Search

Spectroscopic observations of the eccentric binary system SY Phe were made at the South African Astronomical Observatory in 2019, 2020, and 2021, and its mid-resolution spectra were obtained. The radial velocities of the component stars were measured using the cross-correlation method and Fourier disentangling of the spectra. The spectral type (hence the effective temperature) of the primary star was determined from a model-atmosphere analysis. The radial velocity and Transiting Exoplanet Survey Satellite (TESS) light curves of the system were analysed, and its absolute parameters were derived. A strong (5.2 mmag) periodic signal with a frequency typical of |$\gamma$| Dor stars (1.169 cycles per day) dominates the Fourier spectrum of the light curve between the eclipses. Apsidal motion parameters of SY Phe were calculated by studying eclipse timing variations. The Geneva evolution models indicate an evolutionary age of 2 Gyr and solar metallicity for the primary component; however, although the position of the secondary component in the H–R diagram matches the isochrone of 2 Gyr, it appears to have a larger radius and higher effective temperature than expected for its determined mass. Here, the secondary component has too large a radius, which is in accordance with the radius discrepancy problem that has been encountered in other studies, especially in late-type dwarfs, and has not been solved for half a century. [ABSTRACT FROM AUTHOR]

Gamma-ray bursts (GRBs) can be studied with their linearly dependent parameters alongside the standard |$T_{90}$| distribution. The generalized linear model (GLM) identifies the number of linear dependences in a two-parameter space. Classically, GRBs are classified into two classes by the presence of bimodality in the histogram of |$T_{90}$|⁠. However, additional classes and different features of GRBs are fascinating topics to explore. In this work, we investigate GRB features in the |$T_{90} {-}T_{50}$| plane using the GLM for three major catalogues: Swift , the Fermi Gamma-ray Burst Monitor (GBM), and the Burst And Transient Source Experiment (BATSE). This study shows five linear features for the Fermi GBM catalogue and four linear features for the BATSE catalogue, directing us towards the possibility of non-Gaussianity in the light curves of GRBs. [ABSTRACT FROM AUTHOR]

We present the most comprehensive catalogue to date of Type I superluminous supernovae (SLSNe), a class of stripped-envelope supernovae (SNe) characterized by exceptionally high luminosities. We have compiled a sample of 262 SLSNe reported through 2022 December 31. We verified the spectroscopic classification of each SLSN and collated an exhaustive data set of ultraviolet, optical, and infrared photometry totalling over 30 000 photometric detections. Using these data, we derive observational parameters such as the peak absolute magnitudes, rise and decline time-scales, as well as bolometric luminosities, temperature, and photospheric radius evolution for all SLSNe. Additionally, we model all light curves using a hybrid model that includes contributions from both a magnetar central engine and the radioactive decay of |$^{56}$| Ni. We explore correlations among various physical and observational parameters, and recover the previously found relation between ejecta mass and magnetar spin, as well as the overall progenitor pre-explosion mass distribution with a peak at |$\approx 6.5$| M |$_\odot$|⁠. We find no significant redshift dependence for any parameter, and no evidence for distinct subtypes of SLSNe. We find that only a small fraction of SLSNe, |$\lt 3$|  per cent, are best fit with a significant radioactive decay component |$\gtrsim 50$|  per cent. We provide several analytical tools designed to simulate typical SLSN light curves across a broad range of wavelengths and phases, enabling accurate K -corrections, bolometric scaling calculations, and inclusion of SLSNe in survey simulations or future comparison works. [ABSTRACT FROM AUTHOR]

PSR J0737−3039A/B is unique among double neutron star systems. Its near-perfect edge-on orbit causes the fast spinning pulsar A to be eclipsed by the magnetic field of the slow spinning pulsar B. Using high-sensitivity MeerKAT radio observations combined with updated constraints on the system geometry, we studied the impact of these eclipses on the incident polarization properties of pulsar A. Averaging light curves together after correcting for the rotation of pulsar B revealed enormous amounts of circular polarization and rapid changes in the linear polarization position angle, which occur at phases where emission from pulsar A is partially transmitted through the magnetosphere of pulsar B. These behaviours confirm that the eclipse mechanism is the result of synchrotron absorption in a relativistic pair-plasma confined to the closed-field region of pulsar B's truncated dipolar magnetic field. We demonstrate that changes in circular polarization handedness throughout the eclipses are directly tied to the average line of sight magnetic field direction of pulsar B, from which we unambiguously determine the complete magnetic and viewing geometry of the pulsar. [ABSTRACT FROM AUTHOR]

The high-precision measurements of exoplanet transit light curves that are now available contain information about the planet properties, their orbital parameters, and stellar limb darkening (LD). Recent 3D magnetohydrodynamical (MHD) simulations of stellar atmospheres have shown that LD depends on the photospheric magnetic field, and hence its precise determination can be used to estimate the field strength. Among existing LD laws, the uses of the simplest ones may lead to biased inferences, whereas the uses of complex laws typically lead to a large degeneracy among the LD parameters. We have developed a novel approach in which we use a complex LD model but with second derivative regularization during the fitting process. Regularization controls the complexity of the model appropriately and reduces the degeneracy among LD parameters, thus resulting in precise inferences. The tests on simulated data suggest that our inferences are not only precise but also accurate. This technique is used to re-analyse 43 transit light curves measured by the NASA Kepler and Transiting Exoplanet Survey Satellite missions. Comparisons of our LD inferences with the corresponding literature values show good agreement, while the precisions of our measurements are better by up to a factor of 2. We find that 1D non-magnetic model atmospheres fail to reproduce the observations while 3D MHD simulations are qualitatively consistent. The LD measurements, together with MHD simulations, confirm that Kepler-17, WASP-18, and KELT-24 have relatively high magnetic fields (⁠|$\gt 200$| G). This study paves the way for estimating the stellar surface magnetic field using the LD measurements. [ABSTRACT FROM AUTHOR]

We present a statistical, photometric, and spectral energy distribution (SED) analysis to characterize the blue straggler stars (BSSs) populations in the Galactic old open cluster Berkeley 39. Berkeley 39 is a 6.16 Gyr old open cluster located at a distance of 3.99 Kpc. Gaia DR3 astrometry data have been used to estimate the membership probabilities using ensemble-based unsupervised machine learning techniques. We identified 21 BSS candidates on the colour–magnitude diagram, with 19 of them being detected in the Swift /UVOT UVW2 filter. We analysed the radial surface density profile and examined the cluster dynamical states and mass segregation effect. The SEDs of 19 BSSs are constructed using multiwavelength data covering UV to IR wavelengths. A single-component SED is fitted successfully for 14 BSS candidates. We discovered hot companions in five BSS candidates. These hot companions have temperatures of approximately 14 000 to 23 000 K, radii ranging from 0.04 to 0.13 R |$_{\odot }$|⁠ , and luminosities ranging from 0.16 to 2.91 L |$_{\odot }$|⁠. Among these, three are most likely extremely low-mass white dwarfs (WDs) with masses around 0.17 to 0.18 M |$_{\odot }$|⁠ , and two are low-mass WDs with masses around 0.18 to 0.39 M |$_{\odot }$|⁠. This confirms that they are post-mass transfer (Case A or Case B) systems. We also investigated the variable characteristics of BSSs by analysing their light curves using data from TESS. Our analysis confirms that two BSSs identified as eclipsing binaries in Gaia DR3 are indeed eclipsing binaries. Additionally, one of the two eclipsing binary BSSs shows evidence of having hot companions, as indicated by the multiwavelength SEDs. [ABSTRACT FROM AUTHOR]

The Helix is a visually striking and the nearest planetary nebula, yet any companions responsible for its asymmetric morphology have yet to be identified. In 2020, low-amplitude photometric variations with a periodicity of 2.8 d were reported based on Cycle 1 TESS observations. In this work, with the inclusion of two additional sectors, these periodic light curves are compared with lcurve simulations of irradiated companions in such an orbit. Based on the light-curve modelling, there are two representative solutions: (i) a Jupiter-sized body with 0.102 R |$_\odot$| and an arbitrarily small orbital inclination |$i=1^{\circ }$|⁠ , and (ii) a 0.021 R |$_\odot$| exoplanet with |$i\approx 25^{\circ }$|⁠ , essentially aligned with the Helix nebular inclination. Irradiated substellar companion models with equilibrium temperature 4970 K are constructed and compared with existing optical spectra and infrared photometry, where Jupiter-sized bodies can be ruled out, but companions modestly larger than Neptune are still allowed. Additionally, any spatially unresolved companions are constrained based on the multiwavelength, photometric spectral energy distribution of the central star. No ultracool dwarf companion earlier than around L5 is permitted within roughly 1200 au, leaving only faint white dwarfs and cold brown dwarfs as possible surviving architects of the nebular asymmetries. While a planetary survivor is a tantalizing possibility, it cannot be ruled out that the light-curve modulation is stellar in nature, where any substellar companion requires confirmation and may be possible with JWST observations. [ABSTRACT FROM AUTHOR]

