Light Curves Research Articles

Sun-related variability in the light curves of compact radio sources

Context. Compact radio sources can show remarkable flux density variations at gigahertz frequencies on a wide range of timescales. The origin of the variability is a mix of source-intrinsic mechanisms and propagation effects, the latter being generally identified with scattering from the interstellar medium. Some of the most extreme episodes of variability, however, show characteristics that are not consistent with any of the explanations commonly proposed. Aims. We carried out an in-depth analysis of variability at radio frequencies on light curves from the impressive database of the US Navy’s extragalactic source monitoring program at the Green Bank Interferometer (GBI) – a long-term project mainly aimed at the investigation of extreme scattering events. The GBI data have been complemented for selected sources by light curves from the University of Michigan Radio Astronomy Observatory (UMRAO). The purpose of the present work is to identify events of flux density variations that appear to correlate with the position of the Sun. Methods. We inspected the 2 GHz and 8 GHz light curves observed in the framework of the GBI monitoring program in order to search for one-year periodic patterns in the data. Variations on timescales below one year were isolated through a de-trending algorithm and analysed, with the aim of looking for possible correlations with the Sun’s position relative to the sources. Results. Objects at an ecliptic latitude below ∼20° show one-year periodic drops in flux densities, centred close to the time of minimum solar elongation. Both interplanetary scintillation and instrumental effects may contribute to these events. However, in some cases, the drops extend to much larger angular distances, affecting sources at high ecliptic latitudes and causing variability on timescales of months. Three different kinds of such events have been identified in the data, and their exact nature is not yet known. Conclusions. In the present study we show that the variability of compact radio sources is heavily influenced by effects that correlate with solar angular distance. This unexpected contribution significantly alters the sources’ variability characteristics estimated at gigahertz frequencies. In particular, we found that many extreme scattering events previously identified in the GBI monitoring program are actually the consequence of Sun-related effects; others occur simultaneously in several objects, which excludes interstellar scattering as their possible cause. These discoveries have a severe impact on our understanding of extreme scattering events. Furthermore, Sun-related variability, given its amplitude and timescale, can significantly alter results of variability studies, which are very powerful tools for the investigation of active galactic nuclei. Without a thorough comprehension of the mechanisms that cause these variations, the estimation of some essential information about the emitting regions, such as their size and all the derived quantities, might be seriously compromised.

High-cadence stellar variability studies of RR Lyrae stars with DECam: New multiband templates

We present the most extensive set to date of high-quality RR Lyrae light curve templates in the ɡriz bands, based on time-series observations of the Dark Energy Camera Plane Survey (DECaPS) East field, located in the Galactic bulge at coordinates (RA, Dec)(J2000) = (18:03:34, −29:32:02), obtained with the Dark Energy Camera (DECam) on the 4-m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO). Our templates, which cover both fundamental-mode (RRab) and first-overtone (RRc) pulsators, can be especially useful when there is insufficient data for accurately calculating the average magnitudes and colors, hence distances, as well as to inform multiband light curve classifiers, as will be required in the case of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST). In this paper, we describe in detail the procedures that were adopted in producing these templates, including a novel approach to account for the presence of outliers in photometry. Our final sample comprises 136 RRab and 144 RRc templates, all of which are publicly available. Lastly, in this paper we study the inferred Fourier parameters and other light curve descriptors, including rise time, skewness, and kurtosis, as well as their correlations with the pulsation mode, period, and effective wavelength.

