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In the pursuit of understanding the population of stellar remnants within the Milky Way, we analyze the sample of ∼950 microlensing events observed by the Spitzer Space Telescope between 2014 and 2019. In this study we focus on a subsample of nine microlensing events, selected based on their long timescales, small microlensing parallaxes, and joint observations by the Gaia mission, to increase the probability that the chosen lenses are massive and the mass is measurable. Among the selected events we identify lensing black holes and neutron star candidates, with potential confirmation through forthcoming release of the Gaia time-series astrometry in 2026. Utilizing Bayesian analysis and Galactic models, along with the Gaia Data Release 3 proper-motion data, four good candidates for dark remnants were identified: OGLE-2016-BLG-0293, OGLE-2018-BLG-0483, OGLE-2018-BLG-0662, and OGLE-2015-BLG-0149, with lens masses of ${3.0}_{-1.3}^{+1.8}\,{M}_{\odot }$ , ${4.7}_{-2.1}^{+3.2}\,{M}_{\odot }$ , ${3.15}_{-0.64}^{+0.66}\,{M}_{\odot }$ and ${1.40}_{-0.55}^{+0.75}\,{M}_{\odot }$ , respectively. Notably, the first two candidates are expected to exhibit astrometric microlensing signals detectable by Gaia, offering the prospect of validating the lens masses. The methodologies developed in this work will be applied to the full Spitzer microlensing sample, populating and analyzing the timescale ( t _E ) versus parallax ( π _E ) diagram to derive constraints on the population of lenses in general and massive remnants in particular.

ASASSN-14ko is a nuclear transient at the center of the AGN ESO 253−G003 that undergoes periodic flares. Optical flares were first observed in 2014 by the All-Sky Automated Survey for Supernovae (ASAS-SN) and their peak times are well-modeled with a period of ${115.2}_{-1.2}^{+1.3}$ days and period derivative of −0.0026 ± 0.0006. Here we present ASAS-SN, Chandra, HST/STIS, NICER, Swift, and TESS data for the flares that occurred on 2020 December, 2021 April, 2021 July, and 2021 November. These four flares represent flares 18–21 of the total number of flares observed by ASAS-SN so far since 2014. The HST/STIS UV spectra evolve from blueshifted broad absorption features to redshifted broad emission features over ∼10 days. The Swift UV/optical light curves peaked as predicted by the timing model, but the peak UV luminosities that varied between flares and the UV flux in Flare 20 were roughly half the brightness of the other peaks. The X-ray luminosities consistently decreased and the spectra became harder during the UV/optical rise, but apparently without changes in absorption. Finally, two high-cadence TESS light curves from Flare 18 and Flare 12 showed that the slopes during the rising and declining phases changed over time, which indicates some stochasticity in the flare’s driving mechanism. Although ASASSN-14ko remains observationally consistent with a repeating partial tidal disruption event, these rich multi-wavelength data are in need of a detailed theoretical model.

We show recent detections of inter-band continuum lags in three AGN (NGC 5548, NGC 2617, and MCG+08-11-011), which provide new constraints on the temperature profiles and absolute sizes of the accretion disks. We find lags larger than would be predicted for standard geometrically thin, optically thick accretion disks by factors of 2.3–3.3. For NGC 5548, the data span UV through optical/near-IR wavelengths, and we are able to discern a steeper temperature profile than the T ~ R−3/4 expected for a standard thin disk. Using a physical model, we are also able to estimate the inclinations of the disks for two objects. These results are similar to those found from gravitational microlensing of strongly lensed quasars, and provide a complementary approach for investigating the accretion disk structure in local, low luminosity AGN.

We present the discovery and early evolution of ASASSN-19bt, a tidal disruption event (TDE) discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d ≃ 115 Mpc and the first TDE to be detected by TESS. As the TDE is located in the TESS Continuous Viewing Zone, our data set includes 30 minute cadence observations starting on 2018 July 25, and we precisely measure that the TDE begins to brighten ∼8.3 days before its discovery. Our data set also includes 18 epochs of Swift UVOT and XRT observations, 2 epochs of XMM-Newton observations, 13 spectroscopic observations, and ground data from the Las Cumbres Observatory telescope network, spanning from 32 days before peak through 37 days after peak. ASASSN-19bt thus has the most detailed pre-peak data set for any TDE. The TESS light curve indicates that the transient began to brighten on 2019 January 21.6 and that for the first 15 days, its rise was consistent with a flux ∝t2 power-law model. The optical/UV emission is well fit by a blackbody spectral energy distribution, and ASASSN-19bt exhibits an early spike in its luminosity and temperature roughly 32 rest-frame days before peak and spanning up to 14 days, which has not been seen in other TDEs, possibly because UV observations were not triggered early enough to detect it. It peaked on 2019 March 4.9 at a luminosity of L ≃ 1.3 × 1044 erg s−1 and radiated E ≃ 3.2 × 1050 erg during the 41 day rise to peak. X-ray observations after peak indicate a softening of the hard X-ray emission prior to peak, reminiscent of the hard/soft states in X-ray binaries. [ABSTRACT FROM AUTHOR]

