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  1. ABSTRACT

    The progenitor of SN 2023ixf was an ∼104.8 to $10^{5.0}\, \text{L}_\odot$ star (∼9 to $14\, \text{M}_\odot$ at birth) obscured by a dusty $\dot{M} \simeq 10^{-5}\, \text{M}_\odot \rm \, yr^{-1}$ wind with a visual optical depth of τV ≃ 13. This is required by the progenitor spectral energy distribution, the post-SN X-ray and H α luminosities, and the X-ray column density estimates. In Large Binocular Telescope (LBT) data spanning 5600 to 400 d before the supernova (SN), there is no evidence for optical variability at the level of $\sim 10^3\, \text{L}_\odot$ in R band, roughly three times the predicted luminosity of the obscured progenitor. This constrains direct observation of any pre-SN optical outbursts where there are LBT observations. However, models of the effects of any pre-SN outburst on the dusty wind show that an outburst of essentially any duration exceeding ∼5 times the luminosity of the progenitor would have detectable effects on the dust optical depth for decades. While the dust obscuration here is high, all red supergiants have dusty winds, and the destruction (or formation) of dust by even short-lived transients will always have long-term effects on the observed brightness of the star because changes in the dust optical depths after a luminous transient occur very slowly.

     
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  2. ABSTRACT

    We examine the properties of ∼50 000 rotational variables from the ASAS-SN survey using distances, stellar properties, and probes of binarity from Gaia DR3 and the SDSS APOGEE survey. They have higher amplitudes and span a broader period range than previously studied Kepler rotators. We find they divide into three groups of main sequence stars (MS1, MS2s, MS2b) and four of giants (G1/3, G2, G4s, and G4b). MS1 stars are slowly rotating (10–30 d), likely single stars with a limited range of temperatures. MS2s stars are more rapidly rotating (days) single stars spanning the lower main sequence up to the Kraft break. There is a clear period gap (or minimum) between MS1 and MS2s, similar to that seen for lower temperatures in the Kepler samples. MS2b stars are tidally locked binaries with periods of days. G1/3 stars are heavily spotted, tidally locked RS CVn stars with periods of 10s of days. G2 stars are less luminous, heavily spotted, tidally locked sub-subgiants with periods of ∼10 d. G4s stars have intermediate luminosities to G1/3 and G2, slow rotation periods (approaching 100 d), and are almost certainly all merger remnants. G4b stars have similar rotation periods and luminosities to G4s, but consist of sub-synchronously rotating binaries. We see no difference in indicators for the presence of very wide binary companions between any of these groups and control samples of photometric twin stars built for each group.

     
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  3. ABSTRACT

    Masses and radii of stars can be derived by combining eclipsing binary light curves with spectroscopic orbits. In our previous work, we modelled the All-Sky Automated Survey for Supernovae (ASAS-SN) light curves of more than 30 000 detached eclipsing binaries using phoebe. Here, we combine our results with 128 double-lined spectroscopic orbits from Gaia Data Release 3. We also visually inspect ASAS-SN light curves of the Gaia double-lined spectroscopic binaries on the lower main sequence and the giant branch, adding 11 binaries to our sample. We find that only 50 per cent of systems have Gaia periods and eccentricities consistent with the ASAS-SN values. We use emcee and phoebe to determine masses and radii for a total of 122 stars with median fractional uncertainties of 7.9 per cent and 6.3 per cent, respectively.

     
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  4. ABSTRACT

    We searched for and found no higher mass (${\gtrsim}3{\rm M}_\odot$) unbound binary stellar companions to the progenitor of pulsar J1124−5916. There are lower mass candidates, but they all have high probabilities of being false positives. There are no candidates for it now being a fully unbound triple system. Even if one of the lower mass candidates is an unbound companion, it seems unlikely that it could have contributed to stripping the progenitor prior to the supernova. The stars are too low mass to be significant mass gainers, and they are too slowly moving to be the survivors of a compact, post-common envelope binary. The addition of one more system slightly improves the statistical constraints on the binary and triple status of supernova progenitors just before and after death.

     
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  5. ABSTRACT Using blazar light curves from the optical All-Sky Automated Survey for Supernovae (ASAS-SN) and the γ-ray Fermi-LAT telescope, we performed the most extensive statistical correlation study between both bands, using a sample of 1180 blazars. This is almost an order of magnitude larger than other recent studies. Blazars represent more than 98 per cent of the AGNs detected by Fermi-LAT and are the brightest γ-ray sources in the extragalactic sky. They are essential for studying the physical properties of astrophysical jets from central black holes. However, their γ-ray flare mechanism is not fully understood. Multiwavelength correlations help constrain the dominant mechanisms of blazar variability. We search for temporal relationships between optical and γ-ray bands. Using a Bayesian Block Decomposition, we detect 1414 optical and 510 γ-ray flares, we find a strong correlation between both bands. Among all the flares, we find 321 correlated flares from 133 blazars, and derive an average rest-frame time delay of only 1.1$_{-8.5}^{+7.1}$ d, with no difference between the flat-spectrum radio quasars, BL Lacertae-like objects or low, intermediate, and high-synchrotron peaked blazar classes. Our time-delay limit rules out the hadronic proton-synchrotron model as the driver for non-orphan flares and suggests a leptonic single-zone model. Limiting our search to well-defined light curves and removing 976 potential but unclear ‘orphan’ flares, we find 191 (13 per cent) and 115 (22 per cent) clear ‘orphan’ optical and γ-ray flares. The presence of ‘orphan’ flares in both bands challenges the standard one-zone blazar flare leptonic model and suggests multizone synchrotron sites or a hadronic model for some blazars. 
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  6. ABSTRACT We introduce a new model for understanding AGN continuum variability. We start from a Shakura–Sunyaev thin accretion disc with a steady-state radial temperature profile T(R) and assume that the variable flux is due to axisymmetric temperature perturbations δT(R, t). After linearizing the equations, we fit UV–optical AGN light curves to determine δT(R, t) for a sample of seven AGNs. We see a diversity of |δT/T| ∼ 0.1 fluctuation patterns which are not dominated by outgoing waves travelling at the speed of light as expected for the ‘lamppost’ model used to interpret disc reverberation mapping studies. Rather, the most common pattern resembles slow (v ≪ c) ingoing waves. An explanation for our findings is that these ingoing waves trigger central temperature fluctuations that act as a lamppost, producing lower amplitude temperature fluctuations moving outwards at the speed of light. The light curves are dominated by the lamppost signal – even though the temperature fluctuations are dominated by other structures with similar variability time-scales – because the discs exponentially smooth the contributions from the slower moving (v ≪ c) fluctuations to the observed light curves. This leads to light curves that closely resemble the expectations for a lamppost model but with the slow variability time-scales of the ingoing waves. This also implies that longer time-scale variability signals will increasingly diverge from lamppost models because the smoothing of slower moving waves steadily decreases as their period or spatial wavelength increases. 
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  7. ABSTRACT

