Abstracts of Interest
Selected by:
Jemma Pilossof
Abstract: 2403.12264
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Title:Measurement of anisotropies in Supernova Remnant observations and their interpretation using numerical models
View PDF HTML (experimental)Abstract:Supernova remnants (SNRs) exhibit varying degrees of anisotropy, which have been extensively modeled using numerical methods. We implement a technique to measure anisotropies in SNRs by calculating power spectra from their high-resolution images. To test this technique, we develop 3D hydrodynamical models of supernova remnants and generate synthetic x-ray images from them. Power spectra extracted from both the 3D models and the synthetic images exhibit the same dominant angular scale, which separates large scale features from small scale features due to hydrodynamic instabilities. The angular power spectrum at small length scales during relatively early times is too steep to be consistent with Kolmogorov turbulence, but it transitions to Kolmogorov turbulence at late times. As an example of how this technique can be applied to observations, we extract a power spectrum from a \textit{Chandra} observation of Tycho's SNR and compare with our models. Our predicted power spectrum picks out the angular scale of Tycho's fleece-like structures and also agrees with the small-scale power seen in Tycho. We use this to extract an estimate for the density of the circumstellar gas ($n \sim 0.28/\mathrm{cm^3}$), consistent with previous measurements of this density by other means. The power spectrum also provides an estimate of the density profile of the outermost ejecta. Moreover, we observe additional power at large scales which may provide important clues about the explosion mechanism itself.
Abstract: 2403.11946
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Title:Atmospheric muons measured with the KM3NeT detectors in comparison with updated numeric predictions
View PDF HTML (experimental)Abstract:The measurement of the flux of muons produced in cosmic ray air showers is essential for the study of primary cosmic rays. Such measurements are important in extensive air shower detectors to assess the energy spectrum and the chemical composition of the cosmic ray flux, complementary to the information provided by fluorescence detectors. Detailed simulations of the cosmic ray air showers are carried out, using codes such as CORSIKA, to estimate the muon flux at sea level. These simulations are based on the choice of hadronic interaction models, for which improvements have been implemented in the post-LHC era. In this work, a deficit in simulations that use state-of-the-art QCD models with respect to the measurement deep underwater with the KM3NeT neutrino detectors is reported. The KM3NeT/ARCA and KM3NeT/ORCA neutrino telescopes are sensitive to TeV muons originating mostly from primary cosmic rays with energies around 10 TeV. The predictions of state-of-the-art QCD models show that the deficit with respect to the data is constant in zenith angle; no dependency on the water overburden is observed. The observed deficit at a depth of several kilometres is compatible with the deficit seen in the comparison of the simulations and measurements at sea level.
Abstract: 2403.11832
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Title:Precise measurement of the cosmic-ray spectrum and $\left \langle \ln A \right \rangle$ by LHAASO -- connecting the Galactic to the extragalactic components
View PDF HTML (experimental)Abstract:Recently LHAASO Collaboration gives precise measurements of cosmic rays (CR) all particle energy spectrum and mean logarithmic mass $\left \langle \ln A \right \rangle$ from 0.3 PeV to 30 PeV. Combining the CR measurements by AMS-02 and DAMPE in space and that by LHAASO and Auger on the ground we construct a model to recover all these measurements from tens of GeV to tens of EeV. We find the LHAASO measurement is crucial in the model construction by connecting the Galactic component to the extragalactic component. The precise measurements of CR spectra for individual species by AMS-02 and DAMPE together with the newest LHAASO results clearly indicates three Galactic CR components, that is, a soft low energy background, a hard high energy component, and a local source contribution. However, the LHAASO data show that above $\sim 10^{16}$ eV a nonnegligible extragalactic component must be included. Combining the Auger results and the LHAASO results we figure out the extragalactic CRs which need at least two components at lower and higher energies. Thanks to the precise measurements by LHAASO the constraints on the model parameters are quite stringent. The spectra features and mass measurements in all energy range are all well reproduced in the model.
