Emission-line and continuum reverberation mapping of the NLS1 galaxy WPVS 48

¹ Institut für Astrophysik und Geophysik, Universität Göttingen Friedrich-Hund-Platz 1 37077 Göttingen, Germany
² Department of Physics, Faculty of Natural Sciences, University of Haifa Haifa 3498838, Israel
³ Haifa Research Center for Theoretical Physics and Astrophysics, University of Haifa Haifa 3498838, Israel
⁴ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB) 44780 Bochum, Germany
⁵ School of Physics & Astronomy and the Wise Observatory, Tel-Aviv University Tel-Aviv 6997801, Israel

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 1 April 2025
Accepted: 8 November 2025

Abstract

Context. WPVS 48 is a nearby narrow-line Seyfert 1 galaxy without previous analysis of the broad-line region (BLR) by means of optical spectroscopic reverberation mapping.

Aims. By studying the continuum and emission line variability of WPVS 48, our aim was to infer the BLR size as well as the mass of the central supermassive black hole (SMBH).

Methods. We analysed data from a dedicated optical spectroscopic reverberation mapping campaign of WPVS 48 taken with the 10 m Southern African Large Telescope (SALT) at 24 epochs over a period of seven months between December 2013 and June 2014.

Results. WPVS 48 shows variability throughout the campaign. We find a stratified BLR, where the variability amplitude of the integrated emission lines decreases with distance to the ionising continuum source. Specifically, the variable emission of Hα, Hβ, Hγ, and He Iλ5876 originates at distances of 16.0^+4.0_−2.0, 15.0^+4.5_−1.9, 12.5^+3.5_−2.5, and 14.0^+2.5_−2.1 light-days, respectively, to the optical continuum at 5100 Å. The He IIλ4686 lag is ≲5 days. Based on the high S/N spectra, we identified variable emission of N IIIλ4640 and C IVλ4658 in the line complex with He IIλ4686. We derive interband continuum delays increasing with wavelength up to ∼8 days. These delays are consistent with an additional diffuse continuum originating at the same distance as the variable Balmer emission. We derive a central black hole mass of (1.3^+1.1_−0.6) × 10⁷ M_⊙ based on the integrated line-widths and distances of the BLR and discuss corrections for the inclination angle. This gives an Eddington ratio L/L_Edd ≈ 0.39 without correction for inclination.