how the global temperature field on a tidally locked planet can be decomposed into contributions that are balanced by different components of the atmospheric circulation. These are the superrotating jet, stationary Rossby waves, and the divergent circulation. To achieve this, we partition the geopotential field into components balanced by the divergent circulation and the rotational circulation, with the latter comprising the jet and Rossby waves. The partitioned geopotential then implies a corresponding partitioning of the temperature via the hydrostatic relation. We apply these diagnostics to idealized general circulation model simulations, to show how the separate rotational and divergent circulations together make up the total three-dimensional atmospheric temperature structure. We also show how each component contributes distinct signatures to the thermal phase curve of a tidally locked planet. We conclude that this decomposition is a physically meaningful separation of the temperature field that explains its global structure, and can be used to fit observations of thermal emission.

REST: A Java Package for Crafting Realistic Cosmic Dust Particles

The overall understanding of cosmic dust particles is mainly inferred from the different Earth-based measurements of interplanetary dust particles and space missions such as Giotto, Stardust, and Rosetta. The results from these measurements indicate the presence of a wide variety of morphologically significant dust particles. To interpret the light-scattering and thermal emission observations arising due to dust in different regions of space, it is necessary to generate computer-modeled realistic dust structures of various shapes, sizes, porosity, bulk density, aspect ratio, and material inhomogeneity. The present work introduces a Java package called Rough Ellipsoid Structure Tool (REST), which is a collection of multiple algorithms, that aims to craft realistic rough-surface cosmic dust particles from spheres, superellipsoids, and fractal aggregates depending on the measured bulk density and porosity. Initially, spheres having N d dipoles or lattice points are crafted by selecting random material and space seed cells to generate a strongly damaged structure, rough surface, and poked structure. Similarly, REST generates rough-surface superellipsoids and poked structure superellipsoids from initial superellipsoid structures. REST also generates rough fractal aggregates, which are fractal aggregates having rough-surface irregular grains. REST has been applied to create agglomerated debris, agglomerated debris superellipsoids, and mixed-morphology particles. Finally, the light-scattering properties of the respective applied structures are studied to ensure their applicability. REST is a flexible structure tool that shall be useful for generating various types of dust structures that can be applied to studying the physical properties of dust in different regions of space.

K2 and Spitzer phase curves of the rocky ultra-short-period planet K2-141 b hint at a tenuous rock vapor atmosphere

K2-141 b is a transiting, small (1.5 R⊕) ultra-short-period (USP) planet discovered by the Kepler space telescope orbiting a K-dwarf host star every 6.7 h. The planet's high surface temperature of more than 2000 K makes it an excellent target for thermal emission observations. Here we present 65 h of continuous photometric observations of K2-141 b collected with Spitzer's Infrared Array Camera (IRAC) Channel 2 at 4.5 μm spanning ten full orbits of the planet. We measured an infrared eclipse depth of ${f_{{{\rm{p}} \mathord{\left/ {\vphantom {{\rm{p}} {{{\rm{f}}_{\rm{*}}}}}} \right. \kern-\nulldelimiterspace} {{{\rm{f}}_{\rm{*}}}}}}} = 142.9_{ - 39.0}^{38.5}$ ppm and a peak to trough amplitude variation of $A = 120.6_{ - 43.0}^{42.3}$ ppm. The best fit model to the Spitzer data shows no significant thermal hotspot offset, in contrast to the previously observed offset for the well-studied USP planet 55 Cnc e. We also jointly analyzed the new Spitzer observations with the photometry collected by Kepler during two separate K2 campaigns. We modeled the planetary emission with a range of toy models that include a reflective and a thermal contribution. With a two-temperature model, we measured a dayside temperature of ${T_{{\rm{p,d}}}} = 2049_{ - 359}^{362}$ K and a night-side temperature that is consistent with zero (Tp,n &lt; 1712 K at 2σ). Models with a steep dayside temperature gradient provide a better fit to the data than a uniform dayside temperature (ΔBIC = 22.2). We also found evidence for a nonzero geometric albedo ${A_{\rm{g}}} = 0.282_{ - 0.078}^{0.070}$. We also compared the data to a physically motivated, pseudo-2D rock vapor model and a 1D turbulent boundary layer model. Both models fit the data well. Notably, we found that the optical eclipse depth can be explained by thermal emission from a hot inversion layer, rather than reflected light. A thermal inversion may also be responsible for the deep optical eclipse observed for another USP, Kepler-10 b. Finally, we significantly improved the ephemerides for K2-141 b and c, which will facilitate further follow-up observations of this interesting system with state-of-the-art observatories such as James Webb Space Telescope.

