Variable continuum emission from active galactic nuclei (AGNs) can be used to probe the structure of their accretion discs via reverberation mapping. Assuming a variable, hot inner light source irradiates the surrounding accretion disc, time delays between different continuum band light curves reveal light-travel times between their respective emission regions. Inter-band delays measured in several low-luminosity AGNs are ubiquitously similar to 3 times longer than expected from standard disc theory, with evidence that this size discrepancy may decrease in more luminous AGNs. We have analysed high-cadence light curves of 9498 of the brightest quasars between redshift 0.3-2.5 in the largest continuum reverberation study to date. Given the large sample size, we construct bins and fit delays jointly to combine inference across the parameter space and improve lag detections. We find that the size discrepancy persists in our high-luminosity sample, and that the previously seen anticorrelation with luminosity is likely driven by wavelength effects. The complex, non-monotonic wavelength dependence of delay amplitudes strongly suggests that contamination of inter-band delays by variable diffuse emission is widespread in the AGN population. We test delay behaviour against a variety of quasar properties finding longer lags in quasars with: higher Eddington ratios, redder colours, larger optical FeII EWs, higher iron ratios (both UV Fe II /Mg II and optical Fe II/H ,e), C iv broad absorption troughs, and lower C iv blueshift.

The discovery of 2024 YR4 presented the planetary defense community with the most significant impact threat in almost two decades, reaching level 3 on the Torino scale. The community, now mature and well-organized, responded with a global observational effort. Astrometric measurements, forming the basis for orbital refinement and impact prediction, were a central component of this response. In this paper, we present the astrometric data collected by the international community, from the time of discovery until the object became too faint for all existing observational assets, including JWST. We also discuss the coordination role played by the International Asteroid Warning Network, and the importance of publicly available image archives to enable precovery searches.

We report the discovery of ATLAS J101342.5-451656.8 (hereafter ATLAS J1013-4516), an 8.56 minute orbital-period mass-transferring AM Canum Venaticorum (AM CVn) binary with a mean Gaia magnitude of G = 19.51, identified via periodic variability in light curves from the Asteroid Terrestrial-impact Last Alert System (ATLAS) of Gaia white dwarf candidates. Follow-up with the Large Lenslet Array Magellan Spectrograph shows a helium-dominated accretion disk, and high-speed ULTRACAM photometry reveals pronounced primary and secondary eclipses. We construct a decade-long timing baseline leveraging light curves from the ATLAS and Gaia surveys, as well as the high-speed imagers ULTRACAM on the New Energy Telescope and proto-Lightspeed on the Magellan Clay telescope. From this timing baseline, we measure an orbital period derivative of P=-1.60 +/- 0.07 & times;10-12 s s-1. Interpreted in the context of stable mass transfer, the magnitude and sign of P indicate that the orbital evolution is governed by the interplay between gravitational-wave-driven angular-momentum losses and mass transfer, directly probing the donor's structural response to mass loss. We constrain the accretor and donor mass based on stable mass-transfer arguments assuming angular-momentum loss dominated by gravitational-wave emission, allowing us to infer the characteristic gravitational wave strain of the binary for future space-based GW observatories such as the Laser Interferometer Space Antenna (LISA). We predict a characteristic strain corresponding to a 4 yr LISA signal-to-noise ratio greater than or similar to 10, establishing ATLAS J1013-4516 as a strong prospective LISA source that will probe long-term orbital evolution in the mass-transferring regime.

