Search for: All records

ABSTRACT Dust absorption is invoked in a number of contexts for hiding a star that has survived some sort of transient event from view. Dust formed in a transient is expanding away from the star and, in spherical models, the mass and energy budgets implied by a high optical depth at late times make such models untenable. Concentrating the dust in a disc or torus can in principle hide a source from an equatorial observer using less mass and so delay this problem. However, using axisymmetric dust radiation transfer models with a range of equatorial dust concentrations, we find that this is quite difficult to achieve in practice. The polar optical depth must be either low or high to avoid scattering optical photons to equatorial observers. Most of the emission remains at wavelengths easily observed by JWST. The equatorial brightness can be significantly suppressed for very discy configurations with little polar optical depth – but only by a factor of ∼2 for polar optical depths of τp = 1 and ∼5 for τp = 0.1 even for a very high optical depth disc (τe = 1000) viewed edge-on. It is particularly difficult to hide a source with silicate dusts because the absorption feature near 10 µm frequently leads to the emission being concentrated just bluewards of the feature, near 8 µm. 

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. 

Aims.We have estimated black hole masses (M_BH) for 14 gravitationally lensed quasars using Balmer lines; we also provide estimates based on MgII and CIV emission lines for four and two of them, respectively. We compared these estimates to results obtained for other lensed quasars. Methods.We used spectroscopic data from the Large Binocular Telescope (LBT),Magellan, and the Very Large Telescope (VLT) to measure the full width at half maximum of the broad emission lines. Combined with the bolometric luminosity measured from the spectral energy distribution, we estimatedM_BHvalues and provide the uncertainties, including uncertainties from microlensing and variability. Results.We obtainedM_BHvalues using the single-epoch method from the Hαand/or Hβbroad emission lines for 14 lensed quasars, including the first-ever estimates for QJ0158−4325, HE0512−3329, and WFI2026−4536. The masses are typical of non-lensed quasars of similar luminosities, as are the implied Eddington ratios. We have thus increased the sample of lenses withM_BHestimates by 60%. 

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. 

ABSTRACT We present the volumetric rates and luminosity functions (LFs) of Type Ia supernovae (SNe Ia) from the V-band All-Sky Automated Survey for Supernovae (ASAS-SN) catalogues spanning discovery dates from UTC 2014 January 26 to UTC 2017 December 29. Our standard sample consists of 404 SNe Ia with $$m_{\mathrm{{\it V},peak}} \lt 17\, \mathrm{mag}$$ and Galactic latitude |b| > 15°. Our results are both statistically more precise and systematically more robust than previous studies due to the large sample size and high spectroscopic completeness. We make completeness corrections based on both the apparent and absolute magnitudes by simulating the detection of SNe Ia in ASAS-SN light curves. We find a total volumetric rate for all subtypes of $$R_{\mathrm{tot}} = 2.28^{+0.20}_{-0.20} \times 10^{4}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$ for $$M_{\mathrm{{\it V},peak}} \lt -16.5\, \mathrm{mag}$$ ($$R_{\mathrm{tot}} = 1.91^{+0.12}_{-0.12} \times 10^{4}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$ for $$M_{\mathrm{{\it V},peak}} \lt -17.5\, \mathrm{mag}$$) at the median redshift of our sample, zmed = 0.024. This is in agreement (1σ) with the local volumetric rates found by previous studies. We also compile LFs for the entire sample as well as for subtypes of SNe Ia for the first time. The major subtypes with more than one SN include Ia-91bg, Ia-91T, Ia-CSM, and Ia-03fg with total rates of $$R_{\mathrm{Ia-91bg}} = 1.4^{+0.5}_{-0.5} \times 10^{3}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$, $$R_{\mathrm{Ia-91T}} = 8.5^{+1.6}_{-1.7} \times 10^{2}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$, $$R_{\mathrm{Ia-CSM}} = 10^{+7}_{-7}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$, and $$R_{\mathrm{Ia-03fg}} = 30^{+20}_{-20}\, \mathrm{yr}^{-1}\, \mathrm{Gpc}^{-3}\, h^{3}_{70}$$, respectively. We estimate a mean host extinction of $$E(V-r) \approx 0.2\, \mathrm{mag}$$ based on the shift between our V band and the Zwicky Transient Facility r-band LFs. 

Abstract We present 307 type Ia supernova (SN) light curves from the first 4 yr of the Transiting Exoplanet Survey Satellite mission. We use this sample to characterize the shapes of the early-time light curves, measure the rise times from first light to peak, and search for companion star interactions. Using simulations, we show that light curves must have noise <10% of the peak flux to avoid biases in the early-time light-curve shape, restricting our quantitative analysis to 74 light curves. We find that the mean power-law index $t^{{\beta }_1}$of the early-time light curves isβ₁= 1.93 ± 0.57, and the mean rise time to peak is 15.7 ± 3.5 days. The underlying population distribution forβ₁may instead consist of a Gaussian component with mean 2.29, width 0.34, and a long tail extending to values less than 1.0. We find that the data can rarely distinguish between models with and without companion interaction models. Nevertheless, we find three high-quality light curves that tentatively prefer the addition of a companion interaction model, but the statistical evidence for the companion interactions is not robust. We also find two SNe that disfavor the addition of a companion interaction model to a curved power-law model. Taking the 74 SNe together, we calculate 3σupper limits on the presence of companion signatures to control for orientation effects that can hide companions in individual light curves. Our results rule out common progenitor systems with companions having Roche lobe radii >31R_⊙(separations >5.7 × 10¹²cm, 99.9% confidence level) and disfavor companions having Roche lobe radii >10R_⊙(separations >1.9 × 10¹²cm, 95% confidence level). Lastly, we discuss the implications of our results for the intrinsic fraction of single degenerate progenitor systems. 

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. 

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. 

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. 

ABSTRACT The fraction of stars that are in binaries or triples at the time of stellar death and the fraction of these systems that survive the supernova explosion are crucial constraints for evolution models and predictions for gravitational wave source populations. These fractions are also subject to direct observational determination. Here, we search 10 supernova remnants containing compact objects with proper motions for unbound binaries or triples using Gaia EDR3 and new statistical methods and tests for false positives. We confirm the one known example of an unbound binary, HD 37424 in G180.0−01.7, and find no other examples. Combining this with our previous searches for bound and unbound binaries, and assuming no bias in favour of finding interacting binaries, we find that 72.0 per cent (52.2–86.4 per cent, 90 per cent confidence) of supernova producing neutron stars are not binaries at the time of explosion, 13.9 per cent (5.4–27.2 per cent) produce bound binaries, and 12.5 per cent (2.8–31.3 per cent) produce unbound binaries. With a strong bias in favour of finding interacting binaries, the medians shift to 76.0 per cent were not binaries at death, 9.5 per cent leave bound binaries, and 13.2 per cent leave unbound binaries. Of explosions that do not leave binaries, $${\lt}18.9{{\ \rm per\ cent}}$$ can be fully unbound triples. These limits are conservatively for $$M\gt 5\, \mathrm{M}_\odot$$ companions, although the mass limits for some individual systems are significantly stronger. At birth, the progenitor of PSR J0538+2817 was probably a 13–$$19\, \mathrm{M}_\odot$$ star, and at the time of explosion, it was probably a Roche limited, partially stripped star transferring mass to HD 37424 and then producing a Type IIL or IIb supernova.