Abstract: 2403.11387
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Title:Gamma-Ray Burst Pulses and Lateral Jet Motion
View PDF HTML (experimental)Abstract:We propose that gamma-ray burst pulses are produced when highly-relativistic jets sweep across an observer's line-of-sight. We hypothesize that axisymmetric jet profiles, coupled with special relativistic effects, produce the time-reversed properties of gamma-ray burst pulses. Curvature resulting from rapid jet expansion is responsible for much of the observed pulse asymmetry and hard-to-soft evolution. The relative obliqueness with which the jet crosses the line-of-sight explains the known GRB pulse morphological types. We explore two scenarios: one in which a rigid/semi-rigid jet moves laterally, and the other in which a ballistic jet sprays material from a laterally-moving nozzle. The ballistic jet model is favored based upon its consistency with standard emission mechanisms.
Abstract: 2403.10363
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Title:Spectroscopic Observations of the Solar Corona during the 2017 August 21 Total Solar Eclipse: Comparison of Spectral Line Widths and Doppler Shifts Between Open and Closed Magnetic Structures
View PDF HTML (experimental)Abstract:The spectroscopic observations presented here were acquired during the 2017 August 21 total solar eclipse with a three-channel partially multiplexed imaging spectrometer (3PAMIS) operating at extremely high orders ($>$ 50). The 4 $R_\odot$ extent of the slit in the North-South direction scanned the corona starting from the central meridian out to approximately 1.0 $R_\odot$ off the east limb throughout totality. The line widths and Doppler shifts of the Fe X (637.4 nm) and Fe XIV (530.3 nm) emission lines, characteristic of $1.1 \times 10^6$ K and $1.8 \times 10^6$ K electron temperatures respectively, varied across the different coronal structures intercepted by the slit. Fe XIV was the dominant emission in the closed fields of an active region and the base of a streamer, with relatively constant 20 - 30 km s$^{-1}$ line widths independent of the height. In contrast, Fe X emission exhibited broader ($>40 $km s$^{-1}$) line widths in open fields which increased with height, in particular in the polar coronal hole. Inferences of line widths and Doppler shifts were consistent with extreme ultraviolet (EUV) observations from Hinode/EIS, as well as with the near-infrared Fe XIII 1074 nm line observed by CoMP. The differences in the spectral line widths between distinct coronal structures are interpreted as an indication of the predominance of wave heating in open structures versus localized heating in closed structures. This study underscores the unparalleled advantages and the enormous potential of TSE spectroscopy in measuring line widths simultaneously in open and closed fields at high altitudes, with minimal exposure times, stray light levels, and instrumental widths.
Abstract: 2403.10010
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Title:Measurements of All-Particle Energy Spectrum and Mean Logarithmic Mass of Cosmic Rays from 0.3 to 30 PeV with LHAASO-KM2A
View PDF HTML (experimental)Abstract:We present the measurements of all-particle energy spectrum and mean logarithmic mass of cosmic rays in the energy range of 0.3-30 PeV using data collected from LHAASO-KM2A between September 2021 and December 2022, which is based on a nearly composition-independent energy reconstruction method, achieving unprecedented accuracy. Our analysis reveals the position of the knee at $3.67 \pm 0.05 \pm 0.15$ PeV. Below the knee, the spectral index is found to be -$2.7413 \pm 0.0004 \pm 0.0050$, while above the knee, it is -$3.128 \pm 0.005 \pm 0.027$, with the sharpness of the transition measured with a statistical error of 2%. The mean logarithmic mass of cosmic rays is almost heavier than helium in the whole measured energy range. It decreases from 1.7 at 0.3 PeV to 1.3 at 3 PeV, representing a 24% decline following a power law with an index of -$0.1200 \pm 0.0003 \pm 0.0341$. This is equivalent to an increase in abundance of light components. Above the knee, the mean logarithmic mass exhibits a power law trend towards heavier components, which is reversal to the behavior observed in the all-particle energy spectrum. Additionally, the knee position and the change in power-law index are approximately the same. These findings suggest that the knee observed in the all-particle spectrum corresponds to the knee of the light component, rather than the medium-heavy components.
