Takashi J. Moriya, Steve Schulze, Alexander Heger, Sergei I. Blinnikov, Marat Sh. Potashov
SN 2018ibb is one of the best pair-instability supernova (PISN) candidates identified to date. It, however, showed unexpected blue flux excess in late-phase spectra, likely originating from the interaction between supernova (SN) ejecta and dense circumstellar matter (CSM). We develop synthetic light-curve models of PISNe interacting with dense CSM and estimate the CSM properties of SN 2018ibb by comparing the synthetic and observed light curves. We found that the bolometric luminosity evolution of SN 2018ibb from 150 d after the peak can be well reproduced by the interaction with the CSM formed by a mass-loss rate of 0.01 ( v CSM / 1,000 k m s − 1 ) M ⊙ y r − 1 , where v CSM is the CSM velocity. The observed luminosity break at around 300 d from the peak indicates that the CSM interaction ended at this time and the dense CSM radius was 8.5 × 1 0 16 c m . The CSM radius then implies that the mass loss of the progenitor was enhanced for 28 ( v CSM / 1,000 k m s − 1 ) − 1 y r before explosion. We conclude that PISN progenitors may experience short-term mass-loss enhancement within decades before explosion, similar to what is often observed in progenitors of core-collapse SNe.
Elizabeth MacDonald, Feras Natsheh, Laura Brandt Edson, Matthew Heavner
This technical report details Aurorasaurus citizen science data from the operational lifetime of the project, with a particular focus on observations collected during the geomagnetic superstorms of 2024. The report also presents updates to the project’s data filtering protocols and scientific data release pipeline. Aurorasaurus crowdsourced observations are submitted via the project’s website and mobile platforms, forming a robust dataset that is especially abundant during intense geomagnetic storms when traditional auroral precipitation models are most uncertain. This dataset is offered to the scientific community in both raw and scientific formats through an open-access repository. The methods and transformations applied to produce a scientifically usable version of the dataset are documented in detail in this report. Furthermore, this release includes interactive, open-source Jupyter Notebooks that enable exploration, visualization, and comparison of auroral observations in conjunction with geophysical data. By demonstrating the reproducibility and utility of this workflow, we aim to encourage the integration of Aurorasaurus citizen science data into space weather research by amateurs and professionals alike.
General relativity with the observed baryons alone underpredicts the dynamics of galaxies and galaxy clusters at accelerations near the product of the speed of light and the Hubble constant. Here, we develop and evaluate an emergent-scalar-field framework built on one hypothesis: ordinary matter continuously emits scalar waves (not gravitational radiation) with random, uncorrelated phases. The time-averaged intensity of the summed field separates into three parts. The stationary part, one contribution per source, reproduces Newtonian attraction. Waves arriving from all matter within the causal horizon form a fluctuating background that defines an acceleration scale g w =(3/8 π ) cH 0 ≈7.9 × 10 -11 m s -2 , fixed by measured cosmology. Interference between the local field and this background, rectified by the material medium under a single stated assumption, adds an attractive acceleration proportional to √(g N g w ), where g N is the Newtonian acceleration of the baryons. Three phenomenological functions of the local matter distribution (screening, saturation, and an ionized-gas enhancement) modulate this term, motivated by, but not derived from, the covariant theory. Three constants are fixed in advance; one coefficient, γ p , is calibrated on the X-COP cluster sample and frozen. On 3,187 weak-field points in 175 rotation curves from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database, the calibration-free prediction attains a root-mean-square error (RMSE) of 0.228 dex (95% CI = 0.204–0.253), against 0.398 for general relativity with baryons only, 0.270 for modified Newtonian dynamics (MOND) at its standard acceleration constant, and 0.213 for MOND with a re-fitted constant. On X-COP, leave-one-cluster-out validation yields 0.072 dex, and the calibrated γ p = 0.69 (0.60–0.79) lies 36% below an independent ionization estimate. Applied unchanged to 22 eROSITA clusters, the framework roughly halves the central shortfall of baryons alone but retains a radially structured under-prediction (0.435 dex overall), comparable in magnitude to that of MOND. The same model underpredicts the velocity dispersions of four of five dwarf spheroidals. Solar System and wide-binary checks are conditional on the calibrated screening and stated transport convention, and a matter-like scalar background reproduces the baryon-acoustic-oscillation sound horizon to 0.04% (matched drag-epoch prescription). All numerical results were obtained with a single released analysis pipeline.
