Interesting Clues to Detect Hidden Tidal Disruption Events in Active Galactic Nuclei

In the manuscript, effects of Tidal Disruption Events (TDEs) are estimated on long-term AGN variability, to provide interesting clues to detect probable hidden TDEs in normal broad line AGN with apparent intrinsic variability which overwhelm the TDEs expected variability features, after considering the unique TDEs expected variability patterns. Based on theoretical TDEs expected variability plus AGN intrinsic variability randomly simulated by Continuous AutoRegressive process, long-term variability properties with and without TDEs contributions are well analyzed in AGN. Then, interesting effects of TDEs can be determined on long-term observed variability of AGN. First, more massive BHs, especially masses larger than $10^7{\rm M_\odot}$, can lead to more sensitive and positive dependence of $\tau_{TN}$ on $R_{TN}$, with $\tau_{TN}$ as variability timescale ratio of light curves with TDEs contributions to intrinsic light curves without TDEs contributions, and $R_{TN}$ as ratio of peak intensity of TDEs expected variability to the mean intensity of intrinsic AGN variability without TDEs contributions. Second, stronger TDEs contributions $R_{TN}$ can lead to $\tau_{TN}$ quite larger than 5. Third, for intrinsic AGN variability having longer variability timescales, TDEs contributions will lead $\tau_{TN}$ to be increased more slowly. The results actually provide an interesting forward-looking method to detect probable hidden TDEs in normal broad line AGN, due to quite different variability properties, especially different DRW/CAR process expected variability timescales, in different epochs, especially in normal broad line AGN with shorter intrinsic variability timescales and with BH masses larger than $10^7{\rm M_\odot}$.Comment: 17 pages, 2 tables, 9 figures, accepted to be published in MNRA

Modeling the flare in NGC 1097 from 1991 to 2004 as a tidal disruption event

In the Letter, interesting evidence is reported to support a central tidal disruption event (TDE) in the known AGN NGC 1097. Considering the motivations of TDE as one probable origination of emission materials of double-peaked broad emission lines and also as one probable explanation to changing-look AGN, it is interesting to check whether are there clues to support a TDE in NGC 1097, not only a changing-look AGN but also an AGN with double-peaked broad emission lines. Under the assumption that the onset of broad H$\alpha$ emission was due to a TDE, the 13years-long (1991-2004) variability of double-peaked broad H$\alpha$ line flux in NGC 1097 can be well predicted by theoretical TDE model, with a $(1-1.5){\rm M_\odot}$ main-sequence star tidally disrupted by the central BH with TDE model determined mass about $(5-8)\times10^7{\rm M_\odot}$. The results provide interesting evidence to not only support TDE-related origin of double-peaked broad line emission materials but also support TDE as an accepted physical explanation to physical properties of changing-look AGN.Comment: 5 pages, 3 figures, 1 table, Accepted to be published in MNRAS Lette

SDSS J1619 with blue-shifted broad components in Hα\alpha and in [O~{\sc iii}] having similar line width and velocity shifts: a recoiling SMBH candidate?

In this Letter, we report a potential candidate of recoiling supermassive black hole (rSMBH) in SDSS J1619 based on similar velocity shifts and line widths of the blue-shifted broad components in H$\alpha$ and [O~{\sc iii}] doublet. The measured line width ratio between blue-shifted broad H$\alpha$ and broad [O~{\sc iii}] line is 1.06, if compared with common values around 5.12 for normal Type-1 AGN, indicating different properties of the blue-shifted broad components in SDSS J1619 from those of normal QSOs. The virial BH mass $M_{BHr}$ derived from the broad H$\alpha$ is consistent with the mass expected from the M_{BH}-\sigma relation. The similar velocity shifts and line widths of the blue-shifted broad components in H$\alpha$ and [O~{\sc iii}] and the virial BH mass derived from the H$\alpha$ broad line emissions that is consistent with the mass expected from the M_{BH}-\sigma~ relation, can be explained by a rSMBH scenario. Besides the rSMBH scenario, either the similar line widths of the blue-shifted broad components in H$\alpha$ and in [O~{\sc iii}] or the consistency between the virial BH mass and the mass expected from the M_{BH}-\sigma~ relation cannot be explained by the other proposed models in SDSS J1619.Comment: 6 pages, 4 figures, 2 tables, accepted to be published in MNRAS Letter

Are there higher electron densities in narrow emission line regions of Type-1 AGN than Type-2 AGN?

In the manuscript, we check properties of electron densities $n_e$ traced by flux ratio $R_{sii}$ of [S~{\sc ii}]$\lambda6716$\AA~ to [S~{\sc ii}]$\lambda6731$\AA~ in narrow emission line regions (NLRs) between Type-1 AGN and Type-2 AGN in SDSS DR12. Under the framework of Unified Model considering kpc-scale structures, similar $n_e$ in NLRs should be expected between Type-1 AGN and Type-2 AGN. Based on reliable measurements of [S~{\sc ii}] doublet with measured parameters at least five times larger than corresponding uncertainties, there are 6039 Type-1 AGN and 8725 Type-2 AGN (excluding the Type-2 LINERs and the composite galaxies) collected from SDSS DR12. Then, lower $R_{sii}$ (higher $n_e$) in NLRs can be well confirmed in Type-1 AGN than in Type-2 AGN, with confidence level higher than 5$\sigma$, even after considering necessary effects including effects of electron temperatures traced by [O~{\sc iii}]$\lambda4364,4959,5007$\AA~ on estimating $n_e$ in NLRs. Two probable methods are proposed to explain the higher $n_e$ in NLRs in Type-1 AGN. First, the higher $n_e$ in NLRs of Type-1 AGN could indicate longer time durations of AGN activities in Type-1 AGN than in Type-2 AGN, if AGN activities triggering galactic-scale outflows leading to more electrons injecting into NLRs were accepted to explain the higher $n_e$ in NLRs of Type-2 AGN than HII galaxies. Second, the lower $n_e$ in NLRs of Type-2 AGN could be explained by stronger star-forming contributions in Type-2 AGN, considering lower $n_e$ in HII regions. The results provide interesting challenges to the commonly and widely accepted Unified Model of AGN.Comment: 45 pages, 2 long tables, 16 figures, accepted to be published in Ap