Abstract: 2403.09824
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Title:The Fermi/eROSITA Bubbles: A look into the nuclear outflow from the Milky Way
View PDF HTML (experimental)Abstract:Galactic outflows are ubiquitous in galaxies containing active star formation or supermassive black hole activity. The presence of a large-scale outflow from the center of our own Galaxy was confirmed after the discovery of two large ($\sim 8-10$ kpc) \gamma-ray bubbles using the \textit{Fermi-LAT} telescope. These bubbles, known as the Fermi Bubbles, are highly symmetric about the Galactic disk as well as around the Galactic rotation axis and appear to emanate from the center of our Galaxy. The sharp edges of these bubbles suggest that they are related to the Galactic outflow. These bubbles are surrounded by two even bigger ($\sim 12-14$ kpc) X-ray structures, known as the eROSITA bubbles. Together, they represent the characteristics of an outflow from the Galaxy into the circumgalactic medium. Multi-wavelength observations such as in radio, microwave, and UV toward the Fermi Bubbles have provided us with much information in the last decade. However, the origin and the nature of these bubbles remain elusive. In this review, I summarize the observations related to the Fermi/eROSITA Bubbles at different scales and wavelengths, and give a brief overview of our current understanding of them.
Abstract: 2403.12942
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Title:The physics of Core-Collapse Supernovae: explosion mechanism and explosive nucleosynthesis
View PDF HTML (experimental)Abstract:Recent developments in multi-dimensional simulations of core-collapse supernovae have considerably improved our understanding of this complex phenomenon. In addition to that, one-dimensional (1D) studies have been employed to study the explosion mechanism and its causal connection to the pre-collapse structure of the star, as well as to explore the vast parameter space of supernovae. Nonetheless, many uncertainties still affect the late stages of the evolution of massive stars, their collapse, and the subsequent shock propagation. In this review, we will briefly summarize the state-of-the-art of both 1D and 3D simulations and how they can be employed to study the evolution of massive stars, supernova explosions, and shock propagation, focusing on the uncertainties that affect each of these phases. Finally, we will illustrate the typical nucleosynthesis products that emerge from the explosion.
Abstract: 2403.12872
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Title:H$α$/H$β$ a Galactic Low Energy Cosmic Rays tracer
View PDF HTML (experimental)Abstract:Context. Investigating the diagnostic power of H$\alpha$/H$\beta$ Charge-Exchange (CE) emission as Low-Energy Galactic Cosmic Rays(LECRs) tracer in diffuse regions. Aims. In this work, we define and test a spectroscopic indicator of CE reactions between LECRs protons and neutral hydrogen atoms of the diffuse medium. This indicator can be used for mapping LECRs density in diffuse clouds and can lead to the identification of new LECRs sources as we expect density variations caused by the distance between an observed cloud and the nearest site of particle acceleration. We also lay the foundations for the definition of a photometric indicator to be used in the next full-sky photometric surveys such as the Vera Rubin 10-year Legacy Survey of Space and Time (LSST). Methods. Based on literature cross-sections, we calculate H$\alpha$/H$\beta$ line profile ratio in the case of CE and compare it with the recombination ratio. We then test our results on the Balmer-dominated filaments of the SNR RCW 86 and we explore how the spectroscopic constraints can turn into a photometric indicator based on colour indices. Results. We find that, in shocked environments, CE between LECRS and neutral hydrogen become the dominant process for Balmer lines emission. The hydrogen spectroscopic emission is expected to be modified, with respect to the recombination Balmer decrement,to result in double the H$\alpha$/H$\beta$ with respect to a similar but quiescent region. The test on the known Balmer-dominated filaments of the SNR RCW 86 confirm the efficiency of our spectroscopic indicator. Therefore we explore possible conversions of the spectroscopic indicator into colour indices combinations. This is the first step toward the definition and test of a photometric indicator for tracing LECRs to be applied in the LSST pipelines to photometrically identify new LECRs accelerators in the whole Galaxy.
