ABSTRACT We present the mid-infrared (MIR) light curves (LC) of 10 superluminous supernovae (SLSNe) at z &amp;lt; 0.12 based on WISE data at 3.4 and 4.6 $\mu$m. Three of them, including PS15br, SN 2017ens, and SN 2017err show rebrightening which started at 200–400 d and ended at 600–1000 d, indicating the presence of dust. In four of the left seven SLSNe, dust emission was detected with monochromatic luminosities of $10^7\sim 10^8\, {\rm L}_\odot$ at epochs of 100–500 d based on MIR colours W1 − W2 ∼ 1. Among the three SLSNe which show rebrightening, we further analysed PS15br and SN 2017ens. We modelled the SEDs at 500–700 d, which gives dust temperatures of 600–1100 K, dust masses of $\gtrsim 10^{-2}\, {\rm M}_\odot$, and luminosities of $10^8\sim 10^9\, {\rm L}_\odot$. Considering the time delay and the huge amount of energy released, the emitting dust can hardly be pre-existing dust heated whether collisionally by shocks or radiatively by peak SLSN luminosity or shock emission. Instead, it can be newly formed dust additionally heated by the interaction of circumstellar medium, indicated by features in their spectra and slowly declining bolometric LCs. The dust masses appear to be ten times greater than those formed in normal core-collapse supernovae at similar epochs. Combining with the analysis of SN 2018bsz by Chen et al. (2021), we suggest that SLSNe have higher dust formation efficiency, although future observations are required to reach a final conclusion. 

OUP accepted manuscript

We present the mid-infrared (MIR) light curves (LC) of 10 superluminous supernovae (SLSNe) at z < 0 . 12 based on WISE data at 3.4 and 4.6 µ m. Three of them, including PS15br, SN 2017ens, and SN 2017err show rebrightening which started at 200–400 days and ended at 600–1000 days, indicating the presence of dust. In four of the left seven SLSNe, dust emission was detected with monochromatic luminosities of 10 7 ∼ 10 8 L (cid:12) at epochs of 100–500 days based on MIR colors W 1 − W 2 ∼ 1. Among the three SLSNe which show rebrightening, we further analysed PS15br and SN 2017ens. We modeled the SEDs at 500–700 days, which gives dust temperatures of 600–1100 K, dust masses of (cid:38) 10 − 2 M (cid:12) , and luminosities of 10 8 ∼ 10 9 L (cid:12) . Considering the time delay and the huge amount of energy released, the emitting dust can hardly be pre-existing dust heated whether collisionally by shocks or radiatively by peak SLSN luminosity or shock emission. Instead, it can be newly formed dust additionally heated by the interaction of circum-stellar medium, indicated by features in their spectra and slowly declining bolometric LCs. The dust masses appear to be ten times greater than those formed in normal core-collapse supernovae at similar epochs. Combining with the analysis of SN 2018bsz by Chen et al. (2022), we suggest that SLSNe have higher dust formation eﬃciency, although future observations are required to reach a ﬁnal conclusion.

/pdf/a-mid-infrared-study-of-superluminous-supernovae-14xd5kqz.pdf

A Mid-infrared Study of Superluminous Supernovae


 Most ultra hot Jupiters (UHJs) show evidence of temperature inversions, in which temperature increases with altitude over a range of pressures. Temperature inversions can occur when there is a species that absorbs the stellar irradiation at a relatively high level of the atmospheres. However, the species responsible for this absorption remains unidentified. In particular, the UHJ KELT-20b is known to have a temperature inversion. Using high resolution emission spectroscopy from LBT/PEPSI we investigate the atomic and molecular opacity sources that may cause the inversion in KELT-20b, as well as explore its atmospheric chemistry. We confirm the presence of Fe i with a significance of 17σ. We also report a tentative 4.3σ detection of Ni i. A nominally 4.5σ detection of Mg i emission in the PEPSI blue arm is likely in fact due to aliasing between the Mg i cross-correlation template and the Fe i lines present in the spectrum. We cannot reproduce a recent detection of Cr i, while we do not have the wavelength coverage to robustly test past detections of Fe ii and Si i. Together with non-detections of molecular species like TiO, this suggests that Fe i is likely to be the dominant optical opacity source in the dayside atmosphere of KELT-20b and may be responsible for the temperature inversion. We explore ways to reconcile the differences between our results and those in literature and point to future paths to understand atmospheric variability.

