Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. II. X-ray and Ultraviolet Continuum Variability

Abstract

We report on two Chandra observations, and a simultaneous Hubble Space Telescope ultraviolet observation, of the dwarf Seyfert 1 galaxy NGC 4395. Each Chandra observation had a duration of ~30 ks, with a separation of ~50 ks. The spectrum was observed to harden between these observations via a scaling down of the soft-band flux. The inter-observation variability is in a different sense to the observed variability within each observation and is most likely the result of increased absorption. Spectral variations were seen during the first observation suggesting that the X-ray emission is produced in more than one disconnected region. We have also re-analyzed a ~17 ks Chandra observation conducted in 2000. During the three Chandra observations the 2-10 keV flux is about a factor of 2 lower than seen during an XMM-Newton observation conducted in 2003. Moreover, the fractional variability amplitude exhibited during the XMM-Newton observation is significantly softer than seen during the Chandra observations. A power-spectral analysis of the first of the two new Chandra observations revealed a peak at 341s with a formal detection significance of 99%. A similar peak was seen previously in the 2000 Chandra data. However, the detection of this feature is tentative given that it was found in neither the second of our two new Chandra observations nor the XMM-Newton data, and it is much narrower than expected. The Hubble Space Telescope observation was conducted during part of the second Chandra visit. A zero-lag correlation between the ultraviolet and X-ray fluxes was detected with a significance of about 99.5%, consistent with the predictions of the two-phase model for the X-ray emission from active galactic nuclei.

arXiv comment31 pages, 10 figures, accepted for publication in ApJ

References in corpus (38)

• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
• Advection-Dominated Accretion and the Spectral States of Black Hole X-Ray Binaries: Application to Nova Muscae 1991
• On characterising the variability properties of X-ray light curves from active galaxies
• On Uncertainties in Cross-Correlation Lags and the Reality of Wavelength-Dependent Continuum Lags in Active Galactic Nuclei
• Non-linear X-ray variability in X-ray binaries and active galaxies
• On the X-ray time lags in the black hole candidates
• A simple test for periodic signals in red noise
• A Model for the X-Ray and UV Emission from Seyfert Galaxies and Galactic Black Holes
• A Low-Mass Central Black Hole in the Bulgeless Seyfert 1 Galaxy NGC 4395
• The flux-dependent amplitude of broadband noise variability in X-ray binaries and active galaxies
• Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. I. A Reverberation-Based Measurement of the Black Hole Mass
• Soft state of Cygnus X-1: stable disk and unstable corona
• An unstable central disk in the superluminal black-hole X-ray binary GRS 1915+105
• A unified model for the spectral variability in GRS 1915+105
• Iron fluorescence from within the innermost stable orbit of black hole accretion disks
• Broad-band X-ray/gamma-ray spectra and binary parameters of GX 339-4 and their astrophysical implications
• ON THE GEOMETRY OF THE X-RAY EMITTING REGION IN SEYFERT GALAXIES
• Multiwavelength observations of short time-scale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
• A long, hard look at MCG-6-30-15 with XMM-Newton II: detailed EPIC analysis and modelling
• X-ray continuum variability of MCG-6-30-15
• X-ray variability and correlations in the two phase disk-corona model for Seyfert galaxies
• The Origin of the X-ray and Ultraviolet Emission in NGC 7469
• The nature of X-ray spectral variability in Seyfert Galaxies
• Simultaneous Ultraviolet and X-ray Observations of the Seyfert Galaxy NGC 4151. I. Physical Conditions in the X-ray Absorbers
• Intensive HST, RXTE and ASCA Monitoring of NGC 3516: Evidence Against Thermal Reprocessing
• Extreme X-ray Behavior of the Low-Luminosity Active Nucleus in NGC 4395
• Complex Optical-X-ray Correlations in the Narrow-Line Seyfert 1 Galaxy NGC 4051
• Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Akn 564. III. Optical Observations and the Optical--UV--X-ray Connection
• X-ray vs. Optical Variations in the Seyfert 1 Nucleus NGC 3516: A Puzzling Disconnectedness
• Hot accretion discs with thermal Comptonisation and advection in luminous black hole sources
• Temporal characteristics of the X-ray emission of NGC 7469
• Evidence for an intermediate mass black hole and a multi-zone warm absorber in NGC 4395
• X-ray absorption and rapid variability of the dwarf Seyfert nucleus of NGC4395
• The Ionized Gas and Nuclear Environment in NGC 3783 III. Detection of a Decreasing Radial Velocity in an Intrinsic UV Absorber
• SAX J1808.4-3658 and the origin of X-ray variability in X-ray binaries and active galactic nuclei
• Simultaneous EUV and X-ray variability of NGC 4051
• Fourier Resolved Spectroscopy of the XMM-Newton Observations of MCG -6-30-15
• Short time-scale optical variability of the dwarf Seyfert nucleus in NGC 4395

Cited by in corpus (9)

• X-ray nature of the LINER nuclear sources
• An X-ray Selected Sample of Candidate Black Holes in Dwarf Galaxies
• The Host Galaxy and Central Engine of the Dwarf AGN POX 52
• Correlated X-ray/Ultraviolet/Optical variability in the very low mass AGN NGC 4395
• X-Ray Monitoring of Ultraluminous X-Ray Sources
• Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. III. Optical Variability and X-ray/UV/Optical Correlations
• EUCLIA. II. On the puzzling large UV to X-ray lags in Seyfert galaxies
• The X-ray variability of Seyfert 1.8/1.9 galaxies
• Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. IV. The Variable UV Absorption Lines