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Spectroscopically, tidal disruption events (TDEs) are characterized by broad (∼104 km s−1) emission lines and show a large diversity as well as different line profiles. After carefully and consistently performing a series of data reduction tasks including host galaxy light subtraction, we present here the first detailed, spectroscopic population study of 16 optical and UV TDEs. We study a number of emission lines prominent among TDEs including Hydrogen, Helium, and Bowen lines and we quantify their evolution with time in terms of line luminosities, velocity widths, and velocity offsets. We report a time lag between the peaks of the optical light curves and the peak luminosity of Hα spanning between ∼7 and 45 days. If interpreted as light echoes, these lags correspond to distances of ∼2 − 12 × 1016 cm, which are one to two orders of magnitudes larger than the estimated blackbody radii (RBB) of the same TDEs and we discuss the possible origin of this surprisingly large discrepancy. We also report time lags for the peak luminosity of the He I 5876 Å line, which are smaller than the ones of Hα for H TDEs and similar or larger for N III Bowen TDEs. We report that N III Bowen TDEs have lower Hα velocity widths compared to the rest of the TDEs in our sample and we also find that a strong X-ray to optical ratio might imply weakening of the line widths. Furthermore, we study the evolution of line luminosities and ratios with respect to their radii (RBB) and temperatures (TBB). We find a linear relationship between Hα luminosity and the RBB (Lline ∝ RBB) and potentially an inverse power-law relation with TBB (Lline ∝ TBB−β), leading to weaker Hα emission for TBB ≥ 25 000 K. The He II/He I ratio becomes large at the same temperatures, possibly pointing to an ionization effect. The He II/Hα ratio becomes larger as the photospheric radius recedes, implying a stratified photosphere where Helium lies deeper than Hydrogen. We suggest that the large diversity of the spectroscopic features seen in TDEs along with their X-ray properties can potentially be attributed to viewing angle effects., We thank Tom Holoien for providing us with the spectra of AT2018zr. P.C., G.L., D.B.M. and M.P. are supported by a research grant (19054) from VILLUM FONDEN. IA is a CIFAR Azrieli Global Scholar in the Gravity and the Extreme Universe Program and acknowledges support from that program, from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement number 852097), from the Israel Science Foundation (grant number 2752/19), from the United States – Israel Binational Science Foundation (BSF), and from the Israeli Council for Higher Education Alon Fellowship. M.N. is supported by a Royal Astronomical Society Research Fellowship and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 948381). T.-W.C. acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471. L.G. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramón y Cajal program RYC2019-027683 and from the Spanish MICIU project PID2020-115253GA-I00. M.G. is supported by the EU Horizon 2020 research and innovation programme under grant agreement No 101004719. T.M.B. was funded by the CONICYT PFCHA/DOCTORADOBECAS CHILE/2017-72180113. This work is based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of PESSTO/ePESSTO/ePESSTO+ (the extended Public ESO Spectroscopic Survey for Transient Objects Survey). PESSTO/ePESSTO/ePESSTO+ observations were obtained under ESO program IDs 188.D-3003, 191.D-0935, 199.D-0143, 1103.D-0328. This work is based on observations made with the Nordic Optical Telescope, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias.

SOXS (Son Of X-Shooter) is a single object spectrograph built by an international consortium for the ESO NTT telescope. SOXS is based on the heritage of the X-Shooter at the ESO-VLT with two arms (UV-VIS and NIR) working in parallel, with a Resolution-Slit product of about 4500, capable of simultaneously observing over the entire band the complete spectral range from the U- to the H-band. SOXS will carry out rapid and long-term Target of Opportunity requests on a variety of astronomical objects. The SOXS vacuum and cryogenic control system has been designed to evacuate, cool down and maintain the UV-VIS detector and the entire NIR spectrograph to their operating temperatures. The design chosen allows the two arms to be operated independently. This paper describes the final design of the cryo-vacuum control system, its functionalities and the tests performed in the integration laboratories., 12 pages, 6 figures, SPIE proceedings of the conference Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV

We report the implemented architecture for monitoring the health and the quality of the Son Of X-Shooter (SOXS) spectrograph for the New Technology Telescope in La Silla at the European Southern Observatory. Briefly, we report on the innovative no-SQL database approach used for storing time-series data that best suits for automatically triggering alarm, and report high-quality graphs on the dashboard to be used by the operation support team. The system is designed to constantly and actively monitor the Key Performance Indicators (KPI) metrics, as much automatically as possible, reducing the overhead on the support and operation teams. Moreover, we will also detail about the interface designed to inject quality checks metrics from the automated SOXS Pipeline (Young et al. 2022).