Energetic GeV photons expected from the closest and the most energetic Gamma-ray bursts (GRBs) provide a unique opportunity to study the very-high-energy emission as well as the possible correlations with lower energy bands in realistic GRB afterglow models. In the standard GRB afterglow model, the relativistic homogeneous shock is usually considered to be fully adiabatic, however, it could be partially radiative. Based on the external forward-shock scenario in both stellar wind and constant-density medium, we present a radiative-adiabatic analytical model of the synchrotron self-Compton (SSC) and synchrotron processes considering an electron energy distribution with a power-law index of |$1\lt p\lt 2$| and |$2\le p$|⁠. We show that the SSC scenario plays a relevant role in the radiative parameter |$\epsilon$|⁠ , leading to a prolonged evolution during the slow cooling regime. In a particular case, we derive the Fermi /LAT light curves together with the photons with energies |$\ge 100$|  MeV in a sample of nine bursts from the second Fermi /LAT GRB catalogue that exhibited temporal and spectral indices with |$\gtrsim 1.5$| and |$\approx 2$|⁠ , respectively. These events can hardly be described with closure relations of the standard synchrotron afterglow model, and also exhibit energetic photons above the synchrotron limit. We have modelled the multiwavelength observations of our sample to constrain the microphysical parameters, the circumburst density, the bulk Lorentz factor, and the mechanism responsible for explaining the energetic GeV photons. [ABSTRACT FROM AUTHOR]

We present the results obtained from X-ray and optical analysis of the Be/X-ray binary IGR J06074+2205, focusing on before, during, and after the X-ray outbursts in 2023 October and December. The properties of the neutron star in the binary are investigated using NICER and NuSTAR observations during the X-ray outbursts. The pulse profiles across a broad energy range, are found to be strongly dependent on luminosity and energy, revealing the complex nature of the emitting region. An absorbed power law can describe each NICER spectrum in the 1–7 keV band. The 3–79 keV NuSTAR spectrum can be well described by a negative and positive power law with an exponential cut-off model. Utilizing the MAXI/GSC long-term light curve, we estimate the probable orbital period to be 80 or 80/n (n = 2, 3, 4) d. We investigate the evolution of the circumstellar disc around the Be star by using optical spectroscopic observations of the system between 2022 and 2024. We observe variable H  |$\alpha$| and Fe  ii emission lines with an increase in equivalent width, indicating the presence of a dynamic circumstellar disc. A distinct variation in the V/R value for H  |$\alpha$| and Fe  ii lines is also observed. The appearance of additional emission lines, such as He  i (5875.72 Å), He  i (6678 Å), and He  i (7065 Å), during the post-outburst observation in 2024 February suggests the growing of a larger or denser circumstellar disc. The disc continues to grow without any noticeable mass-loss, even during the 2023 X-ray outbursts, which may lead to a future giant X-ray outburst. [ABSTRACT FROM AUTHOR]

The variability data for the BL Lacertae object TXS 1902+556 in the optical and |$\gamma$| -ray wavebands were obtained from the 0.76-m Katzman Automatic Imaging Telescope and the Fermi Large Area Telescope (Fermi -LAT), covering periods of 14.4 and 14.7 yr, respectively. The variability properties were systematically analysed, with particular emphasis on the first comprehensive investigation of radiation variation in the optical waveband. Four well-established techniques were employed for this purpose: the Lomb–Scargle periodogram, REDFIT program, Jurkevich method, and discrete correlation function (DCF) approach. The optical waveband exhibits quasi-periodic oscillations (QPO) with a time-scale of |$P_{\rm O}=276.8\pm 6.1$|  d at a significance level |$3.87\sigma$|⁠ , while the |$\gamma$| -ray waveband does not exhibit any significant periodicity. However, it should be noted that the QPO time-scale is consistent with the Sun-gaps in the optical light curve within 2 |$\sigma$| uncertainties. The optical QPO behaviour is most likely attributed to the helical motion of the jet driven by the orbital motion in a supermassive black hole binary system. Moreover, we have provided an explanation for the absence of QPO in the |$\gamma$| -ray light curves. Furthermore, utilizing the DCF method, a weak correlation between the variability in the optical and |$\gamma$| -ray wavebands was observed, suggesting that the emission of TXS 1902+556 may be generated through a combination of synchrotron self-Compton (SSC) and external Compton (EC) processes, or a leptonic–hadronic hybrid process. [ABSTRACT FROM AUTHOR]

Binary systems comprise approximately 15 per cent of the near-Earth asteroid population, yet thermal-infrared (IR) data are often interpreted for these bodies as if they are single objects. Thermal-IR light curves of binary asteroids (3905) Doppler and (175706) 1996 FG3 are analysed using an adaptation of the Advanced Thermophysical Model, deriving new constraints on their thermal inertias as |$\Gamma = 114 \pm 31\, \, \mathrm{J}\, \mathrm{m}^{-2}\, \mathrm{K}^{-1}\, \mathrm{s}^{-1/2}$| and |$\Gamma = 142 \pm 6\, \, \mathrm{J}\, \mathrm{m}^{-2}\, \mathrm{K}^{-1}\, \mathrm{s}^{-1/2}$|⁠ , respectively. We determine that this adapted model is suitable for binary systems where their primary rotation to secondary orbit period ratios can be approximately characterized by small integers. Objects with more complex orbital states require a model with alternative temperature convergence methodologies. Thermal inertia is shown to have a strong effect on binary thermophysical light-curve morphology, introducing significant modulations both inside and outside of mutual event times. The depths of eclipse events are shown to be suppressed at longer wavelengths due to the sensitivity to cooler parts of the surface, meanwhile surface roughness is shown to have little effect on the thermal light-curve morphology. A proof of concept model for the (65803) Didymos system is demonstrated, showing how such a binary model could be used to study the system during the European Space Agency's Hera mission, and the applicability of this adapted model to NASA's Lucy mission is also briefly discussed. [ABSTRACT FROM AUTHOR]

The mechanism of X-ray outbursts in Be X-ray binaries remains a mystery, and understanding their circumstellar discs is crucial for a solution of the mass-transfer problem. In particular, it is important to identify the Be star activities (e.g. pulsations) that cause mass ejection and, hence, disc formation. Therefore, we investigated the relationship between optical flux oscillations and the infrared (IR) excess in a sample of five Be X-ray binaries. Applying the Lomb–Scargle technique to high-cadence optical light curves from the Transiting Exoplanet Survey Satellite (⁠|${\it TESS}$|⁠), we detected several significant oscillation modes in the 3–24 h period range for each source. We also measured the IR excess (a proxy for disc growth) of those five sources, using J -band light curves from Palomar Gattini-IR. In four of the five sources, we found anticorrelations between the IR excess and the amplitude of the main flux oscillation modes. This result is inconsistent with the conventional idea that non-radial pulsations drive mass ejections. We propose an alternative scenario where internal temperature variations in the Be star cause transitions between pulsation-active and mass-ejection-active states. [ABSTRACT FROM AUTHOR]

We present a new method to distinguish between different states (e.g. high and low, quiescent and flaring) in astronomical sources with count data. The method models the underlying physical process as latent variables following a continuous-space Markov chain that determines the expected Poisson counts in observed light curves in multiple passbands. For the underlying state process, we consider several autoregressive processes, yielding continuous-space hidden Markov models of varying complexity. Under these models, we can infer the state that the object is in at any given time. The continuous state predictions from these models are then dichotomized with the help of a finite mixture model to produce state classifications. We apply these techniques to X-ray data from the active dMe flare star EV Lac, splitting the data into quiescent and flaring states. We find that a first-order vector autoregressive process efficiently separates flaring from quiescence: flaring occurs over 30 per cent–40 per cent of the observation durations, a well-defined persistent quiescent state can be identified, and the flaring state is characterized by higher plasma temperatures and emission measures. [ABSTRACT FROM AUTHOR]

Fast blue optical transients (FBOTs) represent a new class of highly energetic sources observed from radio to X-rays. High luminosity, light curves and spectra of the sources can be understood if they are associated with supernova-like or tidal disruption events. Radio observations of the transient sources revealed a mildly relativistic expansion of some of the remnants. The high power and mildly relativistic shock velocities are providing favorable conditions for very high energy particle acceleration. In this paper we present a model of particle acceleration in mildly relativistic magnetohydrodynamic (MHD) outflow of the transient source. To construct the non-thermal radiation and cosmic ray spectra in a broad range of energies we combined the microscopic particle-in-cell simulations of electron and proton injection at mildly relativistic shock with Monte Carlo technique for high energy particle transport and acceleration. The model allows describing the observed non-thermal radio and X-ray emission of CSS161010, and predicts that such sources can accelerate cosmic rays to energies above 10 PeV, and possible upper limit of maximum energy is 100 PeV. With the expected event rate of FBOTs they can contribute to the very high energy cosmic rays population in galaxies. [ABSTRACT FROM AUTHOR]

