TY - JOUR
T1 - The spectral evolution of AT 2018DYB and the presence of metal lines in tidal disruption events
AU - Leloudas, Giorgos
AU - Dai, Lixin
AU - Arcavi, Iair
AU - Vreeswijk, Paul M.
AU - Mockler, Brenna
AU - Roy, Rupak
AU - Malesani, Daniele Bjørn
AU - Schulze, Steve
AU - Wevers, Thomas
AU - Fraser, Morgan
AU - Ramirez-Ruiz, Enrico
AU - Auchettl, Katie
AU - Burke, Jamison
AU - Cannizzaro, Giacomo
AU - Charalampopoulos, Panos
AU - Chen, Ting-Wan
AU - Cikota, Aleksandar
AU - Della Valle, Massimo
AU - Galbany, Lluis
AU - Gromadzki, Mariusz
AU - Heintz, Kasper E.
AU - Hiramatsu, Daichi
AU - Jonker, Peter G.
AU - Kostrzewa-Rutkowska, Zuzanna
AU - Maguire, Kate
AU - Mandel, Ilya
AU - Onori, Francesca
AU - Roth, Nathaniel
AU - Smartt, Stephen J.
AU - Wyrzykowski, Lukasz
AU - Young, Dave R.
PY - 2019
Y1 - 2019
N2 - We present light curves and spectra of the tidal disruption event (TDE) ASASSN-18pg / AT 2018dyb spanning a period of seven months. The event shows a plethora of strong emission lines, including the Balmer series, He II, He I and metal lines of O III λ3760 and N III λλ 4100 and 4640. The latter lines are consistent with originating from the Bowen fluorescence mechanism. By analyzing literature spectra of past events, we conclude that these lines are common in TDEs. The spectral diversity of optical TDEs is thus larger than previously thought and includes N-rich besides H- and He-rich events. We study how the spectral lines evolve with time, by means of their width, relative strength and velocity offsets. The velocity width of the lines starts at ~ 12,000 km s−1 and decreases with time. The ratio of Hα to Hβ remains close to three, while the ratio of He II over N III increases with time. The same is true for ASASSN-14li, which has a very similar spectrum to AT 2018dyb but its lines are narrower by a factor of >2. High-resolution spectroscopy at maximum light does not reveal any narrow features that can be attributed to the TDE. By fitting the light curves of AT 2018dyb we estimate a mass of 4+5/−2×106M⊙ for the black hole and of 0.7+4/−0.6M⊙ for the disrupted star. The detection of strong Bowen lines in the optical spectrum is an indirect proof for extreme ultraviolet and (re-processed) X-ray radiation and favors an accretion origin for the TDE optical luminosity. A model where photons escape after multiple scatterings through a super-Eddington thick disk and its optically-thick wind, viewed at an angle close to the disk plane, is consistent with the observations. (Abridged)
AB - We present light curves and spectra of the tidal disruption event (TDE) ASASSN-18pg / AT 2018dyb spanning a period of seven months. The event shows a plethora of strong emission lines, including the Balmer series, He II, He I and metal lines of O III λ3760 and N III λλ 4100 and 4640. The latter lines are consistent with originating from the Bowen fluorescence mechanism. By analyzing literature spectra of past events, we conclude that these lines are common in TDEs. The spectral diversity of optical TDEs is thus larger than previously thought and includes N-rich besides H- and He-rich events. We study how the spectral lines evolve with time, by means of their width, relative strength and velocity offsets. The velocity width of the lines starts at ~ 12,000 km s−1 and decreases with time. The ratio of Hα to Hβ remains close to three, while the ratio of He II over N III increases with time. The same is true for ASASSN-14li, which has a very similar spectrum to AT 2018dyb but its lines are narrower by a factor of >2. High-resolution spectroscopy at maximum light does not reveal any narrow features that can be attributed to the TDE. By fitting the light curves of AT 2018dyb we estimate a mass of 4+5/−2×106M⊙ for the black hole and of 0.7+4/−0.6M⊙ for the disrupted star. The detection of strong Bowen lines in the optical spectrum is an indirect proof for extreme ultraviolet and (re-processed) X-ray radiation and favors an accretion origin for the TDE optical luminosity. A model where photons escape after multiple scatterings through a super-Eddington thick disk and its optically-thick wind, viewed at an angle close to the disk plane, is consistent with the observations. (Abridged)
KW - Black hole physics
KW - Galaxies: nuclei
KW - Galaxies: individual: ASASSN-18pg, AT 2018dyb
U2 - 10.3847/1538-4357/ab5792
DO - 10.3847/1538-4357/ab5792
M3 - Journal article
SN - 0004-637X
VL - 887
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 218
ER -