SOXS (Son Of X-Shooter) is a single object spectrograph offering a simultaneous spectral coverage from U- to H-band, built by an international consortium for the 3.58-m ESO New Technology Telescope at the La Silla Observatory. It is designed to observe all kind of transients and variable sources discovered by different surveys with a highly flexible schedule maintained by the consortium, based on the Target of Opportunity concept. SOXS is going to be a fundamental spectroscopic partner for any kind of imaging survey, becoming one of the premier transient follow-up instruments in the Southern hemisphere. This paper gives an updated status of the project, when the instrument is in the advanced phase of integration and testing in Europe, prior to the activities in Chile., Proc. SPIE 12184, Ground-based and Airborne Instrumentation for Astronomy IX, 121840O (2022)

The Son Of X-Shooter (SOXS) is a single object spectrograph, built by an international consortium for the 3.58-m ESO New Technology Telescope at the La Silla Observatory, ranging from 350 to 2000 nm. In this paper, we present the progress in the AIT phase of the Near InfraRed (NIR) arm. We describe the different AIT phases of the cryo, vacuum, opto-mechanics and detector subsystems, that finally converged at the INAF-OAB premises in Merate (Italy), where the NIR spectrograph is currently being assembled and tested, before the final assembly on SOXS., Comment: 6 pages, 8 Figures, SPIE: Astronomical Telescope + Instrumentation, Montreal 2022

SOXS is the new spectrograph for the ESO NTT telescope able to cover the optical and NIR bands thanks to two different arms: the UV-VIS (350-850 nm), and the NIR (800-2000 nm). In this article, we describe the final design of the visible camera cryostats, the test facilities for the CCD characterization, and the first results with the scientific detector. The UV-VIS detector system is based on a e2v CCD 44-82, a custom detector head coupled with the ESO Continuous Flowing Cryostat (CFC) cooling system and the New General Detector Controller (NGC) developed by ESO. The laboratory facility is based on an optical bench equipped with a Xenon lamp, filter wheels to select the wavelength, an integrating sphere, and a calibrated diode to measure the flux. This paper outlines the visible camera cryostat, the test facilities for the CCD characterization and the first results with the scientific detector in the laboratory and after the integration to the instrument.

A star crossing the tidal radius of a supermassive black hole will be spectacularly ripped apart with an accompanying burst of radiation. A few tens of such tidal disruption events (TDEs) have now been identified in the optical wavelengths, but the exact origin of the strong optical emission remains inconclusive. Here we report polarimetric observations of three TDEs. The continuum polarization is independent of wavelength, while emission lines are partially depolarized. These signatures are consistent with optical photons being scattered and polarized in an envelope of free electrons. An almost axisymmetric photosphere viewed from different angles is in broad agreement with the data, but there is also evidence for deviations from axial symmetry before the peak of the flare and significant time evolution at early times, compatible with the rapid formation of an accretion disk. By combining a super-Eddington accretion model with a radiative transfer code we generate predictions for the degree of polarization as a function of disk mass and viewing angle, and we show that the predicted levels are compatible with the observations, for extended reprocessing envelopes of $\sim$1000 gravitational radii. Spectropolarimetry therefore constitutes a new observational test for TDE models, and opens an important new line of exploration in the study of TDEs., Author's version of paper to appear in Nature Astronomy. In the journal version the detailed discussion on the ISP determination will be moved from the Methods section to a Supplementary Information section. 58 pages in double spacing format, including 5 Figures, 10 Extended Data Figures and 2 Tables