Abstract: 2403.13482
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Title:From known to unknown: cosmic rays transition from the Sun, the Galaxy, and the Extra-Galaxy
View PDF HTML (experimental)Abstract:The Sun stands out as the closest and clearest astrophysical accelerator of cosmic rays, while other objects within and beyond the galaxy remain enigmatic. It is probable that the cosmic ray spectrum and mass components from these celestial sources share similarities, offering a novel approach to study their origin. In this study, we analyze of spectra and mass in the energy range from MeV to 10~EeV. We find: (1) the mean-logarithmic mass $\rm\left\langle lnA \right\rangle$ distribution with energy exhibits much clearer feature structures than the spectra; (2) a 100~TeV bump is presented in the $\rm\left\langle lnA \right\rangle$ distribution; (3) for protons, the knee is located at $\sim2$ PeV, the boundary between the galaxy and extra-galaxy occurs at $\sim30$ PeV, marked by a sharp dip; (4) the all-particle spectrum exhibits hardening at $\sim30$~PeV due to the contribution of nearby galaxies, and the extra-galactic dominate $\sim0.7$~EeV. We hope the LHAASO experiment can perform spectral measurements of individual species to validate our results.
Abstract: 2403.13305
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Title:Shock and Cosmic Ray Chemistry Associated with the Supernova Remnant W28
View PDF HTML (experimental)Abstract:Supernova remnants (SNRs) exert strong influence on the physics and chemistry of the nearby molecular clouds (MCs) through shock waves and the cosmic rays (CRs) they accelerate. To investigate the SNR-cloud interaction in the prototype interacting SNR W28 (G6.4$-$0.1), we present new observations of $\rm HCO^+$, HCN and HNC $J=1\text{--}0$ lines, supplemented by archival data of CO isotopes, $\rm N_2H^+$ and $\rm H^{13}CO^+$. We compare the spatial distribution and spectral line profiles of different molecular species. Using local thermodynatic equilibrium (LTE) assumption, we obtain an abundance ratio $N({\rm HCO^+})/N({\rm CO})\sim10^{-4}$ in the northeastern shocked cloud, which is higher by an order of magnitude than the values in unshocked clouds. This can be accounted for by the chemistry jointly induced by shock and CRs, with the physical parameters previously obtained from observations: preshock density $n_{\rm H}\sim 2\times 10^{5}\rm \ cm^{-3}$, CR ionization rate $\zeta=2.5\times 10^{-15} \rm \ s^{-1}$ and shock velocity $V_{\rm s}=15\text{--}20\rm \ km\ s^{-1}$. Towards a point outside the northeastern boundary of W28 with known high CR ionization rate, we estimate the abundance ratio $ N({\rm HCO^+})/N({\rm N_2H^+}) \approx 0.6\text{--}3.3$, which can be reproduced by a chemical simulation if a high density $n_{\rm H}\sim 2\times 10^5 \ \rm cm^{-3}$ is adopted.
Abstract: 2403.13933
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Title:Joint Deconvolution of Astronomical Images in the Presence of Poisson Noise
View PDF HTML (experimental)Abstract:We present a new method for joint likelihood deconvolution (Jolideco) of a set of astronomical observations of the same sky region in the presence of Poisson noise. The observations may be obtained from different instruments with different resolution, and different point spread functions. Jolideco reconstructs a single flux image by optimizing the posterior distribution based on the joint Poisson likelihood of all observations under a patch-based image prior. The patch prior is parameterised via a Gaussian Mixture model which we train on high-signal-to-noise astronomical images, including data from the James Webb Telescope and the GLEAM radio survey. This prior favors correlation structures among the reconstructed pixel intensities that are characteristic of those observed in the training images. It is, however, not informative for the mean or scale of the reconstruction. By applying the method to simulated data we show that the combination of multiple observations and the patch-based prior leads to much improved reconstruction quality in many different source scenarios and signal to noise regimes. We demonstrate that with the patch prior Jolideco yields superior reconstruction quality relative to alternative standard methods such as the Richardson-Lucy method. We illustrate the results of Jolideco applied to example data from the Chandra X-ray Observatory and the Fermi-LAT Gamma-ray Space Telescope. By comparing the measured width of a counts based and the corresponding Jolideco flux profile of an X-ray filament in SNR 1E 0102.2-721} we find the deconvolved width of 0.58+- 0.02 arcsec to be consistent with the theoretical expectation derived from the known width of the PSF.
