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Catalina Sky Survey (CSS) is a major survey of Near-Earth Objects (NEOs). In a recent work, we used CSS observations from 2005–2012 to develop a new population model of NEOs (NEOMOD). CSS’s G96 telescope was upgraded in 2016 and detected over 10,000 unique NEOs since then. Here we characterize the NEO detection efficiency of G96 and use G96’s NEO detections from 2013–2022 to update NEOMOD. This resolves previous model inconsistencies related to the population of large NEOs. We estimate there are 936 ± 29 NEOs with absolute magnitude 𝐻 < 17.75 (diameter 𝐷 > 1 km for the reference albedo 𝑝V = 0.14) and semimajor axis 𝑎 < 4.2 au. The slope of the NEO size distribution for 𝐻 = 25–28 is found to be relatively shallow (cumulative index ≃ 2.6) and the number of 𝐻 < 28 NEOs (𝐷 > 9 m for 𝑝V = 0.14) is determined to be (1.20 ± 0.04) × 107 , about 3 times lower than in Harris & Chodas (2021). Small NEOs have a different orbital distribution and higher impact probabilities than large NEOs. We estimate 0.034 ± 0.002 impacts of 𝐻 < 28 NEOs on the Earth per year, which is near the low end of the impact flux range inferred from atmospheric bolide observations. Relative to a model where all NEOs are delivered directly from the main belt, the population of small NEOs detected by G96 shows an excess of low-eccentricity orbits with 𝑎 ≃ 1–1.6 au that appears to increase with 𝐻 (≃ 30% excess for 𝐻 = 28). We suggest that the population of very small NEOs is boosted by tidal disruption of large NEOs during close encounters to the terrestrial planets. When the effect of tidal disruption is (approximately) accounted for in the model, we estimate 0.06 ± 0.01 impacts of 𝐻 < 28 NEOs on the Earth per year, which is more in line with the bolide data. The impact probability of a 𝐻 < 22 (𝐷 > 140 m for 𝑝V = 0.14) object on the Earth in this millennium is estimated to be ≃ 4.5% 

Abstract We present upgraded infrastructure for Searches After Gravitational waves Using ARizona Observatories (SAGUARO) during LIGO, Virgo, and KAGRA’s fourth gravitational-wave (GW) observing run (O4). These upgrades implement many of the lessons we learned after a comprehensive analysis of potential electromagnetic counterparts to the GWs discovered during the previous observing run. We have developed a new web-based target and observation manager (TOM) that allows us to coordinate sky surveys, vet potential counterparts, and trigger follow-up observations from one centralized portal. The TOM includes software that aggregates all publicly available information on the light curves and possible host galaxies of targets, allowing us to rule out potential contaminants like active galactic nuclei, variable stars, solar system objects, and preexisting supernovae, as well as to assess the viability of any plausible counterparts. We have also upgraded our image-subtraction pipeline by assembling deeper reference images and training a new neural-network-based real–bogus classifier. These infrastructure upgrades will aid coordination by enabling the prompt reporting of observations, discoveries, and analysis to the GW follow-up community, and put SAGUARO in an advantageous position to discover kilonovae in the remainder of O4 and beyond. Many elements of our open-source software stack have broad utility beyond multimessenger astronomy, and will be particularly relevant in the “big data” era of transient discoveries by the Vera C. Rubin Observatory. 

