Radiative Transfer Code Research Articles

ZTF SN Ia DR2: The spectral diversity of Type Ia supernovae in a volume-limited sample

More than 3000 spectroscopically confirmed Type Ia supernovae (SNe Ia) are presented in the second data release (DR2) of the Zwicky Transient Facility survey. In this paper we detail the spectral properties of 482 SNe Ia near maximum light, up to a redshift limit of z leq 0.06. We measured the velocities and pseudo-equivalent widths (pEW) of key spectral features ( and and investigated the relation between the properties of the spectral features and the photometric properties from the SALT2 light-curve parameters as a function of spectroscopic sub-class. We discuss the non-negligible impact of host galaxy contamination on SN Ia spectral classifications, and we investigate the accuracy of spectral template matching of the DR2 sample. We define a new subclass of underluminous SNe Ia (04gs-like) that lie spectroscopically between normal SNe Ia and transitional 86G-like SNe Ia (stronger than normal SNe Ia, but significantly weaker features than 86G-like SNe). We model these 04gs-like SN Ia spectra using the radiative-transfer spectral synthesis code tardis and show that cooler temperatures alone are unable to explain their spectra; some changes in elemental abundances are also required. However, the broad continuity in spectral properties seen from bright (91T-like) to faint normal SN Ia, including the transitional and 91bg-like SNe Ia, suggests that variations within a single explosion model may be able to explain their behaviour.

The grazing-angle icy protoplanetary disk PDS 453

Observations of highly inclined protoplanetary disks provide a different point of view, in particular, they provide a more direct access to the vertical disk structure when compared to less steeply inclined more pole-on disks. PDS 453 is a rare highly inclined disk where the stellar photosphere is seen at grazing incidence on the disk surface. Our goal is take advantage of this geometry to constrain the structure and composition of this protoplanetary disk. In particular, it shows a 3.1\,mu m water-ice band in absorption that can be uniquely related to the disk. We observed the system in polarized intensity with the VLT/SPHERE instrument, as well as in polarized light and total intensity using the HST/NICMOS camera. Infrared archival photometry and a spectrum showing the water-ice band were used to model the spectral energy distribution under the Mie scattering theory. Based on these data, we fit a model using the radiative transfer code MCFOST to retrieve the geometry and dust and ice content of the disk. PDS 453 has the typical morphology of a highly inclined system with two reflection nebulae in which the disk partially attenuates the stellar light. The upper nebula is brighter than the lower nebula and shows a curved surface brightness profile in polarized intensity. This indicates a ring-like structure. With an inclination of 80° estimated from models, the line of sight crosses the disk surface, and a combination of absorption and scattering by ice-rich dust grains produces the water-ice band. PDS 453 is seen at high inclination and is composed of a mixture of silicate dust and water ice. The radial structure of the disk includes a significant jump in density and scale height at a radius of 70 au that produces a ring-like image. The depth of the 3.1\,mu m water-ice band depends on the amount of water ice, until it saturates when the optical thickness along the line of sight becomes too large. Therefore, quantifying the exact amount of water from absorption bands in edge-on disks requires a detailed analysis of the disk structure and tailored radiative transfer modeling. Further observations with JWST and ALMA will allow us to refine our understanding of the structure and content of this interesting system.

A fully coupled solid-particle microphysics scheme for stratospheric aerosol injections within the aerosol–chemistry–climate model SOCOL-AERv2

