Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. I. A Reverberation‐based Measurement of the Black Hole Mass

Abstract

A reverberation-mapping program on NGC 4395, the least luminous known Seyfert 1 galaxy, undertaken with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope yields a measurement of the mass of the central black hole M BH ¼ (3:6 AE 1:1) ; 10 5 M. The observations consist of two visits of five orbits each, in 2004 April and July. During each of these visits, the UV continuum varied by at least 10% (rms), and only C iv k1549 showed corresponding variations large enough to reliably determine the emission-line lag, which was measured to be of order 1 hr for both visits. The size of the C iv-emitting region is about a factor of 3 smaller than expected if the slope of the broad-line region radius-luminosity relationship is identical to that for the H emission line. NGC 4395 is underluminous even for its small black hole mass; the Eddington ratio of $1:2 ; 10 À3 is lower than that of any other active galactic nucleus for which a black hole mass measurement has been made by emission-line reverberation.

The Suzaku broadband X-ray spectrum of the dwarf Seyfert galaxy NGC 4395

“…Some researchers (e.g., McHardy et al 2006) propose a lower mass, of even an order of magnitude below the value obtained from reverberation mapping. As pointed out by Peterson et al (2005), the Eddington ratio (L bol /L Edd ) is low 1.3 × 10 −3 [M BH /(3.6 × 10 5 M )] −1 . Provided that the estimate of the bolometric luminosity derived from the 5100 Å luminosity is correct, even for the lower mass estimate (∼10 4 M ), the accretion rate is the order of 10 −2 of the Eddington limit.…”

“…The mass derived from the reverberation mapping technique is found to be (3.6 ± 1.1) × 10 5 M (Peterson et al 2005). However, the low bulge velocity dispersion ≤30 km s −1 (Filippenko & Ho 2003) deviates from the extrapolation of the M-σ relation (e.g., Tremaine et al 2002) when this estimate of the black hole mass is adopted.…”

“…Unlike LINER-like, low-luminosity AGN, the optical/UV spectrum of NGC 4395 shows broad Balmer emission and high-excitation lines, reminiscent of genuine Seyfert nuclei but of higher luminosity (e.g., Ho et al 1997a). Using the relation usually applied to higher luminosity AGN (Kaspi et al 2000), the bolometric luminosity estimated from the 5100 Å luminosity is 5.4 × 10 40 erg s −1 (Peterson et al 2005), which can be powered by a black hole of a few 100 M if it accretes close to the Eddington limit.…”

Active galactic nuclei as scaled-up Galactic black holes

“…For NGC3227 we take the recent mass based on detailed stellar dynamics 26 which should be more accurate than that based on reverberation mapping 21 . For NGC4395 we take the mass as listed by Uttley and M c Hardy 20 which is based on the very low stellar velocity dispersion (σ < 30 km s -1 ) and very low nuclear optical emission 27,28 rather than the x10 higher estimate, based on short HST reverberation mapping observations 29 . We suspect that the former is more reliable as only one cycle of variation is covered in each HST visit so the line and continuum variations, upon whose relative lag the mass is based, may not be physically related.…”

Search for gamma rays from dark matter annihilations around intermediate mass black holes with the HESS experiment

“…Observational hints of the existence of IMBHs come from the detection of ultraluminous x-ray sources , apparently not associated with active galactic nuclei [53][54][55], from stellar kinematics in globular clusters [56,57] and emission-line time lags in galaxies [58].…”