Observing Planet-driven Dust Spirals with ALMA

Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations of thermal emission from the dust component of protoplanetary disks have revealed an abundance of substructures that may be interpreted as evidence for embedded planets, but planet-driven spiral arms—perhaps one of the most compelling lines of evidence—have proven comparatively elusive. In this work, we test the capabilities of ALMA to detect the planet-driven spiral signal in continuum emission. Carrying out hydrodynamic simulations and radiative transfer calculations, we present synthetic Band 7 continuum images for a wide range of disk and observing conditions. We show that thermal mass planets at tens of astronomical units typically drive spirals detectable within a few hours of integration time, and the detectable planet mass may be as low as ∼Neptune mass (0.3 M th). The grains probed by ALMA form spirals morphologically identical to the underlying gas spiral. The temperature of the dust spiral is crucial in determining its contrast, and spirals are easier to detect in disks with an adiabatic equation of state and longer cooling times. Resolving the spiral is not necessary for its detection; with the help of residual maps, the optimal beam size is a few times the spiral width at a constant noise level. Finally, we show how the presence of gaps and rings can impair our ability to recognize colocated spirals. Our work demonstrates the planet-finding potential of the current design specification of ALMA, and suggests that observing capability is not the bottleneck in searching for spirals induced by thermal mass planets.

Detection of CO emission lines in the dayside atmospheres of WASP-33b and WASP-189b with GIANO

Ultra-hot Jupiters (UHJs) are expected to possess temperature inversion layers in their dayside atmospheres. Recent thermal emission observations have discovered several atomic and molecular species along with temperature inversions in UHJs. We observed the thermal emission spectra of two UHJs (WASP-33b and WASP-189b) with the GIANO-B high-resolution near-infrared spectrograph. Using the cross-correlation technique, we detected carbon monoxide (CO) in the dayside atmospheres of both planets. The detected CO lines are in emission, which agrees with previous discoveries of iron emission lines and temperature inversions in the two planets. This is the first detection of CO lines in emission with high-resolution spectroscopy. Further retrieval work combining the CO lines with other spectral features will enable a comprehensive understanding of the atmospheric properties such as temperature structures and C/O ratios. The detected CO and iron emission lines of WASP-189b have redshifted radial velocities of several km s−1, which likely originate from a dayside to nightside wind in its atmosphere. Such a redshifted velocity has not been detected for the emission lines of WASP-33b, suggesting that the atmospheric circulation patterns of the two UHJs may be different.

Why is it So Hot in Here? Exploring Population Trends in Spitzer Thermal Emission Observations of Hot Jupiters Using Planet-specific, Self-consistent Atmospheric Models

Abstract Thermal emission has now been observed from dozens of exoplanet atmospheres, opening the gateway to population-level characterization. Here, we provide theoretical explanations for observed trends in Spitzer IRAC channel 1 (3.6 μm) and channel 2 (4.5 μm) photometric eclipse depths (EDs) across a population of 34 hot Jupiters. We apply planet-specific, self-consistent atmospheric models, spanning a range of recirculation factors, metallicities, and C/O ratios, to probe the information content of Spitzer secondary eclipse observations across the hot-Jupiter population. We show that most hot Jupiters are inconsistent with blackbodies from Spitzer observations alone. We demonstrate that the majority of hot Jupiters are consistent with low-energy redistribution between the dayside and nightside (hotter dayside than expected with efficient recirculation). We also see that high-equilibrium temperature planets (T eq ≥ 1800 K) favor inefficient recirculation in comparison to the low temperature planets. Our planet-specific models do not reveal any definitive population trends in metallicity and C/O ratio with current data precision, but more than 59% of our sample size is consistent with the C/O ratio ≤ 1 and 35% are consistent with whole range (0.35 ≤ C/O ≤ 1.5). We also find that for most of the planets in our sample, 3.6 and 4.5 μm model EDs lie within ±1σ of the observed EDs. Intriguingly, few hot Jupiters exhibit greater thermal emission than predicted by the hottest atmospheric models (lowest recirculation) in our grid. Future spectroscopic observations of thermal emission from hot Jupiters with the James Webb Space Telescope will be necessary to robustly identify population trends in chemical compositions with its increased spectral resolution, range, and data precision.