The tidal forces of a black hole can rip apart a star that passes too close to it, resulting in a stellar Tidal Disruption Event (TDE, (1)). In some such encounters, the black hole can launch a powerful relativistic jet (2-6). If this jet fortuitously aligns with our line of sight, the overall brightness is Doppler boosted by several orders of magnitude. Consequently, such on-axis relativistic TDEs have the potential to unveil cosmological (redshift z>1) quiescent black holes and are ideal test beds to understand the radiative mechanisms operating in super-Eddington jets. Here, we present multi-wavelength (X-ray, UV, optical, and radio) observations of the optically discovered transient AT 2022cmc at z=1.193 (7). Its unusual X-ray properties, including a peak observed luminosity of >1048 erg s-1, systematic variability on timescales as short as 1000 seconds, and overall duration lasting more than 30 days in the rest-frame are traits associated with relativistic TDEs. This makes AT 2022cmc only the fourth member of this rare class and the first one identified in the optical and with well-sampled optical data. The X-ray to radio spectral energy distributions spanning 5-50 days after discovery can be explained as synchrotron emission from a relativistic jet (radio), synchrotron self-Compton (X-rays), and thermal emission similar to that seen in low-redshift TDEs (UV/optical). Our modeling implies a beamed, highly relativistic jet akin to blazars (e.g., (8,9)) but requires extreme matter-domination, i.e, high ratio of electron-to-magnetic field energy densities in the jet, and challenges our theoretical understanding of jets. This work provides one of the best multi-wavelength datasets of a newborn relativistic jet to date and will be invaluable for testing more sophisticated jet models, and for identifying more such events in transient surveys.

Ni, Y. Q., et al., Type Ia supernovae are thermonuclear explosions of white dwarf stars. They play a central role in the chemical evolution of the Universe and are an important measure of cosmological distances. However, outstanding questions remain about their origins. Despite extensive efforts to obtain natal information from their earliest signals, observations have thus far failed to identify how the majority of them explode. Here, we present infant-phase detections of SN 2018aoz from a very low brightness of −10.5 AB absolute magnitude, revealing a hitherto unseen plateau in the B band that results in a rapid redward colour evolution between 1.0 and 12.4 hours after the estimated epoch of first light. The missing B-band flux is best explained by line-blanket absorption from Fe-peak elements in the outer 1% of the ejected mass. The observed B − V colour evolution of the supernova also matches the prediction from an over-density of Fe-peak elements in the same outer 1% of the ejected mass, whereas bluer colours are expected from a purely monotonic distribution of Fe-peak elements. The presence of excess nucleosynthetic material in the extreme outer layers of the ejecta points to enhanced surface nuclear burning or extended subsonic mixing processes in some normal type Ia SN explosions., D.-S.M., M.R.D. and C.D.M. are supported by Discovery Grants from the Natural Sciences and Engineering Research Council of Canada. D.-S.M. was supported in part by a Leading Edge Fund from the Canadian Foundation for Innovation (project no. 30951). M.R.D. was supported in part by the Canada Research Chairs Program, the Canadian Institute for Advanced Research (CIFAR) and the Dunlap Institute at the University of Toronto. D.J.S. acknowledges support by NSF grant nos. AST-1821987, 1821967 and 1908972 and from the Heising–Simons Foundation under grant no. 2020-1864. S.G.-G. acknowledges support by FCT under project CRISP PTDC/FIS-AST-31546 and project UIDB/00099/2020. H.S.P. was supported in part by a National Research Foundation (NRF) of Korea grant funded by the Korean government (MSIT, Ministry of Science and ICT; no. NRF-2019R1F1A1058228). P.J.B. acknowledges support from the Swift GI program 80NSSC19K0316. S.V., Y.D. and K.A.B. acknowledge support by NSF grant nos. AST-1813176 and AST-2008108. C.M. acknowledges support by NSF grant AST-1313484. I.A. is a CIFAR Azrieli Global Scholar in the Gravity and the Extreme Universe Program and acknowledges support from that program, from the Israel Science Foundation (grant nos. 2108/18 and 2752/19), from the United States – Israel Binational Science Foundation (BSF) and from an Israeli Council for Higher Education Alon Fellowship. R.L.B. acknowledges support by NASA through Hubble Fellowship grant no. 51386.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract no. NAS 5-26555. A.G.-Y. acknowledges support from the European Union via ERC grant no. 725161, the ISF GW Excellence Center, an IMOS space infrastructure grant and BSF/Transformative and GIF grants, as well as from the Benoziyo Endowment Fund for the Advancement of Science, the Deloro Institute for Advanced Research in Space and Optics, the Veronika A. Rabl Physics Discretionary Fund, P. and T. Gardner, the Yeda-Sela Center for Basic Research and a WIS-CIT joint research grant. A.G.-Y. is the recipient of the Helen and Martin Kimmel Award for Innovative Investigation. L.G. acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, the European Social Fund (ESF) ‘Investing in your future’ under the 2019 Ramón y Cajal program RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, as well as from the Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016. G.P. acknowledges support from the Millennium Science Initiative through grant no. IC120009. J.A. is supported by the Stavros Niarchos Foundation (SNF) and the Hellenic Foundation for Research and Innovation (HFRI) under the 2nd Call of ‘Science and Society’ Action ‘Always strive for excellence – Theodoros Papazoglou’ (project no. 01431).

