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  1. Free, publicly-accessible full text available June 8, 2023
  2. ABSTRACT We present observations from the Transiting Exoplanet Survey Satellite (TESS) of twenty bright core-collapse supernovae with peak TESS-band magnitudes ≲18 mag. We reduce this data with an implementation of the image subtraction pipeline used by the All-Sky Automated Survey for Supernovae (ASAS-SN) optimized for use with the TESS images. In empirical fits to the rising light curves, we do not find strong correlations between the fit parameters and the peak luminosity. Existing semi-analytic models fit the light curves of the Type II supernovae well, but do not yield reasonable estimates of the progenitor radius or explosion energy, likely because they are derived for use with ultraviolet observations while TESS observes in the near-infrared. If we instead fit the data with numerically simulated light curves, the rising light curves of the Type II supernovae are consistent with the explosions of red supergiants. While we do not identify shock breakout emission for any individual event, when we combine the fit residuals of the Type II supernovae in our sample, we do find a >5σ flux excess in the ∼1 d before the start of the light-curve rise. It is likely that this excess is due to shock breakout emission, and that during its extendedmore »mission TESS will observe a Type II supernova bright enough for this signal to be detected directly.« less
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  4. ABSTRACT Using ASAS-SN data, we find that the bright ($V\sim 13.5$ mag) variable star MACHO 80.7443.1718 (ASASSN-V J052624.38–684705.6) is the most extreme heartbeat star yet discovered. This massive binary, consisting of at least one early B-type star, has an orbital period of $P_{\rm ASAS-SN}=32.83627\pm 0.00846\, {\rm d},$ and is located towards the LH58 OB complex in the LMC. Both the ASAS-SN and TESS light curves show extreme brightness variations of ${\sim }40{{\ \rm per\ cent}}$ at periastron and variations of $ \sim 10{{\ \rm per\ cent}}$ due to tidally excited oscillations outside periastron. We fit an analytical model of the variability caused by the tidal distortions at pericentre to find orbital parameters of $\omega =-61.4^\circ$, $i=44.8^\circ$, and $e=0.566$. We also present a frequency analysis to identify the pulsation frequencies corresponding to the tidally excited oscillations.
  5. ABSTRACT We broadly explore the effects of systematic errors on reverberation mapping lag uncertainty estimates from javelin and the interpolated cross-correlation function (ICCF) method. We focus on simulated light curves from random realizations of the light curves of five intensively monitored AGNs. Both methods generally work well even in the presence of systematic errors, although javelin generally provides better error estimates. Poorly estimated light-curve uncertainties have less effect on the ICCF method because, unlike javelin , it does not explicitly assume Gaussian statistics. Neither method is sensitive to changes in the stochastic process driving the continuum or the transfer function relating the line light curve to the continuum. The only systematic error we considered that causes significant problems is if the line light curve is not a smoothed and shifted version of the continuum light curve but instead contains some additional sources of variability.
  6. ABSTRACT We characterize an all-sky catalogue of ∼8400 δ Scuti variables in ASAS-SN, which includes ∼3300 new discoveries. Using distances from Gaia DR2, we derive period–luminosity relationships for both the fundamental mode and overtone pulsators in the WJK, V, Gaia DR2 G, J, H, Ks, and W1 bands. We find that the overtone pulsators have a dominant overtone mode, with many sources pulsating in the second overtone or higher order modes. The fundamental mode pulsators have metallicity-dependent periods, with log10(P) ∼ −1.1 for $\rm [Fe/H]\lt -0.3$ and log10(P) ∼ −0.9 for $\rm [Fe/H]\gt 0$, which leads to a period-dependent scale height. Stars with $P\gt 0.100\, \rm d$ are predominantly located close to the Galactic disc ($\rm |\mathit{ Z}|\lt 0.5\, kpc$). The median period at a scale height of $Z\sim 0\, \rm kpc$ also increases with the Galactocentric radius R, from log10(P) ∼ −0.94 for sources with $R\gt 9\, \rm kpc$ to log10(P) ∼ −0.85 for sources with $R\lt 7\, \rm kpc$, which is indicative of a radial metallicity gradient. To illustrate potential applications of this all-sky catalogue, we obtained 30 min cadence, image subtraction TESS light curves for a sample of 10 fundamental mode and 10 overtone δ Scuti stars discoveredmore »by ASAS-SN. From this sample, we identified two new δ Scuti eclipsing binaries, ASASSN-V J071855.62−434247.3 and ASASSN-V J170344.20−615941.2 with short orbital periods of Porb = 2.6096 and 2.5347 d, respectively.« less
  7. Abstract We have recently initiated the first spectroscopic dust reverberation programme on active galactic nuclei in the near-infrared. Spectroscopy enables measurement of dust properties, such as flux, temperature, and covering factor, with higher precision than photometry. In particular, it enables measurement of both luminosity-based dust radii and dust response times. Here we report results from a 1 yr campaign on NGC 5548. The hot dust responds to changes in the irradiating flux with a lag time of ∼70 light-days, similar to what was previously found in photometric reverberation campaigns. The mean and rms spectra are similar, implying that the same dust component dominates both the emission and the variations. The dust lag time is consistent with the luminosity-based dust radius only if we assume a wavelength-independent dust emissivity law, i.e. a blackbody, which is appropriate for grains of large sizes (of a few μm). For such grains the dust temperature is ∼1450 K. Therefore, silicate grains have most likely evaporated and carbon is the main chemical component. But the hot dust is not close to its sublimation temperature, contrary to popular belief. This is further supported by our observation of temperature variations largely consistent with a heating/cooling process. Therefore, the inner dust-free regionmore »is enlarged and the dusty torus rather a ‘dusty wall’, whose inner radius is expected to be luminosity-invariant. The dust-destruction mechanism that enlarges the dust-free region seems to also partly affect the dusty region. We observe a cyclical decrease in dust mass with implied dust reformation times of ∼5–6 months.« less