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- Nicholl, M., et al.
(författare)
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An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:1, s. 482-504
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Tidskriftsartikel (refereegranskat)abstract
- At 66 Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to date, with a luminosity intermediate between the bulk of the population and the faint-and-fast event iPTF16fnl. Its proximity allowed a very early detection and triggering of multiwavelength and spectroscopic follow-up well before maximum light. The velocity dispersion of the host galaxy and fits to the TDE light curve indicate a black hole mass approximate to 10(6) M-circle dot, disrupting a star of approximate to 1 M-circle dot. By analysing our comprehensive UV, optical, and X-ray data, we show that the early optical emission is dominated by an outflow, with a luminosity evolution L proportional to t(2), consistent with a photosphere expanding at constant velocity (greater than or similar to 2000 km s(-1)), and a line-forming region producing initially blueshifted H and He II profiles with v = 3000-10 000 km s(-1). The fastest optical ejecta approach the velocity inferred from radio detections (modelled in a forthcoming companion paper from K. D. Alexander et al.), thus the same outflow may be responsible for both the fast optical rise and the radio emission - the first time this connection has been observed in a TDE. The light-curve rise begins 29 +/- 2 d before maximum light, peaking when the photosphere reaches the radius where optical photons can escape. The photosphere then undergoes a sudden transition, first cooling at constant radius then contracting at constant temperature. At the same time, the blueshifts disappear from the spectrum and Bowen fluorescence lines (N III) become prominent, implying a source of far-UV photons, while the X-ray light curve peaks at approximate to 10(41) erg s(-1). Assuming that these X-rays are from prompt accretion, the size and mass of the outflow are consistent with the reprocessing layer needed to explain the large optical to X-ray ratio in this and other optical TDEs, possibly favouring accretion-powered over collision-powered outflow models.
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- Short, P., et al.
(författare)
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Delayed appearance and evolution of coronal lines in the TDE AT2019qiz
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 525:1, s. 1568-1587
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Tidskriftsartikel (refereegranskat)abstract
- Tidal disruption events (TDEs) occur when a star gets torn apart by a supermassive black hole as it crosses its tidal radius. We present late-time optical and X-ray observations of the nuclear transient AT2019qiz, which showed the typical signs of an optical-UV transient class commonly believed to be TDEs. Optical spectra were obtained 428, 481, and 828 rest-frame days after optical light-curve peak, and a UV/X-ray observation coincided with the later spectrum. The optical spectra show strong coronal emission lines, including [Fe VII], [Fe X], [Fe XI], and [Fe XIV]. The Fe lines rise and then fall, except [Fe XIV] that appears late and rises. We observe increasing flux of narrow H α and H β and a decrease in broad H α flux. The coronal lines have full width at half-maximum ranging from ∼150−300 km s−1, suggesting they originate from a region between the broad- and narrow-line emitting gas. Between the optical flare and late-time observation, the X-ray spectrum softens dramatically. The 0.3–1 keV X-ray flux increases by a factor of ∼50, while the hard X-ray flux decreases by a factor of ∼6. Wide-field Infrared Survey Explorer fluxes also rose over the same period, indicating the presence of an infrared echo. With AT2017gge, AT2019qiz is one of two examples of a spectroscopically confirmed optical-UV TDE showing delayed coronal line emission, supporting speculations that Extreme Coronal Line Emitters in quiescent galaxies can be echos of unobserved past TDEs. We argue that the coronal lines, narrow lines, and infrared emission arise from the illumination of pre-existing material likely related to either a previous TDE or active galactic nucleus activity.
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- Charalampopoulos, P., et al.
(författare)
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A detailed spectroscopic study of tidal disruption events
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 659
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Tidskriftsartikel (refereegranskat)abstract
- Spectroscopically, tidal disruption events (TDEs) are characterized by broad (similar to 10(4) 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 H alpha spanning between similar to 7 and 45 days. If interpreted as light echoes, these lags correspond to distances of similar to 2 - 12 x 10(16) cm, which are one to two orders of magnitudes larger than the estimated blackbody radii (R-BB) 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 angstrom line, which are smaller than the ones of H alpha for H TDEs and similar or larger for N III Bowen TDEs. We report that N III Bowen TDEs have lower H alpha 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 (R-BB) and temperatures (T-BB). We find a linear relationship between H alpha luminosity and the R-BB (L-line proportional to R-BB) and potentially an inverse power-law relation with T-BB (L-line proportional to T-BB(-beta)), leading to weaker H alpha emission for T-BB >= 25 000 K. The He II/He I ratio becomes large at the same temperatures, possibly pointing to an ionization effect. The He II/H alpha 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.
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- Charalampopoulos, P., et al.
(författare)
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AT 2020wey and the class of faint and fast tidal disruption events
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 673
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Tidskriftsartikel (refereegranskat)abstract
- We present an analysis of the optical and ultraviolet properties of AT 2020wey, a faint and fast tidal disruption event (TDE) at 124.3 Mpc. The light curve of the object peaked at an absolute magnitude of M-g = 17.45 +/- 0.08 mag and a maximum bolometric luminosity of L-peak = (8.74 +/- 0.69) x 10(42) erg s 1, making it comparable to iPTF16fnl, the faintest TDE to date. The time from the last non-detection to the g-band peak is 23 +/- 2 days, and the rise is well described by L proportional to/ t(1.80 +/- 0.22). The decline of the bolometric light curve is described by a sharp exponential decay steeper than the canonical t(-5/3) power law, making AT 2020wey the fastest declining TDE to date. The multi-band light curve analysis shows first a slowly declining blackbody temperature of T-BB similar to 20 000 K around the peak brightness followed by a gradual temperature increase. The blackbody photosphere is found to expand at a constant velocity (similar to 1300 km s(-1)) to a value of R-BB similar to 3.5 x 10(14) cm before contracting rapidly. Multi-wavelength fits to the light curve indicate a complete disruption of a star of M-star = 0.11(-0.0)(+0.05) M-circle dot by a black hole of M-BH = 106(-0.09)(6.46+0.09) M-circle dot. Our spectroscopic dataset reveals broad (similar to 10(4) km s(-1)) Balmer and He II 4686 angstrom lines, with H alpha reaching its peak with a lag of similar to 8.2 days compared to the continuum. In contrast to previous faint and fast TDEs, there are no obvious Bowen fluorescence lines in the spectra of AT 2020wey. There is a strong correlation between the MOSFIT-derived black hole masses of TDEs and their decline rate. However, AT 2020wey is an outlier in this correlation, which could indicate that its fast early decline may be dictated by a different physical mechanism than fallback. After performing a volumetric correction to a sample of 30 TDEs observed between 2018 and 2020, we conclude that faint TDEs are not rare by nature; they should constitute up to similar to 50-60% of the entire population and their numbers could alleviate some of the tension between the observed and theoretical TDE rate estimates. We calculate the optical TDE luminosity function and we find a steep power-law relation dN=dL(g) proportional to / L-g(-2.36 +/- 0.16).
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