Studying invisible objects in space that are hundreds of millions of light years away may sound impossible. But, in recent years, astronomers have developed a new way to investigate a type of invisible and distant objects—super-massive black holes. Black holes are the most densely packed objects in the Universe. When stars get close to super-massive black holes they can be torn apart, which produces a relatively brief but informative flash of light. These star-destroying events can help us to discover the locations of the most massive black holes in the Universe, but only if we know how to find and interpret them. In this article, we will discuss different ways we can “see” black holes, and particularly what we do and do not yet understand about stars getting “tidally disrupted” by them. Light YearThe distance light travels in a year, which is 5,878,625,370,000 miles.

The Son Of X-Shooter (SOXS) is a two-channel spectrograph along with imaging capabilities, characterized by a wide spectral coverage (350nm to 2000nm), designed for the NTT telescope at the La Silla Observatory. Its main scientific goal is the spectroscopic follow-up of transients and variable objects. The UV-VIS arm, of the Common Path sub-system, is characterized by the presence of a powered Atmospheric Dispersion Corrector composed (ADC) by two counter-rotating quadruplets, two prisms, and two lenses each. The presence of powered optics in both the optical groups represents an additional challenge in the alignment procedures. We present the characteristics of the ADC, the analysis after receiving the optics from the manufacturer, the emerging issues, the alignment strategies we followed, and the final results of the ADC in dispersion and optical quality.

SOXS (SOn of X-Shooter) is a medium resolution (~4500) wide-band (0.35 - 2.0 {\mu}m) spectrograph which passed the Final Design Review in 2018. The instrument is in the final integration phase and it is planned to be installed at the NTT in La Silla by next year. It is mainly composed of five different optomechanical subsystems (Common Path, NIR spectrograph, UV-VIS spectrograph, Camera, and Calibration) and other mechanical subsystems (Interface flange, Platform, cable corotator, and cooling system). A brief overview of the optomechanical subsystems is presented here as more details can be found in the specific proceedings while a more comprehensive discussion is dedicated to the other mechanical subsystems and the tools needed for the integration of the instrument. Moreover, the results obtained during the acceptance of the various mechanical elements are presented together with the experiments performed to validate the functionality of the subsystems. Finally, the mechanical integration procedure is shown here, along with all the modifications applied to correct the typical problems happening in this phase., Comment: arXiv admin note: text overlap with arXiv:2012.12693

We present early observations and analysis of the double-peaked Type IIb supernova (SN IIb) 2021zby. $TESS$ captured the prominent early shock cooling peak of SN 2021zby within the first $\sim$10 days after explosion with a 30-minute cadence. We present optical and near-infrared spectral series of SN 2021zby, including three spectra during the shock cooling phase. Using a multi-band model fit, we find that the inferred properties of its progenitor are consistent with a red supergiant or yellow supergiant, with an envelope mass of $\sim$0.3-3.0 M$_\odot$ and an envelope radius of $\sim$50-350$ R_\odot$. These inferred progenitor properties are similar to those of other SNe IIb with double-peak feature, such as SNe 1993J, 2011dh, 2016gkg and 2017jgh. This study further validates the importance of the high cadence and early coverage in resolving the shape of the shock cooling light curve, while the multi-band observations, especially UV, is also necessary to fully constrain the progenitor properties., Comment: 12 pages, 5 figures, 2 tables, submitted to ApJL