Abstract. Recent studies have suggested that injection of solid particles such as alumina and calcite particles for stratospheric aerosol injection (SAI) instead of sulfur-based injections could reduce some of the adverse side effects of SAI such as ozone depletion and stratospheric heating. Here, we present a version of the global aerosol–chemistry–climate model SOCOL-AERv2 and the Earth system model (ESM) SOCOLv4 which incorporate a solid-particle microphysics scheme for assessment of SAI of solid particles. Microphysical interactions of the solid particle with the stratospheric sulfur cycle were interactively coupled to the heterogeneous chemistry scheme and the radiative transfer code (RTC) for the first time within an ESM. Therefore, the model allows simulation of heterogeneous chemistry at the particle surface as well as feedbacks between microphysics, chemistry, radiation and climate. We show that sulfur-based SAI results in a doubling of the stratospheric aerosol burden compared to the same mass injection rate of calcite and alumina particles with a radius of 240 nm. Most of the sulfuric acid aerosol mass resulting from SO2 injection does not need to be lifted to the stratosphere but is formed after in situ oxidation and subsequent water uptake in the stratosphere. Therefore, to achieve the same radiative forcing, larger injection rates are needed for calcite and alumina particle injection than for sulfur-based SAI. The stratospheric sulfur cycle would be significantly perturbed, with a reduction in stratospheric sulfuric acid burden by 53 %, when injecting 5 Mt yr−1 (megatons per year) of alumina or calcite particles of 240 nm radius. We show that alumina particles will acquire a sulfuric acid coating equivalent to about 10 nm thickness if the sulfuric acid is equally distributed over the whole available particle surface area in the lower stratosphere. However, due to the steep contact angle of sulfuric acid on alumina particles, the sulfuric acid coating would likely not cover the entire alumina surface, which would result in available surface for heterogeneous reactions other than the ones on sulfuric acid. When applying realistic uptake coefficients of 1.0, 10−5 and 10−4 for H2SO4, HCl and HNO3, respectively, the same scenario with injections of calcite particles results in 94 % of the particle mass remaining in the form of CaCO3. This likely keeps the optical properties of the calcite particles intact but could significantly alter the heterogeneous reactions occurring on the particle surfaces. The major process uncertainties of solid-particle SAI are (1) the solid-particle microphysics in the injection plume and degree of agglomeration of solid particles on the sub-ESM grid scale, (2) the scattering properties of the resulting agglomerates, (3) heterogeneous chemistry on the particle surface, and (4) aerosol–cloud interactions. These uncertainties can only be addressed with extensive, coordinated experimental and modelling research efforts. The model presented in this work offers a useful tool for sensitivity studies and incorporating new experimental results on SAI of solid particles.

Extension of the multilevel radiative transfer code PyRaTE to model linear polarization of molecular lines

Linear polarization of spectral lines, commonly known as the Goldreich-Kylafis effect within the star formation community, is one of the most underutilized techniques for probing magnetic fields in the dense and cold interstellar medium. In this study, we implement linear polarization of molecular spectral lines into the multilevel, non-local thermodynamic equilibrium radiative transfer code PyRaTE Different modes of polarized radiation are treated individually, with separate optical depths computed for each polarization direction. Our implementation is valid in the so-called strong magnetic field limit and is exact for either a system satisfying the large-velocity-gradient approximation, and/or for any system with a uniform magnetic field. We benchmark our implementation against analytical results and provide tests for various limiting cases. In agreement with previous theoretical results, we find that in the multilevel case the amount of fractional polarization decreases when compared to the two-level approximation, but this result is subject to the relative importance between radiative and collisional processes. Finally, we post-process an axially symmetric, nonideal magnetohydrodynamic chemo-dynamical simulation of a collapsing prestellar core and provide theoretical predictions regarding the shape (as a function of velocity) of the polarization fraction of $ CO $ during the early stages in the evolution of molecular clouds.