MOA-2022-BLG-033Lb, KMT-2023-BLG-0119Lb, and KMT-2023-BLG-1896Lb: Three low mass-ratio microlensing planets detected through dip signals

Aims. We examined the anomalies in the light curves of the lensing events MOA-2022-BLG-033, KMT-2023-BLG-0119, and KMT- 2023-BLG-1896. These anomalies share similar traits: they occur near the peak of moderately to highly magnified events and display a distinct short-term dip feature. Methods. We conducted detailed modeling of the light curves to uncover the nature of the anomalies. This modeling revealed that all signals originated from planetary companions to the primary lens. The planet-to-host mass ratios are very low: q ~ 7.5 × 10−5 for MOA-2022-BLG-033, q ~ 3.6 × 10−4 for KMT-2023-BLG-0119, and q ~ 6.9 × 10−5 for KMT-2023-BLG-1896. The anomalies occurred as the source passed through the negative deviation region behind the central caustic along the planet-host axis. The solutions are subject to a common inner-outer degeneracy, which results in varying estimations of the projected planet-host separation. For KMT-2023-BLG-1896, although the planetary scenario provides the best explanation for the anomaly, the binary companion scenario is possible. Results. We estimated the physical parameters of the planetary systems through Bayesian analyses based on the lensing observables. While the event timescale was measured for all events, the angular Einstein radius was not measured for any. Additionally, the microlens parallax was measured for MOA-2022-BLG-033. The analysis identifies MOA-2022-BLG-033L as a planetary system with an ice giant with a mass of approximately 12 times that of Earth orbiting an early M dwarf star. The companion of KMT-2023-BLG-1896L is also an ice giant, with a mass of around 16 Earth masses, orbiting a mid-K-type main-sequence star. The companion of KMT-2023-BLG- 0119L, which has a mass around that of Saturn, orbits a mid-K-type dwarf star. The lens for MOA-2022-BLG-033 is highly likely to be located in the disk, whereas for the other events the probabilities of the lens being in the disk or the bulge are roughly equal.

Black hole accretion and radiation variability in general relativistic magnetohydrodynamic simulations with Rezzolla–Zhidenko spacetime

The Event Horizon Telescope (EHT) has unveiled the horizon-scale radiation properties of Sagittarius A* (Sgr A*), the supermassive black hole at the center of our galaxy, providing a novel platform for testing gravitational theories by comparing observations with theoretical models. A key next step is to investigate the nature of accretion flows and spacetime structures near black holes by analyzing the time variability observed in EHT data alongside general relativistic magnetohydrodynamic (GRMHD) simulations. We explored the dynamics of accretion flows in spherically symmetric black hole spacetimes with deviations from general relativity utilizing two dimensional GRMHD simulations based on the Rezzolla–Zhidenko parameterized spacetime. This study marks the first systematic investigation into how variability amplitudes in light curves, derived from non-Kerr GRMHD simulations, depend on deviations from the Schwarzschild spacetime. The deviation parameters are consistent with the constraints from weak gravitational fields and the size of Sgr A*’s black hole shadow. We find that the dynamics of accretion flows systematically depend on these parameters. In spacetimes with a deeper gravitational potential, fluid and Alfvén velocities consistently decrease relative to the Schwarzschild metric, indicating weaker dynamical behavior. We also examined the influence of spacetime deviations on radiation properties by computing luminosity fluctuations at 230 GHz using general relativistic radiative transfer simulations, in line with EHT observations. The amplitude of these fluctuations exhibits a systematic dependence on the deviation parameters, decreasing for deeper gravitational potentials compared to the Schwarzschild metric. These features are validated using one of the theoretically predicted metrics, the Hayward metric, a model that describes nonsingular black holes. This characteristic is expected to have similar effects in more comprehensive simulations that include more realistic accretion disk models and electron cooling in the future, potentially aiding in distinguishing black hole solutions that explain the variability of Sgr A*.

Three warm Jupiters orbiting TOI-6628, TOI-3837, and TOI-5027 and one sub-Saturn orbiting TOI-2328