Confirmation of Iron Emission Lines and Nondetection of TiO on the Dayside of KELT-9b with MAROON-X

Abstract We present dayside thermal emission observations of the hottest exoplanet KELT-9b using the new MAROON-X spectrograph. We detect atomic lines in emission with a signal-to-noise ratio of 10 using cross-correlation with binary masks. The detection of emission lines confirms the presence of a thermal inversion in KELT-9b’s atmosphere. We also use M-dwarf stellar masks to search for TiO, which has recently been invoked to explain the unusual Hubble Space Telescope WFC3 spectrum of the planet. We find that the KELT-9b atmosphere is inconsistent with the M-dwarf masks. Furthermore, we use an atmospheric retrieval approach to place an upper limit on the TiO volume mixing ratio of 10−8.5 (at 99% confidence). This upper limit is inconsistent with the models used to match the WFC3 data, which require at least an order of magnitude more TiO, thus suggesting the need for an alternate explanation of the space-based data. Our retrieval results also strongly prefer an inverted temperature profile and atomic/ion abundances largely consistent with the expectations for a solar composition gas in thermochemical equilibrium. The exception is the retrieved abundance of Fe+, which is about 1–2 orders of magnitude greater than predictions. These results highlight the growing power of high-resolution spectrographs on large ground-based telescopes to characterize exoplanet atmospheres when used in combination with new retrieval techniques.

Where Is the Water? Jupiter-like C/H Ratio but Strong H2O Depletion Found on τ Boötis b Using SPIRou

Abstract The present-day envelope of gaseous planets is a relic of how these giant planets originated and evolved. Measuring their elemental composition therefore presents a powerful opportunity to answer long-standing questions regarding planet formation. Obtaining precise observational constraints on the elemental inventory of giant exoplanets has, however, remained challenging owing to the limited simultaneous wavelength coverage of current space-based instruments. Here, we present thermal emission observations of the nontransiting hot Jupiter τ Boo b using the new wide wavelength coverage (0.95–2.50 μm) and high spectral resolution (R = 70,000) CFHT/SPIRou spectrograph. By combining a total of 20 hr of SPIRou data obtained over five nights in a full atmospheric retrieval framework designed for high-resolution data, we constrain the abundances of all the major oxygen- and carbon-bearing molecules and recover a noninverted temperature structure using a new free-shape, nonparametric temperature–pressure profile retrieval approach. We find a volume mixing ratio of log(CO) = − 2.46 − 0.29 + 0.25 and a highly depleted water abundance of less than 0.0072 times the expected value for a solar composition envelope. Combined with upper limits on the abundances of CH4, CO2, HCN, TiO, and C2H2, this results in a gas-phase C/H ratio of 5.85 − 2.82 + 4.44 × solar, consistent with the value of Jupiter, and an envelope C/O ratio robustly greater than 0.60, even when taking into account the oxygen that may be sequestered out of the gas phase. Combined, the inferred supersolar C/H, O/H, and C/O ratios on τ Boo b support a formation scenario beyond the water snowline in a disk enriched in CO owing to pebble drift.

New Results on the Direct Observations of Thermal Radio Emission from a Solar Coronal Mass Ejection

AbstractWe report observations of thermal emission from the frontal structure of a coronal mass ejection (CME) using data obtained with the Gauribidanur RAdioheliograPH simultaneously at 80 and 53 MHz on May 1, 2016. The CME was due to activity on the far side of the Sun, but near its limb. No nonthermal radio burst activity was noticed. This provided an opportunity to observe the faint thermal radio emission from the CME, and hence directly estimate the electron density, mass, and magnetic field strength of the plasma entrained in the CME. Considering that CMEs are mostly observed only in whitelight and reports on their plasma characteristics are also limited, the rare direct radio observations of thermal emission from a CME and independent diagnosis of its plasma parameters are important measurements in the field of CME physics.