Abstract: 2403.13723
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Title:Examining a hadronic $γ$-ray scenario for the radiative shell & molecular clouds of the old GeV supernova remnant G298.6$-$0.0
View PDFAbstract:Based on the 13.7~yr Fermi-LAT data, Yeung et al. (2023) claimed detection of two $\gamma$-ray sources (Src-NE and Src-NW) associated with the supernova remnant (SNR) G298.6$-$0.0, and interpreted it as an old GeV SNR interacting with molecular clouds (MCs). In this follow-up study, we refine the flux measurements below 2~GeV with Fermi-LAT event types of better angular reconstruction. Then, we report our cosmic-ray phenomenology in a hadronic scenario, considering both the shell and MC regions of SNR G298.6$-$0.0. We confirm that both the $\gamma$-ray spectra of Src-NE and Src-NW exhibit spectral breaks at $1.50_{-0.50}^{+0.60}$~GeV and $0.68_{-0.11}^{+0.32}$~GeV, respectively. Src-NW has a harder broadband photon index than Src-NE, suggesting an appreciable difference between the physical separations of their respective emission sites from SNR G298.6$-$0.0. The cosmic-ray spectrum responsible for Src-NE starts with a minimum energy $E_\mathrm{CR,min}=1.38_{-0.16}^{+0.47}$~GeV, and has a proton index $\Gamma_\mathrm{CR}=2.57_{-0.21}^{+0.18}$ below the exponential cutoff energy $E_\mathrm{CR,max}=240_{-150}^{+240}$~GeV. Accordingly, we argue that Src-NE is dominated by the SNR shell, while only a minor portion of lower-energy emission is contributed by the MCs interacting with the SNR. The cosmic-ray population for Src-NW starts at a higher energy such that the $E_\mathrm{CR,min}$ ratio of Src-NW to Src-NE is $\gtrsim$2. The high $E_\mathrm{CR,min}$, as well as the high cosmic-ray energy density required ($\sim$26~eV~cm$^{-3}$), supports the interpretation that Src-NW is predominantly the $\gamma$-ray emission from the farther MCs being bombarded by protons that had earlier escaped from SNR G298.6$-$0.0. By comparing the high-energy features of G298.6$-$0.0 with those of analogical SNRs, especially SNR W28 and SNR W44, we further constrain the age of SNR G298.6$-$0.0 to be 10--30~kyr.
Abstract: 2403.12608
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Title:Spectrum and extension of the inverse-Compton emission of the Crab Nebula from a combined Fermi-LAT and H.E.S.S. analysis
View PDF HTML (experimental)Abstract:The Crab Nebula is a unique laboratory for studying the acceleration of electrons and positrons through their non-thermal radiation. Observations of very-high-energy $\gamma$ rays from the Crab Nebula have provided important constraints for modelling its broadband emission. We present the first fully self-consistent analysis of the Crab Nebula's $\gamma$-ray emission between 1 GeV and $\sim$100 TeV, that is, over five orders of magnitude in energy. Using the open-source software package Gammapy, we combined 11.4 yr of data from the Fermi Large Area Telescope and 80 h of High Energy Stereoscopic System (H.E.S.S.) data at the event level and provide a measurement of the spatial extension of the nebula and its energy spectrum. We find evidence for a shrinking of the nebula with increasing $\gamma$-ray energy. Furthermore, we fitted several phenomenological models to the measured data, finding that none of them can fully describe the spatial extension and the spectral energy distribution at the same time. Especially the extension measured at TeV energies appears too large when compared to the X-ray emission. Our measurements probe the structure of the magnetic field between the pulsar wind termination shock and the dust torus, and we conclude that the magnetic field strength decreases with increasing distance from the pulsar. We complement our study with a careful assessment of systematic uncertainties.