We report the discovery and characterization of three new transiting giant planets orbiting TOI-6628, TOI-3837, and TOI-5027 and one new warm sub-Saturn orbiting TOI-2328, whose transits events were detected in the light curves of the Transiting Exoplanet Survey Satellite (TESS) space mission. By combining TESS light curves with ground-based photometric and spectroscopic followup observations, we confirm the planetary nature of the observed transits and radial velocity variations. TOI-6628 b has a mass of 0.74±0.06 MJ and a radius of 0.98−0.05+0.06 RJ and orbits a metal-rich star with a period of 18.18424 ± 0.00001 days and an eccentricity of 0.670−0.016+0.015, making it one of the most eccentric orbits of all known warm giants. TOI-3837 b has a mass of 0.59±0.05 MJ and a radius of 0.97−0.06+0.05 RJ and orbits its host star every 11.88865 ± 0.00003 days, with a moderate eccentricity of 0.221−0.046+0.042. With a mass of 2.02±0.13 MJ and a radius of 0.96−0.06+0.05 RJ, TOI-5027 b orbits its host star in an eccentric orbit with e = 0.385−0.026+0.025 every 10.24368±0.00001 days. TOI-2328 b is a Saturn-like planet with a mass of 0.16±0.02 MJ and a radius of 0.89−0.05+0.04 RJ; it orbits its host star in a nearly circular orbit with e = 0.057−0.029+0.046 at a period of 17.10197±0.00001 days. All four planets have orbital periods above ten days, and our planet’s interior structure models are consistent with a rocky-icy core with an H/He envelope, providing evidence supporting the core-accretion model of planet formation for this kind of planet.

Time-integrated polarizations in the prompt phase of gamma-ray bursts via the multi-window interpretation

Aims. We used multi-window observations, including the light curve and evolutions of the spectral peak energy (Ep), the polarization degree (PD), and the polarization angle (PA), to infer the model parameters for predicting the time-integrated PD in the prompt phase of gamma-ray bursts (GRBs). Methods. We selected 23 GRBs that were codetected by Fermi/GBM and polarization detectors (i.e., GAP, POLAR, and AstroSat). In our multi-window fitting, the light curve, Ep curve, PD curve, and PA curve were interpreted simultaneously under the synchrotron radiation model in ordered magnetic fields (i.e., the aligned-field case and the toroidal-field case). Results. For bursts with strong (∼90°) PA rotations, the predicted time-integrated PD of the aligned-field case roughly matches the corresponding observed best-fit value, while it is higher for the toroidal-field case. For bursts without strong (∼90°) PA rotation(s), the predicted PDs of the aligned-field case and the toroidal-field case are comparable and can interpret the observational data equally well. The observed time-resolved and time-integrated PDs for GRB 170206A are comparable and are both lower than our predicted upper limits in ordered magnetic fields. This means that mixed magnetic fields, that is, magnetic fields with both ordered and random components, probably reside in the radiation regions of this burst. Except for one out of the total 23 bursts, the predicted time-integrated PDs, which are ∼44% for the aligned-field case and around 49% for the toroidal-field case, are consistent with the corresponding observed values. Consistent with previous study, the models with synchrotron radiation in ordered magnetic fields can therefore interpret most of the current polarization data within an error bar of 1σ.

Searching for new variable white dwarfs: The discovery of the three new pulsating and three new binary systems

In recent years, approximately 150 low-mass white dwarfs (WDs), typically with masses below 0.4 M⊙, have been discovered. Observational evidence indicates that most of these low-mass WDs are in binary systems, supporting binary evolution scenarios as their primary formation pathway. A few extremely low-mass (ELM) WDs in this population have also been found to be pulsationally variable. In this work we present a comprehensive analysis aimed at identifying new variable low-mass WDs. From our candidate selection, 16 objects were identified as being within the ZZ Ceti instability strip. Those objects were observed over multiple nights using high-speed photometry from the SOAR/Goodman and SMARTS-1 m telescopes. Our analysis led to the discovery of three new pulsating WDs: one pulsating ELM WD, one low-mass WD, and one ZZ Ceti star. Additionally, we identified three objects in binary systems, two with ellipsoidal variations in their light curves (one of which is likely a pre-ELM star) and a third that shows a reflection effect.

Can Well-sampled Phase Curves Be Used to Infer Asteroid Spectral Features?

