6,365 research outputs found
The Spectral Energy Distribution and Emission-Line properties of the NLS1 Galaxy Arakelian 564
We present the intrinsic spectral energy distribution (SED) of the NLS1
Arakelian 564, constructed with contemporaneous data obtained during a
multi-wavelength, multi-satellite observing campaign in 2000 and 2001. We
compare it with that of the NLS1 Ton S180 and with those obtained for BLS1s to
infer how the relative accretion rates vary among the Sy1 population. Although
the peak of the SED is not well constrained, most of the energy is emitted in
the 10-100 eV regime, constituting roughly half of the emitted energy in the
optical/X-ray ranges. This is consistent with a primary spectral component
peaking in the extreme UV/soft X-ray band, and disk-corona models, hence high
accretion rates. Indeed, we estimate that \dot{m}~1. We examine the emission
lines in its spectrum, and we constrain the physical properties of the
line-emitting gas through photoionization modeling. The line-emitting gas is
characterized by log n~11 and log U~0, and is stratified around log U~0. Our
estimate of the radius of the H\beta-emitting region ~10 \pm 2 lt-days is
consistent with the radius-luminosity relationships found for Sy1 galaxies. We
also find evidence for super-solar metallicity in this NLS1. We show that the
emission lines are not good diagnostics for the underlying SEDs and that the
absorption line studies offer a far more powerful tool to determine the
ionizing continuum of AGNs, especially if comparing the lower- and
higher-ionization lines.Comment: 15 pages, 10 figures; accepted for publication in The Astrophysical
Journal, LaTeX emulateapj.st
Chandra Grating Spectroscopy of the Seyfert Galaxy Ton S180
This paper presents results from spectral observations of Ton S180 using
Chandra and ASCA. The data confirm the presence of the soft excess but the
Chandra LETG spectrum reveals it to be broad and smooth, rather than resolved
into individual emission lines. This excess may represent either a primary or
reprocessed continuum component or a blend of broad lines from an ionized
accretion disk. The occurrence of a similar feature in five other NLSy1s leads
us to conclude that this soft X-ray component may be a characteristic of
sources accreting at a very high rate. The X-ray spectrum shows no evidence for
absorption lines, indicating that if gas exists in the line-of-sight then it is
in a very high ionization-state or has an extremely broad velocity
distribution. The new ASCA data confirm that the narrow component of the Fe
Kalpha line peaks close to a rest-energy of 7 keV, indicating the presence of a
significant amount of highly-ionized material in the nuclear environs.Comment: 12 pages, 2 figures. LaTeX with postscript figures. Accepted for
publication in the Astrophysical Journal Letter
Reddening, Emission-Line, and Intrinsic Absorption Properties in the Narrow-Line Seyfert 1 Galaxy Akn 564
We use Hubble Space Telescope UV and optical spectra of the narrow-line
Seyfert 1 (NLS1) galaxy Akn 564 to investigate its internal reddening and
properties of its emission-line and intrinsic UV absorption gas. We find that
the extinction curve of Akn 564, derived from a comparison of its UV/optical
continuum to that of an unreddened NLS1, lacks a 2200 A bump and turns up
towards the UV at a longer wavelength (4000 A) than the standard Galactic, LMC,
and SMC curves. However, it does not show the extremely steep rise to 1200 A
that characterizes the extinction curve of the Seyfert 1 galaxy NGC 3227. The
emission-lines and continuum experience the same amount of reddening,
indicating the presence of a dust screen that is external to the narrow-line
region (NLR). Echelle spectra from the Space Telescope Imaging Spectrograph
show intrinsic UV absorption lines due to Ly-alpha, N V, C IV, Si IV, and Si
III, centered at a radial velocity of -190 km/s (relative to the host galaxy).
Photoionization models of the UV absorber indicate that it has a sufficient
columnand is at a sufficient distance from the nucleus (D > 95 pc) to be the
source of the dust screen. Thus, Akn 564 contains a dusty ``lukewarm absorber''
similar to that seen in NGC 3227.Comment: 25 pages, 4 figures. LaTeX with encapsulated postscript figures.