We present development progress of the scheduler for the Son Of X-Shooter (SOXS) instrument at the ESO-NTT 3.58 meter telescope. SOXS will be a single object spectroscopic facility, consisting of a two-arms high-efficiency spectrograph covering the spectral range 350-2000 nanometer with a mean resolving power R$\approx$4500. SOXS will be uniquely dedicated to the UV-visible and near infrared follow up of astrophysical transients, with a very wide pool of targets available from the streaming services of wide-field telescopes, current and future. This instrument will serve a variety of scientific scopes in the astrophysical community, with each scope eliciting its specific requirements for observation planning, that the observing scheduler has to meet. Due to directions from the European Southern Observatory (ESO), the instrument will be operated only by La Silla staff, with no astronomer present on the mountain. This implies a new challenge for the scheduling process, requiring a fully automated algorithm that should be able to present the operator not only with and ordered list of optimal targets, but also with optimal back-ups, should anything in the observing conditions change. This imposes a fast-response capability to the scheduler, without compromising the optimization process, that ensures good quality of the observations. In this paper we present the current state of the scheduler, that is now almost complete, and of its web interface., Accepted for publication in SPIE Astronomical Telescope and Instrumentation Conference proceedings - Montreal (Canada) July 2022

SOXS (SOn of X-Shooter) is a high-efficiency spectrograph with a mean Resolution-Slit product of 3500 over the entire band capable of simultaneously observing the complete spectral range 350-2000 nm. It consists of three scientific arms (the UV-VIS Spectrograph, the NIR Spectrograph and the Acquisition Camera) connected by the Common Path system to the NTT, and the Calibration Unit. We present an overview of the flow from the scientific to the technical requirements, and the realization of the sub-systems. Further, we give an overview of the methodologies used for planning and managing the assembly of the sub-systems, their integration and tests before the acceptance of the instrument in Europe (PAE) along with the plan for the integration of SOXS to the NTT. SOXS could be used as an example for the system engineering of an instrument of moderate complexity, with a large geographic spread of the team., Comment: 12 pages, 4 Figures, SPIE: Astronomical Telescope + Instrumentation, Montreal 2022. arXiv admin note: text overlap with arXiv:1812.07401

The Son-Of-XShooter (SOXS) is a single object spectrograph (UV-VIS & NIR) and acquisition camera scheduled to be mounted on the ESO 3.58-m New Technology Telescope at the La Silla Observatory. Although the underlying data reduction processes to convert raw detector data to fully-reduced science ready data are complex and multi-stepped, we have designed the SOXS Data Reduction pipeline with the core aims of providing end-users with a simple-to-use, well-documented command-line interface while also allowing the pipeline to be run in a fully automated state; streaming reduced data into the ESO Science Archive Facility without need for human intervention. To keep up with the stream of data coming from the instrument, there is the requirement to optimise the software to reduce each observation block of data well within the typical observation exposure time. The pipeline is written in Python 3 and has been built with an agile development philosophy that includes CI and adaptive planning., 10 pages, 7 figures, published in SPIE proceedings volume 12189. arXiv admin note: substantial text overlap with arXiv:2012.12678

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Tidal Disruption Events (TDEs) have been found to show a preference for post-starburst (PS) and quiescent Balmer-strong (QBS) galaxies. This preference can be used to help find TDEs in transient surveys. But what other transients might "contaminate" such a search, and by how much? We examine all reported transients coincident with the centers of galaxies in the French & Zabludoff (2018) catalog of spectroscopically confirmed PS and QBS galaxies and photometrically identified PS and QBS galaxy candidates. We find that TDEs and Type Ia supernovae (SNe) are the only types of transients classified in the centers of these galaxies (aside from one active galactic nucleus flare), with Type Ia SNe being 8.3+-0.2 times more prevalent than TDEs (1-sigma confidence bounds). This factor is ~2.7 times lower than in a control sample of quiescent galaxies. Narrowing the sample to spectroscopically confirmed QBS galaxies does not change these statistics much. In spectroscopically confirmed PS galaxies, however, TDEs are the ones that outnumber Type Ia SNe 2+-0.6 to 1. Unfortunately, there are few such galaxies in the catalog. By classifying transients from the entire catalog, three times more TDEs are expected to be found, but with a ~16-times larger Type Ia SN contamination. We use the public ZTF photometric archive to search for possibly missed TDEs in the French & Zabludoff (2018) galaxies. We find three unclassified clear transients -- none of which are likely missed TDEs based on their light-curve colors., Accepted to ApJ