Abstract The relationship of an asteroid's reduced magnitude to its phase has a long history of study. Included in this history have been efforts to study the correlation between these parameters and spectral type. However, these efforts often suffer from the inclusion of only a few asteroids, missing phase curve data, uncorrected rotational or apparitional aberrations, and other issues. In this paper, we build upon previous approaches and address these issues. Broadly, this paper is split into two parts. The first is primarily concerned with carefully deriving phase curve parameters using a combined data set from several different sources, including observations from Gaia, the Transiting Exoplanet Survey Satellite, Palomar Transient Factory, Asteroid Terrestrial-impact Last Alert System, and Asteroid Lightcurve Data Exchange Format database using an ellipsoidal model that can correct for rotational and apparitional effects. The second concerns itself with making predictions on that data set and quantifying what can and cannot be inferred from phase parameters, both as a function of the phase curve parameterization chosen and as a function of the chosen model. We find that, while individual spectral classes remain hard to infer from the phase curves, broader statements on the presence of absorption features can dependably be made.

The T16 Project: Image Subtraction Light Curves from TESS Cycle 1 Full-frame Images for Stars with T < 16

The T16 Project: Image Subtraction Light Curves from TESS Cycle 1 Full-frame Images for Stars with T < 16

Repeated pattern of γ-ray flares in the blazar PKS 1502+106 coincident with the IC190730A neutrino event

Context. It has been demonstrated that at least 10% of the brightest blazars in the fourth Fermi-LAT catalog of γ-ray sources exhibit repeating patterns of γ-ray flares. These events may be associated with the presence of a non-uniform sheath surrounding a fast jet spine in some blazars. Theoretical models suggest that such a sheath could facilitate neutrino production in these structured jets. Aims. We aim to test the marginal statistical evidence previously reported for a connection between repeating patterns of γ-ray flares in blazars and high-energy neutrino events that are positionally consistent with these sources. Methods. We identified a repeating pattern of flares in the γ-ray light curve of the blazar PKS 1502+106, which lies within the 50% uncertainty region of the IC190730A neutrino candidate event. This occurrence is combined with two other high-energy (≥200 TeV) neutrino events from ICECAT-1, which arrived in both positional and temporal coincidence with two blazars exhibiting ongoing repeating flare patterns. We conducted a Monte Carlo simulation to evaluate the likelihood of accidental coincidences between the repeating flare patterns and neutrino events, accounting for potential unrecognized systematic uncertainties in the arrival directions of the ICECAT-1 events. Results. Our findings indicate the probability of a random coincidence, in both time and arrival direction for three high-energy neutrino candidates and three blazars with ongoing recurring patterns of γ-ray flares, is 1.56 × 10−3 (3.2σ).

Statistical investigation of solar flares showing quasi-periodicity based on STIX quick-look light curves

Context. The emission of radiation associated with the release of energy in solar flares is often modulated according to a quasi-oscillatory pattern. This behavior is known as quasi-periodic pulsation (QPP). In this work, the STIX instrument on board Solar Orbiter was used to study solar flares that show quasi-periodic variations in X-ray emission. Aims. This work aimed to conduct a statistical study of the periods and amplitudes of QPPs observed in quick-look light curves of the STIX instrument. Methods. The quick-look light curves recorded from April 14, 2020 (the beginning of the mission) to the end of March, 2022 were scrutinized. 129 flares with the most distinct pulses were selected, for which the periodicity analysis was carried out using the Lomb-Scargle periodogram and the autocorrelation method. This sample contained mostly weak B- and C-class flares. Results. It was found that 70% of examined flares showed statistically significant oscillations. Longer periods occur less frequently than shorter ones. We also identified a relationship between the period and the duration in which the oscillations were observed.

