Reverberation Mapping of the Intermediate-mass Nuclear Black Hole in SDSS J114008.71+030711.4

Abstract

We present the results of a reverberation mapping (RM) campaign on the black hole (BH) associated with the active galactic nucleus (AGN) in SDSS J114008.71+030711.4 (hereafter GH08). This object is selected from a sample of 19 candidate intermediate-mass BHs (M _BH < 10⁶ M _sun) found by Greene & Ho in the Sloan Digital Sky Survey. We used the Hobby-Eberly Telescope to obtain 30 spectra over a period of 178 days in an attempt to resolve the reverberation time lag (τ) between the continuum source and the broad-line region (BLR) in order to determine the radius of the BLR (R _BLR) in GH08. We measure τ to be two days with an upper limit of six days. We estimate the AGN luminosity at 5100 Å to be λL ₅₁₀₀ ≈ 1.1 × 10⁴³ erg s^-1 after deconvolution from the host galaxy. The most well-calibrated R _BLR-L relation predicts a time lag that is four times larger than what we measure. Using the measured Hβ full width at half-maximum of 703 ± 110 km s^-1 and an upper limit for R _BLR =6 light days, we find M _BH <~ 5.8 × 10⁵ M _sun as an upper limit to the BH virial mass in GH08, which implies super-Eddington accretion. Based on our measured M _BH we propose that GH08 may be another candidate to add to the very short list of AGNs with M _BH < 10⁶ M _sun determined using RM.