We present the discovery and early observations of the nearby Type II supernova (SN) 2024ggi in NGC 3621 at 6.64 +/- 0.3 Mpc. The SN was caught 5.8 (+1.9 -2.9) hours after its explosion by the ATLAS survey. Early-phase, high-cadence, and multi-band photometric follow-up was performed by the Kinder (Kilonova Finder) project, collecting over 1000 photometric data points within a week. The combined o- and r-band light curves show a rapid rise of 3.3 magnitudes in 13.7 hours, much faster than SN 2023ixf (another recent, nearby, and well-observed SN II). Between 13.8 and 18.8 hours after explosion SN 2024ggi became bluer, with u-g colour dropping from 0.53 to 0.15 mag. The rapid blueward evolution indicates a wind shock breakout (SBO) scenario. No hour-long brightening expected for the SBO from a bare stellar surface was detected during our observations. The classification spectrum, taken 17 hours after the SN explosion, shows flash features of high-ionization species such as Balmer lines, He I, C III, and N III. Detailed light curve modeling reveals critical insights into the properties of the circumstellar material (CSM). Our favoured model has an explosion energy of 2 x 10^51 erg, a mass-loss rate of 10^-3 solar_mass/yr (with an assumed 10 km/s wind), and a confined CSM radius of 6 x 10^14 cm. The corresponding CSM mass is 0.4 solar_mass. Comparisons with SN 2023ixf highlight that SN 2024ggi has a smaller CSM density, resulting in a faster rise and fainter UV flux. The extensive dataset and the involvement of citizen astronomers underscore that a collaborative network is essential for SBO searches, leading to more precise and comprehensive SN characterizations.

We report initial observations aimed at the characterization of a third interstellar object. This object, 3I/ATLAS or C/2025 N1 (ATLAS), was discovered on 2025 July 1 UT and has an orbital eccentricity of e ∼ 6.1, perihelion of q ∼ 1.36 au, inclination of ∼175°, and hyperbolic velocity of V _∞ ∼ 58 km s ^−1 . We report deep stacked images obtained using the Canada–France–Hawaii Telescope and the Very Large Telescope that resolve a compact coma. Using images obtained from several smaller ground-based telescopes, we find minimal light-curve variation for the object over a ∼4 day time span. The visible/near-infrared spectral slope of the object is 17.1% ± 0.2%/100 nm, comparable to other interstellar objects and primitive solar system small bodies (comets and D-type asteroids). Moreover, 3I/ATLAS will be observable through early 2025 September, then unobservable by Earth-based observatories near perihelion due to low solar elongation. It will be observable again from the ground in late 2025 November. Although this limitation unfortunately prohibits detailed Earth-based observations at perihelion when the activity of 3I/ATLAS is likely to peak, spacecraft at Mars could be used to make valuable observations at this time.

In an effort to search for faint sources of emission over arbitrary timescales, we present a novel method for analyzing forced photometry light curves in difference imaging from optical surveys. Our method “ATLAS Clean,” or ATClean, utilizes the reported fluxes, uncertainties, and fits to the point-spread function (PSF) from difference images to quantify the statistical significance of individual measurements. We apply this method to control light curves across the image to determine whether any source of flux is present in the data for a range of specific timescales. From ATLAS o -band imaging at the site of the Type II supernova (SN) 2023ixf in M101 from 2015–2023, we show that this method accurately reproduces the 3 σ flux limits produced from other, more computationally expensive methods. We derive limits for emission on timescales of 5 days and 80–300 days at the site of SN 2023ixf, which are 19.8 and 21.3 mag, respectively. The latter limits rule out variability for unextinguished red supergiants with initial masses >22 M ⊙ , comparable to the most luminous predictions for the SN 2023ixf progenitor system. We also compare our limits to short-timescale outbursts, similar to those expected for Type IIn SN progenitor stars or the Type II SN 2020tlf, and rule out outburst ejecta masses of >0.021 M ⊙ , much lower than the inferred mass of circumstellar matter around SN 2023ixf in the literature. In the future, these methods can be applied to any forced photometry on difference imaging from other surveys, such as Rubin optical imaging.