Accepted for publication in the Astrophysical Journa
Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Akn 564. I. ASCA Observations and the Variability of the X-ray Spectral Components
We present a 35 day ASCA observation of the NLS1 Akn 564, which was part of a
multiwavelength AGN Watch monitoring campaign. Akn 564 shows a photon index
varying across the range 2.45--2.72. The presence of the soft hump component
below 1 keV, previously detected in ASCA data, is confirmed. Time-resolved
spectroscopy with ~daily sampling reveals a distinction in the variability of
the soft hump and power-law components over a timescale of weeks, with the hump
varying by a factor of 6 across the 35-day observation compared to a factor 4
in the power-law. Flux variations in the power-law component are measured down
to a timescale of ~1000s and accompanying spectral variability suggests the
soft hump is not well-correlated with the power-law on such short timescales.
We detect Fe Ka and a blend of Fe Kb plus Ni Ka, indicating an origin in highly
ionized gas. Variability measurements constrain the bulk of the Fe Ka to
originate within a light week of the nucleus. The large EW of the emission
lines may be due to high metallicity in NLS1s, supporting some evolutionary
models for AGN.Comment: 41 pages, 15 figures. Accepted for publication in the Astrophysical
Journal (v3 has final fixes for publication
The Correlation between X-ray spectral slope and FeKalpha line energy in radio-quiet active galactic nuclei
A significant correlation between FeKalpha line energy and X-ray spectral
slope has been discovered among radio-quiet active galactic nuclei. The
ionization stage of the bulk of the FeKalpha emitting material is not the same
in all active galactic nuclei and is related to the shape of the X-ray
continua. Active galactic nuclei with a steep X-ray spectrum tend to have a
fluorescence FeKalpha line from highly ionized material. In the narrow-line
Seyfert 1 galaxies with steeper X-ray spectrum (Gamma_X > 2.1), the FeKalpha
line originates from highly ionized material. In the Seyfert 1 galaxies and
quasars with flatter X-ray spectrum (Gamma_X < 2.1), bulk of the FeKalpha
emission arises from near neutral or weakly ionized material. The correlation
is an important observational characteristic related to the accretion process
in radio quiet active galactic nuclei and is driven by a fundamental physical
parameter which is likely to be the accretion rate relative to the Eddington
rate.Comment: 4 pages, To apear in ApJ Letter
Probing the Complex and Variable X-ray Absorption of Markarian 6 with XMM-Newton
We report on an X-ray observation of the Seyfert 1.5 galaxy Mrk 6 obtained
with the EPIC instruments onboard XMM-Newton. Archival BeppoSAX PDS data from
18-120 keV were also used to constrain the underlying hard power-law continuum.
The results from our spectral analyses generally favor a double
partial-covering model, although other spectral models such as absorption by a
mixture of partially ionized and neutral gas cannot be firmly ruled out. Our
best-fitting model consists of a power law with a photon index of 1.81+/-0.20
and partial covering with large column densities up to 10^{23} cm**-2. We also
detect a narrow emission line consistent with Fe Kalpha fluorescence at
6.45+/-0.04 keV with an equivalent width of ~93+/-25 eV. Joint analyses of
XMM-Newton, ASCA, and BeppoSAX data further provide evidence for both spectral
variability (a factor of ~2 change in absorbing column) and
absorption-corrected flux variations (by ~60%) during the ~4 year period probed
by the observations.Comment: 7 pages, 2 figures. accepted for publication in the Astronomical
Journa
Two-temperature coronal flow above a thin disk
We extended the disk corona model (Meyer & Meyer-Hofmeister 1994; Meyer, Liu,
& Meyer-Hofmeister 2000a) to the inner region of galactic nuclei by including
different temperatures in ions and electrons as well as Compton cooling. We
found that the mass evaporation rate and hence the fraction of accretion energy
released in the corona depend strongly on the rate of incoming mass flow from
outer edge of the disk, a larger rate leading to more Compton cooling, less
efficient evaporation and a weaker corona. We also found a strong dependence on
the viscosity, higher viscosity leading to an enhanced mass flow in the corona
and therefore more evaporation of gas from the disk below. If we take accretion
rates in units of the Eddington rate our results become independent on the mass
of the central black hole. The model predicts weaker contributions to the hard
X-rays for objects with higher accretion rate like narrow-line Seyfert 1
galaxies (NLS1s), in agreement with observations. For luminous active galactic
nuclei (AGN) strong Compton cooling in the innermost corona is so efficient
that a large amount of additional heating is required to maintain the corona
above the thin disk.Comment: 17 pages, 6 figures. ApJ accepte
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