V745 Sco is a Galactic symbiotic recurrent nova with nova eruptions in 1937, 1989, and 2014. We study the behaviour of V745 Sco at radio wavelengths (0.6–37 GHz), covering both its 1989 and 2014 eruptions and informed by optical, X-ray, and |$\gamma$| -ray data. The radio light curves are synchrotron-dominated. Surprisingly, compared to expectations for synchrotron emission from explosive transients such as radio supernovae, the light curves spanning 0.6–37 GHz all peak around the same time (⁠|$\sim$| 18–26 d after eruption) and with similar flux densities (5–9 mJy). We model the synchrotron light curves as interaction of the nova ejecta with the red giant wind, but find that simple spherically symmetric models with wind-like circumstellar material (CSM) cannot explain the radio light curve. Instead, we conclude that the shock suddenly breaks out of a dense CSM absorbing screen around 20 d after eruption, and then expands into a relatively low-density wind (⁠|$\dot{M}_{out} \approx 10^{-9}\!-\!10^{-8}$|  M |$_{\odot }$|  yr |$^{-1}$| for |$v_w = 10$|  km s |$^{-1}$|⁠) out to |$\sim$| 1 yr post-eruption. The dense, close-in CSM may be an equatorial density enhancement or a more spherical red giant wind with |$\dot{M}_{in} \approx [5\!-\!10] \times 10^{-7}$| M |$_{\odot }$| yr |$^{-1}$|⁠ , truncated beyond several |$\times 10^{14}$|  cm. The outer lower-density CSM would not be visible in typical radio observations of Type Ia supernovae: V745 Sco cannot be ruled out as a Type Ia progenitor based on CSM constraints alone. Complementary constraints from the free–free radio optical depth and the synchrotron luminosity imply the shock is efficient at accelerating relativistic electrons and amplifying magnetic fields, with |$\epsilon _e$| and |$\epsilon _B \approx 0.01\!-\!0.1$|⁠. [ABSTRACT FROM AUTHOR]

• This study aims to investigate the stability of SX Crv and XX Sex. • The light curves of the SX Crv and XX Sex were carried out in detail. • The orbital period of the XX Sex system was conducted for the first time. • The nature and evolution of SX Crv and XX Sex were discussed. The photometric analyses of the extreme low mass ratio contact binaries SX Crv and XX Sex were conducted in detail. Light curves of SX Crv and XX Sex were retrieved from TESS, and light curve analyses were performed simultaneously with radial velocities. The mass ratios for SX Crv and XX Sex were calculated as 0.077 (1) and 0.099 (2). The masses of the primary components account for about 90 % of the total masses of the systems and were determined to be 1.256 (48) M ⊙ and 1.337 (37) M ⊙ for SX Crv and XX Sex, respectively. It has been observed that the orbital periods of both systems have increased. The orbital period change rate of SX Crv has been calculated to be 0.39 s per century, while that of XX Sex has been calculated to be 2.68 s per century. The orbital angular momentum (J o) determined for both systems is more than 3 times the spin angular momentum (J s), and it can be said that the SX Crv and XX Sex systems are stable. The calculated instability separation (a ins.) and instability mass ratio (q ins.) values for both systems are smaller than those obtained in the analyses, which supports the stability. The estimated ages of the systems are 7.4 Gyr for SX Crv and 3.9 Gyr for XX Sex. logM tot – logJ and logT eff – logL diagrams were also interpreted to better understand the evolution of the extreme low mass ratio contact binaries. [ABSTRACT FROM AUTHOR]

Based on the results of several articles devoted to the study of the average power spectra () of γ-ray bursts (GRBs), a list of features has been compiled that need to be explained. Using the possibility, proven in a number of publications, of decomposing the time profile of each γ-ray burst into the sum of several two-sided pulses, GRB modeling is performed in the time domain and the study of the average power spectra of models is carried out in the frequency domain. Brief reviews of the results of a number of theoretical works are made. A Monte Carlo simulation of time series consisting of a set of two-sided pulses with a Poisson distribution of the position of the pulses on the time scale, with different pulse shapes and distributions of amplitude and pulse duration, was carried out. All the basic properties of the average power spectrum in the form of a quasi-Lorentzian theoretically derived in various published studies have been confirmed. of superposition of two-sided pulses randomly distributed over time are not described by a single power law. In general, the shape consists of three quasi-power sections separated by two breaks. The position of the two breaks in the is determined by the parameters of asymmetry and the effective pulse duration. The pulse-duration distribution and their shape affect the shape of the , and the pulse amplitude distribution has practically no such effect. The amount of intermittency (at large values of γ ≥ 1) affects the shape of the . Based on previous theoretical work and the Monte Carlo simulations carried out in this study, it can be argued that all the features of the average power spectra of GRBs are explained using a simple light curve model in the form of a superposition of uncorrelated random two-sided pulses. The main features of the of GRBs are determined only by such pulse characteristics as the asymmetry parameter, the duration distribution, and the shape of the pulses. [ABSTRACT FROM AUTHOR]

We present the Transiting Exoplanet Survey Satellite (TESS) light curve analysis of HX Velorum, located in the Southern Hemisphere, where one of the components is found for the first time to be a β$$ \beta $$ Cep (BCEP) type pulsator. The TESS observations of HX Velorum were published in a total of 6 sectors. Fourier analysis of the observations reveals that the frequencies can be divided into two categories, one of which is related to the orbital period and the other related to the β$$ \beta $$ Cep‐type pulsation. Its non‐eclipsing light curve was analyzed with the well‐known Wilson–Devinney code, and we obtained the geometric and physical parameters of the components using published radial velocity and light curve data by making some assumptions. We obtained plausible masses and radii of the primary and secondary components as M1=9.48±0.27M⊙$$ {M}_1=9.48\pm 0.27{M}_{\odot } $$, M2=5.92±0.17M⊙$$ {M}_2=5.92\pm 0.17{M}_{\odot } $$ and R1=3.93±0.04R⊙$$ {R}_1=3.93\pm 0.04{R}_{\odot } $$, R2=3.59±0.03R⊙$$ {R}_2=3.59\pm 0.03{R}_{\odot } $$, respectively. The obtained system's distance of ∼400$$ \sim 400 $$ pc is smaller than the Gaia distances found in the literature. [ABSTRACT FROM AUTHOR]

We estimate the progenitor and explosion properties of the nearby Type II SN 2023ixf using a synthetic model grid of Type II supernova light curves. By comparing the light curves of SN 2023ixf with the pre-existing grid of Type II supernovae containing about 228000 models with different combinations of the progenitor and explosion properties, we obtain the |$\chi ^2$| value for every model and evaluate the properties of the models providing small values of |$\chi ^2$|⁠. We found that the light-curve models with a progenitor zero-age main-sequence mass of |$10\, {M}_\odot$|⁠ , explosion energy of |$(2\\!-\\!3) \times 10^{51}\:\mbox{erg}$|⁠ , |$^{56}\mbox{Ni}$| mass of 0.04– |$0.06\, {M}_\odot$|⁠ , mass-loss rate of |$10^{-3}$| – |$10^{-2}\, {M}_\odot \:\mbox{yr}^{-1}$| with wind velocity of |$10\:\mbox{km}\:\mbox{s}^{-1}$|⁠ , and dense, confined circumstellar matter radius of |$(6\\!-\\!10) \times 10^{14}\:\mbox{cm}$| match well to the observed light curves of SN 2023ixf. The photospheric velocity evolution of these models is also consistent with the observed velocity evolution. We note that the progenitor mass estimate could be affected by the adopted progenitor models. Although our parameter estimation is based on a pre-existing model grid and we do not perform any additional computations, the estimated parameters are consistent with those obtained by the detailed modeling of SN 2023ixf previously reported. This result shows that comparing the pre-existing model grid is a reasonable way to obtain a rough estimate for the properties of Type II supernovae. This simple way to estimate the properties of Type II supernovae will be essential in the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) era when thousands of Type II supernovae are expected to be discovered yearly. [ABSTRACT FROM AUTHOR]

We present an analysis of a stellar occultation event caused by a near-Earth asteroid (98943) 2001 CC21, an upcoming flyby target in the Hayabusa2 extended mission, on 2023 March 5. To determine the asteroid's shape from diffraction-affected light curves accurately, we developed a novel data-reduction technique named the Diffracted Occultation's United Simulator for Highly Informative Transient Explorations (DOUSHITE). Using DOUSHITE-generated synthetic models, we derived constraints on (98943) 2001 CC21's shadow shape from the single-chord occultation data. Our results suggest a significant elongation of the shadow with an axis ratio of |$b/a = 0.37\pm 0.09$|⁠. This shape could be crucial for planning Hayabusa2's high-speed flyby to optimise the limited imaging opportunities. [ABSTRACT FROM AUTHOR]