Impact of Systematic Modeling Uncertainties on Kilonova Property Estimation

The precise atomic structure and therefore the wavelength-dependent opacities of lanthanides are highly uncertain. This uncertainty introduces systematic errors in modeling transients like kilonovae and estimating key properties such as mass, characteristic velocity, and heavy metal content. Here, we quantify how atomic data from across the literature as well as choices of thermalization efficiency of r-process radioactive decay heating impact the light curve and spectra of kilonovae. Specifically, we analyze the spectra of a grid of models produced by the radiative transfer code Sedona that span the expected range of kilonova properties to identify regions with the highest systematic uncertainty. Our findings indicate that differences in atomic data have a substantial impact on estimates of lanthanide mass fraction, spanning approximately 1 order of magnitude for lanthanide-rich ejecta, and demonstrate the difficulty in precisely measuring the lanthanide fraction in lanthanide-poor ejecta. Mass estimates vary typically by 25%–40% for differing atomic data. Similarly, the choice of thermalization efficiency can affect mass estimates by 20%–50%. Observational properties such as color and decay rate are highly model dependent. Velocity estimation, when fitting solely based on the light curve, can have a typical error of ∼100%. Atomic data of light r-process elements can strongly affect blue emission. Even for well-observed events like GW170817, the total lanthanide production estimated using different atomic data sets can vary by a factor of ∼6.

A public grid of radiative transfer simulations for Lyα and metal lines in idealised galactic outflows

The vast majority of star-forming galaxies are surrounded by large reservoirs of gas ejected from the interstellar medium. Ultraviolet absorption and emission lines represent powerful diagnostics to constrain the cool phase of these outflows, through resonant transitions of hydrogen and metal ions. The interpretation of these observations is often remarkably difficult as it requires detailed modelling of the propagation of the continuum and emission lines in the gas. To this aim, we present a large public grid of ≈20 000 simulated spectra that includes H I Lyα and five metal transitions associated with Mg II, C II, Si II, and Fe II which is accessible online. The spectra have been computed with the RASCAS Monte Carlo radiative transfer code for 5760 idealised spherically symmetric configurations surrounding a central point source emission, and characterised by their column density, Doppler parameter, dust opacity, wind velocity, as well as various density and velocity gradients. Designed to predict and interpret Lyα and metal line profiles, our grid exhibits a wide diversity of resonant absorption and emission features, as well as fluorescent lines. We illustrate how it can help better constrain the wind properties by performing a joint modelling of observed Lyα, C II, and Si II spectra. Using CLOUDY simulations and virial scaling relations, we also show that Lyα is expected to be a faithful tracer of the gas at T ≈ 104 − 105 K, even if the medium is highly ionised. While C II is found to probe the same range of temperatures as Lyα, other metal lines merely trace cooler phases (T ≈ 104 K). As their gas opacity strongly depends on gas temperature, incident radiation field, metallicity and dust depletion, we caution that optically thin metal lines do not necessarily originate from low H I column densities and may not accurately probe Lyman continuum leakage.

Kinematical signatures: Distinguishing between warps and radial flows

Increasing evidence shows that warped disks are common, challenging the methods used to model their velocity fields. Molecular line emission of these disks is characterized by a twisted pattern, similar to the signal from radial flows, complicating the study of warped disk kinematics. Previous attempts to model these features have encountered difficulties in distinguishing between the underlying kinematics of different disks. This study aims to advance gas kinematics modeling capabilities by extending the Extracting Disk Dynamics ( eddy ) package to include warped geometries and radial flows. We assess the performance of eddy in recovering input parameters for scenarios involving warps, radial flows, and combinations of the two. Additionally, we provide a basis to break the visual degeneracy between warped disks and radial flow, establishing a criterion to distinguish them. We extended the eddy package to handle warped geometries by including a parametric prescription of a warped disk and a ray-casting algorithm to account for the surface self-obscuration arising from the 3D to 2D projection. The effectiveness of the tool was tested using the radiative transfer code RADMC3D generating synthetic models for disks with radial flows, warped disks, and warped disks with radial flows. We demonstrate the efficacy of our tool in accurately recovering the geometrical parameters of systems, particularly in data with sufficient angular resolution. Importantly, we observe minimal impact from thermal noise levels typical in Atacama Large Millimeter/submillimeter Array (ALMA) observations. Furthermore, our findings reveal that fitting an incorrect model type produces characteristic residual signatures, which serve as kinematic criteria for disk classification. Characterizing gas kinematics requires careful consideration of twisted motions. While our model provides insights into disk geometries, caution is needed when interpreting parameters in regions with complex kinematics or low-resolution data. Future ALMA baseline observations should help clarify warped disk kinematics.