In the transitional mass range (~8–10 solar masses) between white dwarf formation and iron core-collapse supernovae, stars are expected to produce an electron-capture supernova. Theoretically, these progenitors are thought to be super-asymptotic giant branch stars with a degenerate O + Ne + Mg core, and electron capture onto Ne and Mg nuclei should initiate core collapse1–4. However, no supernovae have unequivocally been identified from an electron-capture origin, partly because of uncertainty in theoretical predictions. Here we present six indicators of electron-capture supernovae and show that supernova 2018zd is the only known supernova with strong evidence for or consistent with all six: progenitor identification, circumstellar material, chemical composition5–7, explosion energy, light curve and nucleosynthesis8–12. For supernova 2018zd, we infer a super-asymptotic giant branch progenitor based on the faint candidate in the pre-explosion images and the chemically enriched circumstellar material revealed by the early ultraviolet colours and flash spectroscopy. The light-curve morphology and nebular emission lines can be explained by the low explosion energy and neutron-rich nucleosynthesis produced in an electron-capture supernova. This identification provides insights into the complex stellar evolution, supernova physics, cosmic nucleosynthesis and remnant populations in the transitional mass range. Electron-capture supernovae are thought to come from progenitors with a narrow range of masses, and thus they are rare. Here the authors present six indicators of an electron-capture supernova origin, and find that supernova 2018zd fulfils all six criteria., Instituto de Astrofísica de La Plata, Facultad de Ciencias Astronómicas y Geofísicas

Changing-look active galactic nuclei (AGNs) present an important laboratory to understand the origin and physical properties of the broad-line region (BLR). We investigate follow-up optical spectroscopy spanning $\sim 500$ days after the outburst of the changing-look AGN 1ES\,1927+654. The emission lines displayed dramatic, systematic variations in intensity, velocity width, velocity shift, and symmetry. Analysis of optical spectra and multi-band images indicate that the host galaxy contains a pseudobulge and a total stellar mass of $3.56_{-0.35}^{+0.38} \times 10^{9}\, M_\odot$. Enhanced continuum radiation from the outburst produced an accretion disk wind, which condensed into BLR clouds in the region above and below the temporary eccentric disk. Broad Balmer lines emerged $\sim 100$ days after the outburst, together with an unexpected, additional component of narrow-line emission. The newly formed BLR clouds then traveled along a similar eccentric orbit ($e \approx 0.6$). The Balmer decrement of the BLR increased by a factor of $\sim 4-5$ as a result of secular changes in cloud density. The drop in density at late times allowed the production of \hei\ and \heii\ emission. The mass of the black hole cannot be derived from the broad emission lines because the BLR is not virialized. Instead, we use the stellar properties of the host galaxy to estimate $M_\mathrm{BH} = 1.38_{-0.66}^{+1.25} \times 10^{6}\, M_\odot$. The nucleus reached near or above its Eddington limit during the peak of the outburst. We discuss the nature of the changing-look AGN 1ES\,1927+654 in the context of other tidal disruption events., 29 pages, 13 figures, published in the Astrophysical Journal

Core-collapse supernovae (CCSNe) mark the deaths of stars more massive than about eight times the mass of the Sun and are intrinsically the most common kind of catastrophic cosmic explosions. They can teach us about many important physical processes, such as nucleosynthesis and stellar evolution, and thus they have been studied extensively for decades. However, many crucial questions remain unanswered, including the most basic ones regarding which kinds of massive stars achieve which kind of explosions, and how. Observationally, this is related to the open puzzles of whether CCSNe can be divided into distinct types or whether they are drawn from a population with a continuous set of properties, and what progenitor characteristics drive the diversity of observed explosions. Recent developments in wide-field surveys and rapid-response follow-up facilities are helping us answer these questions by providing new tools, such as: (1) large statistical samples that enable population studies of the most common SNe and reveal rare (but extremely informative) events that question our standard understanding of the explosion physics involved; and (2) observations of early SNe emission taken shortly after explosion, which carry signatures of the progenitor structure and mass-loss history. Future facilities will increase our observational capabilities and allow us to answer many open questions related to these extremely energetic phenomena of the Universe. The diversity of core-collapse supernovae — the explosions of massive stars — has increased greatly recently, driven by developments in observing facilities and techniques. Here Modjaz, Gutierrez and Arcavi survey the current observational classifications, question whether the lines are starting to blur and look forward to the large samples of supernovae that are to come.