In this manuscript, strong clues are reported to support the normal broad line AGN SDSS J1617+0638 as the host galaxy harbouring a central tidal disruption event (TDE). Through the optical flare in the CSS 8.5yr-long light curve and the none-variability in the up-to-date ASAS-SN light curves, the theoretical TDE model described by the mosfit code can be applied in SDSS J1617+0638. Meanwhile, considering the assumed central TDE expected continuum emissions not strong enough to describe the continuum emissions in the SDSS spectrum of SDSS J1617+0638, an additional power-law component from pre-existing AGN activity should be necessary in SDSS J1617+0638. Furthermore, considering the short time duration to the observed date for the SDSS spectrum from the starting time of the assumed central TDE in SDSS J1617+0638, TDE model expected accreting mass only about 0.03 |$\mathrm{ M}_\odot$| can lead to few effects of TDEs debris on the observed broad emission lines in the SDSS spectrum of SDSS J1617+0638, indicating the TDE model determined BH mass simply consistent with the virial BH mass by broad emission lines, as determined results in SDSS J1617+0638. Therefore, through both the photometric variability and the spectroscopic results, a central TDE can be preferred in the normal broad line AGN SDSS J1617+0638 with pre-existing central AGN activity and pre-existing broad emission line regions. [ABSTRACT FROM AUTHOR]

Palomar Gattini-IR (PGIR) is a wide-field, synoptic infrared time domain survey covering ≈15,000 sq. deg. of the accessible sky at ≈1–3 night cadence to a depth of J ≈ 13.0 and ≈14.9 Vega mag in and outside the Galactic plane, respectively. Here, we present the first data release of J -band light curves of Two Micron All Sky Survey (2MASS) sources within the survey footprint covering approximately the first four years of operations. We describe the construction of the source catalog based on 2MASS point sources, followed by exposure filtering criteria and forced PSF photometry. The catalog contains light curves of ≈286 million unique sources with 2MASS magnitudes of J < 15.5 mag, with a total of ≈50 billion photometric measurements and ≈20 billion individual source detections at signal-to-noise-ratio > 3. We demonstrate the photometric fidelity of the catalog by (i) quantifying the magnitude-dependent accuracy and uncertainty of the photometry with respect to 2MASS and (ii) comparing against forced PGIR aperture photometry for known variable sources. We present simple filtering criteria for selecting reliable photometric measurements as well as example Python notebooks for users. This catalog is one of the largest compilation of nightly cadence, synoptic infrared light curves to date, comparable to those in the largest optical surveys, providing a stepping stone to upcoming infrared surveys in the coming decade. [ABSTRACT FROM AUTHOR]

The Meteosat Third Generation - Imager 1 satellite, launched on 13 December 2022, features the first Lightning Imager instrument, a high-speed optical camera providing near real-time lightning detection over Europe and Africa. This study demonstrates that signatures of fireballs (i.e. bright meteors) can be detected in Lightning Imager data. We describe a method to analyse this data to determine the timing, light signal, and trajectory of fireballs, highlighting the instrument's usefulness for bright meteor observation and proposing avenues for further research. By using known fireball locations and timings from external sources, the Lightning Imager data can be filtered to isolate 'lightning events' induced by the meteor. From this data set, the fireball light curve is computed by aggregating signal increases measured by instrument pixels. A trajectory is then deduced using a weighted average of pixel locations based on observed intensity. Three examples of fireballs detected by the Lightning Imager are presented, including a man-made meteor from space debris re-entry, with estimated timing, light curves, and trajectories. [ABSTRACT FROM AUTHOR]

We present radio observations of the long-duration gamma-ray burst (GRB) 221009A that has become known to the community as the Brightest Of All Time or the BOAT. Our observations span the first 475 d post-burst and three orders of magnitude in observing frequency, from 0.15 to 230 GHz. By combining our new observations with those available in the literature, we have the most detailed radio data set in terms of cadence and spectral coverage of any GRB to date, which we use to explore the spectral and temporal evolution of the afterglow. By testing a series of phenomenological models, we find that three separate synchrotron components best explain the afterglow. The high temporal and spectral resolution allows us to conclude that standard analytical afterglow models are unable to explain the observed evolution of GRB 221009A. We explore where the discrepancies between the observations and the models are most significant and place our findings in the context of the most well-studied GRB radio afterglows to date. Our observations are best explained by three synchrotron-emitting regions that we interpret as a forward shock, a reverse shock, and an additional shock potentially from a cocoon or wider outflow. Finally, we find that our observations do not show any evidence of any late-time spectral or temporal changes that could result from a jet break but note that any lateral structure could significantly affect a jet break signature. [ABSTRACT FROM AUTHOR]

In an attempt to further characterize the near-Earth asteroid (NEA) population, we present 38 new light curves acquired between 2020 September and 2023 November for NEAs (7335) 1989 JA, (7822) 1991 CS, (154244) 2002 KL6, and (159402) 1999 AP10, obtained from observations taken at the Teide Observatory (Tenerife, Spain). With these new observations along with archival data, we computed their first shape models and spin solutions by applying the light-curve inversion method. The obtained rotation periods are in good agreement with those reported in previous works, with improved uncertainties. Additionally, besides the constant period models for (7335) 1989 JA, (7822) 1991 CS, and (159402) 1999 AP10, our results for (154244) 2002 KL6 suggest that it could be affected by a Yarkovsky–O'Keefe–Radzievskii–Paddack acceleration with a value of |$\upsilon \simeq -7\times 10^{-9}$| rad d |$^{-2}$|⁠. This would be one of the first detections of this effect slowing down an asteroid. [ABSTRACT FROM AUTHOR]

Pair-instability supernovae (PISNe) have long been predicted to be the final fates of near-zero-metallicity very massive stars (⁠|$Z \lt Z_\odot /3$|⁠ , M |$_\mathrm{ZAMS} \gtrsim 140\, \text{M}_\odot$|⁠). However, no definite PISN has been observed to date, leaving theoretical modelling validation open. To investigate the observability of these explosive transients, we combine detailed stellar evolution models for PISNe formation, computed from the binary population and spectral synthesis code suite, bpass , with the star formation history of all individual computational elements in the Illustris-TNG simulation. This allows us to compute comic PISN rates and predict their host galaxy properties. Of particular importance is that IllustrisTNG galaxies do not have uniform metallicities throughout, with metal-enriched galaxies often harbouring metal-poor pockets of gas where PISN progenitors may form. Accounting for the chemical inhomogeneities within these galaxies, we find that the peak redshift of PISNe formation is |$z=3.5$| instead of the value of |$z=6$| when ignoring chemical inhomogeneities within galaxies. Furthermore, the rate increases by an order of magnitude from 1.9 to 29 PISN Gpc |$^{-3}$| yr |$^{-1}$| at |$z=0$|⁠ , if the chemical inhomogeneities are considered. Using state-of-the-art theoretical PISN light curves, we find an observed rate of 13.8 (1.2) visible PISNe per year for the Euclid-Deep survey, or 83 (7.3) over the 6-yr lifetime of the mission when considering chemically inhomogeneous (homogenous) systems. Interestingly, only 12 per cent of helium PISN progenitors are sufficiently massive to power a superluminous supernova event, which can potentially explain why PISN identification in time-domain surveys remains elusive and progress requires dedicated strategies. [ABSTRACT FROM AUTHOR]

Most of the stars in the Universe are M spectral class dwarfs, which are known to be the source of bright and frequent stellar flares. In this paper, we propose new approaches to discover M-dwarf flares in ground-based photometric surveys. We employ two approaches: a modification of a traditional method of parametric fit search and a machine learning algorithm based on active anomaly detection. The algorithms are applied to Zwicky Transient Facility (ZTF) data release 8, which includes the data from the ZTF high-cadence survey, allowing us to reveal flares lasting from minutes to hours. We analyse over 35 million ZTF light curves and visually scrutinize 1168 candidates suggested by the algorithms to filter out artefacts, occultations of a star by an asteroid, and other types of known variable objects. The result of this analysis is the largest catalogue of ZTF flaring stars to date, representing 134 flares with amplitudes ranging from −0.2 to −4.6 mag, including repeated flares. Using Pan-STARRS DR2 colours, we assign a spectral subclass to each object in the sample. For 13 flares with well-sampled light curves and available geometric distances from Gaia DR3, we estimate the bolometric energy. This research shows that the proposed methods combined with the ZTF's cadence strategy are suitable for identifying M-dwarf flares and other fast transients, allowing for the extraction of significant astrophysical information from their light curves. [ABSTRACT FROM AUTHOR]

We present the largest optical photometry compilation of gamma-ray bursts (GRBs) with redshifts (z). We include 64813 observations of 535 events (including upper limits) from 28 February 1997 to 18 August 2023. We also present a user-friendly web tool grbLC which allows users to visualize photometry, coordinates, redshift, host galaxy extinction, and spectral indices for each event in our database. Furthermore, we have added a Gamma-ray Coordinate Network (GCN) scraper that can be used to collect data by gathering magnitudes from the GCNs. The web tool also includes a package for uniformly investigating colour evolution. We compute the optical spectral indices for 138 GRBs, for which we have at least four filters at the same epoch in our sample, and craft a procedure to distinguish between GRBs with and without colour evolution. By providing a uniform format and repository for the optical catalogue, this web-based archive is the first step towards unifying several community efforts to gather the photometric information for all GRBs with known redshifts. This catalogue will enable population studies by providing light curves (LCs) with better coverage since we have gathered data from different ground-based locations. Consequently, these LCs can be used to train future LC reconstructions for an extended inference of the redshift. The data gathering also allows us to fill some of the orbital gaps from Swift in crucial points of the LCs, e.g. at the end of the plateau emission or where a jet break is identified. [ABSTRACT FROM AUTHOR]