On the Temperature Profiles and Emission Spectra of Mini-Neptune Atmospheres

Abstract Atmospheric observations of mini-Neptunes orbiting M dwarfs are beginning to provide constraints on their chemical and thermal properties, while also providing clues about their interiors and potential surfaces. With their relatively large scale heights and large planet–star contrasts, mini-Neptunes are currently ideal targets toward the goal of characterizing temperate low-mass exoplanets. Understanding the thermal structures and spectral appearances of mini-Neptunes is important to understand various aspects of their atmospheres, including radiative/convective energy transport, boundary conditions for the interior, and their potential habitability. In the present study, we explore these aspects of mini-Neptunes using self-consistent models of their atmospheres. We begin by exploring the effects of irradiation, internal flux, metallicity, clouds, and hazes on the atmospheric temperature profiles and thermal emission spectra of temperate mini-Neptunes. In particular, we investigate the impact of these properties on the radiative–convective boundary and the thermodynamic conditions in the lower atmosphere, which serves as the interface with the interior and/or a potential surface. Building on recent suggestions of habitability of the mini-Neptune K2-18 b, we find a range of physically motivated atmospheric conditions that allow for liquid water under the H2-rich atmospheres of such planets. We find that observations of thermal emission with JWST/MIRI spectrophotometry can place useful constraints on the habitability of temperate mini-Neptunes such as K2-18 b and provide more detailed constraints on the chemical and thermal properties of warmer planets such as GJ 3470 b. Our results underpin the potential of temperate mini-Neptunes such as K2-18 b as promising candidates in the search for habitable exoplanets.

Earth as an Exoplanet. I. Time Variable Thermal Emission Using Spatially Resolved Moderate Imaging Spectroradiometer Data

Abstract Among the more than 4000 exoplanets known today, some terrestrial planets have been detected in the so-called habitable zone of their host stars and their number is expected to increase in the near future, energizing a drive to understand and interpret the eagerly awaited wealth of data to identify signs of life beyond our solar system. So far, Earth remains the best and only example of a habitable (and inhabited) world. Although, it seems extremely unlikely that any other exoplanets will be true Earth twins, it is important to explore and understand the full range of spectral signatures and variability of Earth in order to inform the design of future instruments and missions, and understand their diagnostic power as well as potential limitations. In this work we use Earth observation data collected by the MODIS instrument aboard the Aqua satellite. The complete data set comprises 15 years of thermal emission observations in the 3.66–14.40 μm range for five different locations on Earth (Amazon Rainforest, Antarctica, Arctic, Indian Ocean, and the Sahara Desert). We then determine flux levels and variations as a function of wavelength and surface type (i.e., climate zone and surface thermal properties) and investigate whether periodic signals indicating Earth’s tilted rotation axis can be detected. Our findings suggest that (1) viewing geometry plays an important role when thermal emission data is analyzed as Earth’s spectrum varies by a factor of three and more depending on the dominant surface type underneath; (2) typically strong absorption bands from CO2 (15 μm) and O3 (9.65 μm) are significantly less pronounced and partially absent in data from the polar regions implying that estimating correct abundance levels for these molecules might be challenging in these cases; and (3) the time-resolved thermal emission spectrum encodes information about seasons/planetary obliquity, but the significance depends on the viewing geometry and spectral band considered.

A multiannual record of gravity wave activity in Mars’s lower atmosphere from on-planet observations by the Mars Climate Sounder

Gravity waves in Mars’s atmosphere strongly affect the general circulation as well as middle atmospheric cloud formation, but the climatology and sources of gravity waves in the lower atmosphere remain poorly understood. At Earth, the statistical variance in satellite observations of thermal emission above the instrumental noise floor has been used to enable measurement of gravity wave activity at a global scale. Here is presented an analysis of variance in calibrated radiance at 15.4μm (635–665 cm−1) from off-nadir and nadir observations by the Mars Climate Sounder (MCS) on board Mars Reconnaissance Orbiter (MRO); a major expansion in the observational data available for validating models of Martian gravity wave activity. These observations are sensitive to gravity waves at 20–30 km altitude with wavelength properties (λh=10–100 km, λz> 5 km) that make them likely to affect the dynamics of the middle and upper atmosphere. We find that: (1) strong, moderately intermittent gravity wave activity is scattered over the tropical volcanoes and throughout the middle to high latitudes of both hemispheres during fall and winter, (2) gravity wave activity noticeably departs from climatology during regional and global dust storms; and (3) strong, intermittent variance is observed at night in parts of the southern tropics during its fall/winter, but frequent CO2 ice clouds prevents unambiguous attribution to GW activity. The spatial distribution of wave activity is consistent with topographic sources being dominant, but contributions from boundary layer convection and other convective processes are possible.