We present a high-cadence short term photometric and spectroscopic monitoring campaign of a type Ibn SN 2019wep, which is one of the rare SN Ibn after SNe 2010al and 2019uo to display signatures of flash ionization (\ion{He}{2}, \ion{C}{3}, \ion{N}{3}). We compare the decline rates and rise time of SN 2019wep with other SNe Ibn and fast transients. The post-peak decline in all bands (0.1 mag d$^{-1}$) are consistent with SNe Ibn but less than the fast transients. On the other hand, the $\Delta$m$_{15}$ values are slightly lower than the average values for SNe Ibn but consistent with the fast transients. The rise time is typically shorter than SNe Ibn but longer than fast transients. SN 2019wep lies at the fainter end of SNe Ibn but possesses an average luminosity amongst the fast transients sample. The peculiar color evolution places it between SNe Ib and the most extreme SNe Ibn. The bolometric light curve modelling shows resemblance with SN 2019uo with ejecta masses consistent with SNe Ib. SN 2019wep belongs to the "P cygni" sub-class of SNe Ibn and shows faster evolution in line velocities as compared to the "emission" sub-class. The post-maximum spectra show close resemblance with ASASSN-15ed hinting it to be of SN Ib nature. The low \ion{He}{1} CSM velocities and residual H$\alpha$ further justifies it and gives evidence of an intermittent progenitor between WR and LBV star., Comment: 19 pages, 14 figures, 2 Tables, Accepted for publication in ApJ main journal

Recent claimed detections of tidal disruption events (TDEs) in multi-wavelength data have opened potential new windows into the evolution and properties of otherwise dormant supermassive black holes (SMBHs) in the centres of galaxies. At present, there are several dozen TDE candidates, which share some properties and differ in others. The range in properties is broad enough to overlap other transient types, such as active galactic nuclei (AGN) and supernovae (SNe), which can make TDE classification ambiguous. A further complication is that "TDE signatures" have not been uniformly observed to similar sensitivities or even targeted across all candidates. This chapter reviews those events that are unusual relative to other TDEs, including the possibility of TDEs in pre-existing AGN, and summarises those characteristics thought to best distinguish TDEs from continuously accreting AGN, strongly flaring AGN, SNe, and Gamma-Ray Bursts (GRBs), as well as other potential impostors like stellar collisions, "micro-TDEs," and circumbinary accretion flows. We conclude that multiple observables should be used to classify any one event as a TDE. We also consider the TDE candidate population as a whole, which, for certain host galaxy or SMBH characteristics, is distinguishable statistically from non-TDEs, suggesting that at least some TDE candidates do in fact arise from SMBH-disrupted stars., 57 pages, 17 figures. Accepted for publication in Springer Space Science Reviews. Chapter in ISSI review "The Tidal Disruption of Stars by Massive Black Holes" vol. 79. Corrected several typos from previous submission

We present the detailed optical evolution of a Type Ib SN 2015dj in NGC 7371, using data spanning up to ∼170 days after discovery. SN 2015dj shares similarity in light-curve shape with SN 2007gr and peaks at M V = -17.37 0.02 mag. Analytical modeling of the quasi bolometric light curve yields 0.06 0.01 M o˙ of 56Ni, ejecta mass M o˙, and kinetic energy erg. The spectral features show a fast evolution and resemble those of spherically symmetric ejecta. The analysis of nebular phase spectral lines indicates a progenitor mass between 13-20 M o˙, suggesting a binary scenario., K.M. acknowledges the support from the Department of Science and Technology (DST), Government of India, and Indo-US Science and Technology Forum (IUSSTF) for the WISTEMM fellowship and the Department of Physics, UC Davis, where part of this work was carried out. K.M. also acknowledges BRICS grant DST/IMRCD/BRICS/Pilotcall/ProFCheap/2017(G) for the present work. Research by S.V. is supported by NSF grant AST-1813176. NUTS is supported in part by the Instrument Center for Danish Astrophysics (IDA). E.C., N.E.R., L.T., S. B., and M.T. are partially supported by PRIN-INAF 2016 with the project “Toward the SKA and CTA era: discovery, localization, and physics of transient sources” (P.I. M. Giroletti).