In 2020, two telescopes of the State Astrophysical Observatory of the Russian Academy of Sciences, ZA-320M and MTM-500M, obtained series of observations of the potentially dangerous asteroid 65690 (1991 DG) during its approach to the Earth and carried out their astrometric and photometric processing. Using the coordinates of the asteroid and observations from the MRS site, the orbit of the asteroid was clarified, and the circumstances of the approaches to the Earth and Mars were determined, and an assessment was made of the influence of nongravitational effects on its orbit. Based on the results of photometric processing of the asteroid, a light curve was constructed and the period of its axial rotation was determined: P = 4.3193 ± 0.0028 h. [ABSTRACT FROM AUTHOR]

We present a precise measurement of cosmological time dilation using the light curves of 1504 Type Ia supernovae from the Dark Energy Survey spanning a redshift range |$0.1\lesssim z\lesssim 1.2$|⁠. We find that the width of supernova light curves is proportional to |$(1+z)$|⁠ , as expected for time dilation due to the expansion of the Universe. Assuming Type Ia supernovae light curves are emitted with a consistent duration |$\Delta t_{\rm em}$|⁠ , and parametrizing the observed duration as |$\Delta t_{\rm obs}=\Delta t_{\rm em}(1+z)^b$|⁠ , we fit for the form of time dilation using two methods. First, we find that a power of |$b \approx 1$| minimizes the flux scatter in stacked subsamples of light curves across different redshifts. Secondly, we fit each target supernova to a stacked light curve (stacking all supernovae with observed bandpasses matching that of the target light curve) and find |$b=1.003\pm 0.005$| (stat) |$\pm \, 0.010$| (sys). Thanks to the large number of supernovae and large redshift-range of the sample, this analysis gives the most precise measurement of cosmological time dilation to date, ruling out any non-time-dilating cosmological models at very high significance. [ABSTRACT FROM AUTHOR]

Context. It is generally accepted that all massive galaxies host supermassive black holes (BHs) in their center and that mergers of two galaxies lead to the formation of BH binaries. The most interesting among them comprise the mergers in their final state, that is to say with parsec (3.2 light years) or sub-parsec orbital separations. It is possible to detect these systems with binary self-lensing. Aims. Here we report the potential detection of a central supermassive BH binary in the active galaxy (AGN) NGC 1566 based on a microlensing outburst. The light curve of the outburst – based on observations with the All Sky Automated Survey for SuperNovae – lasted from the beginning of 2017 until the beginning of 2020. The steep symmetric light curve as well as its shape look very different with respect to normal random variations in AGN. Results. However, the observations could be easily reproduced with a best-fit standard microlensing light curve. Based on the light curve, we derived a characteristic timescale of 155 days. During the outburst, the continuum as well as the broad line intensities varied; however, the narrow emission lines did not. This is an indication that the lensing object orbits the AGN nucleus between the broad line region (BLR) and the narrow line region (NLR), that is, at a distance on the order of 250 light days. The light curve can be reproduced by a lens with a BH mass of 5 × 105 M⊙. This implies a mass ratio to the central AGN on the order of 1–10. [ABSTRACT FROM AUTHOR]

Context. At the dawn of the gamma–ray burst (GRB) afterglow era, a Cepheid-like correlation was discovered between the time variability V and the isotropic-equivalent peak luminosity Liso of the prompt emission of about a dozen long GRBs with measured redshift available at that time. Soon afterwards, the correlation was confirmed in a sample of about 30 GRBs, even though it was affected by significant scatter. Unlike the minimum variability timescale (MVT), V measures the relative power of short-to-intermediate timescales. Aims. We aim to test the correlation using about 200 long GRBs with spectroscopically measured redshift, detected by Swift, Fermi, and Konus/WIND, for which both observables can be accurately estimated. Methods. The variability for all selected GRBs was calculated according to the original definition using the 64 ms background-subtracted light curves of Swift/BAT (Fermi/GBM) in the 15–150 (8–900) keV energy passband. Peak luminosities were either taken from the literature or derived from modelling broad-band spectra acquired with either Konus/WIND or Fermi/GBM. Results.The statistical significance of the correlation has weakened to ≲2%, mostly due to the appearance of a number of smooth and luminous GRBs that are characterised by a relatively small V. At odds with most long GRBs, three out of four long-duration merger candidates have high V and low Liso. Conclusions. The luminosity is more tightly connected with shortest timescales measured by MVT than the short to intermediate timescales measured by V. We discuss the implications for internal dissipation models and the role of the e± photosphere. We identified a few smooth GRBs with a single broad pulse and low V that might have an external shock origin, in contrast with most GRBs. The combination of high variability (V ≳ 0.1), low luminosity Liso ≲ 1051 erg s−1, and short MVT (≲0.1 s) could be a good indicator for a compact binary merger origin. [ABSTRACT FROM AUTHOR]

Context. Based on the V-shape search method, two families, Athor and Zita, have been identified within the X-complex population of asteroids located in the inner main belt. The Athor family is ~3 Gyr old while the Zita family could be as old as the Solar System. Both families were found to be capable of delivering near-Earth asteroids (NEAs). Moreover, the Athor family was linked to the low-iron enstatite (EL) meteorites. Aims. The aim of our study is to characterise the spin states of the members of the Athor and Zita collisional families and test whether these members have a spin distribution consistent with a common origin from the break up of their respective family parent asteroids. Methods. To perform this test, our method is based on the well-established asteroid family evolution, which indicates that there should be a statistical predominance of retrograde-rotating asteroids on the inward side of family's V-shape, and prograde-rotating asteroids on the outward side of family's V-shape. To implement the method, we used photometric data from our campaign and the literature in order to reveal the spin states, and hence their rotation sense (prograde or retrograde), of the asteroids belonging to these families. We combined dense and sparse-in-time photometric data in order to construct asteroid rotational light curves; we performed the light curve inversion method to estimate the sidereal period and 3D convex shape along with the spin axis orientation in space of several family member asteroids. Results. We obtained 34 new asteroid models for Athor family members and 17 for Zita family members. Along with the literature and revised models, the Athor family contains 60% (72% considering only the family's core) of retrograde asteroids on the inward side and, conversely, 76% (77% considering only the family's core) of prograde asteroids on the outward side. We also found that the Zita family exhibits 80% of retrograde asteroids on the inward side. In addition, the Zita family presents an equal amount of prograde and retrograde rotators (50% each) on the outward side. However, when we applied Kernel density estimation (KDE), we also found a clear peak for prograde asteroids on the outward side, as expected from the theory. Conclusions. The spin states of these asteroids validate the existence of both families, with the Athor family exhibiting a stronger signature for the presence of retrograde-rotating and prograde-rotating asteroids on the inner and outer side of the family, respectively. Our work provides an independent confirmation and characterisation of these very old families, whose presence and characteristics offer constraints for theories and models of the Solar System's evolution. [ABSTRACT FROM AUTHOR]

We present a dynamical study of the intermediate polar cataclysmic variable YY Dra based on time-series observations in the K band, where the donor star is known to be the major flux contributor. We covered the 3.97-h orbital cycle with 44 spectra taken between 2020 and 2022 and two epochs of photometry observed in 2021 March and May. One of the light curves was simultaneously obtained with spectroscopy to better account for the effects of irradiation of the donor star and the presence of accretion light. From the spectroscopy, we derived the radial velocity curve of the donor star metallic absorption lines, constrained its spectral type to M0.5–M3.5 with no measurable changes in the effective temperature between the irradiated and non-irradiated hemispheres of the star, and measured its projected rotational velocity vrot sin i = 103 ± 2 km s−1. Through simultaneous modelling of the radial velocity and light curves, we derived values for the radial velocity semi-amplitude of the donor star, K2 = 188−2+1 km s−1, the donor to white dwarf mass ratio, q = M2/M1 = 0.62 ± 0.02, and the orbital inclination, i = 42°−1°+2°. These binary parameters yield dynamical masses of M1 = 0.99−0.09+0.10 M⊙ and M2 = 0.62−0.06+0.07 M⊙ (68 per cent confidence level). As found for the intermediate polars GK Per and XY Ari, the white dwarf dynamical mass in YY Dra significantly differs from several estimates obtained by modelling the X-ray spectral continuum. [ABSTRACT FROM AUTHOR]