Binaries containing a compact object orbiting a supermassive black hole are thought to be precursors of gravitational wave events, but their identification has been extremely challenging. Here, we report quasi-periodic variability in x-ray absorption, which we interpret as quasi-periodic outflows (QPOuts) from a previously low-luminosity active galactic nucleus after an outburst, likely caused by a stellar tidal disruption. We rule out several models based on observed properties and instead show using general relativistic magnetohydrodynamic simulations that QPOuts, separated by roughly 8.3 days, can be explained with an intermediate-mass black hole secondary on a mildly eccentric orbit at a mean distance of about 100 gravitational radii from the primary. Our work suggests that QPOuts could be a new way to identify intermediate/extreme-mass ratio binary candidates.

The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs) 1 , sources of high-frequency gravitational waves (GWs) 2 and likely production sites for heavy-element nucleosynthesis by means of rapid neutron capture (the r-process) 3 . Here we present observations of the exceptionally bright GRB 230307A. We show that GRB 230307A belongs to the class of long-duration GRBs associated with compact object mergers 4-6 and contains a kilonova similar to AT2017gfo, associated with the GW merger GW170817 (refs.  7-12 ). We obtained James Webb Space Telescope (JWST) mid-infrared imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns, which we interpret as tellurium (atomic mass A = 130) and a very red source, emitting most of its light in the mid-infrared owing to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy-element nucleosynthesis across the Universe., (© 2023. The Author(s).)

Temperate Earth-sized exoplanets around late-M dwarfs offer a rare opportunity to explore under which conditions planets can develop hospitable climate conditions. The small stellar radius amplifies the atmospheric transit signature, making even compact secondary atmospheres dominated by N 2 or CO 2 amenable to characterization with existing instrumentation 1 . Yet, despite large planet search efforts 2 , detection of low-temperature Earth-sized planets around late-M dwarfs has remained rare and the TRAPPIST-1 system, a resonance chain of rocky planets with seemingly identical compositions, has not yet shown any evidence of volatiles in the system 3 . Here we report the discovery of a temperate Earth-sized planet orbiting the cool M6 dwarf LP 791-18. The newly discovered planet, LP 791-18d, has a radius of 1.03 ± 0.04 R ⊕ and an equilibrium temperature of 300-400 K, with the permanent night side plausibly allowing for water condensation. LP 791-18d is part of a coplanar system 4 and provides a so-far unique opportunity to investigate a temperate exo-Earth in a system with a sub-Neptune that retained its gas or volatile envelope. On the basis of observations of transit timing variations, we find a mass of 7.1 ± 0.7 M ⊕ for the sub-Neptune LP 791-18c and a mass of [Formula: see text] for the exo-Earth LP 791-18d. The gravitational interaction with the sub-Neptune prevents the complete circularization of LP 791-18d's orbit, resulting in continued tidal heating of LP 791-18d's interior and probably strong volcanic activity at the surface 5,6 ., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The interiors of giant planets remain poorly understood. Even for the planets in the Solar System, difficulties in observation lead to large uncertainties in the properties of planetary cores. Exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. Planets found in and near the typically barren hot-Neptune 'desert' 1,2 (a region in mass-radius space that contains few planets) have proved to be particularly valuable in this regard. These planets include HD149026b 3 , which is thought to have an unusually massive core, and recent discoveries such as LTT9779b 4 and NGTS-4b 5 , on which photoevaporation has removed a substantial part of their outer atmospheres. Here we report observations of the planet TOI-849b, which has a radius smaller than Neptune's but an anomalously large mass of [Formula: see text] Earth masses and a density of [Formula: see text] grams per cubic centimetre, similar to Earth's. Interior-structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than [Formula: see text] per cent of the total planetary mass. The planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation 6 . Although photoevaporation rates cannot account for the mass loss required to reduce a Jupiter-like gas giant, they can remove a small (a few Earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on TOI-849b is likely to be enriched by water or other volatiles from the planetary interior. We conclude that TOI-849b is the remnant core of a giant planet.

We report the detection of a transiting planet around π Men (HD 39091), using data from the Transiting Exoplanet Survey Satellite ( TESS ). The solar-type host star is unusually bright ( V = 5.7) and was already known to host a Jovian planet on a highly eccentric, 5.7-year orbit. The newly discovered planet has a size of 2.04 ± 0.05 R ⊕ and an orbital period of 6.27 days. Radial-velocity data from the HARPS and AAT/UCLES archives also displays a 6.27-day periodicity, confirming the existence of the planet and leading to a mass determination of 4.82±0.85 M ⊕ . The star's proximity and brightness will facilitate further investigations, such as atmospheric spectroscopy, asteroseismology, the Rossiter-McLaughlin effect, astrometry, and direct imaging.