Type Ia supernovae (SNe Ia), critical for studying cosmic expansion, arise from thermonuclear explosions of white dwarfs, but their precise progenitor pathways remain unclear. Growing evidence supports the “double-degenerate scenario,” where two white dwarfs interact. The absence of nondegenerate companions capable of explaining the observed SN Ia rate, along with observations of hypervelocity white dwarfs, interpreted as surviving companions of such systems, provide compelling evidence for this scenario. Upcoming millihertz gravitational-wave observatories like the Laser Interferometer Space Antenna (LISA) are expected to detect thousands of double-degenerate systems, though the most compact known candidate SN Ia progenitors produce marginally detectable signals. Here, we report observations of ATLAS J1138-5139, a binary white dwarf system with an orbital period of just 28 minutes. Our analysis reveals a 1 M _☉ carbon–oxygen white dwarf accreting from a high-entropy helium-core white dwarf. Given its mass, the accreting carbon–oxygen white dwarf is poised to trigger a typical-luminosity SN Ia within a few million years, to evolve into a stably transferring AM Canum Venaticorum (or AM CVn) system, or undergo a merger into a massive white dwarf. ATLAS J1138-5139 provides a rare opportunity to calibrate binary evolution models by directly comparing observed orbital parameters and mass-transfer rates closer to merger than any known SN Ia progenitor. Its compact orbit ensures detectability by LISA, demonstrating the potential of millihertz gravitational-wave observatories to reveal a population of SN Ia progenitors on a Galactic scale, paving the way for multimessenger studies offering insights into the origins of these cosmologically significant explosions.

Period-luminosity relations of long period variables (LPVs) are a powerful tool to map the distances of stars in our galaxy, and are typically calibrated using stars in the Large Magellanic Cloud (LMC). Recent results demonstrated that these relations show a strong dependence on the amplitude of the variability, which can be used to greatly improve distance estimates. However, one of the only highly sampled catalogs of such variables in the LMC is based on OGLE photometry, which does not provide all-sky coverage. Here, we provide the first measurement of the period-luminosity relation of long-period variables in the LMC using photometry from the Asteroid Terrestrial-impact Last Alert System (ATLAS). We derive conversions between ugriz, Gaia, and ATLAS c and o passbands with a precision of approximately 0.02 mag, which enable the measurement of reliable amplitudes with ATLAS for crowded fields. We successfully reproduce the known PL sequences A through E, and show evidence for sequence F using the ratios of amplitudes observed in both ATLAS pass-bands. Our work demonstrates that the ATLAS survey can recover variability in evolved red giants and lays the foundation for an all-sky distance map of the Milky Way using long-period variables.

We present calibrated ATLAS photometry of the interstellar comet 3I/ATLAS (C/2025 N1) from 28 March through 29 Aug 2025, obtained with the five-site, robotic ATLAS network in the c (420-650 nm), o (560-820 nm), and Teide w (420-720 nm) bands. Stacked difference images yield reliable light curves measured in four fixed apertures that capture the evolving coma. We observe 3I/ATLAS transitioning in color from red (c-o) 0.7 before MJD 60860 to near-solar (c-o) 0.3 after MJD 60870, coincident with the appearance of a prominent anti-solar tail. The absolute magnitude curve H(t) shows a slope break near MJD 60890 at r 3.3 au from -0.035 to -0.014 mag/day, or in terms of coma cross section as a function of heliocentric distance, r^-3.9 to r^-1.2. We interpret the evolution as a shift from dust lifted from a reddened surface to production of small, optically bright icy grains and changing coma optical depth. We release the aperture photometry with geometry and uncertainties to enable cross-instrument synthesis of 3I/ATLAS activity and color evolution.

Jupiter-family comets (JFCs) have orbital periods of less than 20 yr and therefore undergo more frequent sublimation compared to other comet populations. The JFCs therefore represent the ideal dynamical population for investigating the dust production rates at high cadence. We analyzed observations by the Asteroid Terrestrial-impact Last Alert System (ATLAS) of 74 JFCs that reached perihelion in 2022 and 2023. The work contained in this study builds on our previous work, for a total of 116 JFCs over a 4 yr period. Using the Afρ parameter, we measured the dust production rates of each JFC as a function of heliocentric distance. We found that there remained a clear preference for JFCs to reach their maximum A (0°) fρ post-perihelion, with 170P/Christensen, 254P/McNaught, and P/2020 WJ5 (Lemmon) reaching a maximum A (0°) fρ between 200 and 400 days after perihelion. However, all JFCs reached their maximum dust production within 10% of their orbital period relative to perihelion. Fitting A (0°) fρ as a function of ${({R}_{h})}^{n}$ , we measured statistically significant differences in the distribution of pre-perihelion and post-perihelion activity index n , with average activity indices of −5.2 ± 4.5 and −3.2 ± 2.7, respectively. We derived upper limits for the nuclear radii of comets 444P/WISE-PANSTARRS and 459P/Catalina as R _n ≤ 1.5 ± 0.2 km and R _n ≤ 1.7 ± 0.1 km, respectively. We measured six outbursts in comets 97P/Metcalf-Brewington, 99P/Kowal 1, 118P/Shoemaker-Levy 4, 285P/LINEAR, and 382P/Larson. From our 4 yr of observing JFC outbursts in the ATLAS data, the average increase in magnitude was −1.3 ± 0.8.