Context. High-precision and high-cadence photometric surveys such as Kepler or TESS are making huge progress not only in the detection of new extrasolar planets but also in the study of a great number of variable stars. This is the case for central stars of planetary nebulae (PNe), which have similarly benefited from the capabilities of these missions, increasing the number of known binary central stars and helping us to constrain the relationship between binarity and the complex morphologies of their host PNe. Aims. In this paper, we analyse the TESS light curves of a large sample of central stars of PNe with the aim of detecting signs of variability that may hint at the presence of short-period binary nuclei. This will have important implications in understanding PN formation evolution as well as the common envelope phase. Methods. We analysed 62 central stars of true, likely, or possible PNe and modelled the detected variability through an MCMC approach accounting for three effects: reflection, ellipsoidal modulations due to tidal forces, and the so-called Doppler beaming. Among the 62 central stars, only 38 are amenable for this study. The remaining 24 show large contamination from nearby sources preventing an optimal analysis. Also, eight targets are already known binary central stars, which we revisit here with the new high precision of the TESS data. Results. In addition to recovering the eight already known binaries in our sample, we find that 18 further central stars show clear signs of periodic variability in the TESS data, probably resulting from different physical effects compatible with the binary scenario. We propose them as new candidate binary central stars. We also discuss the origin of the detected variability in each particular case by using the TESS_localize algorithm. Finally, 12 targets show no or only weak evidence of variability at the sensitivity of TESS. Conclusions. Our study demonstrates the power of space-based photometric surveys in searching for close binary companions of central stars of PNe. Although our detections can only be catalogued as candidate binaries, we find a large percentage of possible stellar pairs associated with PNe, supporting the hypothesis that binarity plays a key role in shaping these celestial structures. [ABSTRACT FROM AUTHOR]

The planetary system K2-24 is composed of two transiting low-density Neptunians locked in an almost perfect 2:1 resonance and showing large transit time variations (TTVs), and it is an excellent laboratory to search for signatures of planetary migration. Previous studies performed with K2, Spitzer, and RV data tentatively claimed a significant non-zero eccentricity for one or both planets, possibly high enough to challenge the scenario of pure disk migration through resonant capture. With 13 new CHEOPS light curves (seven of planet b, six of planet c), we carried out a global photometric and dynamical re-analysis by including all the available literature data as well. We obtained the most accurate set of planetary parameters to date for the K2-24 system, including radii and masses at 1% and 5% precision (now essentially limited by the uncertainty on stellar parameters) and non-zero eccentricities eb = 0.0498−0.0018+0.0011, ec = 0.0282−0.0007+0.0003 detected at very high significance for both planets. Such relatively large values imply the need for an additional physical mechanism of eccentricity excitation during or after the migration stage. Also, while the accuracy of the previous TTV model had drifted by up to 0.5 days at the current time, we constrained the orbital solution firmly enough to predict the forthcoming transits for the next ~15 years, thus enabling efficient follow-up with top-level facilities such as JWST or ESPRESSO. [ABSTRACT FROM AUTHOR]

Context. The slowly positively drifting bursts (SPDBs) are rarely observed in radio emission of solar flares. Aims. To understand how the SPDBs are generated, we studied the radio observations at 600–5000 MHz together with the imaging observations made in ultraviolet (UV) and extreme ultraviolet (EUV) during the SPDB-rich C8.7 flare of 2014 May 10 (SOL2014-05-10T0702). Methods. Because the SPDBs propagate towards locations of higher plasma density, we studied their associations with individual flare kernels, located either within the flare core itself, or distributed at longer distances, but connected to the flaring region by large-scale hot loops. For each kernel we constructed light curves using 1600 Å and 304 Å observations and compared these light curves with the temporal evolution of radio flux at 1190 MHz, representing all observed groups of SPDBs. We also analysed the UV/EUV observations to understand the evolution of magnetic connectivity during the flare. Results. The flare starts with a growing hot sigmoid observed in 131 Å. As the sigmoid evolves, it extends to and interacts with a half dome present within the active region. The evolving sigmoid reconnects at the respective hyperbolic flux tube, producing large-scale magnetic connections and an EUV swirl. Three groups of SPDBs are observed during this large-scale magnetic reconnection, along with a group of narrow-band type III bursts. The light curves of a kernel corresponding to the footpoint of spine line analogue show good agreement with the radio flux at 1190 MHz, indicating that the SPDBs are produced by the large-scale magnetic reconnection at the half dome. In addition, one of the kernels appeared in the neighbouring active region and also showed a similar evolution to the radio flux, implying that beams of accelerated particles can synchronize radio and UV/EUV light curves across relatively large distances. [ABSTRACT FROM AUTHOR]

The study of apsidal motion in eccentric eclipsing binaries provides an important observational test of theoretical models of stellar structure and evolution. New ground-based and space-based photometric data have been obtained and archival spectroscopic measurements were used in this study of three detached early-type and southern-hemisphere eccentric eclipsing binaries GM Nor (P = 1d​​.88, e = 0.05), V397 Pup (3d​​.00, 0.30), and PT Vel (1d​​.80, 0.12). Their TESS observations in several sectors have also been included and the corresponding light curves were solved using the PHOEBE code. As a result, new accurate photoelectric times of minimum light have been obtained. The newly completed O − C diagrams were analyzed using all reliable timings found in the literature and calculated using the TESS light curves. New or improved values for the elements of apsidal motion were obtained. Using ESO archive spectroscopy, for V397 Pup, the precise absolute parameters were newly derived: M1 = 3.076(35) M⊙, M2 = 2.306(35) M⊙, and R1 = 2.711(55) R⊙, R2 = 1.680(55) R⊙. For PT Vel the absolute dimensions were improved: M1 = 2.204(25) M⊙, M2 = 1.638(25) M⊙, and R1 = 2.108(30) R⊙, R2 = 1.605(30) R⊙. For GM Nor, the less accurate absolute parameters based on the light curve analysis were evaluated: M1 = 1.94(15) M⊙, M2 = 1.84(14) M⊙, and R1 = 2.27(20) R⊙, R2 = 2.25(20) R⊙. We found more precise and relatively short periods of apsidal motion of about 80, 335, and 160 years, along with the corresponding internal structure constants, log k2, –2.524, –2.361, and –2.563, for GM Nor, V397 Pup, and PT Vel, respectively. Relativistic effects are small but not negligible, making up to 10% of the total apsidal motion rate in all systems. No marks of the presence of the third body were revealed in the light curves, on the O − C diagrams, or in the reduced spectra of the eccentric systems studied here. [ABSTRACT FROM AUTHOR]

Context. Two millisecond pulsars, PSR J1513−2550 and PSR J2017−1614, with spin periods of about 2.1 and 2.3 ms were recently discovered in the radio and γ-rays and classified as black widow pulsars in tight binary stellar systems with orbital periods of about 4.3 and 2.3 h. Aims. Our goals are to reveal the fundamental parameters of both systems and their binary components using multi-wavelength observations. Methods. We carried out the first time-series multi-band optical photometry of the objects with the 2.1-m telescope of the Observatorio Astronómico Nacional San Pedro Mártir, the 6.5-m Magellan-1 telescope, and the 10.4-m Gran Telescopio Canarias. To derive the parameters of both systems, we fitted the obtained light curves with a model assuming heating of the companion by the pulsar. We also analysed archival X-ray data obtained with the XMM-Newton observatory. Results. For the first time, we firmly identified J1513−2550 in the optical and both pulsars in X-rays. The optical light curves of both systems have a single peak per orbital period with a peak-to-peak amplitude of ≳2 magnitudes. The J2017−1614 light curves are symmetric, while J1513−2550 demonstrates strong asymmetry whose nature remains unclear. Conclusions. We constrained the orbital inclinations, pulsar masses, companion temperatures and masses, and the distances to both systems. We also conclude that J2017−1614 may contain a massive neutron star of 2.4 ± 0.6 M⊙. The X-ray spectra of both sources can be fitted by power laws with parameters typical of black widow systems. [ABSTRACT FROM AUTHOR]

Context. Extragalactic fast X-ray transients (FXTs) are short-duration (∼ks) X-ray flashes of unknown origin, potentially arising from binary neutron star (BNS) mergers, tidal disruption events, or supernova shock breakouts. Aims. In the context of the BNS scenario, we investigate the possible link between FXTs and the afterglows of off-axis merger-induced gamma-ray bursts (GRBs). Methods. By modelling well-sampled broadband afterglows of 13 merger-induced GRBs, we make predictions for their X-ray light curve behaviour had they been observed off-axis, considering both a uniform jet with core angle θC and a Gaussian-structured jet whose edge lies at an angle θW = 2θC. We compare their peak X-ray luminosity, duration, and temporal indices α (where F ∝ tα) with those of the currently known extragalactic FXTs. Results. Our analysis reveals that a slightly off-axis observing angle of θobs ≈ (2.2 − 3)θC and a structured jet are required to explain the shallow (|α|≲0.3) temporal indices of the FXT light curves, which cannot be reproduced in the uniform-jet case at any viewing angle. In the case of a structured jet with truncation angle θW = 2θC, the distributions of the duration of the FXTs are consistent with those of the off-axis afterglows for the same range of observing angles, θobs ≈ (2.2 − 3)θC. While the distributions of the off-axis peak X-ray luminosity are consistent only for θobs = 2.2θC, focussing on individual events with different intrinsic luminosities reveals that the match of all three properties (peak X-ray luminosity, duration and temporal indices) of the FXTs at the same viewing angle is possible in the range θobs ∼ (2.2 − 2.6)θC. Despite the small sample of GRBs analysed, these results show that there is a region of the parameter space – although quite limited – where the observational properties of off-axis GRB afterglow can be consistent with those of the newly discovered FXTs. Future observations of FXTs discovered by the recently launched Einstein Probe mission and GRB population studies combined with more complex afterglow models will shed light on this possible GRB-FXT connection, and eventually unveil the progenitors of some FXTs. [ABSTRACT FROM AUTHOR]