Chromospheric Modeling of the Active M3V Star G 80–21 with RH1.5D

This study investigates the active regions of the M3.0V star G 80–21 using the observed data from the CARMENES project with synthetic spectra generated by the RH1.5D radiative transfer code. The CARMENES project aims to search for exoplanets around M dwarfs using high-resolution near-infrared and optical echelle spectrographs. By comparing the observed data and models for the chromospheric lines of H α and the bluest Ca ii infrared triplet line, we obtain the best-fit models for this star. The optimal fitting for the observed spectrum of G 80–21 is achieved by employing two active areas in conjunction with an inactive region, with a calcium abundance of [Ca/H] = −0.4. This combination successfully fits all the observed data across varying ratios. The minor active component consistently comprises approximately 18% of the total (ranging from 14% to 20%), which suggests that the minor active component is likely located in the polar regions. Meanwhile, the major active component occupies a variable proportion, ranging from 51% to 82%. Our method allows for the determination of the structure and size of stellar chromospheric active regions by analyzing high-resolution observed spectra.

Mg II h&k spectra of an enhanced network region simulated with the MURaM-ChE code. Results using 1.5D synthesis

The lines are key diagnostics of the solar chromosphere. They are sensitive to the temperature, density, and nonthermal velocities in the chromosphere. The average line profiles arising from previous 3D chromospheric simulations are too narrow compared to observations. We study the formation and properties of the lines in a model atmosphere. We also compare the average spectrum, peak intensity, and peak separation of with a representative observation taken by the Interface Region Imaging Spectrograph (IRIS). We use a model based on the recently developed nonequilibrium version of the radiative magneto-hydrodynamics code MURaM, the MURaM Chromospheric Extension ( in combination with forward modeling using the radiative transfer code RH1.5D to obtain synthetic spectra. Our model resembles an enhanced network region created using an evolved MURaM quiet Sun simulation and adding an imposed large-scale bipolar magnetic field similar to that in the public Bifrost snapshot of a bipolar magnetic feature. The line width and the peak separation of the spatially averaged spectrum of the lines from the simulation are close to a representative observation of the quiet Sun, which also includes network fields. However, we find the synthesized line width to be still slightly narrower than in the observation. We find that velocities in the chromosphere play a dominant role in the broadening of the spectral lines. While the average synthetic spectrum also shows a good match to the observations in the pseudo continuum between the two emission lines, the peak intensities are higher in the modeled spectrum. This discrepancy may be due in part to the larger magnetic flux density in the simulation than in the considered observations, but could also be a result of the 1.5D radiative transfer approximation. Our findings show that strong maximum-velocity differences or turbulent velocities in the chromosphere and lower atmosphere are necessary to reproduce the observed line widths of chromospheric spectral lines.

Magnetic Fields in a Sample of Planet-hosting M Dwarf Stars from Kepler, K2, and TESS Observed by APOGEE

Stellar magnetic fields have a major impact on space weather around exoplanets orbiting low-mass stars. From an analysis of Zeeman-broadened Fe i lines measured in near-infrared SDSS/APOGEE spectra, mean magnetic fields are determined for a sample of 29 M dwarf stars that host closely orbiting small exoplanets. The calculations employed the radiative transfer code Synmast and MARCS stellar model atmospheres. The sample M dwarfs are found to have measurable mean magnetic fields ranging between ∼0.2 and ∼1.5 kG, falling in the unsaturated regime on the 〈B〉 versus P rot plane. The sample systems contain 43 exoplanets, which include 23 from Kepler, nine from K2, and nine from Transiting Exoplanet Survey Satellite. We evaluated their equilibrium temperatures, insolation, and stellar habitable zones and found that only Kepler-186f and TOI-700d are inside the habitable zones of their stars. Using the derived values of 〈B〉 for the stars Kepler-186 and TOI-700 we evaluated the minimum planetary magnetic field that would be necessary to shield the exoplanets Kepler-186f and TOI-700d from their host star’s winds, considering reference magnetospheres with sizes equal to those of the present-day and young Earth, respectively. Assuming a ratio of 5% between large- to small-scale B-fields, and a young-Earth magnetosphere, Kepler-186f and TOI-700d would need minimum planetary magnetic fields of, respectively, 0.05 and 0.24 G. These values are considerably smaller than Earth’s magnetic field of 0.25 G ≲ B ≲ 0.65 G, which suggests that these two exoplanets might have magnetic fields sufficiently strong to protect their atmospheres and surfaces from stellar magnetic fields.

