The Variability of the Broad Line Profiles of SDSS J1430+2303

The Variability of the Broad Line Profiles of SDSS J1430+2303

SDSS J1430+2303 has been argued to possess a supermassive black hole binary which is predicted to merge within a few months or three years from January 2022. We conducted follow-up optical spectroscopic observations of SDSS J1430+2303 with KOOLS-IFU on Seimei Telescope in May, June, and July 2022, and April 2023. The observed spectrum around $mathrm{H}mathrm{alpha}$ shows a central broad component $sim 10^3 mathrm{km s^{-1}}$ blueshifted from the narrow H$mathrm{alpha}$ line as well as the broader double-peaked component with a separation of $simpm 5times10^3 mathrm{km s^{-1}}$, similar to the spectrum reported in January 2022. We investigate the variability of the complex broad $mathrm{H}mathrm{alpha}$ emission line relative to the continuum over the observation period. The continuum-normalized relative flux of the central broad component shows the increasing trend from May to July 2022 which is interpreted to be caused by the decrease of the continuum as also supported by damping of the X-ray, UV, and optical light curves observed for the same period. From July 2022 to April 2023, however, the central broad component decreased significantly. For the relative flux of the broader double-peaked component, on the other hand, no significant change appears at any epoch. These results suggest that the complicated broad line profile of SDSS J1430+2303 is generated from at least two distinct regions. While the central broad component originates from a broad line region, the broader double-peaked component arises in the vicinity of the continuum source.SDSS J1430+2303 has been argued to possess a supermassive black hole binary which is predicted to merge within a few months or three years from January 2022. We conducted follow-up optical spectroscopic observations of SDSS J1430+2303 with KOOLS-IFU on Seimei Telescope in May, June, and July 2022, and April 2023. The observed spectrum around $mathrm{H}mathrm{alpha}$ shows a central broad component $sim 10^3 mathrm{km s^{-1}}$ blueshifted from the narrow H$mathrm{alpha}$ line as well as the broader double-peaked component with a separation of $simpm 5times10^3 mathrm{km s^{-1}}$, similar to the spectrum reported in January 2022. We investigate the variability of the complex broad $mathrm{H}mathrm{alpha}$ emission line relative to the continuum over the observation period. The continuum-normalized relative flux of the central broad component shows the increasing trend from May to July 2022 which is interpreted to be caused by the decrease of the continuum as also supported by damping of the X-ray, UV, and optical light curves observed for the same period. From July 2022 to April 2023, however, the central broad component decreased significantly. For the relative flux of the broader double-peaked component, on the other hand, no significant change appears at any epoch. These results suggest that the complicated broad line profile of SDSS J1430+2303 is generated from at least two distinct regions. While the central broad component originates from a broad line region, the broader double-peaked component arises in the vicinity of the continuum source.