Characterising WASP-43b’s interior structure: Unveiling tidal decay and apsidal motion

Context. Recent developments in exoplanetary research highlight the importance of Love numbers in understanding the internal dynamics, formation, migration history, and potential habitability of exoplanets. Love numbers represent crucial parameters that gauge how exoplanets respond to external forces such as tidal interactions and rotational effects. By measuring these responses, insights into the internal structure, composition, and density distribution of exoplanets can be gained. The rate of apsidal precession of a planetary orbit is directly linked to the second-order fluid Love numbers. Thus, Love numbers can also offer valuable insights into the mass distribution of a planet. Aims. In this context, we aim to re-determine the orbital parameters of WASP-43b – in particular, the orbital period, eccentricity, and argument of the periastron – and its orbital evolution. We study the outcomes of the tidal interaction with the host star in order to identify whether tidal decay and periastron precession occur in the system. Methods. We observed WASP-43b with HARPS, whose data we present for the first time, and we also analysed the newly acquired JWST full-phase light curve. We jointly fit new and archival radial velocity and transit and occultation mid-times, including tidal decay, periastron precession, and long-term acceleration in the system. Results. We detected a tidal decay rate of Ṗa = (−l.99±0.50) ms yr−1 and a periastron precession rate of ω = 0.1727−0.0089+0.0083)° d−1 = (621.72−32.04+29.88)″ d−1). This is the first time that both periastron precession and tidal decay are simultaneously detected in an exoplanetary system. The observed tidal interactions can neither be explained by the tidal contribution to apsidal motion of a non-aligned stellar or planetary rotation axis nor by assuming a non-synchronous rotation for the planet, and a value for the planetary Love number cannot be derived. Moreover, we excluded the presence of a second body (e.g. a distant companion star or a yet undiscovered planet) down to a planetary mass of ≳0.3 MJ and up to an orbital period of ≲3700 days. We leave the question of the cause of the observed apsidal motion open.

SN 2018is: A low-luminosity Type IIP supernova with narrow hydrogen emission lines at early phases

We present a comprehensive photometric and spectroscopic study of the Type IIP supernova (SN) 2018is. The V band luminosity and the expansion velocity at 50 days post-explosion are −15.1 ± 0.2 mag (corrected for AV = 1.34 mag) and 1400 km s−1, classifying it as a low-luminosity SN II. The recombination phase in the V band is shorter, lasting around 110 days, and exhibits a steeper decline (1.0 mag per 100 days) compared to most other low-luminosity SNe II. Additionally, the optical and near-infrared spectra display hydrogen emission lines that are strikingly narrow, even for this class. The Fe II and Sc II line velocities are at the lower end of the typical range for low-luminosity SNe II. Semi-analytical modelling of the bolometric light curve suggests an ejecta mass of ∼8 M⊙, corresponding to a pre-supernova mass of ∼9.5 M⊙, and an explosion energy of ∼0.40 × 1051 erg. Hydrodynamical modelling further indicates that the progenitor had a zero-age main sequence mass of 9 M⊙, coupled with a low explosion energy of 0.19 × 1051 erg. The nebular spectrum reveals weak [O I] λλ6300,6364 lines, consistent with a moderate-mass progenitor, while features typical of Fe core-collapse events, such as He I, [C I], and Fe I, are indiscernible. However, the redder colours and low ratio of Ni to Fe abundance do not support an electron-capture scenario either. As a low-luminosity SN II with an atypically steep decline during the photospheric phase and remarkably narrow emission lines, SN 2018is contributes to the diversity observed within this population.

Ground-based Characterization of (98943) Torifune 2001 CC21, the Target of the Hayabusa2# Space Mission**Based on observations made with the Two-meter Twin Telescope (TTT) and the Telescopio Carlos Sanchez (TCS) in the Spanish Observatorio del Teide, the Gran Telescopio Canarias (GTC) telescope and the Isaac Newton Telescope (INT) in the Spanish Observatorio del Roque de los Muchachos of the Instituto de