Hot spots around Sagittarius A*. Joint fits to astrometry and polarimetry

Observations of Sagittarius A* ( in the near-infrared (NIR) show irregular flaring activity. Flares coincide with the astrometric rotation of the brightness centroid and with looping patterns in fractional linear polarization. These signatures can be explained with a model of a bright hot spot, transiently orbiting the black hole. We extend the capabilities of the existing algorithms to perform parameter estimation and model comparison in the Bayesian framework using NIR observations from the GRAVITY instrument, and simultaneously fitting the astrometric and polarimetric data. Using the numerical radiative transfer code we defined several geometric models describing a hot spot orbiting Sgr A*, threaded with a magnetic field, and emitting synchrotron radiation. We then explored the posterior space of our models with a nested sampling code We used Bayesian evidence to make comparisons between the models. We have used 11 models to sharpen our understanding of the importance of various aspects of the orbital model, such as non-Keplerian motion, hot-spot size, and off-equatorial orbit. All considered models converge to realizations that fit the data well, but the equatorial super-Keplerian model is favoured by the currently available NIR dataset. We have inferred an inclination of $ deg, which corroborates previous estimates, a preferred period of $ minutes, and an orbital radius of $ gravitational radii with the orbital velocity of $ times the Keplerian value. A hot spot with a diameter smaller than 5 gravitational radii is favoured. Black hole spin is not constrained well.

Toward a robust physical and chemical characterization of heterogeneous lines of sight: The case of the Horsehead nebula

Dense and cold molecular cores and filaments are surrounded by an envelope of translucent gas. Some of the low- J emission lines of and isotopologues are more sensitive to the conditions either in the translucent environment or in the dense and cold one because their intensities result from a complex interplay of radiative transfer and chemical properties of these heterogeneous lines of sight (LoSs). We extend our previous single-zone modeling with a more realistic approach that introduces multiple layers to take account of possibly varying conditions along the LoS. We used the IRAM-30m data from the ORION-B large program toward the Horsehead nebula in order to demonstrate our method's capability and effectiveness. We propose a cloud model composed of three homogeneous slabs of gas along each LoS, representing an outer envelope and a more shielded inner layer. We used the non-LTE radiative transfer code RADEX to model the line profiles from the kinetic temperature ( the volume density ( kinematics, and chemical properties of the different layers. We then used a fast and robust maximum likelihood estimator to simultaneously fit the observed lines of the and isotopologues. To limit the variance on the estimates, we propose a simple chemical model by constraining the column densities. A single-layer model cannot reproduce the spectral line asymmetries that result from a combination of different radial velocities and absorption effects among layers. A minimal heterogeneous model (three layers only) is sufficient for the Horsehead application, as it provides good fits of the seven fitted lines over a large part of the studied field of view. The decomposition of the intensity into three layers allowed us to discuss the distribution of the estimated physical or chemical properties along the LoS. About 80<!PCT!> of the integrated intensity comes from the outer envelope, while $ of the integrated intensity of the and lines of comes from the inner layer. For the lines of the and the isotopologues, integrated intensities are more equally distributed over the cloud layers. The estimated column density ratio NCeiO in the envelope increases with decreasing visual extinction, and it reaches $25$ in the pillar outskirts. While the inferred of the envelope varies from $25$ to K$ that of the inner layer drops to K$ in the western dense core. The estimated in the inner layer is pccm$ toward the filament, and it increases by a factor of ten toward dense cores. Our proposed method correctly retrieves the physical and chemical properties of the Horsehead nebula. It also offers promising prospects for less supervised model fits of wider-field datasets.