Context. Galaxy cluster mergers are believed to generate large-scale shock waves that are ideal sites for cosmic ray production. In these so-called radio relic shocks, synchrotron radiation is produced mainly as a result of electron acceleration in the presence of intracluster magnetic fields. Aims. We aim to compute radio emission light curves for a sample of galaxy group and cluster mergers simulated in a cosmological context in order to study the dependence of radio luminosity on cluster mass, redshift, and impact parameter. Methods. We used model galaxy clusters from THE THREE HUNDRED project, a sample of 324 simulated high-density regions of radius 15 h−1 Mpc extracted from a cosmological volume, to identify cluster mergers characterised by the two main merging structures, construct their light curves, and follow their evolution throughout the complete simulated cosmic history. Results. We found that the median non-thermal radio relic luminosity light curve produced in galaxy cluster mergers can be described by a skewed Gaussian function abruptly rising after core-passage of the secondary cluster that peaks after ~0.1–0.8 Gyr as a function of M200,1, the mass of the primary, displaying a mass-dependent luminosity output increase of ≲10 to about ≳10–50 times relative to the radio emission measured at core-passage for galaxy groups and clusters, respectively. In general, most merger orbits are fairly radial with a median opening angle of ~20º before the collision. We also found that, independent of the cluster mass, less radial mergers tend to last longer, although the trend is weak. Finally, in agreement with previous works, we found that the peak radio luminosity shows a significant correlation with mass, P1.4 ∝ M200,12.05 demonstrating that this relation holds all the way up from galaxy group scales to the most massive galaxy clusters. Conclusions. We conclude that cluster mass is the primary driver for radio 'gischt' median luminosity, although there are significant variations for a given cluster mass related to the specifics of each merging process. In general, binary mergers are responsible for many of the well-known observed radio relic structures but complex situations involving three or more substructures are also common. Our simulations suggest that the shock-driven, non-thermal radio emission observed on cluster outskirts are the result of massive galaxy cluster mergers at ɀ ≲ 1, peaking at ɀ ~ 0–0.5. [ABSTRACT FROM AUTHOR]

Context. To date, three pulsars have been firmly detected by imaging atmospheric Cherenkov telescopes (IACTs). Two of them reached the TeV energy range, challenging models of very high-energy (VHE) emission in pulsars. More precise observations are needed to better characterize pulsar emission at these energies. The LST-1 is the prototype of the large-sized telescopes, which will be part of the Cherenkov Telescope Array Observatory (CTAO). Its improved performance over previous IACTs makes it well suited for studying pulsars. Aims. In this work we study the Crab pulsar emission with the LST-1, improving upon and complementing the results from other telescopes. Crab pulsar observations can also be used to characterize the potential of the LST-1 to study other pulsars and detect new ones. Methods. We analyzed a total of ∼103 hours of gamma-ray observations of the Crab pulsar conducted with the LST-1 in the period from September 2020 to January 2023. The observations were carried out at zenith angles of less than 50 degrees. To characterize the Crab pulsar emission over a broader energy range, a new analysis of the Fermi/LAT data, including ∼14 years of observations, was also performed. Results. The Crab pulsar phaseogram, long-term light curve, and phase-resolved spectra are reconstructed with the LST-1 from 20 GeV to 450 GeV for the first peak and up to 700 GeV for the second peak The pulsed emission is detected with a significance level of 15.2σ. The two characteristic emission peaks of the Crab pulsar are clearly detected (> 10σ), as is the so-called bridge emission between them (5.7σ). We find that both peaks are described well by power laws, with spectral indices of ∼3.44 and ∼3.03, respectively. The joint analysis of Fermi/LAT and LST-1 data shows a good agreement between the two instruments in their overlapping energy range. The detailed results obtained from the first observations of the Crab pulsar with the LST-1 show the potential that CTAO will have to study this type of source. [ABSTRACT FROM AUTHOR]

We present a comparative analysis of photometric observations of the cataclysmic variable TT Ari in its bright state obtained by the TESS orbital observatory in 2021 and 2023 and by ground-based amateur telescopes in 2022. The light curves from 2021 and 2022 are dominated by modulations with a period slightly shorter than the orbital one (negative superhumps), 0.13292 and 0.13273 d, respectively. From the data obtained in 2023, we see much stronger modulations appearing on a much longer timescale of a few days with an amplitude of up to 0.5 mag, compared to 0.2 mag in 2021. We also find the negative superhump variability with the period of 0.1338 d in the 2023 observations, but the significance of these negative superhumps is much lower than in the previous seasons. We detect less significant additional modulations with a period exceeding the orbital one (positive superhumps) in the observations from 2021 and 2022. Their periods are 0.15106 and 0.1523 d, respectively. We also find a previously unnoticed periodic signal corresponding to the orbital period of 0.13755 d in the TESS observations in 2021. Theoretical models of tidal precession of an elliptical disk predict a decrease in the precession period (and an increase in the period of the positive superhumps) with increasing disk radius, which is consistent with the observed photometric behavior of the system. This enables us to estimate the mass ratio q of the components in TT Ari to be in the range of 0.24–0.29. The tilted disk precession model predicts a period of nodal precession whose value is in general agreement with observations. [ABSTRACT FROM AUTHOR]

Context. The Kepler space mission provided high-quality light curves for more than 16 000 red giants. The global stellar oscillations extracted from these light curves carry information about the interior of the stars. Several hundred red giants were found to have low amplitudes in their dipole modes (i.e. they are suppressed dipole-mode stars). A number of hypotheses (involving e.g. a magnetic field, binarity, or resonant mode coupling) have been proposed to explain the suppression of the modes, yet none has been confirmed. Aims. We aim to gain insight into the mechanism at play in suppressed dipole-mode stars by investigating the mode properties (linewidths, heights, and amplitudes) of the radial oscillation modes of red giants with suppressed dipole modes. Methods. We selected from the literature suppressed dipole-mode stars and compared the radial-mode properties of these stars to the radial-mode properties of stars in two control samples of stars with typical (i.e. non-suppressed) dipole modes. Results. We find that the radial-mode properties of the suppressed dipole-mode stars are consistent with the ones in our control samples, and hence not affected by the suppression mechanism. Conclusions. From this we conclude that (1) the balance between the excitation and damping in radial modes is unaffected by the suppression, and by extrapolation the excitation of the non-radial modes is not affected either; and (2) the damping of the radial modes induced by the suppression mechanism is significantly less than the damping from turbulent convective motion, suggesting that the additional damping originates from the more central non-convective regions of the star, to which the radial modes are least sensitive. [ABSTRACT FROM AUTHOR]

Context. The Transiting Exoplanet Survey Satellite (TESS) performs high-precision photometry over almost the whole sky primarily in search of exoplanet transits. It also provides exquisite data to study stellar variability, in particular for pulsating hot B subdwarf (sdB) stars. Aims. We present a detailed analysis of a new hybrid (p- and g-mode) sdB pulsator, TIC 441725813 (TYC 4427-1021-1), discovered and monitored by TESS for 670 days. Methods. The TESS light curves available for this star were analysed using prewhitening techniques to extract mode frequencies accurately. The pulsation spectrum was then interpreted through methods that include asymptotic period spacing relationships and the identification of rotational multiplets. We also exploited a high signal-to-noise ratio (S/N), low-resolution spectrum of TIC 441725813 using grids of non-local thermodynamic equilibrium (NLTE) model atmospheres to derive its atmospheric parameters. Results. The light curve analysis reveals that frequencies are mostly found in the g-mode region, but several p-modes are also detected, indicating that TIC 441725813 is a hybrid sdB pulsator. We identify 25 frequencies that can be associated with ℓ = 1 g-modes, 15 frequencies corresponding to ℓ = 2 g-modes, and six frequencies characteristic of p-modes. Interestingly, several frequency multiplets interpreted as rotational splittings of deep-probing g-modes indicate a slow rotation period of at least 85.3 ± 3.6 day, while splittings of mostly envelope-probing p-modes suggest a significantly shorter rotation period of 17.9 ± 0.7 day, which implies the core (mainly the helium mantle with possibly the deeper partially mixed helium-burning core that it surrounds) rotates at least 4.7 times slower than the envelope. The radial velocity curves indicate that TIC 441725813 is in a close binary system with a low-luminosity companion, possibly a white dwarf. While elusive in the available TESS photometry, a low-frequency signal that would correspond to a period of ∼6.7 h is found, albeit at a low S/N. Furthermore, we estimate the inclination angle to be ∼60° by two independent means. Conclusions. TIC 441725813 is a particularly interesting sdB star whose envelope rotates faster than the core. We hypothesise that this might be caused by the effects of a tidal interaction with a companion, although in the present case, the presence of such a companion will have to be further investigated. This analysis paves the way towards a more detailed seismic probing of TIC 441725813 using optimisation techniques, which will be presented in a second paper. [ABSTRACT FROM AUTHOR]