Abstract The near-Earth asteroid (98943) Torifune, previously designated 2001 CC21, is the flyby target of the Hayabusa2 extended mission, nicknamed Hayabusa2# (Small Hazardous Asteroid Reconnaissance Probe (SHARP)). The ground-based telescope observations offer a key science input for the mission's scientific investigation. During 2022–2024, this asteroid was at visible apparent magnitudes brighter than 18.5, allowing for a detailed characterization using ground-based telescope observations. We determined its rotation period P = 5.021516 ± 0.000106 hr and its absolute magnitude H = 18.78 ± 0.14. The large number of light curves allows us to estimate its axis ratio, its convex shape, and its pole orientation, λ = 301∘ ± 35∘, β = 8 9 − 6 + 1 ° , and ϵ = 5∘ ± 3∘, respectively, which indicate a prograde rotation. We report the semiaxis of the equivalent ellipsoid, a = 0.42 0.06 + 0.08 km, b = 0.16 0.04 + 0.05 km, and c = 0.17 ± 0.03 km. Consequently, the volume-equivalent diameter is D eq = 0.44 ± 0.06 km. Using observations conducted simultaneously with four broadband filters, we determined (g − r) = 0.663 ± 0.022 mag, (r − i) = 0.177 ± 0.012 mag, and (i − z s ) = −0.061 ± 0.032 mag. Additionally, we found that Torifune exhibits no detectable large-scale heterogeneity. We classified the object using a high signal-to-noise ratio spectrum (over the visible and near-infrared region) as Sq-type in the Bus–DeMeo taxonomy. We estimate a mineralogy similar to LL/L ordinary chondrites, with an ol/(ol+px) = 0.60, a Fa content of 28.5 mol%, and a Fs content of 23.4 mol%. The spectral data indicate a surface affected by moderate space weathering effects.

Three fast-rotating Jovian trojans identified by TESS set new population density limits

We report on the identification of the three fastest rotating Jovian trojans with reliable population assignments known to date, discovered using light curve data from the Transiting Exoplanet Satellite Survey mission and confirmed by Zwicky Transient Facility data. For two of our targets the rotation periods are moderately below the previously accepted ∼5 h Jovian trojan breakup limit (4.26 and 4.75 h); however, the rotation period of (13383) was found to be P = 2.926 h, leading to a density estimate of ρ ≈1.6 g cm−3, higher than the generally accepted ≲1 g cm−3 density limit of Jovian trojans. If associated with lower densities, this rotation rate requires considerable cohesion, of the order of a few kilopascals. The relatively high albedo (pV ≈ 0.11) and fast rotation suggest that (13383) may have undergone an energetic collision that spun up the body and exposed bright material to the surface.

Intervening nuclear obscuration changing the X-ray look of the z ≈ 6 quasi-stellar object CFHQS J164121+375520

X-ray observations of the optically selected z = 6.025 quasi-stellar object (QSO) CFHQS J164121+375520 (hereafter J1641) revealed that its flux dropped by a factor of ≳7 between 2018, when it was a bright and soft X-ray source, and 2021. Such a strong variability amplitude has not been observed before among z &gt; 6 QSOs, and the underlying physical mechanism was unclear. We carried out a new X-ray and rest-frame UV monitoring campaign of J1641 over 2022–2024. We detected J1641 with Chandra in the 2–7 keV band, while no significant emission is detected at softer X-ray energies, making J1641 an X-ray changing-look QSO at z &gt; 6. Compared with the 2018 epoch, the 0.5–2 keV flux dropped by a factor of &gt; 20. We ascribe this behavior to intervening, and still ongoing, obscuration by Compton-thick gas intercepting our line of sight between 2018 and 2021. The screening material could be an inner disk or a failed nuclear wind whose thickness increased. Another possibility is that we have witnessed an occultation event due to dust-free clouds located at parsec or subparsec scales, similar to those recently invoked to explain the remarkable X-ray weakness of active galactic nuclei discovered by JWST. These interpretations are also consistent with the lack of strong variations in the QSO rest-frame UV light curve over the same period. Future monitoring of J1641 and the possible discovery of other X-ray changing look QSOs at z &gt; 6 will return precious information about the physics of rapid supermassive black hole growth at high redshifts.

Harmful effects of the semiconductor copper tungstate (CuWO4) on multiple photosynthetic parameters of the green microalga Raphidocelis subcapitata.