The stochastic photometric variability of quasars is known to follow a random-walk phenomenology on emission time-scales of months to years. Some high-cadence rest-frame optical monitoring in the past has hinted at a suppression of variability amplitudes on shorter time-scales of a few days or weeks, opening the question of what drives the suppression and how it might scale with quasar properties. Here, we study a few thousand of the highest luminosity quasars in the sky, mostly in the luminosity range of L-bol= [46.4, 47.3]$ and redshift range of z=[0.7, 2.4]. We use a data set from the NASA/Asteroid Terrestrial-impact Last Alert System facility with nightly cadence, weather permitting, which has been used before to quantify strong regularity in longer term rest-frame-UV variability. As we focus on a careful treatment of short time-scales across the sample, we find that a linear function is sufficient to describe the UV variability structure function. Although the result can not rule out the existence of breaks in some groups completely, a simpler model is usually favoured under this circumstance. In conclusion, the data are consistent with a single-slope random walk across rest-frame time-scales of Delta t=[10, 250] d.

Centaurs are small solar system objects on chaotic orbits in the giant planet region, forming an evolutionary continuum with the Kuiper Belt objects and Jupiter-family comets. Some Centaurs are known to exhibit cometary activity, though unlike comets, this activity tends not to correlate with heliocentric distance, and the mechanism behind it is currently poorly understood. We utilize serendipitous observations from the Asteroid Terrestrial-impact Last Alert System, Zwicky Transient Facility, Panoramic Survey Telescope and Rapid Response System, Dark Energy Survey, and Gaia in addition to targeted follow-up observations from the Las Cumbres Observatory, TRAnsiting Planets and PlanetesImals Small Telescope South (TRAPPIST-South), and Gemini North telescope to analyze an unexpected brightening exhibited by the known active Centaur (2060) Chiron in 2021. This is highly indicative of a cometary outburst. As of 2023 February, Chiron had still not returned to its prebrightening magnitude. We find Chiron's rotational lightcurve, phase curve effects, and possible high-albedo surface features to be unlikely causes of this observed brightening. We consider the most likely cause to be an epoch of either new or increased cometary activity, though we cannot rule out a possible contribution from Chiron's reported ring system, such as a collision of as-yet-unseen satellites shepherding the rings. We find no evidence for a coma in our Gemini or TRAPPIST-South observations, though this does not preclude the possibility that Chiron is exhibiting a coma that is too faint for observation or constrained to the immediate vicinity of the nucleus.

Jupiter-family comets (JFCs) exhibit a wide range of activity levels and mass loss over their orbits. We analyzed high-cadence observations of 42 active JFCs with the wide-field Asteroid Terrestrial-impact Last Alert System (ATLAS) in 2020–2021. We measured the dust production rates of the JFCs using the Af ρ parameter and its variation as a function of heliocentric distance. There is a tendency for our JFC sample to exhibit a maximum Af ρ after perihelion, with 254P/McNaught and P/2020 WJ5 (Lemmon) having their maximum Af ρ over a year after perihelion. On average, the rate of change of activity postperihelion was shallower than preperihelion. We also estimated the maximum mass-loss rate for 17 of the JFCs in our sample, finding 4P/Faye to be the most active. We present a subset of comets whose measured Af ρ have been interpolated and extrapolated to a common distance of 2 au preperihelion and postperihelion. From these measurements we found no correlation of intrinsic activity with current perihelion distance. For three of the JFCs in our sample, 6P/d’Arrest, 156P/Russell–LINEAR, and 254P/McNaught, there was no visible coma but a constant absolute magnitude, which we attribute to a probable detection of the nucleus. We derived upper limits for the nuclear radii of ≤2.1 ± 0.3 km, ≤2.0 ± 0.2 km, and ≤4.0 ± 0.8 km, respectively. Finally, we found that 4P/Faye, 108P/Ciffreo, 132P/Helin–Roman–Alu 2, 141P/Machholz 2, and 398P/Boattini experienced outbursts between 2020 and 2022.

