Time-delay Measurement of Mg II Broad-line Response for the Highly Accreting Quasar HE 0413-4031: Implications for the Mg II-based Radius-Luminosity Relation
Abstract
We present the monitoring of the active galactic nuclei continuum and Mg II broad-line emission for the quasar HE 0413-4031 (z = 1.38) based on the six-year monitoring by the South African Large Telescope (SALT). We manage to estimate a time-delay of ${302.6}_{-33.1}^{+28.7}$ days in the rest frame of the source using seven different methods: interpolated cross-correlation function, discrete correlation function (DCF), z-transformed DCF, JAVELIN, two estimators of data regularity (Von Neumann, Bartels), and χ2 method. This time-delay is below the value expected from the standard radius-luminosity relation. However, based on the monochromatic luminosity of the source and the spectral energy distribution modeling, we interpret this departure as the shortening of the time-delay due to the higher accretion rate of the source, with the inferred Eddington ratio of ∼0.4. The Mg II line luminosity of HE 0413-4031 responds to the continuum variability as ${L}_{\mathrm{line}}\propto {L}_{\mathrm{cont}}^{0.43\pm 0.10}$ , which is consistent with the light-travel distance of the location of Mg II emission at Rout ∼ 1018 cm. Using the data of 10 other quasars, we confirm the radius-luminosity relation for the broad Mg II line, which was previously determined for the broad Hβ line for lower-redshift sources. In addition, we detect a general departure of higher-accreting quasars from this relation in analogy to the Hβ sample. After the accretion-rate correction of the light-travel distance, the Mg II-based radius-luminosity relation has a small scatter of only 0.10 dex.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2020
- DOI:
- 10.3847/1538-4357/ab94ae
- arXiv:
- arXiv:2005.09071
- Bibcode:
- 2020ApJ...896..146Z
- Keywords:
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- Radio-loud quasars;
- 14;
- 17;
- 1319;
- 1349;
- 1663;
- 1558;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Instrumentation and Methods for Astrophysics;
- General Relativity and Quantum Cosmology
- E-Print:
- 39 pages (23 pages - Main text, 16 pages - Appendix), 21 figures, 14 tables