Under restrictive elevation-cutoff conditions, Global Navigation Satellite System (GNSS) precise point positioning (PPP) time transfer can suffer delayed convergence because fewer satellites are available and the timing geometry degrades. However, it remains unclear whether low Earth orbit (LEO) geometric augmentation yields a consistent elevation-cutoff response for both convergence and steady-state performance. Using 5 days of Multi-GNSS Experiment (MGEX) GNSS observations and simulated Walker 288/24/1 LEO observations, we construct a GPS/BDS-3/Galileo (GCE) solution and a LEO-augmented solution (GCE + LEO), and compare the number of visible satellites, the time dilution of precision (TDOP), convergence time, steady-state standard deviation (STD) and modified Allan deviation (MDEV) at elevation cutoffs of 10°, 20°, 30° and 40°. As the cutoff increases from 10° to 40°, the mean number of visible satellites for GCE decreases from 26.06 to 11.42, while the mean TDOP increases from 0.547 to 3.482. Adding LEO observations increases satellite visibility by 17.2%–44.9% and reduces TDOP by 14.6%–27.6%. Across all four cutoffs, GCE + LEO shortens time-link convergence; the six-link median reductions are 16.4%, 25.0%, 22.2% and 31.6%, respectively, with a generally larger convergence benefit at higher cutoffs. The steady-state STD shows a different cutoff dependence: at 10°, all six links exhibit STD reductions, with a median link-wise relative reduction of 22.7%; at 20° and 30°, the median changes are both about −1.5%, and some links show slight increases of only a few percent; at 40°, the median change is only about 0.2%, indicating only a marginal difference between the two schemes. At an averaging time of τ = 3000 s, the six-link median MDEV reduction decreases from 48.9% at 10° to 2.1% at 40°. These results indicate that LEO augmentation of PPP time transfer is stage dependent: under restricted observing conditions it mainly accelerates the time link into a usable state, whereas under more favourable observing conditions it more clearly improves steady-state dispersion and medium-to-long-term frequency stability.
Since the early 1960s, many studies have documented ionospheric virtual height oscillation with periods ranging from 30 min to 3 h. However, in this investigation, we find a consistent, much larger period in the oscillations of virtual height, as estimated using Coastal Ocean Dynamics Applications Radars (CODARs), whereas few previous studies have consistently observed periods of oscillation in this range. The purpose of this investigation is to investigate day-to-day bottomside variability, and we report a consistently observed 4–5-h period of virtual height oscillation, along with providing potential physical interpretations of the observations. We use bistatic high-frequency data from CODARs, collected nearly continuously between 2020 and 2023 at a 2-min time cadence. The frequency modulated continuous wave (FMCW) waveforms of these radars are suitable as a single-frequency oblique ionospheric sounder. We estimate the group delay from which the virtual height of an ionospheric layer can be estimated. We present statistical results from several virtual height oscillations with varying periods across September, October, November, and December during 2020–2023. For each year, we compare three to four CODAR transmitters located in the Eastern United States, operating at 4–5 MHz. The receiver is located near Clemson University. We frequently observe ( ≈ 25% of the time) the 4–5-h period of virtual height oscillation each September through December over the 4-year span, which has a longer period than the standard categorization of a Large Scale Traveling Ionospheric Disturbance (LSTID). To further understand the characteristics of these structures, we separate them into both propagating and non-propagating structures. We found that for all 4–5-h structures with southward propagation, the night prior was geomagnetically active. We also find significant similarities between the non-propagating structures and two ionospheric phenomena, the midnight collapse and post-midnight enhancement.