Context. The extreme teraelectronvolt (TeV) blazar 1ES 0229+200 is a high-frequency-peaked BL Lacertae object. It has not shown intraday variability in extensive optical and X-ray observations, nor has it shown any significant variability on any measurable timescale in the 1–100 GeV energy range over a 14-year span; however, variations in the source flux around its average are present in the energy range above 200 GeV. Aims. We aim to search for intraday optical variability in 1ES 0229+200 as part of an ongoing project to search for variability and quasi-periodic oscillations in the high-cadence (2 min), nearly uniformly sampled optical light curves of blazars provided by the Transiting Exoplanet Survey Satellite (TESS). Methods. 1ES 0229+200 was monitored by TESS in its Sectors 42, 43, and 44. We analysed the data of all these three sectors both with the TESS-provided lightkurve software and the eleanor reduction pipeline. We detected a strong, essentially symmetric flare that lasted about 6 h in Sector 42. We fitted the flare's rising and declining phases to exponential functions. We also analysed the light curve of Sector 42 using the Lomb-Scargle periodogram (LSP) and continuous auto-regressive moving average (CARMA) methods. Results. The optical light curve of Sector 42 of the TESS observations displayed in the present work provides the first evidence of a strong, rapid, short-lived optical flare on the intraday timescale in the TeV blazar 1ES 0229+200. The variability timescale of the flare provides the upper limit for the size of the emission region to be within (3.3 ± 0.2–8.3 ± 0.5)×1015 cm. Away from the flare, the slope of the periodogram's power spectrum is fairly typical of many blazars (α < 2), but the nominal slopes for the flaring regions are very steep (α ∼ 4.3), which may indicate that the electron distribution undergoes a sudden change. We discuss possible emission mechanisms that could explain this substantial and rapid flare. [ABSTRACT FROM AUTHOR]

Aims. In this work, we study the X-ray spectral and temporal properties of an ultraluminous X-ray source (ULX) in NGC 628 by using multi-epoch archival X-ray data. The physical parameters were estimated in each epoch in order to constrain the nature of the compact object in the system. Also, the optical counterpart candidates of the ULX were examined using the archival Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) data. Methods.XMM-Newton, Chandra, and Swift data were used to create the long-term light curve (which covers a period of 22 years) and perform the spectral analysis. Lomb-Scargle periodograms of the source were constructed to examine the short-term variability in each epoch. In order to search for an optical counterpart in the HST/WFC3 images, a relative astrometric correction was initially applied to the Chandra and HST/WFC3 images. Results. The X-ray flux of the source changes by a factor of ∼200 throughout the observations. The previously detected quasi-periodic signal (in the range of 0.1−0.4 mHz) was confirmed by using the Lomb-Scargle method. After astrometric correction, two optical counterpart candidates were detected for the source. The obtained spectral energy distributions in the optical band for both candidates indicate that the optical emission is dominated by the irradiation of the accretion disc. Considering the best-fit model parameters of the multi-colour disc black-body model, we derived the mass of the black hole in the system as being in the range of (5−28) M⊙. Nonetheless, the long-term variability and the spectral transitions in the hardness–luminosity diagram make it difficult to rule out the neutron star scenario. [ABSTRACT FROM AUTHOR]

Context. Long gamma-ray bursts (GRBs) are produced by the collapse of some very massive stars, that emit ultra-relativistic jets. When the jets collide with the interstellar medium they decelerate and generate the so-called afterglow emission, which has been observed to be polarised. Aims. We study the polarimetric evolution of the GRB 210610B afterglow, at z = 1.1341. This allows us to evaluate the role of geometric and/or magnetic mechanisms in the GRB afterglow polarisation. Methods. We observed GRB 210610B using imaging polarimetry with CAFOS on the 2.2 m Calar Alto Telescope and FORS2 on the 4 × 8.1 m Very Large Telescope. Complementary optical spectroscopy was obtained with OSIRIS on the 10.4 m Gran Telescopio Canarias. We studied the GRB light-curve from X-rays to the optical bands and the Spectral Energy Distribution (SED). This allowed us to strongly constrain the line-of-sight extinction. Finally, we studied the GRB host galaxy using optical to NIR data to fit the SED and derive its integrated properties. Results. GRB 210610B had a bright afterglow with a negligible line-of-sight extinction. Polarimetry was obtained at three epochs: during an early plateau phase, at the time when the light curve breaks, and after the light curve steepened. We observe an initial polarisation of ∼4% that goes to zero at the time of the break, and it then again increases to ∼2%, with a change in the position angle of 54 ± 9 deg. The spectrum shows features with very low equivalent widths. This indicate a small amount of material in the line of sight within the host. Conclusions. The lack of dust and the low amount of material in the line of sight to GRB 210610B allowed us to study the intrinsic polarisation of the GRB optical afterglow. The GRB polarisation signals are consistent with ordered magnetic fields in refreshed shock or/and hydrodynamics-scale turbulent fields in the forward shock. [ABSTRACT FROM AUTHOR]

Context. There is a growing number of peculiar events that cannot be assigned to any of the main classes. SN 1987A and a handful of similar objects, thought to be explosive outcomes of blue supergiant stars, is one of them: while their spectra closely resemble those of H-rich (IIP) SNe, their light curve (LC) evolution is very different. Aims. Here we present the detailed photometric and spectroscopic analysis of SN 2021aatd, a peculiar Type II explosion. While its early-time evolution resembles that of the slowly evolving double-peaked SN 2020faa (although at a lower luminosity scale), after ∼40 days its LC shape becomes similar to that of SN 1987A-like explosions. Methods. In addition to comparing LCs, color curves, and spectra of SN 2021aatd to those of SNe 2020faa, 1987A, and other objects, we compared the observed spectra with our own SYN++ models and with the outputs of published radiative transfer models. We also carried out a detailed modeling of the pseudo-bolometric LCs of SNe 2021aatd and 1987A with a self-developed semi-analytical code, assuming a two-component ejecta (core + shell), and involving the rotational energy of a newborn magnetar in addition to radioactive decay. Results. We find that the photometric and the spectroscopic evolution of SN 2021aatd can be well described with the explosion of a ∼15 M⊙ blue supergiant star. Nevertheless, SN 2021aatd shows higher temperatures and weaker Na I D and Ba II 6142 Å lines than SN 1987A, which is instead reminiscent of IIP-like atmospheres. With the applied two-component ejecta model (accounting for decay and magnetar energy), we can successfully describe the bolometric LC of SN 2021aatd, including the first ∼40-day phase showing an excess compared to 87A-like SNe, but being strikingly similar to that of the long-lived SN 2020faa. Nevertheless, finding a unified model that also explains the LCs of more luminous events (e.g., SN 2020faa) is still a matter of debate. [ABSTRACT FROM AUTHOR]

The origin of high-energy (HE) astrophysical neutrinos has remained an elusive hot topic in the field of HE astrophysics for the past decade. Apart from a handful of individual associations, the vast majority of HE neutrinos arise from unknown sources. While there are theoretically motivated candidate populations, such as blazars – a subclass of active galactic nuclei with jets pointed toward our line of sight – they have not been convincingly linked to HE neutrino production yet. Here, we perform a spatio-temporal association analysis between a sample of blazars (from the CGRaBS catalog) in the radio and optical bands and the most up-to-date IceCube HE neutrino catalog. We find that if the IceCube error regions are enlarged by 1° in quadrature, to account for unknown systematic errors at a maximal level, a spatio-temporal correlation between the multiwavelength light curves of the CGRaBS blazars and the IceCube HE neutrinos is hinted at, least at a 2.17σ significance level. On the other hand, when the IceCube error regions are taken as their published values, we do not find any significant correlations. A discrepancy in the blazar-neutrino correlation strengths, when using such minimal and enlarged error region scenarios, was also obtained in a recent study by the IceCube collaboration. In our study, this difference arises because several flaring blazars – coinciding with a neutrino arrival time – happen to narrowly miss the published 90%-likelihood error region of the nearest neutrino event. For all of the associations driving our most significant correlations, the flaring blazar is much less than 1° away from the published error regions. Therefore, our results indicate that the question of the blazar-neutrino connection is highly sensitive to the reconstruction of the neutrino error regions, whose reliability is expected to improve with the next generation of neutrino observatories. [ABSTRACT FROM AUTHOR]