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1.
The rise and fall of the iron-strong nuclear transient PS16dtm
Tanja Petrushevska, Giorgos Leloudas, D. Ilić, Mateusz Bronikowski, P. Charalampopoulos, G. K. Jaisawal, E. Paraskeva, M. Pursiainen, Andreja Gomboc, Barbara Marčun, 2023, original scientific article

Abstract: Context. Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centers of galaxies – nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN). Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. Aims. Here, we study PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy, which has been proposed to be a TDE candidate. Our aim is to study the spectroscopic and photometric properties of PS16dtm, in order to better understand the outbursts originating in NLSy1 galaxies. Methods. Our extensive multiwavelength follow-up that spans around 2000 days includes photometry and spectroscopy in the UV/optical, as well as mid-infrared (MIR) and X-ray observations. Furthermore, we improved an existing semiempirical model in order to reproduce the spectra and study the evolution of the spectral lines. Results. The UV/optical light curve shows a double peak at ∼50 and ∼100 days after the first detection, and it declines and flattens afterward, reaching preoutburst levels after 2000 days of monitoring. The MIR light curve rises almost simultaneously with the optical, but unlike the UV/optical which is approaching the preoutburst levels in the last epochs of our observations, the MIR emission is still rising at the time of writing. The optical spectra show broad Balmer features and the strongest broad Fe II emission ever detected in a nuclear transient. This broad Fe II emission was not present in the archival preoutburst spectrum and almost completely disappeared +1868 days after the outburst. We found that the majority of the flux of the broad Balmer and Fe II lines is produced by photoionization. We detect only weak X-ray emission in the 0.5−8 keV band at the location of PS16dtm, at +848, +1130, and +1429 days past the outburst. This means that the X-ray emission continues to be lower by at least an order of magnitude, compared to archival, preoutburst measurements. Conclusions. We confirm that the observed properties of PS16dtm are difficult to reconcile with normal AGN variability. The TDE scenario continues to be a plausible explanation for the observed properties, even though PS16dtm shows differences compared to TDE in quiescent galaxies. We suggest that this event is part of a growing sample of TDEs that show broad Balmer line profiles and Fe II complexes. We argue that the extreme variability seen in the AGN host due to PS16dtm may have easily been misclassified as a CLAGN, especially if the rising part of the light curve had been missed. This implies that some changing look episodes in AGN may be triggered by TDEs. Imaging and spectroscopic data of AGN with good sampling are needed to enable testing of possible physical mechanisms behind the extreme variability in AGN.
Keywords: nuclear transients, supermassive black holes, tidal disruption events, active galactic nuclei
Published in RUNG: 24.01.2023; Views: 1707; Downloads: 22
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2.
The rise and fall of the nuclear transient PS16dtm
Tanja Petrushevska, 2022, published scientific conference contribution abstract

Abstract: Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centres of galaxies - nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN).  Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. I will present PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy which has been proposed to be a TDE candidate. I will show our multi-year spectroscopic and photometric study of PS16dtm, which can help us to better understand the outbursts originating in NLSy1 galaxies.
Keywords: supermassive black holes, active galactic nuclei, tidal disruption events
Published in RUNG: 09.11.2022; Views: 1393; Downloads: 6
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3.
The rise and fall of the iron-strong nuclear transient PS16dtm
Tanja Petrushevska, 2022, published scientific conference contribution abstract

Abstract: Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centres of galaxies - nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN).  Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. I will present PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy which has been proposed to be a TDE candidate. I will show our multi-year spectroscopic and photometric study of PS16dtm, which can help us to better understand the outbursts originating in NLSy1 galaxies.
Keywords: supermassive black holes, active galactic nuclei, transients
Published in RUNG: 09.11.2022; Views: 1375; Downloads: 9
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4.
The rise and fall of the nuclear transient PS16dtm
Tanja Petrushevska, 2022, published scientific conference contribution abstract

Abstract: Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centres of galaxies - nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN).  Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. I will present PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy which has been proposed to be a TDE candidate. I will show our multi-year spectroscopic and photometric study of PS16dtm, which can help us to better understand the outbursts originating in NLSy1 galaxies.
Keywords: supermassive black holes, tidal disruption events, active galactic nucleus
Published in RUNG: 09.11.2022; Views: 1524; Downloads: 5
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5.
Observing TDEs in the era of LSST
Katja Bricman, 2020, published scientific conference contribution abstract

Abstract: The upcoming Large Synoptic Survey Telescope (LSST) will observe ~18000 square degrees of the Southern sky and is expected to discover thousands of transients every night due to its large coverage of the sky and its observing strategy. Being an exceptional transient hunter, we expect the LSST to increase the current observed sample of Tidal Disruption Events (TDEs) by a factor of ~1000 in 10 years of survey duration. TDEs are one of the most promising phenomena in the study of dormant supermassive black holes (SMBHs) in the Universe, and if their observed optical light curves are sampled frequently enough, TDEs can serve as indicators of SMBH mass. We present our simulations of TDE observations with the LSST, the resulting SMBH mass distributions of observed TDEs, and the efficiency of different proposed observing strategies of the LSST in finding these rare transients.
Keywords: Tidal Disruption Events, Supermassive black holes, sky surveys
Published in RUNG: 04.01.2021; Views: 2653; Downloads: 0
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6.
Studying TDEs in the era of LSST
Katja Bricman, Andreja Gomboc, 2019, published scientific conference contribution abstract

Keywords: The observing strategy with continuous scanning and large sky coverage of the upcoming ground-based Large Synoptic Survey Telescope (LSST) will make it a perfect tool in search of rare transients, such as Tidal Disruption Events (TDEs). Bright optical flares resulting from tidal disruption of stars by their host supermassive black hole (SMBH) can provide us with important information about the mass of the SMBH involved in the disruption and thus enable the study of quiescent SMBHs, which represent a large majority of SMBHs found in centres of galaxies. These types of transients are extremely rare, with only about few tens of candidates discovered so far. It is expected that the LSST will provide a large sample of new TDE light curves. Here we present simulations of TDE observations using an end-to-end LSST simulation framework. Based on the analysis of simulated light curves we estimate the number of TDEs with good quality light curves the LSST is expected to discover in 10 years of observations. In addition, we investigate whether TDEs observed by the LSST could be used to probe the SMBH mass distribution in the universe. The participation at this conference is supported by the Action CA16104 Gravitational waves, black holes and fundamental physics (GWverse), supported by COST (European Cooperation in Science and Technology).
Published in RUNG: 04.01.2021; Views: 2930; Downloads: 0

7.
TDEs with LSST
Katja Bricman, 2018, published scientific conference contribution abstract

Abstract: The Large Synoptic Survey Telescope (LSST) is an upcoming ground-based survey telescope in Chile, which will produce a multi-color survey of 18000 square degrees of the Southern Sky during its 10 years of observations. Due to its large coverage of the sky and its observing strategy it will be a perfect tool in search for transient astrophysical events, including rare Tidal Disruption Events (TDEs). TDEs occur when a star passes close by a supermassive black hole (SMBH) in a center of a galaxy and gets disrupted by its tidal forces. These events emit a bright flare of light, which can be observed to cosmological distances. In the seminar I will provide an overview of the LSST and TDEs, and present the preliminary results on the estimated absolute rates of TDE detection in 10 years of LSST operations, which were obtained by simulations of TDE light curves with an end-to-end LSST simulations framework.
Keywords: Tidal Disruption Events, Supermassive Black Holes, Sky Surveys
Published in RUNG: 04.01.2021; Views: 3078; Downloads: 64
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