    The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to monitor the entire sky, currently with a cadence of ≲ 24 h down to g ≲ 18.5 mag. ASAS-SN has routinely operated since 2013, collecting ∼ 2 000 to over 7 500 epochs of V- and g-band observations per field to date. This work illustrates the first analysis of ASAS-SN’s newer, deeper, and higher cadence g-band data. From an input source list of ∼55 million isolated sources with g < 18 mag, we identified 1.5 × 106 variable star candidates using a random forest (RF) classifier trained on features derived from Gaia, 2MASS, and AllWISE. Using ASAS-SN g-band light curves, and an updated RF classifier augmented with data from Citizen ASAS-SN, we classified the candidate variables into eight broad variability types. We present a catalogue of ∼116 000 new variable stars with high-classification probabilities, including ∼111 000 periodic variables and ∼5 000 irregular variables. We also recovered ∼263 000 known variable stars.

     
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  8. ABSTRACT

    With Gaia parallaxes, it is possible to study the stellar populations associated with individual Galactic supernova remnants (SNRs) to estimate the mass of the exploding star. Here, we analyse the luminous stars near the Vela pulsar and SNR to find that its progenitor was probably ($\mathrel {\raise.3ex\rm{\gt }\lower0.6ex\rm{\sim }}90\rm \,per\,cent$) low mass (8.1–$10.3\, {\rm M}_\odot$). The presence of the O star γ2 Vel a little over 100 pc from Vela is the primary ambiguity, as including it in the analysis volume significantly increases the probability (to 5 per cent) of higher mass ($\gt 20\, {\rm M}_\odot$) progenitors. However, to be a high-mass star associated with γ2 Vel’s star cluster at birth, the progenitor would have to be a runaway star from an unbound binary with an unusually high velocity. The primary impediment to analysing large numbers of Galactic SNRs in this manner is the lack of accurate distances. This can likely be solved by searching for absorption lines from the SNR in stars as a function of distance, a method which yielded a distance to Vela in agreement with the direct pulsar parallax. If Vela was a $10\, {\rm M}_\odot$ supernova in an external galaxy, the 50-pc search region used in extragalactic studies would contain only $\simeq 10\rm \,per\,cent$ of the stars formed in a 50-pc region around the progenitor at birth and $\simeq 90\rm \,per\,cent$ of the stars in the search region would have been born elsewhere.

     
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  9. ABSTRACT

    We analyse new multifilter Hubble Space Telescope (HST) photometry of the normal Type Ia supernova (SN Ia) 2011fe out to ≈2400 d after maximum light, the latest observations to date of a SN Ia. We model the pseudo-bolometric light curve with a simple radioactive decay model and find energy input from both 57Co and 55Fe are needed to power the late-time luminosity. This is the first detection of 55Fe in a SN Ia. We consider potential sources of contamination such as a surviving companion star or delaying the deposition time-scale for 56Co positrons but these scenarios are ultimately disfavored. The relative isotopic abundances place direct constraints on the burning conditions experienced by the white dwarf (WD). Additionally, we place a conservative upper limit of <10−3 M⊙ on the synthesized mass of 44Ti. Only two classes of explosion models are currently consistent with all observations of SN 2011fe: (1) the delayed detonation of a low-ρc, near-MCh (1.2–1.3 M⊙) WD, or (2) a sub-MCh (1.0–1.1 M⊙) WD experiencing a thin-shell double detonation.

     
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  10. ABSTRACT

    AT2019pev is a nuclear transient in a narrow-line Seyfert 1 galaxy at z = 0.096. The archival ultraviolet, optical, and infrared data showed features of both tidal disruption events and active galactic nuclei (AGNs), and its nature is not fully understood. We present detailed X-ray observations of AT2019pev taken with Swift, Chandra, and NICER over 173 d of its evolution since the first Swift XRT epoch. The X-ray luminosity increases by a factor of 5 in 5 d from the first Swift XRT epoch to the light-curve peak. The light curve decays by a factor of 10 over ∼75 d and then flattens with a weak re-brightening trend at late times. The X-ray spectra show a ‘harder-when-brighter’ trend before peak and a ‘harder-when-fainter’ trend after peak, which may indicate a transition of accretion states. The archival ground-based optical observations show similar time evolution as the X-ray light curves. Beyond the seasonal limit of the ground-based observations, the Gaia light curve is rising towards an equally bright or brighter peak 223 d after the optical discovery. Combining our X-ray analysis and archival multiwavelength data, AT2019pev more closely resembles an AGN transient.

     
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