Spiral structures in an embedded protostellar disk driven by envelope accretion

Hydrodynamical simulations show that a pair of spiral arms can form in the disk around a rapidly growing young star and that the arms are crucial in transporting angular momentum as the disk accretes material from the surrounding envelope1–4. Here we report the detection of a pair of symmetric spiral structures in a protostellar disk, supporting the formation of spiral arms in the disk around a forming star. The HH 111 VLA 1 source is a young Class I source embedded in a massive infalling protostellar envelope and is actively accreting, driving the prominent HH 111 jet. Previous observations showed a ring of shock emission around the disk’s outer edge5, indicating accretion of the envelope material onto the disk at a high rate. Now with ALMA observations of thermal emission from dust particles, we detect a pair of spiral arms extending from the inner region to the disk’s outer edge, similar to that seen in many simulations1–4. Additionally, the disk is massive, with a Toomre Q parameter near unity in the outer parts where the spiral structures are detected, supporting the notion that envelope accretion is making the outer disk gravitationally unstable. In our observations, another source, HH 111 VLA 2, is spatially resolved for the first time, showing a disk-like structure with a diameter of ~26 au and an orientation nearly orthogonal to that of the HH 111 VLA 1 disk. ALMA observations have revealed a pair of symmetric spiral arms in the protostellar disk around HH 111 VLA 1. This discovery would seem to confirm hydrodynamical models that suggest that symmetric spiral structures arise in disks as a consequence of active accretion.

The symmetry energy and incompressibility constrained by the observations of glitching pulsars

We investigate the masses of glitching pulsars in order to constrain their equation of state (EOS). The observations of glitches (sudden jumps in rotational frequency) may provide information on the interior physics of neutron stars. With the assumption that glitches are triggered by superfluid neutrons, the masses of glitching neutron stars can be estimated using observations of maximum glitches. Together with the observations of thermal emission from glitching pulsars Vela and J1709–4429, the slope of symmetry energy and incompressibility of nuclear matter at saturation density can be constrained. The slope of symmetry energy L should be larger than 67 MeV while the lower limit of incompressibility for symmetric nuclear matter K0 is 215 MeV. We also obtain a relationship between L and K0: 6.173 MeV + 0.283 K0 ≤ L ≤ 7.729 MeV + 0.291 K0. The restricted EOSs are consistent with the observations of 2-solar-mass neutron stars and gravitational waves from a binary neutron star inspiral.

Axion cooling of neutron stars. II. Beyond hadronic axions

We study the axion cooling of neutron stars within the Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) model, which allows for tree level coupling of electrons to the axion {and locks the Peccei-Quinn charges of fermions via an angle parameter}. This extends our previous study [Phys. Rev. D 93, 065044 (2016)] limited to hadronic models of axions. We explore the two-dimensional space of axion parameters within the DFSZ model by comparing the theoretical cooling models with the surface temperatures of a few stars with measured surface temperatures. It is found that axions masses $m_a\ge 0.06$ to 0.12 eV can be excluded by x-ray observations of thermal emission of neutron stars (in particular by those of Cas A), the precise limiting value depending on the angle parameter of the DFSZ model. It is also found that axion emission by electron bremsstrahlung in neutron star crusts is negligible except for the special case where neutron Peccei-Quinn charge is small enough, so that the coupling of neutrons to axions can be neglected.

Early X-Ray Flares in GRBs

Abstract We analyze the early X-ray flares in the GRB “flare–plateau–afterglow” (FPA) phase observed by Swift-XRT. The FPA occurs only in one of the seven GRB subclasses: the binary-driven hypernovae (BdHNe). This subclass consists of long GRBs with a carbon–oxygen core and a neutron star (NS) binary companion as progenitors. The hypercritical accretion of the supernova (SN) ejecta onto the NS can lead to the gravitational collapse of the NS into a black hole. Consequently, one can observe a GRB emission with isotropic energy erg, as well as the associated GeV emission and the FPA phase. Previous work had shown that gamma-ray spikes in the prompt emission occur at cm with Lorentz Gamma factors . Using a novel data analysis, we show that the time of occurrence, duration, luminosity, and total energy of the X-ray flares correlate with E iso. A crucial feature is the observation of thermal emission in the X-ray flares that we show occurs at radii ∼1012 cm with . These model-independent observations cannot be explained by the “fireball” model, which postulates synchrotron and inverse-Compton radiation from a single ultrarelativistic jetted emission extending from the prompt to the late afterglow and GeV emission phases. We show that in BdHNe a collision between the GRB and the SN ejecta occurs at ≃1010 cm, reaching transparency at ∼1012 cm with . The agreement between the thermal emission observations and these theoretically derived values validates our model and opens the possibility of testing each BdHN episode with the corresponding Lorentz Gamma factor.