The optical spectrum of PKS 1222+216 and its black hole mass

TL;DR

This study analyzes the optical spectrum of blazar PKS 1222+216 over three years, revealing a stable broad line region despite continuum variability, and estimates the black hole mass as approximately 600 million solar masses.

Contribution

It provides the first detailed analysis of the optical spectral properties of PKS 1222+216 and estimates its black hole mass using multiple broad emission lines and thermal continuum.

Findings

Broad line emission remains constant despite continuum variability.

Thermal continuum component is comparable to minimum activity levels.

Black hole mass estimated at approximately 6x10^8 solar masses.

Abstract

We investigate the optical spectral properties of the blazar PKS 1222+216 during a period of 3 years. While the continuum is highly variable the broad line emission is practically constant. This supports a scenario in which the broad line region is not affected by jet continuum variations. We thus infer the thermal component of the continuum from the line luminosity and we show that it is comparable with the continuum level observed during the phases of minimum optical activity. The mass of the black hole is estimated through the virial method from the FWHM of MgII, Hbeta, and Halpha broad lines and from the thermal continuum luminosity. This yields a consistent black hole mass value of 6x10^8 solar masses.