pdf/the-pepsi-exoplanet-transit-survey-pets-iv-assessing-the-2l7gnsv3w4.pdf

The PEPSI Exoplanet Transit Survey (PETS) IV: Assessing the atmospheric chemistry of KELT-20b

When observing the atmospheres of transiting exoplanets using high-resolution spectroscopy, the aim is to detect well-resolved spectral features with high signal-to-noise ratios (S/Ns), as is possible today with modern spectrographs. However, obtaining such high-quality observations comes with a trade-off: a lower cadence of fewer, longer exposures across the transit collects more photons thanks to reduced overheads, enhancing the S/N of each observation, while a higher cadence of several shorter exposures minimises spectral feature smearing due to the continuously changing radial velocity of the planet. Considering that maximising S/N and minimising smearing are both beneficial to analysis, there is a need to identify the optimal compromise between the two for a given target. In this work, we aim to establish where this compromise lies for a typical exoplanet transit observation in order to benefit future data collection and subsequent interpretation. We modelled real transit events based on targets as they would be observed with VLT/ at Paranal Observatory, Chile. Creating four hypothetical scenarios, we simulated each set of transmission spectra across 100 realisations of the same transit event in order to vary the time resolution only. We removed telluric and stellar lines from these data sets using the algorithm and analysed them through cross-correlation with model templates, measuring how successfully each time resolution and case detected the planetary signal and exploring how the results vary. We demonstrate that there is a continuous change in the significance of the cross-correlation detection based on the trade-off between high and low time resolutions, and that, averaged over a large number of realisations, the function of this significance has clear maxima. The strength and location of these maxima vary depending on, for example, planet system parameters, instrumentation, and the number of removal iterations. We discuss why observers should therefore take several factors into account using a strategy akin to the `exposure triangle' employed in traditional photography where a balance must be struck by considering the full context of the observation. Our method is robust and may be employed by observers to estimate the best observational strategies for other targets.

Optimising spectroscopic observations of transiting exoplanets

We discuss applications of the study of the new and barely explored class of changing-look (CL) narrow-line Seyfert 1 (NLS1) galaxies and comment on their detection with the space mission SVOM (Space Variable Objects Monitor). We highlight the case of NGC 1566, which is outstanding in many respects, for instance as one of the nearest known CL AGN undergoing exceptional outbursts. Its NLS1 nature is discussed, and we take it as a nearby prototype for systems that could be discovered and studied in the near future, including with SVOM. Finally, we briefly examine the broader implications and applications of CL events in NLS1 galaxies and show that such systems, once discovered in larger numbers, will greatly advance our understanding of the physics of the environment of rapidly growing supermassive black holes. This White Paper is part of a sequence of publications which explore aspects of our understanding of (CL) NLS1 galaxy physics with future missions.

Changing-Look Narrow-Line Seyfert 1 Galaxies, their Detection with SVOM, and the Case of NGC 1566

CSS J102913 + 404220 is an atypical narrow-line Seyfert 1 galaxy with an energetic optical outburst occurring co-spatially with its nucleus. We present a detailed analysis of multi-wavelength photometric and spectroscopic observations of this object covering a period of a decade since outburst. We detect mid-infrared (MIR) ﬂares delayed by about two months relative to the optical outburst and with an extremely high peak luminosity of L 4 . 6 µ m > 10 44 erg s − 1 . The MIR peak luminosity is at least an order of magnitude higher than any known supernovae explosions, suggesting the optical outburst might be due to a stellar tidal disruption event (TDE). We ﬁnd late-time X-ray brightening by a factor of (cid:38) 30 with respect to what is observed about 100 days after the optical outburst peak, followed by a ﬂux fading by a factor of ∼ 4 within two weeks, making it one of the active galactic nuclei (AGNs) with extreme variability. Despite the dramatic X-ray variability, there are no coincident strong ﬂux variations in optical, UV, and MIR bands. This unusual variability behavior has been seen in other highly accreting AGNs and could be attributed to absorption variability. In this scenario, the decrease in the covering factor of the absorber with accretion rate could cause the X-ray brightening, possibly induced by the TDE. Most strikingly, while the UV / optical continuum remains almost unchanged with time, an evident enhancement in the ﬂux of the H α broad emission line is observed about a decade after the nuclear optical outburst, which is an anomalous behavior never seen in any other AGN. Such an H α anomaly could be explained by the replenishment of gas clouds and excitation within the broad line region (BLR) that perhaps originates from its interaction with outﬂowing stellar debris. Our results highlight the importance of the late-time evolution of a TDE, which can a ﬀ ect the accreting properties of the AGN, as suggested by recent simulations.