Slick: Modeling a Universe of Molecular Line Luminosities in Hydrodynamical Simulations

We present slick (the Scalable Line Intensity Computation Kit), a software package that calculates realistic CO, [C i], and [C ii] luminosities for clouds and galaxies formed in hydrodynamic simulations. Built on the radiative transfer code despotic, slick computes the thermal, radiative, and statistical equilibrium in concentric zones of model clouds, based on their physical properties and individual environments. We validate our results by applying slick to the high-resolution run of the Simba simulations, testing the derived luminosities against empirical and theoretical/analytic relations. To simulate the line emission from a universe of emitting clouds, we have incorporated random forest machine learning (ML) methods into our approach, allowing us to predict cosmologically evolving properties of CO, [C i], and [C ii] emission from galaxies such as luminosity functions. We tested this model in 100,000 gas particles, and 2500 galaxies, reaching an average accuracy of ∼99.8% for all lines. Finally, we present the first model light cones created with realistic and ML-predicted CO, [C i], and [C ii] luminosities in cosmological hydrodynamical simulations, from z = 0 to z = 10.

Parameter study for hot spot trajectories around SgrA*

Context. Intense flaring events in the near-infrared and X-ray wavebands of our Galactic center have been the subject of research for decades. In recent years, the GRAVITY instrument of the Very Large Telescope captured the motion and polarimetric signature of such a flare in close proximity to the supermassive black hole. Aims. This study aims to investigate a broad parameter space for hot spot motion in the vicinity of SgrA* and reproduce the observed flaring behavior. Methods. To this end, we have developed a general relativistic radiative transfer code and conducted a parameter study including both planar and ejected hot spot configurations around supermassive black holes. Results. Super-Keplerian orbital frequencies are favored by circular equatorial, cylindrical and parabolic models, whereas conical hot spot trajectories provide a better fit for orbital frequencies below the Keplerian value. Additionally, a distant observer cannot effectively differentiate between Schwarzschild and Kerr black holes, as well as face-on orbits at different observation angles.

Photospheric Prompt Emission from Long Gamma Ray Burst Simulations. III. X-Ray Spectropolarimetry

While gamma-ray bursts (GRBs) have the potential to shed light on the astrophysics of jets, compact objects, and cosmology, a major set back in their use as probes of these phenomena stems from our incomplete knowledge surrounding their prompt emission. There are numerous models that can account for various observations of GRBs in the gamma-ray and X-ray energy ranges, due to the flexibility in the number of parameters that can be tuned to increase agreement with data. Furthermore, these models lack predictive power that can test future spectropolarimetric observations of GRBs across the electromagnetic spectrum. In this work, we use the MCRaT radiative transfer code to calculate the X-ray spectropolarimetric signatures expected from the photospheric model for two unique hydrodynamic simulations of long GRBs. We make time-resolved and time-integrated comparisons between the X-ray and gamma-ray mock observations, shedding light on the information that can be obtained from X-ray prompt emission signatures. Our results show that the T 90 derived from the X-ray light curve is the best diagnostic for the time that the central engine is active. We also find that our simulations reproduce the observed characteristics of the Einstein Probe–detected GRB 240315C. Based on our simulations, we are also able to make predictions for future X-ray spectropolarimetric measurements. Our results show the importance of conducting global radiative transfer calculations of GRB jets to better contextualize the prompt emission observations and constrain the mechanisms that produce the prompt emission.