We utilize serendipitous observations from the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the Zwicky Transient Facility (ZTF) in addition to targeted follow-up observations from the Las Cumbres Observatory (LCO) and Liverpool Telescope to analyze the first observed instance of cometary activity by the newly-discovered Jupiter-family comet C/2023 RN3 (ATLAS), whose orbital dynamics place it close to residing on a Centaur-like orbit. Across our 7-month baseline, we observe an epoch of cometary activity commencing in August 2023 with an increase in brightness of >5.4 mag. The lightcurve of 2023 RN3 indicates the presence of continuous cometary activity across our observations, suggesting the onset of a new period of sustained activity. We find no evidence of any outbursts on top of the observed brightening, nor do we find any significant color evolution across our observations. 2023 RN3 is visibly extended in LCO and Liverpool Telescope observations, indicating the presence of a spatially-extended coma. Numerical integration of 2023 RN3's orbit reveals the comet to have recently undergone a slight increase in semimajor axis due to a planetary encounter with Jupiter, however whether this orbital change could trigger 2023 RN3's cometary activity is unclear. Our estimate for the maximum dust production metric of Afrho 400 cm is consistent with previous measurements for the Jupiter-family comet and Centaur populations.

Fast X-ray Transients (FXTs) are extragalactic bursts of soft X-rays first identified >10 years ago. Since then, nearly 40 events have been discovered, although almost all of these have been recovered from archival Chandra and XMM-Newton data. To date, optical sky surveys and follow-up searches have not revealed any multi-wavelength counterparts. The Einstein Probe, launched in January 2024, has started surveying the sky in the soft X-ray regime (0.5-4 keV) and will rapidly increase the sample of FXTs discovered in real time. Here, we report the first discovery of both an optical and radio counterpart to an FXT, the fourth source publicly released by the Einstein Probe. We discovered a fast-fading optical transient within the 3 arcmin localisation radius of EP240315a with the all-sky optical survey ATLAS, and our follow-up Gemini spectrum provides a redshift, z=4.859+/-0.002. Furthermore, we uncovered a radio counterpart in the S-band (3.0 GHz) with the MeerKAT radio interferometer. The optical (rest-frame UV) and radio luminosities indicate the FXT most likely originates from either a long gamma-ray burst or a relativistic tidal disruption event. This may be a fortuitous early mission detection by the Einstein Probe or may signpost a mode of discovery for high-redshift, high-energy transients through soft X-ray surveys, combined with locating multi-wavelength counterparts.

Measurements of type Ia supernovae (SNe Ia) in the near-infrared (NIR) have been used both as an alternate path to cosmology compared to optical measurements and as a method of constraining key systematics for the larger optical studies. With the DEHVILS sample, the largest published NIR sample with consistent NIR coverage of maximum light across three NIR bands ($Y$, $J$, and $H$), we check three key systematics: (i) the reduction in Hubble residual scatter as compared to the optical, (ii) the measurement of a ``mass step'' or lack thereof and its implications, and (iii) the ability to distinguish between various dust models by analyzing slopes and correlations between Hubble residuals in the NIR and optical. We produce SN Ia simulations of the DEHVILS sample and find that it is harder to differentiate between various dust models than previously understood. Additionally, we find that fitting with the current SALT3-NIR model does not yield accurate wavelength-dependent stretch-luminosity correlations, and we propose a limited solution for this problem. From the data, we see that (i) the standard deviation of Hubble residual values from NIR bands treated as standard candles are 0.007--0.042 mag smaller than those in the optical, (ii) the NIR mass step is not constrainable with the current sample size of 47 SNe Ia from DEHVILS, and (iii) Hubble residuals in the NIR and optical are correlated in the data. We test a few variations on the number and combinations of filters and data samples, and we observe that none of our findings or conclusions are significantly impacted by these modifications.

