Investigation Of Variations In Double-Peaked Broad Emission Lines

Quasars(QSO)are a type of galaxies with extremely bright centers,whose radiation is driven by the central supermassive black hole(SMBH).The accreting SMBH paradigm of AGNs(Active Galactic Nuclei)is currently a successful model to describe this mechanism.As a key component of this paradigm,the accretion disk is a place where gravitational potential energy is converted into thermal radiation,and it is also an important part of gas transport to the central black hole.However,due to the small size of the accretion disk(0.01-1pc),this makes the direct spatially resolved observation impossible.There are many theoretical models for the explanation of accretion disks.One view is that there is a high-temperature plasma ring inside the accretion disk,and the inverse Compton effect causes X-ray radiation to be generated on the plasma ring and irradiated on the thin gas disk outside the ring,thereby generating multi-band radiation and wide emission line.At the same time,because the accretion disk approximates Kepler motion,it can be inferred from this model that the broad emission line from the accretion disk gas will exhibit a double-peaked profile.In some studies,this model can well fit the observed double-peaked profile of the broad emission line,thereby limiting the accretion disk.This article first reviews and summarizes the researches on AGN accretion disks so far,and then studies in detail a quasar J1638+4335 that exhibits the characteristics of a wide emission line of Hα.By comparing the epoch optical spectra of SDSS,Keck and BOSS,we found that the double-peaked profile of Ha shows a significant variability.Compared with the former two,the emission flux at the velocity larger than 6000 km/s relative to Ha in the BOSS spectrum almost disappears.Our favorite explanation is that corresponding emitting gas in the accretion disk is further accreted to the inner side of a smaller scale.We assume that this part of the gas is the inner disk of the accretion disk,and the relatively low velocity(<6000km/s)that is significantly present in the three observations is the outer disk of the accretion disk.We use the above disk-emitting model to fit the Ha double-peaked profiles of the three observations of J1638+4335.The radius of the inner disk is about 400-900lightdays,and the radius of the outer disk is about 900.-3000 lightdays,which limits the structure of the accretion disk.We use the standard thin disk model(α-Disk Model)to estimate the mass of the accretioned inner disk to be about 107 M⊙,the mass inflow velocity is much greater than the observed J1638+4335 Accretion rate 0.1-0.5M⊙/yr.This shows that the actual structure of the J1638+4335 accretion disk may be discontinuous.At the same time,the good fit of the J1638+4335 double-peaked structure has also verified the thin disk model,indicating that the Ha emission line may come from the gas possibly above the accretion disk.This research method can also be applied to more AGNs with optical variable and double-peaked broad-line characteristics.We further apply this method to Mrk926 and NGC5252,which also show variations in broad emission lines,and find that they have a comparative disk size with J1638+4335.Such method can be applied to more type I and type II AGNs with variations.