Evidence for Surprising Heavy Nitrogen Isotopic Enrichment in Comet 46P/Wirtanen’s Hydrogen Cyanide

46P/Wirtanen is a Jupiter-family comet, probably originating from the solar system’s Kuiper Belt, that now resides on a 5.4 yr elliptical orbit. During its 2018 apparition, comet 46P passed unusually close to the Earth (within 0.08 au), presenting an outstanding opportunity for close-up observations of its inner coma. Here we present observations of HCN, H13CN, and HC15N emission from 46P using the Atacama Compact Array. The data were analyzed using the SUBLIME non-LTE radiative transfer code to derive 12C/13C and 14N/15N ratios. The HCN/H13CN ratio is found to be consistent with a lack of significant 13C fractionation, whereas the HCN/HC15N ratio of 68 ± 27 (using our most conservative 1σ uncertainties), indicates a strong enhancement in 15N compared with the solar and terrestrial values. The observed 14N/15N ratio is also significantly lower than the values of ∼140 found in previous comets, implying a strong 15N enrichment in 46P’s HCN. This indicates that the nitrogen in Jupiter-family comets could reach larger isotopic enrichments than previously thought, with implications for the diversity of 14N/15N ratios imprinted into icy bodies at the birth of the solar system.

Modeling Multiband SEDs and Light Curves of BL Lacertae Using a Time-dependent Shock-in-jet Model

The origin of fast flux variability in blazars is a long-standing problem, with many theoretical models proposed to explain it. In this study, we focus on BL Lacertae to model its spectral energy distribution (SED) and broadband light curves using a diffusive shock acceleration process involving multiple mildly relativistic shocks, coupled with a time-dependent radiation transfer code. BL Lacertae was the target of a comprehensive multiwavelength monitoring campaign in early 2021 July. We present a detailed investigation of the source’s broadband spectral and light-curve features using simultaneous observations at optical–UV frequencies with the Swift Ultraviolet/Optical Telescope, in X-rays with the Swift X-Ray Telescope and AstroSat-SXT/LAXPC, and in gamma rays with Fermi-LAT, covering the period from 2021 July to August (MJD 59400–59450). A fractional variability analysis shows that the source is most variable in gamma rays, followed by X-rays, UV, and optical. This allowed us to determine the fastest variability time in gamma rays to be on the order of a few hours. The AstroSat-SXT and LAXPC light curves indicate X-ray variability on the order of a few kiloseconds. Modeling simultaneously the SEDs of low- and high-flux states of the source and the multiband light curves provided insights into the particle acceleration mechanisms at play. This is the first instance of a physical model that accurately captures the multiband temporal variability of BL Lacertae, including the hour-scale fluctuations observed during the flare.

X-ray view of dissipative warm corona in active galactic nuclei

Context. Detections of the X-ray spectra of active galactic nuclei (AGNs) typically reveal a noticeable excess of soft X-rays beyond the extrapolation of the power-law trend observed between 2 and 10 keV. However, the cause of this surplus remains unclear. In the scenario of soft Comptonization, observations suggest a warm corona temperature, ranging from 0.1 to 1 keV, and an optical depth of approximately 10 to 30. Furthermore, according to radiative constraints derived from spectral analyses employing Comptonization models, it has been suggested that most of the accretion power is released within the warm corona. At the same time, the disk beneath it is largely non-dissipative, mainly emitting the reprocessed radiation from the corona. Aims. We tested the dissipative warm corona model using the radiative transfer code TITAN-NOAR on a sample of 82 XMM-Newton EPIC-pn observations of 21 AGNs. Based on a spectral modeling of the X-ray data, we aim to estimate the total amount of internal heating inside the warm corona on top of the accretion disk. Methods. By modeling the 0.3–10 keV EPIC-pn spectra with the TITAN-NOAR model component, we estimated the internal heating and optical depth of the warm corona and checked their correlations with such global parameters as the hot corona spectral index, black hole mass, and accretion rate. From the model normalization, we computed the radial extent of the warm corona on top of the cold accretion disk. Results. Our model infers the presence of dissipative warm corona, with optical depths distributed across the range of ∼6–30 and a total internal heating in the range of ∼1–29 × 10−23 erg s−1 cm3. We do not detect any variation between these properties and global properties, such as the black hole mass and accretion rate. The extent of the warm corona is spread across a broad range, from 7–408 gravitational radii, and we find that the warm corona is more extended for higher accretion rates. Conclusions. Soft excess emission is ubiquitous across a wide mass range and accretion rate in AGNs. We confirm that the warm corona responsible for producing the soft X-ray excess is highly dissipative with greater optical depths being associated with lower internal heating and vice versa. The cold standard accretion disk regulates the extent of the warm corona.