GW190425 is the second of only two binary neutron star (BNS) merger events to be significantly detected by the LIGO-Virgo- Kagra gravitational wave detectors. With a detection only in LIGO Livingston, the skymap containing the source was large and no plausible electromagnetic counterpart was found in real time searching in 2019. Here we summarise our ATLAS and Pan-STARRS wide-field optical coverage of the skymap beginning within 1 hour and 3 hours respectively of the GW190425 merger time. More recently, a potential coincidence between GW190425 and a fast radio burst FRB 190425 has been suggested, given their spatial and temporal coincidence. The smaller sky localisation area of FRB 190425 and its dispersion measure have led to the identification of a likely host galaxy, UGC 10667 at a distance of 141 +/- 10 Mpc. Our optical imaging covered the galaxy 6.0 hrs after GW190425 was detected and 3.5 hrs after the FRB 190425. No optical emission was detected and further imaging at +1.2 and +13.2 days also revealed no emission. If the FRB 190425 and GW190425 association were real, we highlight our limits on kilonova emission from a BNS merger in UGC 10667. The model for producing FRB 190425 from a BNS merger involves a supramassive magnetised neutron star spinning down by dipole emission on the timescale of hours. We show that magnetar enhanced kilonova emission is ruled out by optical upper limits. The lack of detected optical emission from a kilonova in UGC 10667 disfavours, but does not disprove, the FRB-GW link for this source.

We present a convolutional neural network (CNN) for use in the real-bogus classification of transient detections made by the Asteroid Terrestrial-impact Last Alert System (ATLAS) and subsequent efforts to improve performance since initial development. In transient detection surveys, the number of alerts made outstrips the capacity for human scanning, necessitating the use of machine learning aids to reduce the number of false positives presented to annotators. We take a sample of recently annotated data from each of the three operating ATLAS telescope with $\sim$340 000 real (known transients) and $\sim$1030 000 bogus detections per model. We retrained the CNN architecture with these data specific to each ATLAS unit, achieving a median false positive rate (FPR) of 0.72 per cent for a 1.00 per cent missed detection rate. Further investigations indicate that if we reduce the input image size it results in increased FPR. Finally architecture adjustments and comparisons to contemporary CNNs indicate that our retrained classifier is providing an optimal FPR. We conclude that the periodic retraining and readjustment of classification models on survey data can yield significant improvements as data drift arising from changes in the optical and detector performance can lead to new features in the model and subsequent deteriorations in performance.

Changing-look active galactic nuclei (CLAGNs) are characterized by extreme variations in line emission over short time-scales, mostly affecting broad H beta lines. While a few hundred CLAGNs are known, a complete sample of turn-on CLAGNs is still elusive. Here, we present a search for turn-on CLAGNs in a complete sample of galaxies, using archival spectra and recent light curves. We obtained light curves from the Asteroid Terrestrial Impact Last Alert System for 16 232 emission-line galaxies, including both star-forming and active galaxies, at z< 0.1 with spectra from the Six-degree Field Galaxy Survey (6dFGS). We first establish typical variability behaviour for different active galactic nucleus (AGN) types, as recorded between 2001 and 2009, and then select outliers from the bulk behaviour as CLAGN candidates. We obtain new spectra for the candidates and identify 12 new turn-on CLAGNs (appearing broad H beta line) and 19 new turn-off CLAGNs (disappearing broad H beta line). We may have missed AGNs that changed and reverted their state over the 15-20 yr since 6dFGS spectra were taken, and thus our CLAGN rates of 1.7 per cent for turn-on and 9.6 per cent for turn-off are lower limits. The turn-on rate is naturally much lower as the type 1.9/2 sample is dominated by obscured AGNs due to orientation, which is not expected to change. However, the number of turn-on (27) and turn-off (24) CLAGNs we find are similar, suggesting that our parent AGN sample is reasonably complete in our search volume at z < 0.1.

