Investigation of Variations in Double-Peaked Broad Emission Lines of Radio Quasar B3 1637+436A

In this paper, by comparing the optical spectra of Sloan Digital Sky Survey (SDSS), Keck LRIS (Low-Resolution Imaging Spectrograph), and Baryon Oscillation Spectroscopic Survey (BOSS), a preliminary study has been done on the properties of the accretion disk of the double-peaked broad line radio quasar B3 1637+436A. The continuum of the SDSS spectrum of B3 1637+436A (May 21, 2001) and the Keck spectrum (June 28, 2003) is not significantly different, while the continuum of the BOSS spectrum (June 17, 2018) is about 1.2 magnitudes lower than the SDSS spectrum in the V band. The H$\alpha$ emission lines of the three spectra have a clear double-peaked broad line profile. Like the continuum, the double-peaked broad line profile is also considered to come from the accretion disk. By fitting the disk model of the double-peaked profile of H$\alpha$ on the three spectra, we found that the double-peaked H$\alpha$ profile of the BOSS spectrum can be well fit with a single disk model, and the emission line region lies about 900–3000 gravitational radius away from the central black hole. The double-peaked profiles of SDSS and Keck’s H$\alpha$ need to be fit with two disk models. The corresponding accretion disk emission area has two regions, one of which (“The outer disk”) is similar to BOSS, and the other emission region (“The inner disk”) is located within the range of about 400–900 gravitational radius, which is much smaller than the outer disk. Combining the characteristics of variations of the continuum spectrum, we believe that the disappearance of the inner disk is the main reason for the variation between the SDSS/Keck spectrum and the BOSS spectrum.