The Wanderer: Charting WASP-77A b’s Formation and Migration Using a System-wide Inventory of Carbon and Oxygen Abundances

The elemental and isotopic abundances of volatiles like carbon, oxygen, and nitrogen may trace a planet’s formation location relative to H2O, CO2, CO, NH3, and N2 “snowlines,” or the distance from the star at which these volatile elements sublimate. By comparing the C/O and 12C/13C ratios measured in giant exoplanet atmospheres to complementary measurements of their host stars, we can determine whether the planet inherited stellar abundances from formation inside the volatile snowlines, or nonstellar C/O and 13C enrichment characteristic of formation beyond the snowlines. To date, there are still only a handful of exoplanet systems where we can make a direct comparison of elemental and isotopic CNO abundances between an exoplanet and its host star. Here, we present a 12C/13C abundance analysis for host star WASP-77A (whose hot Jupiter’s 12C/13C abundance was recently measured). We use MARCS stellar atmosphere models and the radiative transfer code TurboSpectrum to generate synthetic stellar spectra for isotopic abundance calculations. We find a 12C/13C ratio of 51 ± 6 for WASP-77A, which is subsolar (∼91) but may still indicate 13C enrichment in its companion planet WASP-77A b (12C/13C = 26 ± 16, previously reported). Together with the inventory of carbon and oxygen abundances in both the host and companion planet, these chemical constraints point to WASP-77A b’s formation beyond the H2O and CO2 snowlines and provide chemical evidence for the planet’s migration to its current location ∼0.024 au from its host star.

The relationship between chlorophyll fluorescence and polarized light field: Polarization-Curve Fluorescence Height

The impact of the un-polarized nature of chlorophyll fluorescence, which causes a dip in the degree of polarization of the underwater light field matching the fluorescence spectrum, led to the development of a theoretical relationship indicating that the resulting fractional reduction in observed polarization is linearly proportional to the magnitude of the fluorescence causing it. To evaluate this relationship, we used a vector radiative transfer code (VRTE) for the coupled atmosphere-ocean system using measured inherent optical properties (IOPs) for a variety of oligotrophic and eutrophic waters as inputs. The VRTE was used to simulate elastic components of the underwater reflectance as well as the degree of linear polarization (DoLP) for these different conditions. These values were compared with the underwater reflectances and the DoLPs measured by a multi-angular hyperspectral polarimeter to determine the magnitude of the fluorescence component in the reflectance spectra at 685 nm, and the decrease of the DoLP due to the fluorescence impact at the same wavelength. Fluorescence magnitudes retrieved from the differences between simulated and measured reflectances were found to match well the magnitudes estimated through the relationship based on the drop of the DoLP. It is noted that retrieval accuracies increase for both larger fluorescence and larger underlying DoLP values. Furthermore, a new method is evolved from the measured polarization analysis, Polarization-Curve Fluorescence Height (PCFH). Measured polarization were used to approximate the elastic signal and derive the inelastic un-polarized signal (fluorescence) from the difference in the fluorescence vicinity. These results open possibilities for estimating the magnitude of natural fluorescence using polarization measurements below or above the water surface, .in-situ, or remotely from aircraft or future satellites. Results of ongoing work on potential sensitivities and retrieval accuracies for these applications will be reported.