Extreme X-Ray Behavior of the Low-Luminosity Active Nucleus in NGC 4395

Moran, Edward C.; Eracleous, Michael; Leighly, Karen M.; Chartas, G.; Filippenko, A. V.; Ho, Luis C.; Blanco, P. R.

doi:10.1086/429522

Cited by 77 publications

(113 citation statements)

References 37 publications

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“…5) by the finding of high-ionization narrow emission lines and broad Balmer emission lines in their optical spectrum (Kunth et al 1987;Filippenko & Sargent 1989). These, together with the detection of hard X-ray emission, indicate the presence of an AGN with a BH mass of M BH ∼ 3 × 10 5 M estimated from the width of the broad emission lines under the assumption that the gas is virialized (Filippenko & Ho 2003;Barth et al 2004;Moran et al 2005;Peterson et al 2005;Vaughan et al 2005;Thornton et al 2008). NGC 4395 has, in addition, a compact radio jet (Wrobel & Ho 2006) and is one of the few dwarf galaxies for which a dynamical BH mass measurement has been possible (M BH = 4 +8 −3 × 10 5 M ; den Brok et al 2015).…”

Section: Dwarf Galaxiesmentioning

confidence: 90%

Observational evidence for intermediate-mass black holes

Mezcua

2017

Int. J. Mod. Phys. D

268

219

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Intermediate-mass black holes (IMBHs), with masses in the range 100 − 10 6 M , are the link between stellar-mass BHs and supermassive BHs (SMBHs). They are thought to be the seeds from which SMBHs grow, which would explain the existence of quasars with BH masses of up to 10 10 M when the Universe was only 0.8 Gyr old. The detection and study of IMBHs has thus strong implications for understanding how SMBHs form and grow, which is ultimately linked to galaxy formation and growth, as well as for studies of the universality of BH accretion or the epoch of reionisation. Proving the existence of seed BHs in the early Universe is not yet feasible with the current instrumentation; however, those seeds that did not grow into SMBHs can be found as IMBHs in the nearby Universe. In this review I summarize the different scenarios proposed for the formation of IMBHs and gather all the observational evidence for the few hundreds of nearby IMBH candidates found in dwarf galaxies, globular clusters, and ultraluminous X-ray sources, as well as the possible discovery of a few seed BHs at high redshift. I discuss some of their properties, such as X-ray weakness and location in the BH mass scaling relations, and the possibility to discover IMBHs through high velocity clouds, tidal disruption events, gravitational waves, or accretion disks in active galactic nuclei. I finalize with the prospects for the detection of IMBHs with up-coming observatories.

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Section: Dwarf Galaxiesmentioning

confidence: 90%

Observational evidence for intermediate-mass black holes

Mezcua

2017

Int. J. Mod. Phys. D

268

219

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“…In comparison with other AGN, the X-ray spectrum of NGC 4395 below 10 keV appears to be very hard even after correcting for absorption, Γ ∼ 1.4 (e.g., Shih et al 2004;Moran et al (2005) suggested an even lower value of Γ ∼ 0.6). Despite the relatively low 2-10 keV flux (∼4 × 10 −13 erg s −1 cm −2 ), NGC 4395 was detected by INTEGRAL IBIS (Beckman et al 2006;Bird et al 2007) in 20-40 keV and 40-100 keV bands.…”

Section: Introductionmentioning

confidence: 88%

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

Iwasawa

Tanaka

Gallo³

2010

A&A

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We present a Suzaku observation of the dwarf Seyfert galaxy NGC 4395 with an estimated black hole mass of ∼10 5 M . Rapid and strong X-ray variability with an rms amplitude of ∼60 per cent is observed in the 0.4-10 keV band with the XIS cameras. The shape of the light curve appears to depend on energies. The hard X-ray emission is detected up to 35 keV with the HXD-PIN detector at a similar flux level as observed with the INTEGRAL IBIS. The X-ray spectrum below 10 keV is strongly absorbed by partially ionized (ξ ∼ 35 erg s cm −1 ) gas with a mean equivalent hydrogen column density of ∼2 × 10 22 cm −2 , when a simple absorption model is applied. The spectral shape is also strongly variable but not a simple function of the source brightness. The spectral variability appears to be accounted for mainly by continuum slope changes, but variability in the ionized absorber may also play some part. The apparently flat spectral slope of Γ 1.4 below 10 keV, obtained after correcting for absorption, is marginally inconsistent with the Γ ∼ 2 inferred from the 14-35 keV PIN spectrum. If the true spectral slope had been as steep as that measured in the hard X-ray band, there would have been an extra absorption component, which we are unable to detect. Combined with the INTEGRAL measurements, the hard X-ray emission above 10 keV exceeds the optical emission in terms of luminosity and dominates the broadband energy output, unless a large excess of UV disk emission is yet to be detected in the unobservable band. A weak Fe K line is seen at 6.4 keV with the average equivalent width of 110 eV, which does not show significant flux changes over the 3-day observation.

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“…NGC 4395 is a very late-type (Sdm) spiral with no bulge component, whose central stellar velocity dispersion is Ã < 30 km s À1 . Nevertheless, it has the emission properties of a type 1 active galactic nucleus (AGN), with broad permitted optical and UV emission lines (Filippenko & Sargent 1989;Filippenko et al 1993), a compact radio core (Ho & Ulvestad 2001) with a nonthermal brightness temperature (Wrobel et al 2001), and a pointlike, hard X-ray source ) that is highly variable (Moran et al 1999(Moran et al , 2004Shih et al 2003). Mass estimates based on the H line width-luminosity mass scaling relation and X-ray variability suggest a BH mass of 10 4 10 5 M .…”

Section: Introductionmentioning

confidence: 99%

Active Galactic Nuclei with Candidate Intermediate‐Mass Black Holes

Greene

2004

ApJ

Self Cite

321

483

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We present an initial sample of 19 intermediate-mass black hole candidates in active galactic nuclei culled from the first data release of the Sloan Digital Sky Survey. Using the line width-luminosity mass scaling relation established for broad-line active nuclei, we estimate black hole masses in the range of M BH % 8 ; 10 4 ð 10 6 Þ M , a regime in which only two objects are currently known. The absolute magnitudes are faint for active galactic nuclei, ranging from M g % À15 to À18 mag, while the bolometric luminosities are all close to the Eddington limit. The entire sample formally satisfies the line width criterion for so-called narrow-line Seyfert 1 galaxies; however, they display a wider range of Fe ii and [O iii] k5007 line strengths than is typically observed in this class of objects. Although the available imaging data are of insufficient quality to ascertain the detailed morphologies of the host galaxies, it is likely that the majority of the hosts are relatively late-type systems. The host galaxies have estimated g-band luminosities $1 mag fainter than M Ã for the general galaxy population at z % 0:1. Beyond simply extending the known mass range of central black holes in galactic nuclei, these objects provide unique observational constraints on the progenitors of supermassive black holes. They are also expected to contribute significantly to the integrated signal for future gravitational wave experiments.

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Extreme X-Ray Behavior of the Low-Luminosity Active Nucleus in NGC 4395

Cited by 77 publications

References 37 publications

Observational evidence for intermediate-mass black holes

Observational evidence for intermediate-mass black holes

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

Active Galactic Nuclei with Candidate Intermediate‐Mass Black Holes

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