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A novel reverberation mapping method for blazars

Junhao Deng, Lizhi Liu, Yifan Wang, Yunguo Jiang

TL;DR

The paper addresses the challenge of applying reverberation mapping to blazars by introducing a spectral-break decomposition to separate disk and jet optical emission. Using this approach on PKS 1510-089 and PKS 0736+017, the authors extract disk and emission-line light curves and measure lags between disk continuum and Hβ/Hγ lines with ICCF and ROA, deriving black hole masses of $M_{ m BH} \approx 1.4\times10^{8}\,M_\odot$ and $8.1\times10^{7}\,M_\odot$, respectively. The method relies on decomposing the optical spectrum into jet and disk components (with a Shakura–Sunyaev disk and a power-law jet) and uses model selection via AIC to identify the disk+jet combination, enabling RM in jet-dominated AGNs. Overall, this work extends RM to a class of blazars, offering a more data-efficient approach and new insights into disk–jet interplay in active galaxies.

Abstract

Reverberation mapping (RM) is the most promising method to measure the masses of supermassive black holes in the center of active galaxy nuclei (AGNs). However, the dominant jet component hinders the application of RM method for blazars. In this work, we present a new algorithm to disentangle the contribution of the accretion disk from that of the relativistic jet in blazars by analyzing the spectral break of the optical spectroscopic data. We applied this method to two flat-spectrum radio quasars (FSRQs), PKS 1510-089 and PKS 0736+017. In PKS 1510-089, the variability of the H$γ$ line is delayed with respect to the disk emission by approximately 94 days, while the H$β$ line shows a lag of about 111 days relative to the disk. In PKS 0736+017, the H$γ$ variability is delayed with respect to the disk by roughly 66 days, and the H$β$ line exhibits a lag of about 67 days. Based on these measured time lags, we estimate black hole masses of $\sim1.4\times10^{8}\,M_{\odot}$ for PKS 1510-089 and $\sim8.1\times10^{7}\,M_{\odot}$ for PKS 0736+017. This method paves the way to apply the RM method for blazars, and improves the understanding of disk and jet activities.

A novel reverberation mapping method for blazars

TL;DR

The paper addresses the challenge of applying reverberation mapping to blazars by introducing a spectral-break decomposition to separate disk and jet optical emission. Using this approach on PKS 1510-089 and PKS 0736+017, the authors extract disk and emission-line light curves and measure lags between disk continuum and Hβ/Hγ lines with ICCF and ROA, deriving black hole masses of and , respectively. The method relies on decomposing the optical spectrum into jet and disk components (with a Shakura–Sunyaev disk and a power-law jet) and uses model selection via AIC to identify the disk+jet combination, enabling RM in jet-dominated AGNs. Overall, this work extends RM to a class of blazars, offering a more data-efficient approach and new insights into disk–jet interplay in active galaxies.

Abstract

Reverberation mapping (RM) is the most promising method to measure the masses of supermassive black holes in the center of active galaxy nuclei (AGNs). However, the dominant jet component hinders the application of RM method for blazars. In this work, we present a new algorithm to disentangle the contribution of the accretion disk from that of the relativistic jet in blazars by analyzing the spectral break of the optical spectroscopic data. We applied this method to two flat-spectrum radio quasars (FSRQs), PKS 1510-089 and PKS 0736+017. In PKS 1510-089, the variability of the H line is delayed with respect to the disk emission by approximately 94 days, while the H line shows a lag of about 111 days relative to the disk. In PKS 0736+017, the H variability is delayed with respect to the disk by roughly 66 days, and the H line exhibits a lag of about 67 days. Based on these measured time lags, we estimate black hole masses of for PKS 1510-089 and for PKS 0736+017. This method paves the way to apply the RM method for blazars, and improves the understanding of disk and jet activities.

Paper Structure

This paper contains 10 sections, 4 equations, 10 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Data Reduction
  3. Spectral Break
  4. Emission Lines Fitting Scheme
  5. Disentangle the disk and jet
  6. NTD parameters
  7. Reverberation Mapping
  8. Discussion and conclusion
  9. Multi-wavelength SED model
  10. Plots of ICCF and ROA for PKS 1510-089 and PKS 0736+017

Figures (10)

  • Figure 1: Top panels: Representative optical spectra of PKS 0736+017 (left) and PKS 1510-089 (right) in three different flux states. The arrows approximately mark the local spectral slope, serving as visual guides. Bottom panels: Broadband SEDs in the low-flux state for PKS 0736+017 (left) and PKS 1510-089 (right), compiled from archival data and modeled by using the one-zone leptonic model (see Appendix A). The reduced $\chi^2$ values are 114.03 for PKS 0736+017 and 153.06 for PKS 1510-089, with radio data excluded from the calculation. The shaded gray regions mark the optical observation window. The overlap of jet and disk components confirms that both contribute to the observed optical emission.
  • Figure 2: An example of the spectral decomposition for PKS 1510–089, using the spectrum observed on MJD 58253.
  • Figure 3: Spectral decomposition of PKS 1510-089 on MJD 58253, shown as a representative example to illustrate the disk–jet emission separation method. The gray points show the optical spectrum after removal of the Fe II emission, prominent emission lines, and atmospheric absorption features. The green dashed line represents the power-law component corresponding to non-thermal jet emission, while the blue dashed line represents thermal emission from the accretion disk, modeled with the Shakura-Sunyaev model. The red solid line shows the total emission combining both components. The reduced $\chi^{2}$ value of the fit is 0.28.
  • Figure 4: From top to bottom: light curves of the NTD parameter, $\lambda5100\text{\AA}$ continuum, broad emission lines (H$\beta$ and H$\gamma$), jet, accretion disk, total flux (disk+jet), and the NTD* parameter for PKS 0736+017 (right) and PKS 1510-089 (left). Grey dashed lines in the top (NTD) and bottom (NTD*) panels indicate NTD=2 and NTD*=2, respectively. The Y-axis units are as follows: NTD and NTD* are dimensionless, the $\lambda5100\,\text{\AA}$ continuum is in $10^{-15}\,\mathrm{erg\,cm^{-2}\,s^{-1}\,\AA^{-1}}$, all other panels are in $10^{-15}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$.
  • Figure 5: Relationship between the rest frequency of spectral break and the value of NTD*. The left panel shows PKS 1510-089, and the right panel shows PKS 0736+017. The red lines indicate the results of linear fits.
  • ...and 5 more figures