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 1 - 3 / 31 1.SIFTING FOR SAPPHIRES: SYSTEMATIC SELECTION OF TIDAL DISRUPTION EVENTS IN iPTFTiara Hung, Suvi Gezari, Tanja Petrushevska, 2018, original scientific articleAbstract: We present results from a systematic selection of tidal disruption events (TDEs) in a wide area (4800 deg2 ) g + R band experiment by the Intermediate Palomar Transient Factory (iPTF) with a rolling cadence of 1 and 3 days. We use photometric selection criteria to down select from a total of 493 nuclear transients detected during the experiment to a sample of 26 blue (g − r < 0 mag) nuclear transients in red host galaxies. Using Swift follow-up UV and X-ray imaging, and ground-based optical spectroscopy, we classify 14 Type Ia supernovae (SNe Ia), 9 highly variable active galactic nuclei (AGNs), 2 confirmed TDEs, and 1 potential core-collapse supernova. From our study, we measure a TDE per galaxy rate of 1.7 +2.85 −1.27 ×10−4 gal−1 yr−1 (90% CL in Poisson statistics) using a galaxy number density estimated from the SDSS luminosity function. We find that it is possible to filter out AGNs by employing a more stringent transient color cut (g − r < −0.2 mag). The UV is an important discriminator for filtering out SN contamination, since in the optical, SNe Ia can appear as blue as TDEs in their early phases. However, the contamination from SN Ia drops significantly with a more stringent spatial offset cut, suggesting higher precision in astrometry is essential for separating TDEs from SNe Ia in the optical. Our most stringent optical photometric selection criteria yields a contamination rate of 4.5:1, allowing for a manageable number of TDE candidates for complete spectroscopic follow-up and real-time classification in the ZTF era.Found in: ključnih besedahSummary of found: ... accretion, accretion disks – black hole physics –...Keywords: accretion, accretion disks – black hole physics – galaxies: nuclei – ultraviolet: generalPublished: 02.03.2022; Views: 532; Downloads: 26 Fulltext (1,18 MB) 2.A study of stellar debris dynamics during a tidal disruption eventAurora Clerici, 2020, doctoral dissertationAbstract: The number of observed tidal disruption events is increasing rapidly with the advent of new surveys. Thus, it is becoming increasingly important to improve TDE models using different stellar and orbital parameters. We study the dynamical behaviour of tidal disruption events produced by a massive black hole like Sgr A* by changing different initial orbital parameters, taking into account the observed orbits of S stars. Investigating different types of orbits and penetration factors is important since their variations lead to different timescales of the tidal disruption event debris dynamics, making mechanisms such as self-crossing and pancaking act strongly or weakly, thus affecting the circularisation and accretion disk formation. We have performed smoothed particle hydrodynamics simulations. Each simulation consists in modelling the star with $10^5$ particles, and the density profile is described by a polytrope with $\gamma$ = 5/3. The massive black hole is modelled with a generalised post-Newtonian potential, which takes into account relativistic effects of the Schwarzschild space-time. Our analyses find that mass return rate distributions of solar-like stars and S-like stars with same eccentricity have similar durations, but S-like stars have higher mass return rate, as expected due to their larger mass. Regarding debris circularisation, we identify four types of evolution, related to the mechanisms and processes involved during circularisation: in type 1 the debris does not circularise efficiently, hence a disk is not formed or is formed after relatively long time; in type 2 the debris slowly circularises and eventually forms a disk with no debris falling back; in type 3 the debris relatively quickly circularises and forms a disk while there is still debris falling back; finally, in type 4 the debris quickly and efficiently circularises, mainly through self-crossings and shocks, and forms a disk with no debris falling back. Finally, we find that the standard relation of circularisation radius $r_{\rm circ} = 2r_{\rm t}$ holds only for $\beta = 1$ and eccentricities close to parabolic.Found in: ključnih besedahSummary of found: ...or weakly, thus affecting the circularisation and accretion disk formation. We have performed smoothed particle hydrodynamics...Keywords: 07.05.Tp Computer modeling and simulation, 95.30.Lz Hydrodynamics, 98.35.Jk Galactic center, bar, circumnuclear matter, and bulge, 98.62.Js Galactic nuclei (including black holes), circumnuclear matter, and bulges, 98.62.Mw Infall, accretion, and accretion disksPublished: 29.09.2020; Views: 2107; Downloads: 48 Fulltext (37,55 MB) 3.Tidal Disruption Events seen through the eyes of Vera C. Rubin ObservatoryKatja Bučar Bricman, 2021, doctoral dissertationAbstract: Tidal Disruption Events (TDEs) are rare transients, which are considered to be promising tools in probing supermassive black holes (SMBHs) and their environments in quiescent galaxies, accretion physics, and jet formation mechanisms. The majority of $\approx$ 60 detected TDEs has been discovered with large field of view time-domain surveys in the last two decades. Currently, about 10 TDEs are discovered per year, and we expect this number will increase largely once the Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory begins its observations. In this work we demonstrate and explore the capabilities of the LSST to study TDEs. To begin with, we simulate LSST observations of TDEs over $10$ years of survey duration by including realistic SED models from MOSFiT into the simulation framework of the LSST. SEDs are then converted into observed fluxes and light curves are simulated with the LSST observing strategy minion_1016. Simulated observations are used to estimate the number of TDEs the LSST is expected to observe and to assess the possibility of probing the SMBH mass distribution in the Universe with the observed TDE sample. We find that the LSST has a potential of observing ~1000 TDEs per year, the exact number depending on the SMBH mass distribution and the adopted observing strategy. In spite of this large number, we find that probing the SMBH mass distribution with LSST observed TDEs will not be straightforward, especially at the low-mass end. This is largely attributed to the fact that TDEs caused by low-mass black holes ($\le 10^6 M_\odot$) are less luminous and shorter than TDEs by heavier SMBHs ($> 10^6 M_\odot$), and the probability of observationally missing them with LSST is higher. Second, we built a MAF TDE metric for photometric identification of TDEs based on LSST data. We use the metric to evaluate the performance of different proposed survey strategies in identifying TDEs with pre-defined identification requirements. Since TDEs are blue in color for months after peak light, which separates them well from SNe and AGN, we include u-band observations as one of the criteria for a positive identification. We find that the number of identified TDEs strongly depends of the observing strategy and the number of u-band visits to a given field in the sky. Observing strategies with a larger number of u-band observations perform significantly better. For these strategies up to 10% of LSST observed TDEs satisfy the identification requirements.Found in: ključnih besedahSummary of found: ...(SMBHs) and their environments in quiescent galaxies, accretion physics, and jet formation mechanisms. The majority...Keywords: Ground-based ultraviolet, optical and infrared telescopes Astronomical catalogs, atlases, sky surveys, databases, retrieval systems, archives, Black holes, Galactic nuclei (including black holes), circumnuclear matter, and bulges, Infall, accretion, and accretion disksPublished: 03.01.2022; Views: 828; Downloads: 18 Fulltext (124,61 MB)
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