Harmful effects of the semiconductor copper tungstate (CuWO4) on multiple photosynthetic parameters of the green microalga Raphidocelis subcapitata.

ZTF SN Ia DR2: The diversity and relative rates of the thermonuclear supernova population

The Zwicky Transient Facility SN Ia Data Release 2 (ZTF SN Ia DR2) contains more than 3000 Type Ia supernovae (SNe Ia), providing the largest homogeneous low-redshift sample of SNe Ia. Having at least one spectrum per event, this data collection is ideal for large-scale statistical studies of the photometric, spectroscopic and host-galaxy properties of SNe Ia, particularly of the rarer ‘peculiar’ sub-classes. In this paper we first present the method we developed to spectroscopically classify the SNe in the sample, and the techniques we used to model their multi-band light curves and explore their photometric properties. We then show a method to distinguish between the peculiar sub-types and the normal SNe Ia. We also explore the properties of their host galaxies and estimate their relative rates, focusing on the peculiar sub-types and their connection to the cosmologically useful SNe Ia. Finally, we discuss the implications of our study with respect to the progenitor systems of the peculiar SN Ia events.

SN 2023ixf: An average-energy explosion with circumstellar medium and a precursor

The fortunate proximity of the Type II supernova (SN) 2023ixf has allowed astronomers to follow its evolution from almost the moment of the collapse of the progenitor's core. SN,2023ixf can be explained as an explosion of a massive star with an energy of 0.7 erg but with a greatly reduced envelope mass, probably because of binary interaction. In our radiative-transfer simulations, the SN ejecta of 6 interact with circumstellar matter (CSM) of (0.55--0.83) extending to 10^15 cm, which results in a light curve (LC) peak matching that of SN,2023ixf. The origin of this required CSM might be gravity waves originating from convective shell burning, which could enhance wind-like mass loss during the late stages of stellar evolution. The steeply rising low-luminosity flux during the first hours after observationally confirmed non-detection, however, cannot be explained by the collision of the energetic SN shock with the CSM. Instead, we consider it as a precursor that we can fit by the emission from (0.5--0.9) of matter that was ejected with an energy of ∼10^49 erg a fraction of a day before the main shock of the SN explosion reached the surface of the progenitor. The source of this energy injection into the outermost shell of the stellar envelope could also be dynamical processes related to the convective activity in the progenitor's interior or envelope. Alternatively, the early rise of the LC could point to the initial breakout of a highly non-spherical SN shock or of fast-moving asymmetrically ejected matter that was swept out well ahead of the SN shock, potentially in a low-energy, nearly relativistic jet. We also discuss that pre-SN outbursts and LC precursors can be used to study or to constrain energy deposition in the outermost stellar layers by the decay of exotic particles, such as axions, which could be produced simultaneously with neutrinos in the newly formed hot neutron star. A careful analysis of the earliest few hours of the LCs of SNe can reveal elusive precursors and provide a unique window onto the surface activity of massive stars during their core collapse. This can greatly improve our understanding of stellar physics and consequently also offer new tools for searching for exotic particles.

Enceladus and Jupiter as exoplanets: the opposition surge effect

Planets and moons in our Solar System have strongly peaked reflected light phase curves at opposition. In this work, we produce a modified reflected light phase curve model and use it to fit the Cassini phase curves of Jupiter and Enceladus. This `opposition effect' is caused by shadow hiding (SH; particles or rough terrain cast shadows which are not seen at zero phase) and coherent backscattering (CB; incoming light constructively interferes with outgoing light). We find tentative evidence for CB preference in Jupiter compared to SH, and no evidence of preference in Enceladus. We show that the full-width half-maximum (FWHM) of Jupiter's opposition peak is an order of magnitude larger than that of Enceladus and conclude that this could be used as a solid-surface indicator for exoplanets. We investigate this and show that modelling the opposition peak FWHM in solid-surface exoplanets would be unfeasible with JWST or the Future Habitable Worlds Observatory due to the very large signal-to-noise required over a small phase range.