INTRODUCTIONThe Asteroid Terrestrial Last-impact Alert System (ATLAS) currently consists of two robotic telescopes in Hawaii. Together they scan the entire visible night sky every two nights in wideband orange and cyan filters down to ~19.5 mag. In addition to rapid discovery and follow up of Near-Earth Objects, ATLAS serendipitously observes a large number of asteroids and other moving objects. Since operations began in 2015 ATLAS has collected a substantial photometric database of ~7x107 observations for ~430,000 asteroids.Asteroids are valuable compositional and dynamical tracers that can be used to constrain the processes of Solar System evolution. The observed size distribution of an asteroid population can inform us of its primordial formation and subsequent collisional evolution. Composition of a population can indicate a common origin; such as a protoplanetary disk formation region or a relation through asteroid collisional families. We aim to utilise the ATLAS database to investigate the physical properties of a large number of asteroids, by fitting phase curve models to the photometric observations.The form of the phase curve depends on the physical properties of the asteroid and is parameterised by a variety of models which are each described by absolute magnitude and slope parameters. Absolute magnitude, H, is related to the size and albedo of the body. The form of the phase curve is determined by the slope parameter in the phase function and depends on the surface composition and structure. Hence these parameters may be used as proxies for the properties of asteroids when more detailed information is unavailable.METHODSAn analysis of an earlier dataset has been performed using MCMC techniques by Mahlke et al. (2021), providing phase curves in the H, G1, G2 and H, G12* systems (Muinonen et al. 2010, Penttilä et al. 2016). In this work we fit both these systems plus the original H, G system (Bowell et al., 1989) to all asteroids in the ATLAS dataset, using Levenberg-Marquardt least squares fitting. We perform a separate fit in both the o and c ATLAS filters. We have investigated various methods of outlier rejection, and use techniques such as initial data cuts, iterative sigma clipping, and avoidance of low galactic latitudes. These have considerably improved the quality of the dataset. However, in some cases the photometric observations may not be well described by the phase curve model due to physical phenomena such as large amplitude rotational variation, or changing aspect angle for asteroids with high spin obliquities.We have created a dataset of phase curve parameters for ~370,000 asteroids, and identify a subset of high quality phase curves where the phase curve model describes the data well and absolute magnitude and slope have low formal uncertainties. We analyse in detail the distribution of these phase curve parameters and verify them with comparison to previous work and catalogue values.RESULTSIn general we find good agreement between our phase curve results and previously published studies, especially for well observed bright asteroids. We identify metrics that indicate the ability to obtain a good fit to the phase function, such as number of observations and phase angle coverage. Furthermore, we demonstrate the scientific value of our database by comparing the properties of the leading and trailing Jupiter Trojans observed with ATLAS.The ability to determine phase curves for large numbers of asteroids, and studying the statistics of their properties, highlights the potential value of sparse photometric survey data for asteroid science. This is especially relevant to the upcoming Legacy Survey of Space and Time (LSST) which will perform photometry of asteroids at a similar cadence to ATLAS. FIGURESFigure 1. The semimajor axis distribution of asteroids in the ATLAS database between 1.5 and 5.5 AU. ATLAS samples a wide range of populations; including the main belt, Hildas and Jupiter Trojans.Figure 2. The distribution of detections for asteroids observed by ATLAS in the o and c filters.Figure 3. Proper orbital elements (semimajor axis versus inclination) of selected asteroids from our database of phase curve fits. Asteroid families appear as distinct clusters with similar surface scattering properties as measured by the phase curve parameter G12*.ACKNOWLEDGEMENTSThis work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory (SAAO), and the Millennium Institute of Astrophysics (MAS), Chile.JR acknowledges the support of STFC Consolidated Grant ST/P000304/1.REFERENCESBowell, E., Hapke, B., Domingue, D., et al. 1989, in Asteroids II, ed. R. P. Binzel, T. Gehrels, & M. S. Matthews, 524–556Mahlke, M., Carry, B., & Denneau, L. 2021, Icarus, 354, 114094, doi: 10.1016/j.icarus.2020.114094Muinonen, K., Belskaya, I. N., Cellino, A., et al. 2010, Icarus, 209, 542, doi: 10.1016/j.icarus.2010.04.003Penttilä, A., Shevchenko, V. G., Wilkman, O., & Muinonen, K. 2016, Planet. Space Sci., 123, 117, doi: 10.1016/j.pss.2015.08.