Abstract: 2403.13902
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Title:Lepto-Hadronic Scenarios for TeV Extensions of Gamma-Ray Burst Afterglow Spectra
View PDF HTML (experimental)Abstract:Recent multi-wavelength observations of gamma-ray burst afterglows observed in the TeV energy range challenge the simplest Synchrotron Self-Compton (SSC) interpretation of this emission, and are consistent with a single power-law component spanning over eight orders of magnitude in energy. To interpret this generic behaviour in the single-zone approximation without adding further free parameters, we perform an exhaustive parameter space study using the public, time-dependent, multi-messenger transport software AM3. This description accounts for the radiation from non-thermal protons and the lepto-hadronic cascade induced by pp- and p{\gamma}-interactions. We summarise the main scenarios which we have found (SSC, Extended-syn, Proton-syn, pp-cascade, and p{\gamma}-cascade), and discuss their advantages and limitations. We find that possible high-density environments, as may be typical for surrounding molecular cloud material, offer an alternative explanation for producing flat hard (source) spectra up to and beyond energies of 10 TeV.
Abstract: 2403.11524
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Title:Probing cold gas with Mg II and Ly$α$ radiative transfer
View PDFAbstract:The Mg II resonance doublet at 2796 Å and 2803 Å is an increasingly important tool to study cold, $T \sim 10^{4}\,$K, gas -- an observational driven development requiring theoretical support. We develop a new Monte Carlo radiative transfer code to systematically study the joined Mg II and Ly$\alpha$ escape through homogeneous and `clumpy' multiphase gas with dust in arbitrary 3D geometries. Our main findings are: (i) The Mg II spectrum differs from Ly$\alpha$ due to the large difference in column densities, even though the atomic physics of the two lines are similar. (ii) the Mg II escape fraction is generally higher than that of Ly$\alpha$ because of lower dust optical depths and path lengths -- but large variations due to differences in dust models and the clumpiness of the cold medium exist. (iii) Clumpy media possess a `critical covering factor' above which Mg II radiative transfer matches a homogeneous medium. The critical covering factors for Mg II and Ly$\alpha$ differ, allowing constraints on the cold gas structure. (iv) The Mg II doublet ratio $R_{\rm MgII}$ varies for strong outflows/inflows ($\gtrsim 700 \mathrm{km\,s}^{-1}$), in particular, $R_{\rm MgII}<1$ being an unambiguous tracer for powerful galactic winds. (v) Scattering of stellar continuum photons can decrease $R_{\rm MgII}$ from two to one, allowing constraints on the scattering medium. Notably, we introduce a novel probe of the cold gas column density -- the halo doublet ratio -- which we show to be a powerful indicator of ionizing photon escape. We discuss our results in the context of interpreting and modeling observations as well as their implications for other resonant doublets.
Abstract: 2403.13265
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Title:LHS 1140 b is a potentially habitable water world
Download PDF HTML (experimental)Abstract:LHS 1140 b is a small planet orbiting in the habitable zone of its M4.5V dwarf host. Recent mass and radius constraints have indicated that it has either a thick H$_2$-rich atmosphere or substantial water by mass. Here we present a transmission spectrum of LHS 1140 b between 1.7 and 5.2 $\mu$m, obtained using the NIRSpec instrument on JWST. By combining spectral retrievals and self-consistent atmospheric models, we show that the transmission spectrum is inconsistent with H$_2$-rich atmospheres with varied size and metallicity, leaving a water world as the remaining scenario to explain the planet's low density. Specifically, a H$_2$-rich atmosphere would result in prominent spectral features of CH$_4$ or CO$_2$ on this planet, but they are not seen in the transmission spectrum. Instead, the data favors a high-mean-molecular-weight atmosphere (possibly N$_2$-dominated with H$_2$O and CO$_2$) with a modest confidence. Forming the planet by accreting C- and N-bearing ices could naturally give rise to a CO$_2$- or N$_2$-dominated atmosphere, and if the planet evolves to or has the climate-stabilizing mechanism to maintain a moderate-size CO$_2$/N$_2$-dominated atmosphere, the planet could have liquid-water oceans. Our models suggest CO$_2$ absorption features with an expected signal of 20 ppm at 4.2 $\mu$m. As the existence of an atmosphere on TRAPPIST-1 planets is uncertain, LHS 1140 b may well present the best current opportunity to detect and characterize a habitable world.
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