Abstract Near-Earth Objects (NEOs) are a transient population of small bodies with orbits near or in the terrestrial planet region. They represent a mid-stage in the dynamical cycle of asteroids and comets, which starts with their removal from the respective source regions—the main belt and trans-Neptunian scattered disk—and ends as bodies impact planets, disintegrate near the Sun, or are ejected from the solar system. Here we develop a new orbital model of NEOs by numerically integrating asteroid orbits from main-belt sources and calibrating the results on observations of the Catalina Sky Survey. The results imply a size-dependent sampling of the main belt with the ν 6 and 3:1 resonances producing ≃30% of NEOs with absolute magnitudes H = 15 and ≃80% of NEOs with H = 25. Hence, the large and small NEOs have different orbital distributions. The inferred flux of H < 18 bodies into the 3:1 resonance can be sustained only if the main-belt asteroids near the resonance drift toward the resonance at the maximal Yarkovsky rate (≃2 × 10 −4 au Myr −1 for diameter D = 1 km and semimajor axis a = 2.5 au). This implies obliquities θ ≃ 0° for a < 2.5 au and θ ≃ 180° for a > 2.5 au, both in the immediate neighborhood of the resonance (the same applies to other resonances as well). We confirm the size-dependent disruption of asteroids near the Sun found in previous studies. An interested researcher can use the publicly available NEOMOD Simulator to generate user-defined samples of NEOs from our model. 

Stars with zero-age main sequence masses between 140 and 260 M_⊙are thought to explode as pair-instability supernovae (PISNe). During their thermonuclear runaway, PISNe can produce up to several tens of solar masses of radioactive nickel, resulting in luminous transients similar to some superluminous supernovae (SLSNe). Yet, no unambiguous PISN has been discovered so far. SN 2018ibb is a hydrogen-poor SLSN atz = 0.166 that evolves extremely slowly compared to the hundreds of known SLSNe. Between mid 2018 and early 2022, we monitored its photometric and spectroscopic evolution from the UV to the near-infrared (NIR) with 2–10 m class telescopes. SN 2018ibb radiated > 3 × 10⁵¹ erg during its evolution, and its bolometric light curve reached > 2 × 10⁴⁴ erg s⁻¹at its peak. The long-lasting rise of > 93 rest-frame days implies a long diffusion time, which requires a very high total ejected mass. The PISN mechanism naturally provides both the energy source (⁵⁶Ni) and the long diffusion time. Theoretical models of PISNe make clear predictions as to their photometric and spectroscopic properties. SN 2018ibb complies with most tests on the light curves, nebular spectra and host galaxy, and potentially all tests with the interpretation we propose. Both the light curve and the spectra require 25–44M_⊙of freshly nucleosynthesised⁵⁶Ni, pointing to the explosion of a metal-poor star with a helium core mass of 120–130M_⊙at the time of death. This interpretation is also supported by the tentative detection of [Co II]λ1.025 μm, which has never been observed in any other PISN candidate or SLSN before. We observe a significant excess in the blue part of the optical spectrum during the nebular phase, which is in tension with predictions of existing PISN models. However, we have compelling observational evidence for an eruptive mass-loss episode of the progenitor of SN 2018ibb shortly before the explosion, and our dataset reveals that the interaction of the SN ejecta with this oxygen-rich circumstellar material contributed to the observed emission. That may explain this specific discrepancy with PISN models. Powering by a central engine, such as a magnetar or a black hole, can be excluded with high confidence. This makes SN 2018ibb by far the best candidate for being a PISN, to date. 

Abstract We present the results of a systematic search for quasars in the Catalina Real-time Transient Survey exhibiting both strong photometric and spectroscopic variability over a decadal baseline. We identify 111 sources with specific patterns of optical and mid-IR photometric behavior and a defined spectroscopic change. These “Changing-State” quasars (CSQs) form a higher luminosity sample to complement existing sets of “Changing-Look” AGN and quasars in the literature. The CSQs (by selection) exhibit larger photometric variability than the CLQs. The spectroscopic variability is marginally stronger in the CSQs than CLQs as defined by the change in Hβ/[O iii] ratio. We find 48 sources with declining Hβ flux, 63 sources with increasing Hβ flux and discover eight sources with z > 0.8, further extending the redshift arm. Our CSQ sample compares to the literature CLQ objects in similar distributions of Hβ flux ratios and differential Eddington ratios between high (bright) and low (dim) states. Taken as a whole, we find that this population of extreme varying quasars is associated with changes in the Eddington ratio and the timescales imply cooling/heating fronts propagating through the disk.