Radio observations of tidal disruption events (TDEs) - when a star is tidally disrupted by a supermassive black hole (SMBH) - provide a unique laboratory for studying outflows in the vicinity of SMBHs and their connection to accretion onto the SMBH. Radio emission has been detected in only a handful of TDEs so far. Here, we report the detection of delayed radio flares from an optically-discovered TDE. Our prompt radio observations of the TDE ASASSN-15oi showed no radio emission until the detection of a flare six months later, followed by a second and brighter flare, years later. We find that the standard scenario, in which an outflow is launched briefly after the stellar disruption, is unable to explain the combined temporal and spectral properties of the delayed flare. We suggest that the flare is due to the delayed ejection of an outflow, perhaps following a transition in accretion states. Our discovery motivates observations of TDEs at various timescales and highlights a need for new models., 15 pages, 7 figures, 1 table. Published in Nature Astronomy on Feb 22, 2021 at https://www.nature.com/articles/s41550-021-01300-8. Free read-only access at https://rdcu.be/cfDOK

We present multiband photometry and spectroscopy of SN 2018cuf, a Type IIP (“P” for plateau) supernova (SN) discovered by the Distance Less Than 40 Mpc Survey within 24 hr of explosion. SN 2018cuf appears to be a typical SN IIP, with an absolute V-band magnitude of −16.73 ± 0.32 at maximum and a decline rate of 0.21 ± 0.05 mag/50 days during the plateau phase. The distance of the object was constrained to be 41.8 ± 5.7 Mpc by using the expanding photosphere method. We used spectroscopic and photometric observations from the first year after the explosion to constrain the progenitor of SN 2018cuf using both hydrodynamic light-curve modeling and late-time spectroscopic modeling. The progenitor of SN 2018cuf was most likely a red supergiant of about 14.5 M⊙ that produced 0.04 ± 0.01 M⊙ ⁵⁶Ni during the explosion. We also found ∼0.07 M⊙ of circumstellar material (CSM) around the progenitor is needed to fit the early light curves, where the CSM may originate from presupernova outbursts. During the plateau phase, high-velocity features at ∼11,000 km s⁻¹ were detected in both the optical and near-infrared spectra, supporting the possibility that the ejecta were interacting with some CSM. A very shallow slope during the postplateau phase was also observed, and it is likely due to a low degree of nickel mixing or the relatively high nickel mass in the SN., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

We report on SRG/eROSITA, ZTF, ASAS-SN, Las Cumbres, NEOWISE-R, and Swift XRT/UVOT observations of the unique ongoing event AT 2019avd, located in the nucleus of a previously inactive galaxy at $z=0.029$. eROSITA first observed AT 2019avd on 2020-04-28 during its first all sky survey, when it was detected as an ultra-soft X-ray source ($kT\sim 85$ eV) that was $\gtrsim 90$ times brighter in the $0.2-2$ keV band than a previous 3$\sigma$ upper flux detection limit (with no archival X-ray detection at this position). The ZTF optical light curve in the $\sim 450$ days preceding the eROSITA detection is double peaked, and the eROSITA detection coincides with the rise of the second peak. Follow-up optical spectroscopy shows the emergence of a Bowen fluorescence feature and high-ionisation coronal lines ([\ion{Fe}{X}] 6375 {\AA}, [\ion{Fe}{XIV}] 5303 {\AA}), along with persistent broad Balmer emission lines (FWHM$\sim 1400$ km s$^{-1}$). Whilst the X-ray properties make AT 2019avd a promising tidal disruption event (TDE) candidate, the optical properties are atypical for optically selected TDEs. We discuss potential alternative origins that could explain the observed properties of AT 2019avd, such as a stellar binary TDE candidate, or a TDE involving a super massive black hole binary., Comment: A&A accepted 18/12/2020. 19 pages, 14 figures, 8 tables. Forthcoming article in A&A special issue: 'First science highlights from SRG/eROSITA'