Discovery of late-time X-ray flare and anomalous emission line enhancement after the nuclear optical outburst in a narrow-line Seyfert 1 Galaxy

Hot giant planets like MASCARA-1 b are expected to have thermally inverted atmospheres, that makes them perfect laboratory for the atmospheric characterization through high-resolution spectroscopy. Nonetheless, previous attempts of detecting the atmosphere of MASCARA-1 b in transmission have led to negative results. In this paper we aim at the detection of the optical emission spectrum of MASCARA-1 b. We used the high-resolution spectrograph PEPSI to observe MASCARA-1 (spectral type A8) near the secondary eclipse of the planet. We cross-correlated the spectra with synthetic templates computed for several atomic and molecular species. We obtained the detection of FeI, CrI and TiI in the atmosphere of MASCARA-1 b with a S/N ~7, 4 and 5 respectively, and confirmed the expected systemic velocity of ~13 km/s and the radial velocity semi-amplitude of MASCARA-1 b of ~200 km/s. The detection of Ti is of particular importance in the context of the recently proposed Ti cold-trapping below a certain planetary equilibrium temperature. We confirm the presence of an the atmosphere around MASCARA-1 b through emission spectroscopy. We conclude that the atmospheric non detection in transmission spectroscopy is due to the high gravity of the planet and/or to the overlap between the planetary track and its Doppler shadow.

The PEPSI Exoplanet Transit Survey (PETS). III. The detection of Fe i, Cr i, and Ti i in the atmosphere of MASCARA-1 b through high-resolution emission spectroscopy


 The widely accepted active galactic nucleus (AGN) paradigm has been recently challenged by the discovery of the so-called ``changing-look'' (CL) phenomenon characterized by spectral-type transitions. By comparing the SDSS-V and SDSS DR16 spectroscopic datasets, here we report the identification of 14 new CL-AGNs (redshift $z<0.5$) exhibiting spectral-type changes on a timescale of $\sim 10$\,yr. Follow-up spectroscopy was conducted with the Lick Shane 3\,m and Keck 10\,m telescopes for three of the objects. Detailed analysis of these spectra enables us to arrive at the following two main results. (1) By compiling a sample of 65 CL-AGNs with good measurements, we reinforce the previous claim that CL-AGNs tend to be biased against both a high Eddington ratio ($\lesssim 0.1$) and a high bolometric luminosity ($\lesssim 10^{46}\,\mathrm{erg\,s^{-1}}$). This bias suggests that the disk-wind broad-line-region model is a plausible explanation of the CL phenomenon. (2) The host galaxies of CL-AGNs tend to be dominated by intermediate stellar populations, which motivates us to propose that CL-AGNs are probably particular AGNs at a special evolutionary stage, such as a transition stage from ``feast'' to ``famine'' fueling of the supermassive black hole. In addition, with our spectra, we identify SDSS\,J025951.22+003744.2 as a new repeat CL narrow-line Seyfert 1 galaxy with a rapid ``turn-on'' timescale of $\sim 1$\,yr.

Accretion and Host-Galaxy Properties of 14 New “Changing-Look” Active Galactic Nuclei Identified from the SDSS-V Survey

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Discovery of late-time X-ray flare and anomalous emission line enhancement after the nuclear optical outburst in a narrow-line Seyfert 1 Galaxy

The PEPSI Exoplanet Transit Survey (PETS). III. The detection of Fe i, Cr i, and Ti i in the atmosphere of MASCARA-1 b through high-resolution emission spectroscopy

Accretion and Host-Galaxy Properties of 14 New “Changing-Look” Active Galactic Nuclei Identified from the SDSS-V Survey